Neurobiology of Disease [2 ed.] 9780190219093, 0190219092, 9780199937837, 0199937834

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NE U R O B IOLOGY OF  DIS E AS E

NEUROBIOLOGY OF DISEASE SECOND EDITION

EDITED BY

Michael V. Johnston, MD B L U M MO SE R E ND O W E D C HAIR K E N N E D Y K R IE GE R INSTITUTE D E PARTME NTS O F NE URO LO GY, P E DIAT RICS , A ND PHYS ICA L MEDICINE A ND REHA BIL ITAT ION J O H N S HO P K INS UNIVE RSITY SC HO OL OF MEDICINE B A LTIMO R E , MD

Harold P. Adams Jr., MD D I V I SIO N O F C E RE BRO VASC ULAR D IS EA S ES D E PARTME NT O F NE UR O LO GY C A R VE R C O LLE GE O F ME D IC INE U N I VE RSITY O F IO WA HO SP ITALS AN D CL INICS S T ROKE CENT ER U N I VE RSITY O F IO WA I O WA C ITY, IA

Ali Fatemi, MD, MBA M O S E R C E NTE R FO R LE UK O D Y STR O PHIES A ND NEU ROGENET ICS K E N N E D Y K R IE GE R INSTITUTE D E PARTME NT O F NE UR O LO GY AND PEDIAT RICS J O H N S HO P K INS UNIVE RSITY SC HO OL OF MEDICINE B A LTIMO R E , MD

1

1 Oxford University Press is a department of the University of Oxford. It furthers the University’s objective of excellence in research, scholarship, and education by publishing worldwide. Oxford is a registered trade mark of Oxford University Press in the UK and certain other countries. Published in the United States of America by Oxford University Press 198 Madison Avenue, New York, NY 10016, United States of America. © Oxford University Press 2016 First Edition Published in 2006 by Sid Gilman All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, without the prior permission in writing of Oxford University Press, or as expressly permitted by law, by license, or under terms agreed with the appropriate reproduction rights organization. Inquiries concerning reproduction outside the scope of the above should be sent to the Rights Department, Oxford University Press, at the address above. You must not circulate this work in any other form and you must impose this same condition on any acquirer. Library of Congress Cataloging-​in-​Publication Data Neurobiology of disease (Johnston) Neurobiology of disease / edited by Michael V. Johnston, Harold P. Adams Jr., Ali Fatemi. — 2nd edition. p. ; cm. Preceded by Neurobiology of disease / edited by Sid Gilman. 2007. Includes bibliographical references and index. ISBN 978–0–19–993783–7 (alk. paper) I.  Johnston, Michael V., 1946– , editor.  II.  Adams, Harold P., Jr., 1944– , editor.  III.  Fatemi, Ali, 1975– , editor.  IV.  Title. [DNLM: 1.  Nervous System Diseases—physiopathology.  2.  Nervous System Physiological Phenomena. 3.  Neurobiology. 4.  Neurosciences. WL 140] QP355.2 612.8—dc232015029196 ISBN 978–​0–​19–​993783–​7 This material is not intended to be, and should not be considered, a substitute for medical or other professional advice. Treatment for the conditions described in this material is highly dependent on the individual circumstances. And, while this material is designed to offer accurate information with respect to the subject matter covered and to be current as of the time it was written, research and knowledge about medical and health issues is constantly evolving and dose schedules for medications are being revised continually, with new side effects recognized and accounted for regularly. Readers must therefore always check the product information and clinical procedures with the most up-to-date published product information and data sheets provided by the manufacturers and the most recent codes of conduct and safety regulation. The publisher and the authors make no representations or warranties to readers, express or implied, as to the accuracy or completeness of this material. Without limiting the foregoing, the publisher and the authors make no representations or warranties as to the accuracy or efficacy of the drug dosages mentioned in the material. The authors and the publisher do not accept, and expressly disclaim, any responsibility for any liability, loss or risk that may be claimed or incurred as a consequence of the use and/or application of any of the contents of this material. 9 8 7 6 5 4 3 2 1 Printed by Sheridan Books, Inc., United States of America

Michael V. Johnston: To my wife Sally with love, and to Peter and Cecilia, Jamie and Kristin, Joe and Jennie, and our grandchildren, Elizabeth, Michael, Andrew, Ryan, and Eli Harold P. Adams Jr.: With love and thanks to Leah, John, Julie, Jessica, and Jeff Ali Fatemi: To my wife and children, Najat, Sami, and Rayan, and my parents, Soheila and Mohsen, for their endless love and support, and to my grandfather, Mohajer, whose dream I live

CONTENTS

Acknowledgments Contributors

xv xvii

11. DYSTONIA: DEFINITION, CLINICAL CLASSIFICATION, EPIDEMIOLOGY, CLINICAL MANIFESTATIONS, EVALUATION, AND CURRENT TREATMENT 

75

Jeri Yvonne Williams and David G. Standaert S E CT I O N I

M O VE M E NT D ISORDERS (JOEL S. PERLMUT T ER, WA S H I NGT O N U N IV ERSITY) 1. HISTORY OF PARKINSONISM 

3

Michael Silver and Stewart A. Factor 2. PARKINSON DISEASE: PATHOPHYSIOLOGY, GENETICS, CLINICAL MANIFESTATIONS, AND COURSE INCLUDING DIAGNOSIS AND DIFFERENTIAL DIAGNOSIS  10

12. PAROXYSMAL DYSKINESIAS AND OTHER PAROXYSMAL MOVEMENT DISORDERS 

80

Olga Waln and Joseph Jankovic 13. THE EXPANDED POLYGLUTAMINE TRACT SPINOCEREBELLAR ATAXIAS 

90

Elsdon Storey 14. ATAXIAS: AUTOSOMAL RECESSIVE AND OTHER ATAXIAS 

99

Vikram G. Shakkottai

Michael J. Soileau and Kelvin L. Chou 3. PARKINSON DISEASE: CURRENT TREATMENTS AND PROMISING CLINICAL TRIALS 

18

DEMENTIAS (DAVID S. KNOPMAN, MAYO CLINIC)

Thien Thien Lim and Hubert H. Fernandez 4. MULTIPLE SYSTEM ATROPHY 

26

Melvin W. Kong and Ejaz A. Shamim 5. PARKINSON SYNDROMES: PROGRESSIVE SUPRANUCLEAR PALSY 

SECTION   II

31

15. ALZHEIMER’S DISEASE: PATHOLOGY AND PATHOGENESIS 

107

Bradley T. Hyman, Beatriz G. Perez-​Nievas, Isabel Barroeta-​Espar, Alberto Serrano-​Pozo, Matthew Frosch, and Teresa Gomez-​Isla

Vikas Kotagal and Praveen Dayalu 16. ALZHEIMER’S DISEASE: CLINICAL MANIFESTATIONS  6. PARKINSON SYNDROMES: CORTICOBASAL SYNDROME 

37

17. ALZHEIMER’S DISEASE: MANAGEMENT AND TREATMENT 

Sami Barmada 7. HUNTINGTON DISEASE: ETIOLOGY, GENETICS, AND CLINICAL MANIFESTATIONS 

42

117

Gregory A. Jicha and Frederick A. Schmitt 18. FRONTOTEMPORAL LOBAR DEGENERATION 

Roger L. Albin and Henry L. Paulson

114

Michael S. Rafii

132

Jonathan Graff-​Radford and Keith A. Josephs 8. HUNTINGTON DISEASE: TREATMENT AND CURRENT CLINICAL TRIALS 

47

Charles S. Venuto and Karl Kieburtz

19. DIAGNOSIS AND THERAPY FOR LEWY BODY DEMENTIA 

138

Bela R. Turk and Ali Fatemi 9. ESSENTIAL TREMOR 

54 20. PATHOGENESIS OF LEWY BODY DEMENTIA 

Arif Dalvi, Kelly E. Lyons, and Rajesh Pahwa 10. THE NEUROBIOLOGY OF DYSTONIA 

H. A. Jinnah, Cecilia N. Prudente, Samuel J. Rose, and Ellen J. Hess

145

Jagan A. Pillai and James B. Leverenz 60

21. VASCULAR COGNITIVE IMPAIRMENT 

157

Rahul Karamchandani and Nancy R. Barbas

C o n t e n t s | vii

S ECT I O N I I I

MOTORNEURON DISEASES (MERIT E. CUDKOWICZ, M A S S A C H U S E TTS G EN ERA L HOSPITA L, HA R VA R D U NI VERSITY) 22. TYPES OF MOTOR NEURON DISEASES 

167

Nimish J. Thakore and Erik P. Pioro 23. CLINICAL PRESENTATIONS, DIAGNOSTIC CRITERIA, AND LAB TESTING 

174

Nimish J. Thakore and Erik P. Pioro 24. SYMPTOMATIC MANAGEMENT IN AMYOTROPHIC LATERAL SCLEROSIS 

192

198

204

218

223

228

236

Arthur H. M. Burghes and Vicki L. McGovern

viii | C o n t e n t s

39. FOCAL CORTICAL DYSPLASIAS 

40. BIOLOGICAL BASES OF SYMPTOMATIC GENERALIZED EPILEPSIES IN CHILDREN 

41. EPILEPSIES THAT OCCUR PREDOMINANTLY IN GIRLS 

42. EPIDEMIOLOGY OF EPILEPSY: INCIDENCE, PREVALENCE, AND RISK FACTORS 

43. CLINICAL PRESENTATION, DIAGNOSIS, AND COURSE: ​EPILEPSY SYNDROMES WITH FOCAL SEIZURES

44. MEDICAL MANAGEMENT OF EPILEPSY 

45. NEUROIMAGING OF EPILEPSY 

289

294

298

307

312

318

331

336

William A. Gomes 241

46. ALTERNATIVE THERAPIES FOR EPILEPSY: DIETARY TREATMENTS 

342

Carl E. Stafstrom 249

Umrao R. Monani and Darryl C. De Vivo 34. SPINAL MUSCULAR ATROPHY: INSIGHTS FROM GENETICS 

38. TEMPORAL LOBE EPILEPSY 

Jules C. Beal and Emilio Perucca

Sabrina Paganoni and Nazem Atassi 33. SPINAL MUSCULAR ATROPHY 

282

Alex Boro and Jerome Engel

John K. Fink 32. UPPER MOTOR NEURON DISORDERS HEREDITARY SPASTIC PARAPLEGIA AND PRIMARY LATERAL SCLEROSIS: CLINICAL TRIALS, PATHOLOGY, INSIGHTS FROM GENETICS AND PATHOGENESIS, IN VITRO AND IN VIVO DISEASE MODELS 

37. BIOLOGICAL BASIS OF PRIMARY GENERALIZED EPILEPSIES: P ​ ATHOPHYSIOLOGY

Dale C. Hesdorffer

Katharine A. Nicholson and James D. Berry 31. UPPER MOTOR NEURON DISORDERS: HEREDITARY SPASTIC PARAPLEGIA AND PRIMARY LATERAL SCLEROSIS 

277

Lynette G. Sadleir, Jozef Gecz, and Ingrid E. Scheffer

Brent T. Harris, Galam A. Khan, and Saed Sadeghi 30. AMYOTROPHIC LATERAL SCLEROSIS CLINICAL TRIALS: PAST REFLECTIONS INFORMING NEW DIRECTIONS 

36. BIOLOGICAL BASIS OF PRIMARY GENERALIZED EPILEPSIES: GENETICS

Dragos A. Nita, Miguel A. Cortez, Jose Luis Perez Velazquez, and O. Carter Snead, III

Brian J. Wainger 29. AMYOTROPHIC LATERAL SCLEROSIS: NEUROPATHOLOGY 

PAROXYSMAL DISORDERS (SOLOMON L. MOSHE, EI NS T EI N COLLEGE OF MED I CI NE)

Ali Mahta and Peter B. Crino

Matthew B. Harms and Timothy M. Miller 28. AMYOTROPHIC LATERAL SCLEROSIS: IN VITRO AND IN VIVO DISEASE MODELS 

SECTION   IV

Edward H. Bertram

Laura Ferraiuolo and Stephen J. Kolb 27. AMYOTROPHIC LATERAL SCLEROSIS: INSIGHTS FROM GENETICS 

W. David Arnold and Arthur H. M. Burghes

Mark W. Youngblood and Hal Blumenfeld

Éilis J. O’Reilly 26. AMYOTROPHIC LATERAL SCLEROSIS: PATHOGENESIS 

264

Carla Marini and Renzo Guerrini 183

Matthew Gladman and Lorne Zinman 25. EPIDEMIOLOGY OF AMYOTROPHIC LATERAL SCLEROSIS 

35. IN VITRO AND IN VIVO MODELS OF SPINAL MUSCULAR ATROPHY 

47. MIGRAINE AND OTHER HEADACHE DISORDERS 

348

Robert W. Charlson and Matthew S. Robbins 258

48. NEUROBIOLOGY OF MIGRAINE 

Victor Rosenfeld and John Stern

354

S E CT I O N V

65. CEREBRAL CREATINE DEFICIENCY DISORDERS 

PEDIATRIC NEUROLOGY AND DEVELOPMENTAL D I S O R D E R S ( TA N JA LA T. G IPSON A N D DEEPA U. MENON, KENNEDY KRIEGER INSTITUTE AND J O H NS HOPKIN S U N IV ERSITY)

66. CONGENITAL DISORDERS OF GLYCOSYLATION 

361

Tanjala T. Gipson and Michael V. Johnston 50. TUBEROUS SCLEROSIS COMPLEX: PEDIATRIC ASPECTS 

366

372

375

385

390

C. L. Smith-​Hicks and Sakkubai Naidu 55. ANGELMAN SYNDROME 

393

Kristin W. Barañano 56. DOWN SYNDROME 

397

405

408

417

496

Joan M. Jasien, Bruce K. Shapiro, and Alexander H. Hoon 72. NEONATAL BRAIN INJURIES 

502

Katharina Goeral, Ali Fatemi, and Michael V. Johnston 73. THE NEUROBIOLOGY OF ENCEPHALOPATHY OF PREMATURITY 

424

522

Gwendolyn J. Gerner and Vera Joanna Burton 527

Verena Staedtke and Eric H. Kossoff 540

Jessica Klein and Christopher Oakley 547

Vera Joanna Burton and Edward Ahn 553

Stephen L. Kinsman 78. SMITH-​LEMLI-​OPITZ SYNDROME 

Mihee J. Bay and Bruce K. Shapiro 61. DISEASES OF MITOCHONDRIAL ENERGY METABOLISM 

71. CEREBRAL PALSY 

77. SPINA BIFIDA AND RELATED CONDITIONS 

Phillip L. Pearl and William P. Welch 60. ATTENTION DEFICIT-​HYPERACTIVITY DISORDER 

488

76. CONGENITAL HYDROCEPHALUS 

Mary Lee Gregory 59. PEDIATRIC NEUROTRANSMITTER DISORDERS 

70. LEUKODYSTROPHIES 

75. MIGRAINE AND HEADACHE IN CHILDREN 

Michael V. Johnston 58. CONGENITAL HYPOTHYROIDISM 

481

74. EPILEPSY SYNDROMES IN CHILDHOOD 

George T. Capone 57. COFFIN-​LOWRY SYNDROME 

69. PEROXISOMAL DISORDERS 

Ulrike Schrifl, SakkuBai Naidu, and Ali Fatemi

Deepa U. Menon 54. RETT SYNDROME 

468

Gerald V. Raymond, Mohamed Y. Jefri, Kristin W. Baranano, and Ali Fatemi

Dejan B. Budimirovic and Megha Subramanian 53. AUTISM AND INTELLECTUAL DISABILITIES: PTEN GENE MUTATION 

Hilary Vernon

Gustavo H. B. Maegawa

David S. Wolf 52. NEUROBIOLOGY OF AUTISM AND INTELLECTUAL DISABILITY: FRAGILE X SYNDROME 

464

68. LYSOSOMAL STORAGE DISORDERS 

Tanjala T. Gipson, Andrea Poretti, Rebecca McClellan, and Michael V. Johnston 51. NEUROFIBROMATOSIS TYPE 1 

460

Marc C. Patterson 67. GLUTARIC ACIDURIA TYPE I 

49. OVERVIEW OF AUTISM AND INTELLECTUAL DISABILITIES 

451

Peter W. Schutz and Sylvia Stockler

558

Ryan W. Lee 79. SICKLE CELL ANEMIA 

566

Eboni I. Lance and Andrew W. Zimmerman 428

Jacqueline Weissman and Lisa Emrick 62. METHYLMALONIC ACIDEMIA 

435

Siddharth Srivastava and Jeffrey Chinsky 63. THE UREA CYCLE DISORDERS 

440

Andrea L. Gropman, Belen Pappa, and Nicholas Ah Mew 64. PHENYLKETONURIA 

Hilary Vernon

SECTION   V I

NEUROI MMUNOLOGI CAL D I S EAS ES (CARLOS PARD O-VI LLAMI Z AR, JOH NS H OP KI NS UNI VERS I T Y ) 80. THE EPIDEMIOLOGY OF MULTIPLE SCLEROSIS: AN HISTORICAL PERSPECTIVE 

447

575

Kassandra L. Munger

C o n t e n t s | ix

81. MULTIPLE SCLEROSIS: PATHOLOGY 

583

Bogdan Florin Gh. Popescu, Yong Guo, and Claudia Francesca Lucchinetti

96. RASMUSSEN ENCEPHALITIS 

97. AUTOIMMUNE ENCEPHALITIS  82. MULTIPLE SCLEROSIS: MRI AND OTHER IMAGING APPROACHES IN MS 

591

Martina Absinta and Daniel S. Reich 83. MULTIPLE SCLEROSIS: WHITE MATTER VERSUS GRAY MATTER INVOLVEMENT (THE CAUSE OF DISABILITY IN MS) 

600

708

Andrew McKeon 98. OTHER PROVEN AND PUTATIVE AUTOIMMUNE DISORDERS OF THE PERIPHERAL NERVOUS SYSTEM: MYASTHENIA GRAVIS 

Massimo Filippi and Maria A. Rocca 84. MULTIPLE SCLEROSIS: MONITORING DISEASE ACTIVITY AND PROGRESSION 

703

Jan Bauer and Christian G. Bien

714

Doris G. Leung 99. VASCULITIS OF THE CENTRAL NERVOUS SYSTEM 

719

Christian Pagnoux and Richard H. Swartz 610

Pavan Bhargava and Shiv Saidha 85. SYMPTOMS OF MULTIPLE SCLEROSIS 

618

Kathleen Costello and Scott D. Newsome 86. EXERCISE AND MULTIPLE SCLEROSIS 

628

Pavan Bhargava and Peter A. Calabresi 88. NEUROMYELITIS OPTICA 

643

652

657

667

Davide Martino and Gavin Giovannoni

104. SURGICAL AND RADIOLOGIC INTERVENTION FOR PREVENTION OF ISCHEMIC STROKE 

675

106. PEDIATRIC STROKE 

743

750

759

763

Melissa Chung and Warren Lo 107. VASCULAR BIOLOGY OF CEREBRAL ISCHEMIA  683

774

Jason A. Ellis and E. Sander Connolly 108. INTRACEREBRAL HEMORRHAGE 

779

Craig Anderson 690

109. THE NATURAL HISTORY OF CEREBRAL ANEURYSMS 

785

David Hasan 695 110. GENETIC DISORDERS AND STROKE 

Andrea Poretti and Michael V. Johnston

x | Contents

738

Enrique C. Leira

Afshin Borhani Haghighi and Bernadette Kalman 95. POSTSTREPTOCOCCAL MOVEMENT DISORDERS 

103. COMMON RISK FACTORS FOR STROKE AND MEDICAL PREVENTION THERAPIES 

105. UNUSUAL CAUSES OF STROKE 

Eoin P. Flanagan and Richard J. Caselli 94. OTHER PROVEN AND PUTATIVE AUTOIMMUNE DISORDERS OF THE CNS: NEURO-​BEHÇET’S SYNDROME 

102. NEUROIMAGING OF ACUTE STROKE 

Andrew Ringer

Scott D. Newsome 93. OTHER PROVEN AND PUTATIVE AUTOIMMUNE DISORDERS OF THE CNS: HASHIMOTO’S ENCEPHALOPATHY 

735

George Khouri, Shelly Ozark, and Bruce Ovbiagele

Elizabeth M. Wells 92. OTHER PROVEN AND PUTATIVE AUTOIMMUNE DISORDERS OF THE CNS: ANTI-​GAD ASSOCIATED NEUROLOGICAL DISORDERS—​STIFF-​PERSON SYNDROME, CEREBELLAR ATAXIA, PROGRESSIVE ENCEPHALOPATHY WITH RIGIDITY AND MYOCLONUS, AND ENCEPHALITIS 

101. ACUTE ISCHEMIC STROKE 

Chelsea S. Kidwell and Kambiz Nael

John C. Probasco 91. ANTI-​N-​METHYL-​D-​ASPARTATE RECEPTOR ENCEPHALITIS 

731

Harold P. Adams Jr.

Benjamin M. Greenberg and Allen Desena 90. PARANEOPLASTIC NEUROLOGICAL DISORDERS 

100. STROKE EPIDEMIOLOGY AND IMPACT:  MORTALITY, INCIDENCE, PREVALENCE, STROKE SUBTYPES, SEX, RACE/​ETHNICITY, GEOGRAPHY U.S. AND WORLD 

Virginia J. Howard

Teri L. Schreiner and Jeffrey L. Bennett 89. ACUTE DISSEMINATED ENCEPHALOMYELITIS 

CEREBROVAS CULAR D I S EAS ES (H AROLD P. AD AMS JR., UNI VERS I T Y O F IO WA)

622

Jeffrey R. Hebert 87. MULTIPLE SCLEROSIS: DISEASE-​MODIFYING THERAPIES 

SECTION   V II

795

111. TARGETS FOR NEUROPROTECTION IN ISCHEMIC STROKE 

125. RADICULOPATHY AND PLEXOPATHY  799

Ryan J. Felling

897

Michael Wheaton, Dustin Nowacek, and Zachary London

112. STURGE-​WEBER SYNDROME AND RELATED CEREBROVASCULAR MALFORMATION SYNDROMES  804

SECTION   IX

Angela Quain and Anne M. Comi

NEOP LAS T I C AND PARANEOP LAS T I C D I S EAS ES (LI S A M. D EANGELI S , MEMO RIAL S LOAN-KET T ERI NG CANCER CENT ER)

S E CT I O N V I I I

PER I P H E R A L A N D A U TON OMIC N ER V OUS S Y S T E M DI S O RDERS A N D PA IN ( NI C H O L A S J . MA RA G A KIS, JOHN S HO P KI NS UNI VE R S I T Y )

126. INFILTRATIVE ASTROCYTOMAS: WHO GRADE II— D ​ IFFUSE ASTROCYTOMA; WHO GRADE III—​ANAPLASTIC ASTROCYTOMA 

113. NEUROPATHIES ASSOCIATED WITH INFECTION OR TOXIC EXPOSURE 

127. PRIMARY AND SECONDARY GLIOBLASTOMA: WHO GRADE IV ASTROCYTOMA 

815

Doris G. Leung 114. MECHANISMS CONTRIBUTING TO THE DEVELOPMENT AND PROGRESSION OF DIABETIC POLYNEUROPATHY 

838 130. MENINGOMAS 

848

854

859

864

Amy I. Davidson, John A. Goodfellow, and Hugh J. Willison

954

133. PRIMARY CENTRAL NERVOUS SYSTEM LYMPHOMA 

961

134. FAMILIAL CNS TUMOR SYNDROMES: NEUROFIBROMATOSIS TYPE 1 

970

Ibrahim Hussain and David H. Gutmann 870

135. FAMILIAL CNS TUMOR SYNDROMES: NEUROFIBROMATOSIS TYPE-​2 

977

Jennie W. Taylor and Scott R. Plotkin 875 136. FAMILIAL CNS TUMOR SYNDROMES: TUBEROUS SCLEROSIS  879

885

John A. Goodfellow, Amy I. Davidson, and Hugh J. Willison 124. IMMUNE-​MEDIATED NEUROPATHIES 

132. PITUITARY TUMORS 

Lisa M. DeAngelis

James W. Teener 123. DEMYELINATING NEUROPATHIES 

947

Toral R. Patel and Viviane S. Tabar

Frank S. Pidcock 122. ENTRAPMENT NEUROPATHIES 

131. PINEAL REGION NEOPLASMS 

Neil Haranhalli and Jerome J. Graber

John D. Markman 121. COMPLEX REGIONAL PAIN SYNDROME 

937

Jennie Taylor and Patrick Y. Wen

Katelyn Donaldson and Ahmet Höke 120. DIAGNOSTIC AND CLINICAL SCALES FOR PERIPHERAL NEUROPATHY 

927

Brett J. Theeler and Mark R. Gilbert

Phillip A. Low 119. ANIMAL MODELS OF PERIPHERAL NEUROPATHY AND NEUROPATHIC PAIN 

923

129. PRIMARY CENTRAL NERVOUS SYSTEM TUMORS: EPENDYMOMAS 

Brian J. Wainger 118. AUTONOMIC NEUROPATHIES 

Aaron Mammoser

831

Noah Kolb and A. Gordon Smith 117. DRUG DISCOVERY AND NEUROPATHIC PAIN 

913

Thomas J. Kaley

Lindsay Zilliox and James W. Russell 116. ANATOMY, LOCALIZATION, AND PATTERN RECOGNITION OF PERIPHERAL NEUROPATHY 

Aaron Mammoser

128. OLIGODENDROGLIOMAS 

Lucy M. Hinder, Kelli A. Sullivan, Stacey A. Sakowski, and Eva L. Feldman 115. DIABETIC AND PREDIABETIC NEUROPATHY 

905

891

981

Darcy A. Krueger and Jamie Capal 137. FAMILIAL CNS TUMOR SYNDROMES: VON HIPPEL-​LINDAU DISEASE 

989

Gurvinder Kaur, Leonel Ampie, Joseph Weiner, and Aruna Ganju 138. PONTINE GLIOMAS 

993

Kristin Schroeder and Oren Becher

C o n t e n t s | xi

139. MEDULLOBLASTOMA 

1000

Kevin C. De Braganca and Roger J. Packer 140. PEDIATRIC BRAIN TUMORS: CEREBELLAR ASTROCYTOMAS 

1006

1011

1023

Myrna R. Rosenfeld, Maarten J. Titulaer, and Josep Dalmau 143. CHEMOTHERAPY AND RADIATION THERAPY 

154. CENTRAL NERVOUS SYSTEM TUBERCULOSIS 

1115

Andrea T. Cruz and Jeffrey R. Starke

Jasmin Jo and David Schiff 142. OVERVIEW: OTHER PROVEN AND PUTATIVE AUTOIMMUNE DISORDERS OF THE CNS 

1101

Ivana Vodopivec and Tracey A. Cho

Vijay Ramaswamy, Jason T. Huse, and Yasmin Khakoo 141. BRAIN METASTASES 

153. NEUROBIOLOGY OF TRANSVERSE MYELITIS AND INFECTIOUS MYELOPATHIES 

155. RABIES 

156. DISORDERS CAUSED BY BOTULINUM TOXIN AND TETANUS TOXIN 

1028

1125

Carl E. Stafstrom 157. RICKETTSIAL DISEASES 

Mary R. Welch and Craig Nolan

1121

Alan C. Jackson

1129

Lisa Sun and Michael V. Johnston 158. EHRLICHIOSIS 

1132

Nicholas S. Havens and William E. Roland 159. NERVOUS SYSTEM LYME DISEASE 

S ECT I O N X

IN F E C T I O U S D ISEA SES OF THE N ER V OUS SYSTEM (KAREN L. ROOS, INDIANA UNIVERSITY) 144. ACUTE BACTERIAL MENINGITIS 

1041

Pratibha Singhi, Naveen Sankhyan, and Sunit Singhi 145. CEREBROSPINAL FLUID 

John E. Greenlee 146. HISTORY OF HUMAN IMMUNODEFICIENCY VIRUS INFECTION AND THE NERVOUS SYSTEM 

1057

1061

1070

1079

Minal A. Shah and Rabih O. Darouiche

xii | C o n t e n t s

163. MALARIA 

1157

1163

Kristyn E. Feldman, Joshua Biddle, and Ana-Claire L. Meyer 1168

Pratibha Singhi and Arushi G. Saini 1174

James A. Mastrianni and Joshuae G. Gallardo 1085

167. NEUROLOGICAL COMPLICATIONS OF INFECTIVE ENDOCARDITIS 

1179

Jonah Grossman, Tanzila Shams, and Cathy Sila 1091

168. POSTINFECTIOUS ENCEPHALITIS 

1190

Agusto A. Miravalle

Tyler R. West and Kelly J. Baldwin 152. SPINAL EPIDURAL ABSCESS 

1151

Pratibha Singhi, Karthi Nallasamy, and Sunit Singhi

166. PRION DISEASES 

Bela R. Turk, Ali Fatemi, and Michael V. Johnston 151. SPINAL AND INTRACRANIAL EPIDURAL ABSCESS, AND SUBDURAL EMPYEMA 

1146

Abelardo Q-​C Araujo

165. AMOEBIC INFECTIONS OF THE CENTRAL NERVOUS SYSTEM 

Don Gilden, Randall J. Cohrs, Ravi Mahalingam, and Maria A. Nagel 150. BRAIN ABSCESS 

James F. Bale

164. BABESIOSIS 

Meena Kannan, Taylor B. Harrison, and William Tyor 149. VARICELLA ZOSTER VIRUS INFECTION OF THE NERVOUS SYSTEM 

1141

Kiran Thakur

Joshua Alexander, David J. Croteau, and Ronald J. Ellis 148. HIV INFECTION: OPPORTUNISTIC INFECTIONS IN HIV-​INFECTED INDIVIDUALS 

160. CONGENITAL AND PERINATAL VIRAL INFECTIONS 

162. FUNGAL INFECTIONS OF THE CENTRAL NERVOUS SYSTEM 

Avindra Nath 147. HIV-​ASSOCIATED NEUROCOGNITIVE DISORDERS 

John J. Halperin

161. NEUROLOGICAL MANIFESTATIONS OF THE HUMAN T-​LYMPHOTROPIC VIRUS TYPE 1  1048

1133

1097

169. CENTRAL NERVOUS SYSTEM WHIPPLE DISEASE 

Arun Venkatesan

1195

170. PROGRESSIVE MULTIFOCAL LEUKOENCEPHALOPATHY 

1198

Arun Swaminathan and Joseph R. Berger

182. NEUROBIOLOGY OF INTRAUTERINE OPIATE AND COCAINE EXPOSURE 

1275

Harolyn M.E. Belcher and Samantha Hutchison

S E CT I O N XI

SECTION   XIII

S L E E P D I S T U R BA N C ES (MA RK DYKEN , UNI VE R S I T Y OF IOWA )

NEUROLOGI C MANI F ES TAT I ONS OF MED I CAL D I S ORD ERS (JOH N C. P ROBASC O , JOH NS H OP KI NS UNI VERS I T Y )

171. REM SLEEP BEHAVIOR DISORDER 

1205

Shannon S. Sullivan 172. RESTLESS LEGS SYNDROME AND PERIODIC LIMB MOVEMENT DISORDER 

183. ELECTROLYTE DISTURBANCES 

1283

Mark N. Rubin and Alejandro A. Rabinstein 184. NUTRITIONAL DEFICIENCIES  1209

Jennifer Accardo

1290

Deanna Saylor and John C. Probasco 185. ALCOHOL ABUSE 

173. THE NEUROBIOLOGY OF INSOMNIA 

1213

Wilfred R. Pigeon and Henry J. Orff

1304

Killian A. Welch 186. THYROID DISEASE 

174. SLEEP APNEA 

1219

Jennifer Accardo 175. NEUROBIOLOGY OF CIRCADIAN RHYTHMS DISORDERS 

1310

Makoto Ishii 187. PARATHYROID, ADRENAL, GONADAL, AND PITUITARY DISEASE 

1223

Christopher R. Jones

1316

Gary M. Abrams 188. CARDIAC DISEASE 

1321

Roger E. Kelley S E CT I O N XI I

S U B S TA NC E A BU SE A N D TOXIC OLOG ICAL DISORDERS (BARRY E. KOSOFSKY, WEILL-CORNELL UNI VE R S I T Y M EDIC A L C EN TER) 176. NEUROLOGIC MANIFESTATIONS OF ORGANIC CHEMICALS 

1233

1245

Leslie R. Whitaker and Bruce T. Hope 178. NEUROLOGICAL EFFECTS OF MARINE TOXINS 

1252

Kazuma Nakagawa 179. NEUROBIOLOGY OF FETAL ALCOHOL SPECTRUM DISORDERS 

191. NEUROLOGICAL MANIFESTATIONS OF RENAL DISEASE 

1344

Joshua S. Hundert, Rashmi Verma, Ritika Suri, Anika T. Singh, and Ajay Singh 1350

Richard B. Rosenbaum 1255

193. NEUROLOGIC MANIFESTATIONS OF HEMATOLOGICAL DISEASE 

1355

Elham Bayat 1261

Index

Edore C. Onigu-​Otite 181. NEUROBIOLOGY OF CHILD MALTREATMENT AND PSYCHOLOGICAL TRAUMA 

1332

Brian P. Bosworth, Brian R. Landzberg, and Elisa McEachern

192. SYSTEMIC LUPUS ERYTHEMATOSUS 

Carmen Lopez-​Arvizu, Carmel Bogle, and Harolyn M.E. Belcher 180. FETAL EXPOSURE TO TOBACCO AND CANNABIS 

1327

Lucia Rivera-​Lara and Romergryko G. Geocadin 190. NEUROLOGICAL MANIFESTATIONS OF GASTROINTESTINAL AND HEPATIC DISEASES 

John L. O’Donoghue 177. NEURAL MECHANISMS OF ADDICTION 

189. NEUROBIOLOGY OF BRAIN INJURY AFTER CARDIAC ARREST 

1361

1269

Nikeea Copeland-​Linder, Edore C. Onigu-​Otite, Jennifer Serico, Mariflor Jamora, and Harolyn M.E. Belcher

C o n t e n t s | xiii

ACKNOWLEDGMENTS

Tanjala Gipson, MD, Author and Outstanding Pediatric Neurologist who kept us organized Raechel Mattison, Editorial Assistant at Kennedy Krieger Craig Panner, Publisher, Oxford University Press, NY Preethi Sundar and her colleagues at Newgen Knowledge Works Pvt Ltd Emily Samulski, Assistant Editor, Oxford University Press, NY

A ck n o wl e dgm e n t s | xv

CONTRIBUTORS

Gary M. Abrams, MD University of California, San Francisco San Francisco, CA Martina Absinta, MD Translational Neuroradiology Unit National Institute of Neurological Disorders and Stroke (NINDS) National Institutes of Health (NIH) Bethesda, MD Harold P. Adams, Jr., MD Division of Cerebrovascular Diseases, Department of Neurology Carver College of Medicine University of Iowa Hospitals and Clinics Stroke Center University of Iowa Iowa City, IA Jennifer Accardo, MD, MSCE Sleep Disorders Clinic and Department of Neurology and Developmental Medicine Kennedy Krieger Institute and Departments of Pediatrics and Neurology Johns Hopkins School of Medicine Baltimore, MD Nicholas Ah Mew, MD Children’s National Medical Center George Washington University of the Health Sciences Washington, DC Edward Ahn, MD Johns Hopkins Hospital Baltimore, MD Leonel Ampie, MD Department of Neurological Surgery Northwestern University Feinberg School of Medicine Evanston, IL Craig Anderson, MD Neurological and Mental Health Division The George Institute for Global Health University of Sydney Neurology Department Royal Prince Alfred Hospital Sydney, Australia Roger L. Albin, MD Neurology Service & Geriatrics Research, Education, and Clinical Center, VAAAHS Department of Neurology University of Michigan Ann Arbor, MI

Joshua Alexander, DO, MPH Assistant Clinical Professor Department of Neurosciences University of California San Diego San Diego, CA Abelardo Q-​C Araujo, MD, MSc, PhD, FAAN Head and Senior Neurologist The Laboratory for Clinical Research in Neuroinfections The National Institute of Infectology (INI-​IPEC) Oswaldo Cruz Foundation (FIOCRUZ) Brazilian Ministry of Health Associate Professor of Neurology The Federal University of Rio de Janeiro Rio de Janeiro, Brazil W. David Arnold, MD Department of Neurology Department of Molecular and Cellular Biochemistry Wexner Medical Center, The Ohio State University Columbus, OH Nazem Atassi, MD, MMSc Harvard Medical School, Department of Neurology Neurological Clinical Research Institute (NCRI) Massachusetts General Hospital Boston, MA Kelly J. Baldwin, MD Neurology Associate Department of Neurology Geisinger Medical Center Danville, PA James F. Bale, Jr., MD Professor, Departments of Pediatrics and Neurology The University of Utah School of Medicine Salt Lake City, UT Kristin W. Barañano, MD, PhD Department of Pediatric Neurology Johns Hopkins University School of Medicine Baltimore, MD Nancy R. Barbas, MD, MSW Associate Professor Department of Neurology and the Alzheimer’s Disease Center University of Michigan Health System Ann Arbor, MI

C o n t ribu t o r s | xvii

Sami Barmada, MD, PhD Assistant Professor of Neurology University of Michigan Medical School Ann Arbor, MI

Edward H. Bertram, MD Department of Neurology University of Virginia Charlottesville, VA

Isabel Barroeta-​Espar, MD Neurology Service Massachusetts General Hospital Institute for Neurodegeneration Charlestown, MA

Pavan Bhargava, MD Department of Neurology Division of Neuroimmunology and Neuroinfectious Diseases Johns Hopkins University School of Medicine Baltimore, MD

Jan Bauer, MD Department of Neuroimmunology Center for Brain Research, Medical University of Vienna Vienna, Austria

Joshua Biddle, MD University of California, San Francisco San Francisco, CA

Mihee J. Bay, MD Department of Neurology and Developmental Medicine Kennedy Krieger Institute Depart of Pediatrics Johns Hopkins University School of Medicine Baltimore, MD Elham Bayat, MD Assistant Professor of Neurology The George Washington University Washington, DC Jules C. Beal, MD Saul R. Korey Department of Neurology Montefiore/​Einstein Epilepsy Management Center Albert Einstein College of Medicine Montefiore Medical Center Bronx, NY Oren Becher, MD Department of Pediatrics Department of Pathology Preston Robert Tisch Brain Tumor Center Duke University Medical Center Durham, NC Harolyn M.E. Belcher, MD, MHS Associate Professor of Pediatrics Johns Hopkins School of Medicine (Joint Appointment) Department of Mental Health Johns Hopkins Bloomberg School of Public Health Director of Research Baltimore, MD Jeffrey L. Bennett, MD, PhD Departments of Neurology and Ophthalmology Neuroscience Program University of Colorado Denver, CO Joseph R. Berger, MD University of Kentucky Lexington, KY James D. Berry, MD Massachusetts General Hospital, Department of Neurology Neurological Clinical Research Institute Boston, MA

xviii | C o n t ribu t o r s

Christian G. Bien, MD Hospital Mara Epilepsy Center Bethel Bielefeld, Germany Hal Blumenfeld, MD Departments of Neurology, Neurobiology, and Neurosurgery Yale University School of Medicine New Haven, CT Carmel Bogle, MD Stanford University School of Medicine Department of Pediatrics Stanford, CA Alex Boro, MD Department of Neurology Montefiore Medical Center Albert Einstein College of Medicine New York, NY Brian P. Bosworth, MD Division of Gastroenterology and Hepatology Center for Advanced Digestive Care Weill Medical College of Cornell University New York-​Presbyterian Hospital Ithaca, NY Dejan B. Budimirovic, MD Assistant Professor of Psychiatry & Behavioral Sciences Department of Psychiatry Johns Hopkins University School of Medicine Attending Neuropsychiatrist, Co-​Director of Fragile X Program and Clinic Main Co-​Investigator at Clinical Trials Unit, Kennedy Krieger Institute, The Johns Hopkins Medical Institutions Baltimore, MD Arthur H.M. Burghes, PhD Department of Molecular and Cellular Biochemistry Department of Neurology and Molecular Genetics Wexner Medical Center, The Ohio State University Columbus, OH Vera Joanna Burton, MD, PhD Kennedy Krieger Institute Johns Hopkins School of Medicine Baltimore, MD

Peter A. Calabresi, MD Division of Neuroimmunology and Neurological Infections Department of Neurology Johns Hopkins University School of Medicine Baltimore, MD Jamie Capal, MD Division of Neurology, Department of Pediatrics Cincinnati Children’s Hospital Medical Center Cincinnati, OH George T. Capone, MD Associate Professor of Pediatrics Johns Hopkins University Director of the Down Syndrome Clinic & Research Center Kennedy Krieger Institute Baltimore, MD Richard J. Caselli, MD Department of Neurology Mayo Clinic Scottsdale, AZ Robert W. Charlson, MD Montefiore Headache Center Department of Neurology Albert Einstein College of Medicine Bronx, NY Jeffrey Chinsky, MD, PhD Department of Pediatrics Johns Hopkins University School of Medicine Baltimore, MD Tracey A. Cho, MD Assistant Professor of Neurology Massachusetts General Hospital Harvard Medical School Boston, MA Kelvin L. Chou, MD Thomas H. and Susan C. Brown Early Career Professor Department of Neurology University of Michigan Ann Arbor, MI Melissa Chung, MD The Divisions of Neurology and Critical Care Medicine Department of Pediatrics The Ohio State University and Nationwide Children’s Hospital Columbus, OH Ana-Claire Meyer, MD Assistant Professor Department of Neurology School of Medicine Yale University Hartford, CT

Nikeea Copeland-​Linder, PhD, MPH Assistant Professor of Psychology Trinity Washington University Washington, DC Miguel A. Cortez, MD Neurosciences and Mental Health Program SickKids Research Institute Division of Neurology, Department of Pediatrics University of Toronto Toronto, Ontario, Canada Kathleen Costello, MS, ANP-​BC, MSCN Nurse Practitioner/​Research Associate Johns Hopkins MS/​TM Center Johns Hopkins Hospital Baltimore, MD Peter B. Crino, MD, PhD Department of Neurology Temple University School of Medicine Shriners Hospital Pediatric Research Center Philadelphia, PA David J. Croteau, MD, FRCPC HIV Neurobehavioral Research Center Assistant Professor of Neurosciences University of California San Diego San Diego, CA Andrea T. Cruz, MD, MPH Department of Pediatrics Baylor College of Medicine Houston, TX Josep Dalmau, MD, PhD Institució Catalana de Recerca i Estudis Avançats (ICREA) at Institut d’Investigació Biomèdica August Pi i Sunyer (IDIBAPS) Service of Neurology, Hospital Clínic, University of Barcelona Barcelona, Spain Arif Dalvi, MD, MBA Movement Disorders Program Palm Beach Neuroscience Institute West Palm Beach, FL Rabih O. Darouiche, MD Infectious Disease Section Michael E. DeBakey Veterans Affairs Medical Center Center for Prostheses Infection Baylor College of Medicine Houston, TX

Randall J. Cohrs, PhD Departments of Neurology and Immunology & Microbiology University of Colorado School of Medicine Aurora, CO

Amy I. Davidson, MD Department of Neurology Institute of Neurological Sciences Southern General Hospital, Glasgow Department of Neuroimmunology Institute of Infection, Immunity and Inflammation University of Glasgow Glasgow, Scotland

Anne M. Comi, MD Associate Professor Hugo Moser Kennedy Krieger Research Institute Johns Hopkins School of Medicine Baltimore, MD

Praveen Dayalu, MD Assistant Professor, Division of Movement & Cognitive Disorders Department of Neurology University of Michigan Ann Arbor, MI C o n t ribu t o r s | xix

Lisa M. DeAngelis, MD Chairman Department of Neurology Memorial Sloan-​Kettering Cancer Center New York, NY

Ryan J. Felling, MD, PhD Assistant Professor Department of Neurology Johns Hopkins School of Medicine Baltimore, MD

Kevin C. De Braganca, MD Memorial Sloan-​Kettering Cancer Center New York, NY

Hubert H. Fernandez, MD Professor of Medicine (Neurology) Center for Neurological Restoration Cleveland Clinic Cleveland, OH

Allen Desena, MD The University of Cincinnati Cincinnati, OH Darryl C. De Vivo, MD Department of Neurology Department of Pediatrics Center for Motor Neuron Biology & Disease Columbia University Medical Center New York, NY Katelyn Donaldson, MD Department of Neurology Johns Hopkins School of Medicine Baltimore, MD Jason A. Ellis, MD Department of Neurological Surgery Columbia University Medical Center New York, NY Ronald J. Ellis, MD, PhD Co-​Director HIV Neurobehavioral Research Center Professor of Neurosciences University of California San Diego San Diego, CA Lisa Emrick, MD Texas Children’s Hospital Houston, TX Jerome Engel, Jr., MD Departments of Neurology, Neurobiology, and Psychiatry and Biobehavioral Sciences The Brain Research Institute at UCLA Los Angeles, CA Stewart A. Factor, DO Department of Neurology, School of Medicine Emory University Atlanta, GA Ali Fatemi, MD Kennedy Krieger Institute Johns Hopkins Medical Institutions Baltimore, MD Eva L. Feldman, MD, PhD Departments of Neurology University of Michigan Ann Arbor, MI Kristyn E. Feldman, MD Department of Neurology University of California, San Francisco San Francisco, CA

xx | C o n t ribu t o r s

Laura Ferraiuolo, MD Sheffield Institute for Translational Neuroscience (SITraN) The University of Sheffield Sheffield, UK Massimo Filippi, MD Neuroimaging Research Unit Institute of Experimental Neurology Division of Neuroscience San Raffaele Scientific Institute Vita-​Salute San Raffaele University Milan, Italy John K. Fink, MD Professor, Department of Neurology University of Michigan Geriatric Research, Education, and Clinical Center Ann Arbor Veterans Affairs Medical Center Ann Arbor, MI Eoin P. Flanagan, MBBCh Department of Neurology Mayo Clinic Rochester, MN Matthew Frosch, MD, PhD Neurology Service Massachusetts General Hospital Institute for Neurodegeneration Charlestown, MA Joshuae G. Gallardo, MD Neurology Chief Resident The University of Chicago Department of Neurology Chicago, IL Aruna Ganju, MD Department of Neurological Surgery Northwestern University Feinberg School of Medicine Evanston, IL Jozef Gecz, MD Professor, Robinson Research Institute School of Paediatrics and Reproductive Health The University of Adelaide Adelaide, Australia Romergryko G. Geocadin, MD Departments of Neurology and Neurosurgery Anesthesiology and Critical Care Medicine Johns Hopkins University Baltimore, MD

Gwendolyn J. Gerner, PsyD Kennedy Krieger Institute Johns Hopkins School of Medicine Baltimore, MD Mark R. Gilbert, MD Chief, Neuro-​Oncology Branch Center for Cancer Research National Cancer Institute Bethesda, MD Don Gilden, MD Departments of Neurology and Immunology & Microbiology University of Colorado School of Medicine Aurora, CO Tanjala T. Gipson, MD Tuberous Sclerosis Clinic Department of Neurology and Developmental Medicine Clinical Trials Center Hugo Moser Research Institute Kennedy Krieger Institute Johns Hopkins University School of Medicine Baltimore, MD Gavin Giovannoni, MBBCh, PhD, FCP (Neurol., SA), FRCP, FRCPath Queen Mary University of London Blizard Institute Barts and the London School of Medicine and Dentistry London, England Matthew Gladman, MD Department of Medicine Kingston General Hospital Kingston, Ontario, Canada Katharina Goeral, MD The Hugo W. Moser Research Institute Kennedy Krieger Institute Departments of Neurology & Pediatrics Johns Hopkins University Baltimore, MD William A. Gomes, MD, PhD Department of Radiology Montefiore Medical Center Albert Einstein College of Medicine Bronx, NY Teresa Gomez-​Isla, MD Neurology Service Massachusetts General Hospital Institute for Neurodegeneration Charlestown, MA John A. Goodfellow, BSc(Hons), BM BCh, MRCP(UK), PhD Department of Neurology Institute of Neurological Sciences Glasgow, United Kingdom Jerome J. Graber, MD, MPH Director of Adult Neuro-​oncology Departments of Neurology and Medical Oncology Montefiore Einstein Medical Center Bronx, NY

Jonathan Graff-​Radford, MD Department of Neurology Behavioral Neurology and Movement Disorders Mayo Clinic Rochester, MN Benjamin M. Greenberg, MD, MHS The University of Texas Southwestern Medical Center Dallas, TX John E. Greenlee, MD Neurology Service  George E. Wahlen Veterans Affairs Health Care System Department of Neurology University of Utah Health Sciences Center Salt Lake City, UT Mary Lee Gregory, MD, PhD Kennedy Krieger Institute Johns Hopkins University Baltimore, MD Andrea L. Gropman, MD Children’s National Medical Center George Washington University of the Health Sciences Washington, DC Jonah Grossman, MD Neurocritical Care Fellow, Department of Neurology Clinical Instructor in the Department of Neurology University of Cincinnati Medical Center Cincinnati, OH Renzo Guerrini, MD Pediatric Neurology Children’s Hospital Anna Meyer University of Florence Florence, Italy Yong Guo, MD Department of Neurology Mayo Clinic Rochester, MN David H. Gutmann, MD, PhD Department of Neurology Washington University School of Medicine Saint Louis, MO Afshin Borhani Haghighi, MD Clinical Neurology Research Center Shiraz University of Medical Sciences Shiraz, Iran John J. Halperin, MD Department of Neurosciences Overlook Medical Center, Summit NJ Professor of Neurology & Medicine Mount Sinai School of Medicine New York, NY Neil Haranhalli, MD Department of Neurosurgery Montefiore Einstein Medical Center Bronx, NY

C o n t ribu t o r s | xxi

Matthew B. Harms, MD Neurology Department Washington University in St. Louis St. Louis, MO

Jason T. Huse, MD, PhD Department of Pathology Memorial Sloan-​Kettering Cancer Center New York, NY

Brent T. Harris, MD, PhD Departments of Neurology and Pathology Georgetown University, School of Medicine Washington, DC

Ibrahim Hussain, BA Department of Neurology Washington University School of Medicine Saint Louis, MO

Taylor B. Harrison, MD Department of Neurology Emory University School of Medicine and Grady Memorial Health Systems Atlanta, GA

Samantha Hutchison, MD Kennedy Krieger Institute, Family Center Baltimore, MD

Nicholas S. Havens, MD University of Missouri-​Columbia School of Medicine Division of Infectious Diseases Columbia, MO Jeffrey R. Hebert, PT, PhD Department of Physical Medicine and Rehabilitation Department of Neurology University of Colorado School of Medicine Aurora, CO Dale C. Hesdorffer, PhD, MPH GH Sergievsky Center and Department of Epidemiology Columbia University New York, NY Ellen J. Hess, PhD Department of Neurology Department of Pharmacology Emory University, School of Medicine Atlanta, GA Lucy M. Hinder, PhD Departments of Neurology University of Michigan Ann Arbor, MI Ahmet Höke, MD, PhD Department of Neurology Johns Hopkins School of Medicine Baltimore, MD Bruce T. Hope, PhD Behavioral Neuroscience Branch NIDA Intramural Research Program, NIH, DHHS Baltimore, MD Alexander H. Hoon, Jr., MD Kennedy Krieger Institute Baltimore, MD Virginia J. Howard, PhD Professor of Epidemiology School of Public Health University of Alabama at Birmingham Birmingham, AL Joshua S. Hundert, MD Renal Division, Brigham and Women’s Hospital Harvard Medical School Boston, MA

xxii | C o n t ribu t o r s

Bradley T. Hyman, MD, PhD Neurology Service Massachusetts General Hospital Institute for Neurodegeneration Charlestown, MA Makoto Ishii, MD, PhD Feil Family Brain and Mind Research Institute Weill Cornell Medical College New York, NY Alan C. Jackson, MD Departments of Internal Medicine (Neurology) and Medical Microbiology University of Manitoba Winnipeg, Manitoba, Canada Joan M. Jasien, MD Kennedy Krieger Institute Baltimore, MD Joseph Jankovic, MD Parkinson’s Disease Center and Movement Disorders Clinic Department of Neurology Baylor College of Medicine Houston, TX Mohamed Y. Jefri, MD Kennedy Krieger Institute Johns Hopkins Medical Institutions Baltimore, MD Gregory A. Jicha, MD, PhD Department of Neurology and the Sanders-​Brown Center on Aging University of Kentucky, College of Medicine Lexington, KY H. A. Jinnah, MD, PhD Department of Neurology Department of Human Genetics Department of Pediatrics Emory University, School of Medicine Atlanta, GA Jasmin Jo, MD Department of Neurology Division of Neuro-​Oncology University of Virginia Charlottesville, VA

Michael V. Johnston, MD Kennedy Krieger Institute and Johns Hopkins University School of Medicine Baltimore, MD

Chelsea S. Kidwell, MD Departments of Neurology and Medical Imaging University of Arizona Tucson, AZ

Christopher R. Jones, MD, PhD Department of Neurology, School of Medicine University of Utah Salt Lake City, UT

Karl Kieburtz, MD, MPH Department of Neurology University of Rochester Medical Center Rochester, NY

Keith A. Josephs, MD, MST, MSc Department of Neurology Behavioral Neurology and Movement Disorders Mayo Clinic Rochester, MN

Stephen L. Kinsman, MD Department of Pediatrics Medical University of South Carolina Charleston, SC

Thomas J. Kaley, MD Memorial Sloan Kettering Cancer Center Weill Cornell Medical College New York, NY Bernadette Kalman, MD, PhD, DSc University of Pecs Markusovszky University Teaching Hospital Center for Science and Education Markusovszky, Hungary Meena Kannan, MD Department of Neurology Oregon Health Sciences University Portland VA Medical Center Portland, OR

Jessica Klein, MD Johns Hopkins University Department of Pediatric Neurology Baltimore, MD Stephen J. Kolb, MD Department of Neurology and Department of Biological Chemistry and Pharmacology Ohio State University Wexner Medical Center Columbus, OH Noah Kolb, MD Assistant Professor of Neurology University of Utah Salt Lake City, UH

Rahul Karamchandani, MD Vascular Neurology Fellow University of Texas, Medical School at Houston Houston, TX

Melvin W. Kong, MD Department of Neurology Mid-​Atlantic Permanente Medical Group Mid-​Atlantic Permanente Research Institute Kaiser Permanente of the Mid-​Atlantic States Rockville, MD

Gurvinder Kaur, MD Department of Neurological Surgery Northwestern University Feinberg School of Medicine Evanston, IL

Eric H. Kossoff, MD Department of Pediatric Neurology The John M Freeman Pediatric Epilepsy Center The Johns Hopkins Hospital Baltimore, MD

Galam A. Khan, MD Departments of Neurology Georgetown University, School of Medicine Washington, DC

Vikas Kotagal, MD, MS Assistant Professor, Division of Movement & Cognitive Disorders Department of Neurology University of Michigan Ann Arbor, MI

Roger E. Kelley, MD Professor and Chairman Department of Neurology Tulane University School of Medicine New Orleans, LA Yasmin Khakoo, MD Departments of Pediatrics and Neurology Memorial Sloan-​Kettering Cancer Center Department of Pediatrics Weill Cornell Medical College New York, NY George Khouri, MD Department of Neurology and Neurosurgery Medical University of South Carolina Charleston, SC

Darcy A. Krueger, MD, PhD Director, Tuberous Sclerosis Clinic Cincinnati Children’s Hospital Associate Professor of Pediatrics University of Cincinnati Medical School Cincinnati, OH Eboni I. Lance, MD Medical Director, Sickle Cell Neurodevelopmental Clinic Kennedy Krieger Institute Assistant Professor, Neurology Johns Hopkins University School of Medicine Baltimore, MD

C o n t ribu t o r s | xxiii

Brian R. Landzberg, MD Division of Gastroenterology and Hepatology Center for Advanced Digestive Care Weill Medical College of Cornell University New York-​Presbyterian Hospital Ithaca, NY

Gustavo H. B. Maegawa, MD, PhD, FACMG McKusick-​Nathans Inst. of Genetic Medicine Department of Pediatrics Johns Hopkins University School of Medicine Baltimore, MD

Ryan W. Lee, MD Department of Pediatrics, University of Hawaii Shriners Hospitals for Children–​Honolulu Honolulu, HI

Ravi Mahalingam, PhD Department of Neurology University of Colorado School of Medicine Aurora, CO

Enrique C. Leira, MD, MS Associate Professor of Neurology University of Iowa Carver College of Medicine University of Iowa Comprehensive Stroke Center Iowa City, IA

Ali Mahta, MD Department of Neurology Temple University School of Medicine Shriners Hospital Pediatric Research Center Philadelphia, PA

Doris G. Leung, MD Department of Neurology Kennedy Krieger Institute Johns Hopkins University, School of Medicine Baltimore, MD

Aaron Mammoser, MD, MS Department of Neurology University of Michigan Ann Arbor, MI

James B. Leverenz, MD Lou Ruvo Center for Brain Health Neurological Institute Cleveland Clinic Cleveland, OH Thien Thien Lim, MD Consultant Neurologist Island Hospital Penang, Malaysia Warren Lo, MD The Divisions of Neurology Department of Pediatrics The Ohio State University and Nationwide Children’s Hospital Columbus, OH Zachary London, MD University of Michigan Ann Arbor, MI Carmen Lopez-​Arvizu, MD Assistant Professor of Psychiatry and Behavior Sciences Child & Adolescent Psychiatry Johns Hopkins School of Medicine Kennedy Krieger Institute Baltimore, MD Phillip A. Low, MD Mayo Clinic Rochester, MN Claudia Francesca Lucchinetti, MD Department of Neurology Mayo Clinic Rochester, MN Kelly E. Lyons, PhD Department of Neurology University of Kansas Medical Center Kansas City, KS

xxiv | C o n t ribu t o r s

Carla Marini, MD Pediatric Neurology Children’s Hospital Anna Meyer Florence, Italy John D. Markman, MD University of Rochester Medical Center School of Medicine and Dentistry Rochester, NY Davide Martino, PhD Queen Mary University of London Blizard Institute Barts and the London School of Medicine and Dentistry London, England James A. Mastrianni, MD, PhD Associate Professor of Neurology Director, Center for Comprehensive Care and Research on Memory Disorders The University of Chicago Pritzker School of Medicine Chicago, IL Rebecca McClellan, MGC, CGC Department of Neurogenetics Johns Hopkins University School of Medicine Baltimore, MD Elisa McEachern, MD Division of Gastroenterology and Hepatology Center for Advanced Digestive Care Weill Medical College of Cornell University New York-​Presbyterian Hospital Ithaca, NY Vicki L. McGovern, MD Department of Molecular and Cellular Biochemistry Wexner Medical Center, The Ohio State University Columbus, OH

Andrew McKeon, MD Neuroimmunology Laboratory Mayo Clinic Rochester, MN Deepa U. Menon, MBBS, MD Kennedy Krieger Institute Baltimore, MD Timothy M. Miller, MD, PhD Neurology Department Washington University in St. Louis St. Louis, MO Agusto A. Miravalle, MD Assistant Professor Neurology Department of Neurology University of Colorado Denver, CO Umrao R. Monani, PhD Department of Pathology & Cell Biology Department of Neurology Center for Motor Neuron Biology & Disease Columbia University Medical Center New York, NY Kassandra L. Munger, ScD Department of Nutrition Harvard School of Public Health Boston, MA Kambiz Nael, MD Department of Medical Imaging University of Arizona Tucson, AZ Maria A. Nagel, MD Department of Neurology University of Colorado School of Medicine Aurora, CO SakkuBai Naidu, MD The Moser Center for Leukodystrophies Kennedy Krieger Institute Johns Hopkins School of Medicine Baltimore, MD Kazuma Nakagawa, MD Neurovascular and Neurocritical Care Department of Medicine, Division of Neurology University of Hawaii, John A. Burns School of Medicine Honolulu, HI Karthi Nallasamy, MD Assistant Professor, Pediatrics Advanced Pediatrics Centre Department of Pediatrics Post Graduate Institute of Medical Education and Research Chandigarh, India Avindra Nath, MD Section of Infections of the Nervous System National Institute of Neurological Diseases and Stroke National Institutes of Health Bethesda, MD

Scott D. Newsome, DO Department of Neurology, Division of Neuroimmunology and Neurological Infections Johns Hopkins University School of Medicine Baltimore, MD Katharine A. Nicholson, MD Massachusetts General Hospital, Department of Neurology Neurological Clinical Research Institute Boston, MA Dragos A. Nita, MD Neurosciences and Mental Health Program SickKids Research Institute Division of Neurology, Department of Pediatrics University of Toronto Toronto, Ontario, Canada Craig Nolan, MD Memorial Sloan-​Kettering Cancer Center New York, NY Dustin Nowacek, MD Bronson Neuroscience Center Kalamazoo, MI Christopher Oakley, MD Johns Hopkins University Department of Pediatric Neurology Baltimore, MD John L. O’Donoghue, VMD, PhD, DABT Adjunct Associate Professor of Environmental Medicine School of Medicine and Dentistry University of Rochester Rochester, NY Edore C. Onigu-​Otite, MD Assistant Professor Menninger Department of Psychiatry and Behavioral Sciences Baylor College of Medicine Houston, TX Éilis J. O’Reilly, ScD Department of Nutrition Harvard School of Public Health Channing Division of Network Medicine Department of Medicine, Harvard Medical Brigham and Women’s Hospital Boston, MA Henry J. Orff, PhD Department of Psychiatry University of California—​San Diego San Diego, CA Bruce Ovbiagele, MD, MSc, MAS Department of Neurology and Neurosurgery Medical University of South Carolina Charleston, SC

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Shelly Ozark, MD Department of Neurology and Neurosurgery Medical University of South Carolina Charleston, SC Roger J. Packer, MD Children’s National Medical Center Washington, DC Sabrina Paganoni, MD, PhD Harvard Medical School, Department of Neurology Neurological Clinical Research Institute (NCRI) Massachusetts General Hospital Department of Physical Medicine and Rehabilitation Spaulding Rehabilitation Hospital VA Boston Healthcare System Boston, MA Christian Pagnoux, MD, MPH, MSc Mount Sinai Hospital, Division of Rheumatology—​Vasculitis Clinic Toronto, Ontario, Canada Rajesh Pahwa, MD Department of Neurology University of Kansas Medical Center Kansas City, KS Belen Pappa, MD Children’s National Medical Center George Washington University of the Health Sciences Washington, DC Toral R. Patel, MD Assistant Professor, Department of Neurosurgery The University of Texas Southwestern Medical Center Dallas, TX Marc C. Patterson, MD, FRACP Professor of Neurology, Pediatrics and Medical Genetics Mayo Clinic College of Medicine Chair, Division of Child and Adolescent Neurology Mayo Clinic Children’s Center Rochester, MN Henry L. Paulson, MD, PhD Department of Neurology University of Michigan Ann Arbor, MI Phillip L. Pearl, MD Director of Epilepsy and Clinical Neurophysiology Boston Children’s Hospital William G. Lennox Chair and Professor of Neurology Harvard Medical School Boston, MA Emilio Perucca, MD Clinical Pharmacology Unit Department of Internal Medicine and Therapeutics University of Pavia C. Mondino National Neurological Institute Pavia, Italy Beatriz G. Perez-​Nievas, PhD Neurology Service Massachusetts General Hospital Institute for Neurodegeneration Charlestown, MA xxvi | C o n t ribu t o r s

Frank S. Pidcock, MD Associate Professor Physical Medicine Rehabilitation and Pediatrics Johns Hopkins School of Medicine Baltimore, MD Wilfred R. Pigeon, PhD The Sleep and Neurophysiology Laboratory Department of Psychiatry University of Rochester Rochester, NY Jagan A. Pillai, MD, PhD Lou Ruvo Center for Brain Health Neurological Institute Cleveland Clinic Cleveland, OH Erik P. Pioro, MD, PhD Department of Neuology and Neurosciences Neuromuscular Center Cleveland Clinic Cleveland, OH Scott R. Plotkin, MD, PhD Stephen E. and Catherine Pappas Center for Neuro-​Oncology Department of Neurology Massachusetts General Hospital Cancer Center Harvard Medical School Boston, MA Bogdan Florin Gh. Popescu, PhD Department of Anatomy and Cell Biology Cameco MS Neuroscience Research Center University of Saskatchewan Saskatoon, Saskatchewan, Canada Andrea Poretti, MD Department of Pediatric Neuroradiology Johns Hopkins University School of Medicine Baltimore, MD John C. Probasco, MD Assistant Professor Department of Neurology Johns Hopkins University School of Medicine Baltimore, MD Cecilia N. Prudente, MD Department of Neurology Emory University, School of Medicine Atlanta, GA Angela Quain, MS, MD Eastern Virginia Medical School Norfolk, VA Alejandro A. Rabinstein, MD Department of Neurology, Mayo Clinic Rochester, MN Michael S. Rafii, MD, PhD Department of Neurosciences University of California San Diego, CA

Vijay Ramaswamy, MD, FRCPC Program in Developmental and Stem Cell Biology Hospital for Sick Children Department of Laboratory Medicine and Pathobiology University of Toronto Toronto, Ontario, Canada Gerald V. Raymond, MD Department of Neurology University of Minnesota Minneapolis, MN Daniel S. Reich, MD, PhD Translational Neuroradiology Unit National Institute of Neurological Disorders and Stroke (NINDS) National Institutes of Health (NIH) Bethesda, MD Andrew Ringer, MD Department of Neurosurgery University of Cincinnati College of Medicine Comprehensive Stroke Center at UC Neuroscience Institute Mayfield Clinic Cincinnati, OH Lucia Rivera-​Lara, MD Instructor of Neurology Dept. Anesthesiology and Critical Care Medicine Division of Neurosciences Critical Care Medicine Johns Hopkins University Baltimore, MD Matthew S. Robbins, MD Montefiore Headache Center Department of Neurology Albert Einstein College of Medicine Bronx, NY Maria A. Rocca, MD Neuroimaging Research Unit Institute of Experimental Neurology Division of Neuroscience San Raffaele Scientific Institute Vita-​Salute San Raffaele University Milan, Italy William E. Roland, MD, FACP University of Missouri-​Columbia School of Medicine Division of Infectious Diseases Columbia, MO Samuel J. Rose, PhD Department of Pharmacology Emory University, School of Medicine Atlanta, GA Richard B. Rosenbaum, MD The Oregon Clinic Affiliate Professor of Neurology Oregon Health and Sciences University Portland, OR Myrna R. Rosenfeld, MD, PhD Hospital Clínic/​IDIBAPS Department of Neurology Barcelona, Spain

Victor Rosenfeld, MD Medical Director, Neurology SouthCoast Medical Group Savannah, GA Mark N. Rubin, MD Department of Neurology, Mayo Clinic Rochester, MN James W. Russell, MD, MS, FRCP Department of Neurology Maryland VA Healthcare System University of Maryland Baltimore, MD Saed Sadeghi, MD Departments of Neurology Georgetown University, School of Medicine Washington, DC Lynette G. Sadleir, MD Associate Professor, Department of Paediatrics School of Medicine and Health Sciences University of Otago Wellington, New Zealand Shiv Saidha, MBBCh, MD, MRCPI Department of Neurology Division of Neuroimmunology and Neuroinfectious Diseases Johns Hopkins University School of Medicine Baltimore, MD Arushi G. Saini, MD, DM Pediatric Neurology Senior Resident, Pediatric Neurology and Neurodevelopment Advanced Pediatrics Centre, Department of Pediatrics Post Graduate Institute of Medical Education and Research Chandigarh, India Stacey A. Sakowski, PhD A. Alfred Taubman Medical Research Institute University of Michigan Ann Arbor, MI E. Sander Connolly, Jr., MD Department of Neurological Surgery Columbia University Medical Center New York, NY Naveen Sankhyan, MD, PhD Assistant Professor, Pediatric Neurology and Neurodevelopment Advanced Pediatrics Centre, Department of Pediatrics Post Graduate Institute of Medical Education and Research Chandigarh, India Deanna Saylor, MD, MHS Chief Resident Department of Neurology Johns Hopkins University School of Medicine Baltimore, MD

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Ingrid E. Scheffer, MD Professor, Epilepsy Research Centre Department of Medicine, University of Melbourne Austin Health Melbourne, Australia Florey Institute, University of Melbourne Victoria, Australia Department of Paediatrics, University of Melbourne Royal Children’s Hospital Melbourne, Australia David Schiff, MD Department of Neurology Division of Neuro-​Oncology University of Virginia Charlottesville, VA Frederick A. Schmitt, PhD Department of Neurology and the Sanders-​Brown Center on Aging University of Kentucky, College of Medicine Lexington, KY Teri L. Schreiner, MD, MPH Departments of Neurology and Pediatrics Children’s Hospital Colorado University of Colorado Denver, CO Ulrike Schrifl, MD The Moser Center for Leukodystrophies Kennedy Krieger Institute Johns Hopkins School of Medicine Baltimore, MD Kristin Schroeder, MD, MPH Duke University Medical Center Department of Pediatrics, Division of Hematology-​Oncology Durham, NC Peter W. Schutz, MD, PhD Department of Pathology and Laboratory Medicine University of British Columbia Resident, Division of Neuropathology Vancouver General Hospital Vancouver, British Colombia, Canada Jennifer Serico, PhD The Family Center at Kennedy Krieger Institute Baltimore, MD Alberto Serrano-​Pozo, MD, PhD Neurology Service Massachusetts General Hospital Institute for Neurodegeneration Charlestown, MA Minal A. Shah, MD Department of Internal Medicine Baylor College of Medicine Houston, TX Vikram G. Shakkottai, MD, PhD Department of Neurology University of Michigan Ann Arbor, MI

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Tanzila Shams, MD Diplomat of American Board of Psychiatry and Neurology Interventional Neurology, Endovascular Surgical Neuroradiology Texas Stroke Institute HCA, North Texas Division Plano, TX Ejaz A. Shamim MD, MS Department of Neurology Mid-​Atlantic Permanente Medical Group Mid-​Atlantic Permanente Research Institute Kaiser Permanente of the Mid-​Atlantic States Rockville, MD Bruce K. Shapiro, MD Department of Neurology and Developmental Medicine Kennedy Krieger Institute Depart of Pediatrics Johns Hopkins University School of Medicine Baltimore, MD Cathy Sila, MD George M. Humphrey II Professor and Vice Chair of Neurology Director, Comprehensive Stroke Center University Hospitals Case Medical Center Case Western Reserve University School of Medicine Cleveland, OH Michael Silver, MD Department of Neurology, School of Medicine Emory University Atlanta, GA A. Gordon Smith, MD Professor of Neurology Chief Division of Neuromuscular Medicine University of Utah Salt Lake City, UH C. L. Smith-​Hicks, MD Department of Neurology Kennedy Krieger Institute Johns Hopkins University School of Medicine Baltimore, MD Ajay Singh, MD Renal Division, Brigham and Women’s Hospital Harvard Medical School Boston, MA Anika T. Singh, MD Renal Division, Brigham and Women’s Hospital Harvard Medical School Boston, MA Pratibha Singhi, MD, PhD Professor and Chief, Pediatric Neurology and Neurodevelopment Advanced Pediatrics Centre, Department of Pediatrics Post Graduate Institute of Medical Education and Research Chandigarh, India Sunit Singhi, MD, PhD Professor and Head, Chief, Pediatric Intensive Care Advanced Pediatrics Centre, Department of Pediatrics Post Graduate Institute of Medical Education and Research Chandigarh, India

O. Carter Snead, III, MD Neurosciences and Mental Health Program SickKids Research Institute Division of Neurology, Department of Pediatrics University of Toronto Toronto, Ontario, Canada Michael J. Soileau, MD Movement Disorders Fellow Department of Neurology University of Texas-​Houston Houston, TX Siddharth Srivastava, MD Department of Neurology and Development Kennedy Krieger Institute Johns Hopkins University Baltimore, MD Carl E. Stafstrom, MD, PhD Division of Pediatric Neurology Departments of Neurology and Pediatrics Johns Hopkins Hospital Baltimore, MD David G. Standaert, MD, PhD John N. Whitaker Professor and Chair of Neurology University of Alabama at Birmingham Birmingham, AL Verena Staedtke, MD, PhD Department of Pediatric Neurology The John M Freeman Pediatric Epilepsy Center The Johns Hopkins Hospital Baltimore, MD Jeffrey R. Starke, MD Department of Pediatrics Baylor College of Medicine Houston, TX John Stern, MD Professor, Department of Neurology Geffen School of Medicine at UCLA Los Angeles, CA Sylvia Stockler, MD, PhD, MBA, FRCPC Professor, Department of Pediatrics University of British Columbia Head, Division of Biochemical Diseases British Columbia Children’s Hospital Vancouver, British Colombia, Canada Elsdon Storey, PhD Department of Medicine (Neuroscience) Monash University Melbourne, Australia Mariflor Jamora, MD Child and Adolescent Psychiatrist Kennedy Krieger Institute Assistant Professor Johns Hopkins School of Medicine Department of Psychiatry Baltimore, MD

Megha Subramanian, BA Neuroscience PhD candidate at Solomon Snyder Department of Neuroscience Johns Hopkins University School of Medicine Baltimore, MD Kelli A. Sullivan, PhD Departments of Neurology and Medical Education University of Michigan Ann Arbor, MI Shannon S. Sullivan, MD Stanford University School of Medicine Palo Alto, CA Lisa Sun, MD Departments of Neurology and Pediatric Johns Hopkins Hospital Baltimore, MD Ritika Suri, MD Renal Division, Brigham and Women’s Hospital Harvard Medical School Boston, MA Arun Swaminathan, MBBS University of Kentucky Lexington, KY Richard H. Swartz, HBSc, MD, PhD, FRCPC Sunnybrook Health Sciences Centre, Division of Neurology—​Stroke Prevention Clinic Toronto, Ontario, Canada Viviane S. Tabar, MD Professor, Department of Neurosurgery Memorial Sloan-​Kettering Cancer Center New York, NY Jennie Taylor, MD Center for Neuro-​Oncology, Dana-​Farber Cancer Institute Division of Neurology, Department of Neurology Brigham and Women’s Hospital Harvard Medical School Boston, MA James W. Teener, MD Director, Neuromuscular Program University of Michigan Medical School Ann Arbor, MI Nimish J. Thakore, MD, DM Assistant Professor of Medicine (Neurology) Cleveland Clinic Lerner College of Medicine Staff Neurologist Neuromuscular Center and Center for Regional Neurology, Cleveland Clinic Cleveland, OH Kiran Thakur, MD Post-​Doctoral Fellow Division of Neuroinfectious Disease and Neuroimmunology Department of Neurology Johns Hopkins Hospital Baltimore, MD

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Brett J. Theeler, MD Major, Medical Corps, United States Army Department of Neurology and John P. Murtha Cancer Center Walter Reed National Military Medical Center Bethesda, MD Maarten J. Titulaer, MD, PhD Hospital Clínic/​IDIBAPS Department of Neurology Barcelona, Spain Bela R. Turk, MD Kennedy Krieger Institute Johns Hopkins University School of Medicine Baltimore, MD William Tyor, MD Professor of Neurology Emery University Atlanta, Georga Jose Luis Perez Velazquez, MD Neurosciences and Mental Health Program SickKids Research Institute Division of Neurology, Department of Pediatrics University of Toronto Toronto, Ontario, Canada Arun Venkatesan, MD, PhD Assistant Professor, Department of Neurology Johns Hopkins University School of Medicine Baltimore, MD Charles S. Venuto, PharmD Department of Neurology University of Rochester Medical Center Rochester, NY Rashmi Verma, MD Renal Division, Brigham and Women’s Hospital Harvard Medical School Boston, MA Hilary Vernon, MD, PhD Assistant Professor of Genetic Medicine McKusick-​Nathans Institute of Genetic Medicine Johns Hopkins University Baltimore, MD Ivana Vodopivec, MD, PhD Clinical Fellow in Neurology and Neuro-​ophthalmology Massachusetts General Hospital Massachusetts Eye and Ear Infirmary Harvard Medical School Boston, MA Brian J. Wainger, MD, PhD Assistant Professor of Neurology Massachusetts General Hospital Harvard Medical School Harvard Stem Cell Institute Boston, MA

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Olga Waln, MD Houston Methodist Neurological Institute Houston, TX Joseph Weiner, MD Department of Neurological Surgery Northwestern University Feinberg School of Medicine Evanston, IL Jacqueline Weissman, MD, MS Kennedy Krieger Institute Johns Hopkins University Baltimore, MD Killian A. Welch, PhD Consultant Neuropsychiatrist and Honorary Clinical Senior Lecturer Robert Fergusson Unit, Astley Ainslie Hospital, Edinburgh Department of Psychiatry, Edinburgh University Edinburgh, Scotland Mary R. Welch, MD Memorial Sloan-​Kettering Cancer Center New York, NY William P. Welch, MD UPMC Child Neurology Pittsburgh, PA Elizabeth M. Wells, MD, MHS Department of Neurology and Brain Tumor Institute Children’s National Washington, DC Patrick Y. Wen, MD Center for Neuro-​Oncology, Dana-​Farber Cancer Institute Division of Neurology, Department of Neurology Brigham and Women’s Hospital Harvard Medical School Boston, MA Tyler R. West, DO Resident Physician Department of Neurology Geisinger Medical Center Danville, PA Jeri Yvonne Williams, MD John N. Whitaker Professor and Chair of Neurology University of Alabama at Birmingham Birmingham, AL Hugh J. Willison, MD Department of Neurology Institute of Neurological Sciences Southern General Hospital, Glasgow Department of Neuroimmunology Institute of Infection, Immunity and Inflammation University of Glasgow Glasgow, Scotland Michael Wheaton, MD University of Michigan Ann Arbor, MI

Leslie R. Whitaker Behavioral Neuroscience Branch NIDA Intramural Research Program, National Institute of Health, Department of Health and Human Services Baltimore, MD Hugh J. Willison MBBS, PhD, FRCP, FRSE University of Glasgow College of Medical, Veterinary, and Life Sciences Institute of Infection, Immunity and Inflammation Glasgow, Scotland David S. Wolf, MD, PhD Division of Child Neurology Emory University School of Medicine Children’s Healthcare of Atlanta Atlanta, GA

Mark W. Youngblood, MD Departments of Neurology Yale University School of Medicine New Haven, CT Lindsay Zilliox, MD Department of Neurology Maryland VA Healthcare System University of Maryland Baltimore, MD Andrew W. Zimmerman, MD Clinical Professor of Pediatrics and Neurology University of Massachusetts Memorial Medical Center Worcester, MA Lorne Zinman, MD, MSc Department of Medicine Sunnybrook Health Sciences Centre Toronto, Ontario, Canada

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S E C T ION   I |  M  OVEMEN T D I SO R DER SJOEL S. PER L M UTTER , WASHIN GT O N UN I VER SI TY

1 | HISTORY OF PARKINSONISM MI CH AE L S ILVE R A N D S T E WA RT A.   FA CTOR

D EFINITION Parkinson’s disease (PD) is characterized by the motor symptoms tremor, rigidity, slow movements (bradykinesia), and a loss of postural reflexes. All neurological disorders that resemble PD are categorized as having parkinsonism because of the presence of some or all of these features. Some of these are referred to as “Parkinson-​plus disorders” because they have the core features plus others such as autonomic dysfunction or extraocular abnormalities.

INTRODU CTION Since its initial description in 1817 by Dr. James Parkinson, a tremendous amount of research into its potential causes has been done in PD, but much work remains. Despite a lack of understanding of the fundamental nature of the disorder, great advances in symptomatic treatment have been developed. Patients with PD now often expect a better quality of life than at any other time in history. Our objective is to review the important clinical discoveries that led us to this point.

brilliantly describes the characteristic rest tremor, stooped posture, slowness, festinating and even freezing gait. He defined the disorder as “Involuntary tremulous motion, with lessened muscular power, in parts not in action and even when supported; with a propensity to bend the trunk forward, and to pass from a walking to a running pace: the senses and intellects being uninjured.” He did not describe the rigidity presumably because he did not touch the patients. With the benefit of two centuries of clinical experience we now know that some aspects of his definition are not valid. The muscular power is typically normal, just seemingly weak because of poor dexterity, coordination and bradykinesia. The senses are in fact affected, as the sense of smell is usually decreased4 and pain occurs in a substantial number of patients.5 Furthermore, the “intellects” are involved because cognitive decline commonly occurs.6 He did, however, accurately remark upon some of the prominent non-​motor symptoms of the disease including sleep disturbance and constipation. He commented on the progressive course, the gait abnormalities, and the less palpable motor symptoms including drooling and dysphagia. With great insight, he included one man without any tremor in his case series, as this subject showed the other classic signs of the disorder.

1800 s J AME S PARKINSON Western medical literature on tremor was scant before James Parkinson’s landmark publication. Ancient texts going as far back to Hippocrates, Celsus, and Galen mention tremor but lack clinical characterization. Sylvius in the 17th century was the first to delineate the difference between rest tremor and action tremor.1 However, tremor was usually discussed in isolation. No connections were made to other motor features that are now known to be central to PD. James Parkinson was a general physician who practiced in London in the late 18th to early 19th century. Besides being an astute physician and surgeon, he was also a noted paleontologist, chemist, and political essayist.2 His medical writing spanned medicine, from the first English description of acute appendicitis to the neurological complications of being struck by lightning. In 1817, toward the end of his career, he published “An Essay on the Shaking Palsy.”3 This small case series was the first published comprehensive clinical description of the shaking palsy. The text is noted for its astute observations and descriptions of almost all the major features of PD. The paper only included six patients and only half were actually seen in the clinic by Parkinson. One was spotted at a distance and Dr. Parkinson never spoke to him, and two were quickly interviewed after he noticed them walking on the street. Of those that he actually saw in clinic, there is no evidence that he actually performed an actual hands-​on physical examination. The disorder that Parkinson described was referred to as the “shaking palsy,” or by its Latinized version paralysis agitans. Parkinson

After his initial description, there were multiple references to James Parkinson’s paper in the literature. Case reports, many times inaccurately identifying cases as paralysis agitans, were published. Paralysis agitans was mentioned in medical text books, but they mostly referenced Parkinson’s original paper. However, there was no effort made to gather a larger cohort of patients with the disorder or describe any new or novel features of the disease.7

C HARC OT It was not until 1861 that the understanding of the disorder was advanced further. The French neurologist Jean-​ Martin Charcot defined more clearly what did and did not qualify as PD. At the time, his contemporaries often confused PD with other neurological disorders such as Multiple Sclerosis. Through his large cohort of patients at the Salpêtrière in Paris, he was able to examine the widest variety of PD patients. He came to the conclusion that true muscular weakness in the condition was overstated. Charcot separated bradykinesia from rigidity as two separate phenomena and emphasized that tremor was not necessary to make the diagnosis. He also suggested that the name be changed from paralysis agitans to Parkinson’s disease. Charcot was known to try several medications to treat PD. Among them were hyoscyamine, which is a naturally occurring anticholinergic agent, and also some ergot products, which are the basis for first-​generation modern-​day dopamine agonists.8

1 H i s t o r y o f Pa r k i n s o n i s m | 3

G OWE RS Sir William Gowers of England expanded further upon previous descriptions of PD, based upon his personal experience with 80 PD patients. He published his findings in 1888’s A Manual of Diseases of the Nervous System.9 Although overemphasizing true weakness as a feature of the disorder, the text did much to expand further upon the phenomenology of PD, especially the characteristic tremor. Gowers identified which muscles were involved in generating the tremor. He quantified tremor frequency by attaching a metal rod to the affected tremoring body part, which would make marks on a steadily moving piece of paper. Gowers made firm distinctions between the tremors of PD and those of alcohol intoxication, hyperthyroidism, hysteria, and other conditions.10

VON E C ONOMO In the second and third decades of the 20th century, the world saw one of the worst pandemics in history. Encephalitis lethargica, aka, epidemic encephalitis or von Economo’s encephalitis, was a frequently fatal form of infectious encephalitis that appeared around the same time as, and perhaps was caused by, the Spanish influenza. This especially virulent form of influenza swept through Europe and then many other parts of the world.11 In 1917, Constantine von Economo described 13 patients in Vienna with encephalitis and their bizarre neurological sequelae.12 Some had an “amyostatic-​akinetic” outcome, characterized by vegetative symptoms, apathy, and tremor. Some patients had lethargy associated with ophthalmoplegia and others had the opposite clinical picture, dominated by hyperkinetic symptoms. By 1920, he started observing a chronic form of parkinsonism in these survivors. It developed in many patients who had made a full recovery from the encephalitis, while others developed it from the “amyostatic-​akinetic” form. This species of parkinsonism was frequently associated with a variety of debilitating psychiatric disturbances and was most unique in its tendency to cause oculogyric crises. Patients would have tonic spasms of the eyes upward and laterally lasting minutes, sometimes associated with involuntary contortions of the neck and body.13 Based on the experience from postencephalitic parkinsonian patients, it was at that time believed that all cases of PD were of viral origin.

PAT HOLOG ICA L STU D Y A D VANC ES Pathological studies in the mid to late 19th century focused on the cerebral cortex and spinal cord and as a consequence the changes in the basal ganglia and brainstem were missed.8 Eduard Brissaud, an associate of Charcot, brought attention to the pathological basis of PD by describing the case of a patient with hemi-​parkinsonism who had a tuberculoma in the substantia nigra.14 Fritz Lewy was a neuropathologist in the first half of the 20th century who made a major contribution to the known pathology of PD. He was a German Jew and Nazi policies forced him out of his position as an academic physician. He later moved to the United States and changed his name to Frederic Lewey. While still in Germany in 1913, he described the characteristic intracytoplasmic neuronal inclusions when he was working with Alzheimer.15,16 These “Lewy bodies” are now considered to be a key feature for the pathological diagnosis of PD. He first discovered these in the dorsal vagal nucleus, but they were later observed in other areas of the brain by himself and others.17–​20 In 1919, Tretiakoff examined the autopsied brains from 12 patients with parkinsonism as part of his doctorate thesis. Nine of his cases 4 | M o v e m e n t D i s o r de r s

had PD and three had postencephalitic parkinsonism. He concluded that the substantia nigra was an important site of pathology in PD. The brainstem specimens from PD patients showed a marked loss of the pigmented nigral neurons with swelling of cell bodies, “grumous” degeneration, and neurofibrillary alterations. In some of the surviving neurons, Tretiakoff found the telltale Lewy bodies.21 In comparison, the postencephalitic cases showed destruction of the substantia nigra with hyaline and granular degeneration in the few surviving cells.17 Despite these key findings, the scientific community did not fully accept the localization of PD until 1953. Joseph Godwin Greenfield, the famed pathologist, examined the brains of 19 PD patients and found Lewy bodies in all.22 The inclusions were primarily in the substantia nigra and the locus coeruleus. He also noted degeneration in the substantia nigra, mostly in the zona compacta.22 In 1988, McGeer and colleagues reported on the presence of active microglia in the nigra that would explain the the progressive nature of the disease. In more recent times the notion that inflammation is a key ingredient in the progressive course of PD has come to the forefront.23

PARKINSON-​P L U S SYN DROM E S The so called “Parkinson-​plus” syndromes or “atypical parkinsonian” syndromes merit discussion in the history of PD because they are important in the differential diagnosis, with overlapping manifestations and pathophysiology. Four of them are particularly important because they also reflect idiopathic neurodegenerative conditions. They were, for the most part, described in the 1960s and include multiple system atrophy, dementia with Lewy bodies (DLB), progressive supranuclear palsy, and corticobasal degeneration. They all resemble PD in some aspect of their phenotype, but brain pathology reveals distinct processes. They are differentiated clinically by their unique characteristics (the “plus” symptoms) and disappointing responses to levodopa. The term “multiple system atrophy” (MSA) first appeared in the literature in 1969,24 but cases had been collected in the past under the names olivopontocerebellar atrophy (OPCA),25 Shy-​Drager syndrome,26 and striatonigral degeneration (SND).27 These conditions were chiefly known for the predominance of particular clinical features, including: cerebellar findings in OPCA, autonomic instability in Shy-​Drager syndrome, and akinetic-​rigid parkinsonism in SND. In 1989, Papp and colleague’s major finding that all of these conditions contain glial cytoplasmic inclusions linked them together into one broad clinicopathological diagnosis.28 The nomenclature has changed and these disparate disorders are now considered subtypes of MSA. Now OPCA is MSA-​C, SND is MSA-​P, and Shy-​Drager syndrome is MSA-​A. Diagnostic criteria have been established for MSA and updated in 2008.29 Dementia with Lewy bodies, a condition involving parkinsonism with early hallucinations and dementia, was first described in 1961.30 The first diagnostic criteria was developed in 1996.31 There is still no universally accepted pathological criteria of DLB, because its histology may be identical to that found in patients with Parkinson’s Disease with dementia with or without some pathological features of Alzheimer’s Disease such as abnormal deposition of Aβ42 amyloid. Some consider this to be the same as idiopathic PD despite the relatively early onset of cognitive impairment with respect to the onset of motor manifestations of PD. Progressive supranuclear palsy (PSP), or Steele-​ Richardson-​ Olszewski disease, was described in 1964 and based on nine patients with limited vertical eye gaze, increased neck tone, and early propensity to fall.32 This became widely recognized worldwide and

several groups developed diagnostic criteria, but the most refined and accepted criteria came out in 1996 with the NINDS-​SPSP report.33 Varied phenotypes of PSP have now been described. Corticobasal degeneration is the least common Parkinson-​plus disorder. Clinically, it is distinguished from PD by its prominent asymmetry and apraxia. It was first described by Rebeiz in 196834 after observing three patients at Massachusetts General Hospital with a similar syndrome. Neuropathological criteria were standardized in 2002.35

PRE -​L EVODO PA M ED S Long before the discovery of levodopa, there were medications known to treat the symptoms of PD. The ancient Indian medical philosophy known as Ayurveda described a disorder called Kampavata involving bradykinesia and tremor, probably the earliest non-​Western description of PD. The seeds of the plant Mucuna Pruriens, which contain naturally occurring levodopa, had been used for centuries in India.36 Hyoscyamine, from the seeds of Hyoscyamus niger, which has anti-​cholinergic effects, also had been prescribed. Western practitioners recommended anticholinergics as well, like belladona or hyoscyamine, and ergot-​based preparations, now known to act as post-​synaptic dopamine agonists.8

demonstrated the unquestionable efficacy of high dose, oral levodopa treatment. His first double-​blind study proved that chronic, large doses of D, L-​dopa improved most patients with PD. Slow titration made levodopa more tolerable.45 Nevertheless, the peripheral effects of dopamine including nausea, vomiting, and orthostatic hypotension frequently limited levodopa therapy. Two years later, Cotzias attempted therapy with L-​dopa alone, instead of the racemic mixture. Twenty-​eight patients were given escalating doses, and the titration was stopped when the optimal dose was achieved. Bradykinesia, rigidity, and tremor all improved, as did gait, dysphagia, drooling, and handwriting. Patients developed a sense of “well being.” The effect lasted, and some of the previously disabled subjects in the study were able to return to work. Even in this early study, some patients developed levodopa-​induced dyskinesias and motor fluctuations.46 The main side effects of levodopa, nausea and vomiting, were caused by the peripheral decarboxylation of levodopa into dopamine before levodopa crossed the blood–​brain barrier. Implementation of the peripherally acting dopa decarboxylase inhibitors drastically reduced these side effects. Several groups tried different compounds, but ultimately carbidopa became the drug of choice after testing proved its efficacy.47–​49 Carbidopa combined with levodopa in one pill substantially simplified drug therapy and was released as Sinemet® in 1975. The name was derived from the Latin sin emet, which means “without vomiting.” The combination of levodopa and benserazide (another dopa decarboxylase inhibitor) was introduced 1 year earlier under the name Madopar® into European markets.

D OPAMIN E AN D L EVO DO PA Wilhelm Raab, a German cardiologist who settled in the United States, was probably the first to discover dopamine’s presence in the brain. In the late 1940s, he isolated a new adrenaline-​like compound from the mammalian brain and named it encephalin.37 He found the highest concentrations in the caudate nucleus and even found that administration of parenteral levodopa raised its levels in the brain.38 This line of research was abandoned, however, only to be rediscovered years later when the full relevance of dopamine was appreciated. Arvid Carlsson brought the importance of dopamine in PD and the therapeutic possibilities of levodopa to light through his work on the effects of the monoamine depleting agent reserpine in animals. He found that reserpine depleted brain dopamine, serotonin, and noradrenalin.39 The drug immobilized animals in a manner that was initially thought to be similar to a tranquilizer. They demonstrated that administered levodopa increased the levels of dopamine in the brain and reversed the akinetic effects of reserpine.40 He ultimately won the Nobel prize in 2000 for this work. In 1959, two workers from Carlsson’s lab, Bertler and Rosengren, showed that the striatum contained the highest concentration of dopamine in dogs’ brains.41 Sano in Japan found the same results in normal human subjects.42 Hornykiewicz and Ehringer then discovered depletion of dopamine in these parts of the brain from postmortem studies on PD brain tissue.43 Over the next 10 years, the most important therapeutic advance in PD took place: the creation of an oral dopamine replacement therapy, levodopa. Degwitz already demonstrated that levodopa could reverse the sedating effects of reserpine in humans; however, it had never been tried in a PD patient.44 Ten months later, in July 1961, Hornykiewicz and Birkmayer intravenously infused small amounts of levodopa into PD patients. These first therapeutic trials demonstrated astounding effects. Previously akinetic, bed-​ridden patients were able to sit and move. Patients who had been able to only stand could now walk. Other investigators used oral formulations of levodopa (L-​dopa) and its enantiomer D-​dopa with mixed results. The investigation of levodopa was nearly abandoned. However, George Cotzias in 1967

NON-​L EVOD O PA T HE RAP Y Levodopa has been established as the cornerstone of therapy for PD, but drug development occurred on other fronts. The synthetic anticholinergic medications benztropine and trihexyphenidyl were developed in the 1950s and their main effect is to dampen tremor.50 Amantadine was originally developed as an antiviral agent for Asian influenza but was serendipitously found in 1968 to improve motor symptoms of PD. A  woman with PD took amantadine to prevent the flu and noted an improvement in her tremor, rigidity, and akinesia. The benefit was later verified in a larger scale trial.51 Since its FDA approval for use in PD in 1973, amantadine has frequently been used to lessen symptoms. Proof-​ of-​ concept studies in the 1990s demonstrated that amantadine also reduces levodopa-​induced dyskinesias.52,53 A number of dopamine receptor agonists have been developed for the treatment of early and advanced PD. Apomorphine was the first drug in class and was actually synthesized from morphine in the 19th century but not initially for use in PD. Schwab et al. showed its short-​term benefits in 1951.54 It failed as an oral medication because it is significantly hepatically metabolized, requiring sufficiently high doses to cause renal toxicity.55 It is primarily utilized in the United States as a bolus subcutaneous injection to rescue patients from “off ” times. In the United Kingdom it is also utilized as a subcutaneous infusion. It was approved in the United Kingdom in 1993 and in the United States in 2004. The infusion is currently being studied in the U.S. In 1974, bromocriptine was the first oral dopamine agonist to be used clinically56 and was FDA approved in 1978. Pergolide followed and was approved in 1989. Both of these are ergot derivatives, which can cause pulmonary fibrosis and cardiac valvulopathy.57 For that reason pergolide was removed from the U.S. market in 2007. The second-​generation dopamine agonists were FDA approved in 1997, the non-​ergot-​derived ropinirole and pramipexole. These are now the most commonly used agonists in clinical practice today. Finally, the first dopamine receptor agonist available in a patch, rotigotine, was 1 H i s t o r y o f Pa r k i n s o n i s m | 5

approved in 2008. It was withdrawn for 4 years because the drug crystallized in the patch. It was reapproved in 2012 for the treatment of early and advanced PD.58 Monoamine oxidase type B inhibitors may improve PD symptoms through their ability to prevent the degradation of presynaptic dopamine; thereby prolonging the action of individual doses of levodopa. L-​deprenyl, currently known as selegiline, was approved in 1989 for treatment of advanced disease.59 Selegiline, used in the first neuroprotective trial in PD referred to as DATATOP, which started in 1986,60 also produced symptomatic effects confounding interpretation of that study. Rasagiline, another monoamine oxidase type B inhibitor, followed with FDA approval in 2006 for early and advanced disease. This drug, which may also have antiapoptotic effects, was the subject of a neuroprotective trial referred to as ADAGIO, but the outcome also generated controversy.61 Catechol-​ O-​ methyltransferase (COMT) inhibitors prevent the metabolism of levodopa peripherally in a manner similar to dopa decarboxylase inhibitors. These agents prevent metabolism of levodopa to 3-​O-​methyldopa. This increases the half-​life of levodopa without increasing its peak plasma concentration, ultimately reducing motor fluctuations. Two COMT inhibitors, tolcapone and entacapone, have been developed. Entacapone, approved by the FDA in 1999, is the most commonly used COMT inhibitor, available either alone or in a combination tablet with carbidopa and levodopa. Tolcapone, introduced in 1997, is the more efficacious of the two and twice as potent. It is not utilized as frequently because it requires hepatic enzyme monitoring for the first 6  months it is prescribed. There were three cases of hepatic failure reported in 1998 that led to removal from the market in some countries and more restrictive regulations in others like the United States.62 As there have been no further reports of hepatic failure, the restrictions have been reduced in the last few years.

S URGE RY James Parkinson, in his original essay, theorized that the neurological disorder localized to the cervical spinal cord and medulla, possibly due to some prior trauma or local inflammation. He held this assertion despite the fact that none of his patients admitted to such an injury. Parkinson recommended surgical intervention, draining excess blood and pus from the cervical spine. His recommended method was to make a blister on the back of the neck through use of “a caustic,” then keep the wound open by wedging in a piece of cork, until a “sufficient quantity” of pus is drained.3 Neurosurgical intervention for PD as we think of it today started in the early 20th century. Early surgeries involved simple resections on the motor cortex; they were effective for tremor but caused hemiparesis. Over time, the focus switched from the cortex to deeper brain structures. After levodopa introduction in the late 1960s, many thought that brain surgery for PD became obsolete. However, as PD progressed many patients developed motor fluctuations and dyskinesias associated with levodopa. This set the stage for re-​emergence of ablative surgery in the early 1990s and deep brain stimulation (DBS) followed later in the 1990s. The first surgery for a movement disorder was performed by Victor Horsley in 1909 on a 14-​year-​old boy with athetotic movements in his arm. Horsley removed the contralateral precentral motor cortex, successfully stopping the movements, but the boy only regained partial control of the arm.63 Horsley advanced the neurosurgical treatment of movement disorders most through his creation of a stereotactic frame in collaboration with physiologist Robert 6 | M o v e m e n t D i s o r de r s

Henry Clarke.64 This equipment permitted Horsley himself and other pioneering neurosurgeons to make precise targeted lesions in deep brain nuclei. The first neurosurgical approach to the basal ganglia was in 1939 in a patient with parkinsonism related to epidemic encephalitis. Meyers resected the head of the caudate nucleus in a patient with PD with great reduction of tremor and rigidity.65 He continued to perform surgery in other patients. Despite the benefits, the mortality rate was prohibitive. Meyers experimented with other areas in the brain such as the internal capsule, globus pallidus, and the pallidothalamic fibers at the level of the ansa lenticuaris. These surgeries demonstrated that tremor and rigidity could be improved without causing weakness found after corticospinal tract lesions.66 Spiegel and Wycis used stereotactic techniques to lesion the pallidum and ansa lenticularis; this technique proved to be safer.67 Hassler turned attention from the basal ganglia to the thalamus, showing great response to tremor with thalamic lesions.68 In 1952, Irving Cooper, a controversial pioneer of neurosurgery, serendipitously discovered the benefit of lesioning the globus pallidus by accidentally ligating the anterior choroidal artery while attempting to perform a pedunculotomy for a patient with a postencepalitic tremor. The patient had relief from tremor and rigidity without suffering motor and sensory consequences. Cooper purposefully ligated this artery in subsequent surgeries with mostly successful outcomes.69 He later refined the technique to instead use chemopallidectomy, the lesioning of the globus pallidus with local injection of absolute alcohol that ensured accurate localization.70 The momentum that developed for neurosurgical treatments for PD in the 1950s and 60s diminished substantially when levodopa became available. However, when it was clear that levodopa was not a cure for PD and the side effects of levodopa became apparent, functional neurosurgery resurged in the late 1980s and early 1990s. A  paper in 1992 by Laitinen et  al. demonstrated that posteroventral pallidotomy improved not only the cardinal features of PD as expected, but also reduced dyskinesias.71 Baron et  al. demonstrated similar results in their pilot study of 15 patients with PD undergoing globus pallidus internus (GPi) lesioning.72 The development of DBS has defined the modern era of functional neurosurgery and replaced ablative procedures for the last 20 years, particularly in Western countries. Ablative procedures are still performed in some countries because of cost. Deep brain stimulation involves the precise placement of electrodes into deep brain nuclei, and stimulating them at a certain frequency, voltage, and pulse width. This appears to be safer than ablative surgery and is reversible. Several groups had experimented with DBS since the 1950s for different neurological and psychiatric conditions.73 However, the modern ubiquity of DBS all stemmed from the successes of a group in Grenoble, France in the late 1980s. Benabid, Pollak, and others were a team of pioneering neurologists and neurosurgeons who showed great benefits from DBS. This started with their 1987 report of DBS placement in a PD patient who already had undergone a contralateral thalamotomy.74 Mahlon DeLong, through his work on microelectrode recording in monkeys’ brains, formulated a model of how the basal ganglia circuitry is structured (http://​www.ncbi.nlm.nih.gov/​pubmed/​3085570). In doing this work, he discovered that the subthalamic nucleus could be a novel target in the brain which could be lesioned or stimulated for improvement of motor symptoms in PD (http://​www.ncbi.nlm. nih.gov/​pubmed/​2402638). In the 1990s the Grenoble group showed the benefits of stimulating the subthalamic nucleus in PD.75,76 Today, stimulation of the GPi and subthalamic nuclei are the primary targets used to treat the cardinal features of PD and thalamic stimulation of the ventral intermediate nucleus is used primarily for the tremors of essential tremor and PD.

TRANSPLANT

G E NE TI C S

Several studies in the 1980s to the 2000s attempted several cell-​based therapies. Fetal mesencephalic tissue and other sources of dopaminergic cells have been attempted. However, these have not shown significant benefit in the primary endpoints of the studies and some recipients have experienced “runaway dyskinesias,” which are dyskinesias that occur even during levodopa “off ” times.77,78 In addition, the grafted tissue is apt to develop Lewy body degeneration, suggesting a host to graft transfer of the pathological protein.79 Other cell types that failed to generate any improvement included adrenal cells and retinal cells in spheramine.80,81

Genetic discoveries were the next significant advances in PD. Several causative genes have been discovered to this point. We will just mention the ones of greatest significance. The notion that PD is an environmental disease changed with the discovery of the Contursi kindred and the gene found to cause their PD in 1997. The Contursi kindred was a large family originally from Greece that immigrated to Italy and the United States that had 60 affected members. In 1997, linkage was made to the 4q21-​23 chromosome.88 Polymeropoulos et al. demonstrated the culprit mutation in the alpha-​synuclein gene, later dubbed “PARK1”or SNCA.89 This gene has had a significant impact on the understanding of the pathology of PD. In 1998 Japanese researchers discovered a second gene. This one is the most common cause of young-​onset PD. The gene was called “parkin,” or “PARK2,” and its protein product parkin. In 2002 a third causative gene was discovered, the Leucine-​Rich Repeat Kinase gene (LRRK2), in a Japanese family with typical late-​onset PD.90 This gene was the first to be discovered in typical PD based on age of onset and symptoms. It has incomplete penetrance so does not cause PD in all those who have it. The level of penetrance is controversial. LRRK2 is the most common genetic cause of PD worldwide and accounts for approximately 20% of Ashkenazi Jews and 40% of north African Arabs with PD. Many other susceptibility genes have since been implicated in the pathogenesis of PD and the number continues to grow. Based on the current knowledge in PD and genetics, there has been an explosion of new research in this century creating animal models with genetic modification. Mostly through mammalian or fly models, normal genes are “knocked out,” or replaced with a known mutation. A common locus to disrupt is alpha-​synuclein.91 The similarities to true PD are uncertain, but these models can be used to study the mechanisms of cell death and protein aggregation.

ANIMA L MODEL S The ability to study PD has always been hampered by the fact that it does not occur naturally in animals. The science has evolved to create useful animal models of the disorder. At first medications were administered to animals that cause a reversible parkinsonism, such as reserpine, and then with the introduction of a toxin-​induced model such as 6-​hydroxy-​dopamine or MPTP, and most recently through genetic knockout models.82 The first animal models caused rapid and reversible losses of striatal dopamine, without actually causing cell death. Reserpine, a medication that interferes with the presynaptic storage of monoamines, was used to treat hypertension in the 1960s. It was noted to cause parkinsonism in humans and rodents, thus making it an adequate model for the symptomatology of PD.6-​hydroxydopamine (6-​OHDA) has been used since the 1970s to deplete central catecholaminergic systems in adult animals. This would cause cell death via oxidative stress. It could be injected into one side of the brain and only interrupt the dopamine production on that side. Typical targets were the substantia nigra, the nigrostriatal tract, and the striatum.82 6-​OHDA was most useful to cause unilateral parkinsonism in rodents; observers could quantify effect by magnitude of asymmetric turns made when attempting to walk.83 This was referred to as the “Ungerstedt model.” The 1-​methyl-​4-​phenyl-​1,2,3,6-​tetrahydropyridine (MPTP) model was the next major experimental model to overtake the basic science research and substantially changed the approach to studying PD. MPTP was the accidental byproduct of a rogue chemist attempting to make synthetic heroin in California in the 1970’s and early 80’s, which was subsequently self-​administered by a group of drug addicts.84,85 The result was the rapid onset of a disorder that shared much of the symptomatology of advanced PD. This discovery was made by William Langston, MD and reported in 1983. This has led to PD models in mice and primates, as it causes selective death of dopaminergic neurons.86,87 Aside from the discovery of levodopa, MPTP is perhaps the most important discovery in PD research. It has provided a primate model and an opportunity for research into the functions of the basal ganglia circuitry and to study the effects of loss of dopamine input. It has been invaluable to study the outcomes of potential medical and surgical effects of novel therapies. This model also permitted advances in neuroimaging biomarkers of nigrostriatal dysfunction. The discovery of MPTP led most researchers to believe that there may be a similar environmental toxin that causes the same, albeit slower, effects in idiopathic PD. Specifically, research focused on environmental toxins with structure similar to MPTP. These toxins, like the organochlorines and rotenone, produced deleterious effects on mitochondria in rodents and nonhuman primates. Unfortunately, these toxin models have limited ability to reveal insights into the etiology of PD or therapies that that may provide neuroprotection.

G E NE T HE RAP Y Genetics has also had a significant impact on the treatment of PD. Several gene therapies in PD have completed phase II trials. They include genes that impact symptoms or are directed at altering the progressive course of disease. Genes are delivered through viral vectors. The first trial to demonstrate benefit was completed in 2011 and involved adeno-​ associated viral vector with glutamic acid decarboxylase gene injection. This was the first gene therapy to show improvement in symptoms in a double blind study.92 Other gene therapies under investigation involve injection of neurotrophic factors (glial cell line derived neurotrophic factor and its relative, neurturin), amino acid decarboxylase genes, and GTP-​cyclohydrolase.93

C ONC L U D ING R E MARKS Parkinson’s disease has come a long way since its first description in 1817. The 19th century brought us the first known cases and crude treatments. Discoveries from the 20th century established underlying dysfunctional dopamine pathways. This led to the development of levodopa therapy, the most effective treatment found for a neurodegenative disease. Born from serendipitous circumstances, MPTP has been an invaluable tool to study the mechanisms of dopaminergic dysfunction. The latter years of the 20th century saw the transition of deep brain stimulation from experimental procedure to standard of care. So far, the new century has shed light on the genetic causes of PD. Looking forward to the future, further strides 1 H i s t o r y o f Pa r k i n s o n i s m | 7

will be made in the genetics and pathogenesis of PD, possibly with the creation of a neuroprotective therapy.

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8 | M o v e m e n t D i s o r de r s

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57. Massel, D., & Suskin, N. (2007). Pergolide and cabergoline increased risk for valvular heart disease in Parkinson disease. ACP J Club, 146(3), 75–​76. 58. Parkinson’s Disease Foundation. (April 3, 2012). Neupro re-​approved by FDA for treatment of Parkinson’s disease. Available from: http://​www.pdf. org/​en/​science_​news/​release/​pr_​1333471029. 59. Kapp, W. (1992). The history of drugs for the treatment of Parkinson’s disease. J Neural Transm Suppl, 38, 1–​6. 60. Anonymous. (1989). Effect of deprenyl on the progression of disability in early Parkinson’s disease. The Parkinson Study Group. N Engl J Med, 321(20), 1364–​1371. 61. Olanow, C.  W., et  al. (2008). A randomized, double-​ blind, placebo-​ controlled, delayed start study to assess rasagiline as a disease modifying therapy in Parkinson’s disease (the ADAGIO study):  Rationale, design, and baseline characteristics. Mov Disord, 23(15), 2194–​2201. 62. Olanow, C. W. (2000). Tolcapone and hepatotoxic effects. Tasmar Advisory Panel. Arch Neurol, 57(2), 263–​267. 63. Horsley, V. (1909). The Linacre lecture on the function of the so-​called motor area of the brain:  Delivered to the master and fellows of St. John’sCollege, Cambridge, May 6th, 1909. Br Med J, 2(2533), 121–​132. 64. Tan, T. C., & Black, P. M. (2002). Sir Victor Horsley (1857–​1916): Pioneer of neurological surgery. Neurosurgery, 50(3), 607–​ 611; discussion 611–​612. 65. Meyers, R. (1941). The modification of alternating tremor, rigidity and festination by surgery of the basal ganglia. Res Publ Assn Nerv Ment Dis, 21, 602. 66. Gildenberg, P. L. (2006). Evolution of basal ganglia surgery for movement disorders. Stereotact Funct Neurosurg, 84(4), 131–​135. 67. Spiegel, E. A., & Wycis, H. T. (1954). Ansotomy in paralysis agitans. AMA Arch Neurol Psychiatry, 71(5), 598–​614. 68. Hassler, R., & Riechert, T. (1954). Indikationen und Lokalisations­ methode der gezielten Hirnoperationen. Nervenarzt, 25, 441–​447. 69. Das, K., et  al. (1998). Irving S.  Cooper (1922–​1985):  Apioneer in functional neurosurgery. J Neurosurg, 89(5), 865–​873. 70. Cooper, I. S., & Bravo, G. J. (1958). Production of basal ganglia lesions by chemopallidectomy. Neurology, 8(5), 344–​346. 71. Laitinen, L. V., Bergenheim, A. T., & Hariz, M. I. (1992). Leksell’s posteroventral pallidotomy in the treatment of Parkinson’s disease. J Neurosurg, 76(1), 53–​61. 72. Baron, M. S., et al. (1996). Treatment of advanced Parkinson’s disease by posterior GPi pallidotomy:  1-​year results of a pilot study. Ann Neurol, 40(3), 355–​366. 73. Hariz, M.  I., Blomstedt, P., & Zrinzo, L. (2010). Deep brain stimulation between 1947 and 1987: The untold story. Neurosurg Focus, 29(2), E1. 74. Benabid, A. L., et al. (1987). Combined (thalamotomy and stimulation) stereotactic surgery of the VIM thalamic nucleus for bilateral Parkinson disease. Appl Neurophysiol, 50(1–​6), 344–​346. 75. Pollak, P., et al. (1993). [Effects of the stimulation of the subthalamic nucleus in Parkinson disease]. Rev Neurol (Paris), 149(3): p. 175–​176.

7 6. Limousin, P., et  al. (1995). Effect of parkinsonian signs and symptoms of bilateral subthalamic nucleus stimulation. Lancet, 345(8942), 91–​9 5. 77. Freed, C. R., et al. (2001). Transplantation of embryonic dopamine neurons for severe Parkinson’s disease. N Engl J Med, 344(10), 710–​719. 78. Olanow, C. W., et al. (2003). A double-​blind controlled trial of bilateral fetal nigral transplantation in Parkinson’s disease. Ann Neurol, 54(3), 403–​414. 79. Kordower, J. H., & Brundin, P. (2009). Lewy body pathology in long-​term fetal nigral transplants: Is Parkinson’s disease transmitted from one neural system to another?Neuropsychopharmacology, 34(1), 254. 80. Goetz, C. G., et al. (1989). Multicenter study of autologous adrenal medullary transplantation to the corpus striatum in patients with advanced Parkinson’s disease. N Engl J Med, 320(6), 337–​341. 81. Gross, R. E., et al. (2011). Intrastriatal transplantation of microcarrier-​bound human retinal pigment epithelial cells versus sham surgery in patients with advanced Parkinson’s disease: Adouble-​blind, randomised, controlled trial. Lancet Neurol, 10(6), 509–​519. 82. Bezard, E., & Przedborski, S. (2011). A tale on animal models of Parkinson’s disease. Mov Disord, 26(6) 993–​1002. 83. Ungerstedt, U., & Arbuthnott, G.  W. (1970). Quantitative recording of rotational behavior in rats after 6-​hydroxy-​dopamine lesions of the nigrostriatal dopamine system. Brain Res, 24(3), 485–​493. 84. Langston, J. W., et al. (1983). Chronic Parkinsonism in humans due to a product of meperidine-​analog synthesis. Science, 219(4587), 979–​980. 85. Burns, R.  S., et  al. (1985). The clinical syndrome of striatal dopamine deficiency. Parkinsonism induced by 1-​methyl-​4-​phenyl-​1,2,3,6-​ tetrahydropyridine (MPTP). N Engl J Med, 312(22), 1418–​1421. 86. Langston, J. W., et al. (1984). Selective nigral toxicity after systemic administration of 1-​methyl-​4-​phenyl-​1,2,5,6-​tetrahydropyrine (MPTP) in the squirrel monkey. Brain Res, 292(2), 390–​394. 87. Heikkila, R. E., Hess, A., & Duvoisin, R. C. (1985). Dopaminergic neurotoxicity of 1-​methyl-​4-​phenyl-​1,2,5,6-​tetrahydropyridine (MPTP) in the mouse:  relationships between monoamine oxidase, MPTP metabolism and neurotoxicity. Life Sci, 36(3), 231–​236. 88. Polymeropoulos, M. H., et al. (1996). Mapping of a gene for Parkinson’s disease to chromosome 4q21-​q23. Science, 274(5290), 1197–​1199. 89. Polymeropoulos, M.  H., et  al. (1997). Mutation in the alpha-​synuclein gene identified in families with Parkinson’s disease. Science, 276(5321), 2045–​2047. 90. Funayama, M., et al. (2002). A new locus for Parkinson’s disease (PARK8) maps to chromosome 12p11.2-​q13.1. Ann Neurol, 51(3), 296–​301. 91. Bellucci, A., et  al. (2012). Alpha-​synuclein synaptic pathology and its implications in the development of novel therapeutic approaches to cure Parkinson’s disease. Brain Res, 1432, 95–​113. 92. LeWitt, P.  A., et  al. (2011). AAV2-​ GAD gene therapy for advanced Parkinson’s disease: a double-​blind, sham-​surgery controlled, randomised trial. Lancet Neurol, 10(4), 309–​319. 93. Coune, P.  G., Schneider, B.  L., & Aebischer, P. (2012). Parkinson’s disease: Gene therapies. Cold Spring Harb Perspect Med, 2(4), a009431.

1 H i s t o r y o f Pa r k i n s o n i s m | 9

2 | PARKINSON DISEASE: Pathophysiology, Genetics, Clinical Manifestations, and Course including Diagnosis and Differential Diagnosis MI CH AE L J .   S OIL E A U A N D K E LVIN L .   CH OU

D EFINITION Parkinson disease (PD) is characterized by tremor, rigidity, slow movements (bradykinesia), and a loss of postural reflexes with underlying loss of nigrostriatal neurons and deposition of abnormal alpha-​synuclein in neuronal cell bodies and neurites. Parkinson disease was first described in 1817 by James Parkinson in his Essay on the Shaking Palsy.1 His description of a clinical syndrome characterized by tremor, weakness (secondary to bradykinesia and rigidity), and an abnormal gait was remarkably detailed and accurate. Although we still make the diagnosis on the basis of the motor symptoms that James Parkinson described, PD is now recognized as a neurodegenerative syndrome not only causing motor dysfunction but non-​motor dysfunction as well. Synonyms: idiopathic Parkinson disease; Parkinson syndrome; and parkinsonism.

PAT HOPHYSIO L O GY OF PARKINSON D IS EASE In 1912, Frederick Lewy made a major breakthrough in understanding PD when he described neuronal cytoplasmic inclusions (later named Lewy bodies) in a variety of brain regions. In 1919, Tretiakoff observed that neuronal degeneration in the substantia nigra pars compacta of the midbrain was likely responsible for the clinical features in PD.2 It was not until the 1950s that investigators discovered the importance of dopamine and its depletion in the basal ganglia. When dopamine deficiency in the striatum of PD patients was discovered, Hornykiewicz in 1960 suggested high doses of levodopa to treat PD.3 Although we still do not completely understand the complex circuitry of the brain, our understanding of the basal ganglia is better now than it was a half-​century ago. The basal ganglia circuit includes the substantia nigra (SN), striatum (caudate and putamen), globus pallidus (GP), subthalamic nucleus (STN), and the thalamus.4 Together, these components are essential to motor control as well as sensory and cognitive function. The basal ganglia loop anatomy is complex, but it is worthwhile to understand a more simplistic model that has become popular.5 In this model, dopamine is the primary neurotransmitter responsible for regulating the function of the basal ganglia. Interestingly, it can serve as either an excitatory or inhibitory transmitter, depending on which of the five receptor subtypes it acts on. D1 and D2 are highly concentrated in the striatum and are most relevant to the pathophysiology of PD. D3 and D4 are found in the mesolimbic part of the brain and deal with emotions. D5 receptors are in the hippocampus/​hypothalamus.6 There are thought to be two pathways in the basal ganglia:  the indirect and the direct (Figure 2.1). In the indirect pathway, dopamine 1 0 | M o v e m e n t D i s o r de r s

release results in an inhibition of D2 receptors in the striatum. Projections from the striatum are inhibitory to neurons in the Globus Pallidus externa, which in turn use GABA to inhibit the STN. The STN provides excitatory input via glutamate to the GPi and SN pars reticularis (SNr). The GPi/​SNr use GABA to inhibit the ventrolateral (VL) and ventroanterior (VA) nuclei of the thalamus. When the indirect pathway is activated, thalamic excitatory output to the cortex is decreased, resulting in decreased movement. In the direct pathway, dopamine is excitatory to D1 receptors and the fibers in this pathway directly inhibit GPi and SNr. This ultimately leads to a disinhibition of the ventrolateral/​ventroanterior (VL/​VA) nuclei of the thalamus. Because the VL/​VA output to the cortex is excitatory, this stimulates the cortex and leads to movement. Therefore, the direct pathway leads to an increase in movement. In PD, there is a reduction in the dopamine-​producing neurons in the substantia nigra pars compacta (SNc). Because of this, the indirect pathway is overactively disinhibiting the STN, leading to less inhibition of the GPi/​SNr. This ultimately results in increased inhibition of the thalamus and decreased excitation of the cortex. The direct pathway has decreased inhibition of the GPi/​SNr, leading to excessive inhibition of the thalamus and decreased excitation in the motor cortex. Thus, the combination of both pathways leads to an overall decrease in movement, manifested as bradykinesia.7 The mechanism of neurodegeneration in PD is not fully understood,8 but much can be learned by evaluating autopsy specimens from those diagnosed with PD. The neuropathological features of PD include depigmentation, neuronal loss, and gliosis in the SNc, pontine locus ceruleus, and in the dorsal nucleus of vagus in the medulla and brainstem nuclei. Postmortem studies vary, and prospective nonhuman primate studies suggest that as low as 35% of nigral dopaminergic cell loss may accompany development of motor manifestations in PD.9,10 The pathological hallmark of PD is the finding of Lewy bodies—​ round, eosinophilic, intracytoplasmic inclusions in the nuclei of neurons. These Lewy bodies contain deposition of alpha-​synuclein and ubiquitin among other types of proteins. Lewy bodies do not contain tau proteins. Abnormal deposition of alpha-​synuclein also occurs in neuronal processes identified as Lewy neurites. Lewy bodies and neurites can be found in the SN, basal nucleus of Meynert, locus ceruleus, cerebral cortex, sympathetic ganglia, the dorsal nucleus of vagus, myenteric plexus of the intestines, and in the cardiac sympathetic plexus. Pathology in these locations causes a number of clinical manifestations, both motor and non-​motor. However, Lewy bodies are not specific to PD and may also be seen in other neurodegenerative disorders such as corticobasal degeneration, Alzheimer disease, progressive supranuclear palsy, and even Down’s syndrome.11

Normal

Parkinsonism

Cortex (M1, PMC, SMA, CMA)

Cortex (M1, PMC, SMA, CMA)

Putamen

D2

D1

CM

Putamen

VA/VL

CM

VA/VL

Dir.

Indir.

SNc

SNc GPe

GPe

STN

Brain stem/ Spinal cord

GPi/SNr

PPN

STN

Brain stem/ Spinal cord

GPi/SNr

PPN

Figure 2.1  Classic depiction of basal ganglia activity in the normal physiologic state and in Parkinsonism. Black arrows indicate inhibition; gray arrows indicate

excitation. Dotted arrows in the Parkinsonism model indicate loss of dopaminergic input in the putamen. Abbreviations: CM, centromedian nucleus of thalamus; CMA, cingulate motor area; Dir., direct pathway; D1, D2, dopamine receptor subtypes; GPe, external segment of the globus pallidus; GPi, internal segment of the globus pallidus; Indir., indirect pathway; M1, primary motor cortex; Pf, parafascicular nucleus of the thalamus; PMC, premotor cortex; PPN, pedunculopontine nucleus; SMA, supplementary motor area; SNc, substantia nigra pars compacta; SNr, substantia nigra pars reticulata; STN, subthalamic nucleus; VA, ventral anterior nucleus of thalamus; VL, ventrolateral nucleus of thalamus.  Galvan, A., & Wichmann, T. (2008). Pathophysiology of Parkinsonism. Clin Neurophysiol, 119(7), 1459–​1474.

The Braak staging system is a classification for Lewy body pathology based on progression from the medulla to the midbrain, diencephalon, and neocortex (Table 2.1). Stage 1 is characterized by Lewy bodies in the dorsal IX/​X motor nuclei and/​or myenteric plexus involvement. This also includes the olfactory bulb. Stage 2 includes the stage 1 pathology plus Lewy bodies in the medulla, pontine tegmentum, caudal raphe nuclei, gigantocellular reticular nucleus, and coeruleus-​subcoeruleus complex. Stage 3 includes the stage 2 pathology plus midbrain lesions including the SNc, amygdala, the pedunculopontine nucleus, and the basal nucleus of Meynert. Stage 4 includes stage 3 pathology plus the mesocortex (transentorhinal region and allocortex) as well as the CA2 plexus. Stage 5 includes the stage 4 pathology plus the sensory association areas and prefrontal areas of

cortex. Stage 6 includes stage 5 pathology plus the primary and secondary motor and sensory association areas.12 The above classification system shows some correlation between pathology and clinical features. Stage 1 and 2 typically have no evidence of parkinsonism, and patients are considered to have preclinical PD. Stage 3 typically involves parkinsonism characterized by a substantial loss of cells in the substantia nigra. However, this staging system is not perfect. For example, some studies show that there is no correlation with the number of Lewy bodies in the cortex and the severity of cognitive impairment.13 Although the Braak staging system may be helpful in classifying severity of disease in the postmortem state, we need in vivo biological markers for diagnosis and quantifying severity of PD.

GENETICS OF PARKINSON DISEASE TAB L E   2. 1 .  Braak Staging System STAGE

SITE OF PATHOLOGY

Stage 1

Enteric nervous system, sympathetic/​parasympathetic ganglia, and olfactory bulb

Stage 2

Locus ceruleus, Raphe nucleus, and magnocellular reticular formation

Stage 3

Substantia nigra, amygdala, pedunculopontine nucleus, and basal nucleus of Meynert.

Stage 4

Temporal lobe, hippocampal CA-​2 field, intralaminar thalamic nuclei, and entorhinal cortex

Stage 5

Prefrontal cortex and tertiary sensory association cortex

Stage 6

Secondary motor and somatosensory cortex, primary motor and somatosensory cortex

The first gene linked to PD, a missense mutation in the alpha-​ synuclein gene (PARK1), was discovered in 1997. Since then, there has been a wealth of new information published on the genetics of PD, and currently, more than 18 PD–​related gene loci have been identified.14 Despite this new influx of knowledge, causative genes only account for approximately 1% to 3% of typical late onset PD and up to 20% of young onset PD.15 Autosomal dominant, autosomal recessive, and X-​linked PD-​related genes have been identified. A comprehensive review of the genetics of PD is beyond the scope of this chapter, but in the following we describe some of the more common or better established causative genes for PD. See Table 2.2 for an overview of PD genes with monogenic loci. The most common genetic mutation is in the LRRK2 gene (PARK8), accounting for approximately 3% of familial autosomal dominant PD, 0.5% to 3% of sporadic PD, up to 41% of PD in North African Arabs, and 18.3% of PD in Ashkenazi Jews.16 LRRK2 is dominantly inherited with incomplete penetrance. Typically, the age of onset is over 50 years old with clinical features similar to that

2 Pa r k i n s o n D i s e a s e :   Pat h o ph y s i o l o g y, G e n e t i c s , C l i n i c a l M a n i f e s tat i o n s , a n d   C o u r s e | 11

TABL E   2. 2 . Monogenic Loci for Parkinson Disease LOCUS

GENE

INHERITANCE

AGE OF ONSET

PARK1 and PARK 4

α-​synuclein

AD

~35–​40 yrs

PARK2

Parkin

AR

PARK3

?

PARK5

LD-​RESPONSIVE

OTHER

PATHOLOGY

+

Rapid progression with comorbid dementia/​ hallucinations. Motor complications early

α-​synuclein LB and LN

~32 yrs

+

Dystonia (LE), mixed tremor. Severe motor complications

LB negative

AD

~61 yrs

+

Dementia early

+ LB, NF tangles, and neuritic plaques

UHCL1

AD

~49–​50 yrs

+

Typical PD

+ LB with UHCL

PARK6

PINK1

AR

~30–​50 yrs

+

Slow progression

?

PARK7

DJ-​1

AR

~ 30 yrs

+

Psychiatric symptoms and dystonia

?

PARK8

LRRK2

AD

~57 yrs

+

Typical PD but with dementia

+/​–​LB, + NF tangles, + Tau

PARK9

ATP13A2

AR

~10–​22 yrs

+

pyramidal signs, dementia and supranuclear gaze palsy

neuronal ceroid lipofuscinosis

PARK14

PLA2G6

AR

~10–​20 yrs

+

Dystonia, parkinsonism, pyramidal signs, cognitive dysfunction

LBs, brain iron accumulation

PARK15

FBX07

AR

~late teens

+/–​

Pyramidal signs

?

PARK17

VPS35

AD

~40–​50 yrs

+

Typical PD with motor complications

?

AD, Autosomal dominant; AR, autosomal recessive; LB, Lewy bodies; LE, lower extremities; LN, Lewy neurites; LRRK, leucine-​rich repeat kinase; NF, neurofibrillary; PINK, PTEN-​induced kinase; PLA2G6, Phospholipase A2, group 6; UHCL, Ubiquitin cyclohydrolase; FBX07, F-​box protein 7; VPS35, Vacuolar protein sorting 35 homolog.

of idiopathic PD, but with less risk of cognitive or olfactory impairment.14 LRRK2 patients may also have more dystonia and tremor than idiopathic PD.17 Mutations in the alpha–​synuclein gene, PARK1 and PARK4, also have an autosomal dominant mode of inheritance. Although patients with alpha-​synuclein gene mutations may appear very similar to sporadic PD, the age of onset is earlier and dementia and psychiatric problems seem to be more prominent. The PARKIN gene (PARK2) is the most common cause of early-​ onset autosomal recessive PD. The mean age of onset is 32 years with parkinsonism, postural and resting tremor, and frequently dystonia, usually in the feet. These patients often respond well to levodopa, progress relatively slowly, but may develop severe motor fluctuations and dyskinesias. PINK1 (PARK6) mutations may be the next most common cause of young onset PD inherited in an autosomal recessive pattern. These patients have a clinical course similar to those with PARKIN mutations, displaying slowly progressive levodopa-​responsive disease. Other features, such as prominent dystonia and sleep benefit also may be observed.18 DJ1 mutations (PARK7) are rare causes for recessive PD, but patients are levodopa-​responsive with onset in the 20s or 30s. In addition to causative genes, susceptibility genes also play a role in parkinsonism. For example, the beta-​glucocerebrosidase gene (GBA) was implicated in parkinsonism after observing that patients and relatives of patients with Gaucher’s disease developed PD more 12 | M o v e m e n t D i s o r de r s

often than expected. Patients with a single GBA mutant allele are at fivefold greater risk for PD than those without. These patients tend to have a greater rate of cognitive change and symmetric onset than those with idiopathic PD without the GBA mutation.19 At this point, genetic testing for PD should be performed only with the assistance of a genetic counselor as well as the patient’s understanding of the risks and benefits. A negative result indicates that the specific mutation was not identified, but does not exclude a genetic risk for PD. The highest yield would likely be in those with early-​onset PD in search of the PARKIN mutation, or in families with an autosomal dominant inheritance such as those of Ashkenazi Jewish heritage or northern African Arab to look for the LRRK2 mutation. However, a positive result in someone with an LRRK2 mutation does not mean that the person will develop clinical features of parkinsonism because the gene is not fully penetrant.

MOTOR MANIF E STATIONS OF   PARKINSON DISE AS E There are four cardinal motor features of PD:  tremor, bradykinesia, rigidity, and postural instability (Table 2.3).20 The typical tremor of PD is characterized as a pill-​rolling tremor of 3 to 7 Hz, but most often is

TAB L E   2. 3 .  Common Motor and Non-​motor Features

of Parkinson Disease Common Motor Features of Parkinson Disease • Tremor • Bradykinesia • Rigidity • Postural Instability Common Non-​motor Features of Parkinson Disease Psychiatric dysfunction • Depression • Anxiety • Psychosis (visual hallucinations) • Delusions • Cognitive dysfunction including dementia Sleep dysfunction • Sleep fragmentation • REM sleep behavior disorder (RBD) • Restless Leg Syndrome (RLS) • Excessive daytime sleepiness • Fatigue Autonomic symptoms • Orthostatic hypotension • Constipation • Urinary dysfunction (overactive bladder or urinary retention) • Erectile dysfunction • Sialorrhea • Dysphagia

between 4 and 5 Hz.21 The tremor is present most often at rest and typically worsens when the patient is anxious or nervous. With purposeful action, the tremor typically will decrease, distinguishing this tremor from that of essential tremor. PD tremor is often asymmetric in presentation, starting unilaterally and spreading contralaterally several years after the onset. The initially affected side typically remains the most affected side. The tremor of PD may involve the legs, lips, jaw, and tongue but will rarely involve the head.22 On examination, tremor is commonly seen in the relaxed patient with hands in their lap. Tremor may often be enhanced or brought out by having the patient perform distracting maneuvers, such as mental calculations, saying the months of the year in reverse order, or by performing voluntary repetitive movements with the contralateral limb. Bradykinesia is defined as a generalized slowness of movement, particularly apparent with reduced amplitude or speed of repetitive movements. PD patients may subjectively complain of motor fatigue and weakness, but the examiner will instead find bradykinesia with normal muscle strength. Small amplitude, fine motor tasks such as buttoning clothes or typing are difficult. In addition, patients may also have a reduction in the size of their handwriting (micrographia). In the lower extremities, bradykinesia manifests as a slow, shuffling gait with difficulty arising from a chair or from a vehicle. Akinesia, or a paucity of spontaneous movement, causes a loss of spontaneous facial expression known as facial masking with decreased blink rate (hypomimia). Bradykinesia also affects facial and oropharyngeal muscles with hypokinetic, hypophonic (soft) speech, drooling (sialorrhea), impaired chewing, and dysphagia. Bradykinesia may be the most disabling feature of PD. On physical exam, bradykinesia can best be appreciated by assessment of the speed, amplitude, and rhythm of the first finger and thumb tapping, opening and closing of hands, pronation-​supination hand movements, and heel/​toe tapping.

Hesitation and pauses frequently occur along with decremental amplitude and dysrhythmia. Similar to tremor, bradykinesia affects one side first and then spreads to the other side. Rigidity is an increased resistance to passive manipulation about a joint. Classically, the rigidity of PD is described as “cogwheel rigidity” because there is often a ratchety pattern of resistance at the elbow or wrist, but the important component is an increased resistance that remains relatively constant throughout the range of motion (like bending a lead pipe) and is not velocity dependent. Rigidity can often be reinforced with repetitive movements of the contralateral limb. Cogwheeling typically occurs when there is a tremor in the affected limb, and the ratchety feeling may reflect superimposed tremor upon rigidity.23 Lead-​pipe rigidity is more often seen in patients without significant tremor. Patients often describe pain and stiffness related to the rigidity. Rigidity affects the axial as well as limb musculature. Flexor biased posturing also occurs across many joints, causing stooped posture at the neck and shoulders, lateral tilt of the trunk, and forward flexion of the thoracolumbar spine (camptocormia), but these features may or may not correspond with severity of axial rigidity. Postural instability is an impairment of righting reflexes in response to a perturbation. This leads to a feeling of imbalance and a tendency to fall. Postural instability is typically not present until later in the disease course. When present early in the course of a patient with parkinsonism, an atypical parkinsonian syndrome such as multiple system atrophy or progressive supranuclear palsy should be considered. Clinically, the examiner may test for postural instability by performing the “pull test.” The examiner stands behind the patient and firmly pulls the patient by the shoulders. The need for the patient to take more than two steps backward is abnormal. In severe cases of postural instability, the patient may fall if not caught. Postural instability may be the motor manifestation of PD that is the least responsive to dopaminergic therapy, particularly later in the course of the disease. Other gait manifestations seen in PD include freezing of gait (FOG) and festination. FOG is a poorly understood phenomenon that generally does not occur until the advanced stages of PD. FOG may be seen during gait initiation, turning, approaching a constricted space, or just before reaching a targeted destination. Dual tasking, such as carrying an object, can enhance freezing. Festination is “an irresistible impulse to take much quicker and shorter steps, and thereby to adopt unwillingly a running pace.”1

NON - ​MOTOR MANIF E STATIONS OF   PARKINSON DISE AS E For quite some time, neurologists have realized that PD is not merely a pure motor disorder. Clinicians also should recognize the psychiatric disorders, cognitive abnormalities, sleep dysfunction, autonomic dysfunction, and sensory manifestations (see Table 2.3). Depression occurs in up to 50% of patients with PD, with 7% to 19% meeting criteria for major depressive disorder2.4 These symptoms include alterations in sleep, decreased interest or anhedonia, feelings of worthlessness or guilt, decreased energy, decreased concentration, either increased or decreased appetite, psychomotor agitation or retardation, or suicidal ideation. Some of these features, such as psychomotor slowing and decreased affect, may mimic bradykinesia and delay diagnosis. Along with depression, PD patients may experience apathy or abulia. However, the two are distinct because apathy may be present in the absence of depression. Apathy is defined by diminished motivation not attributable to a decreased level of consciousness, cognitive impairment, or emotional distress. Most notably, the lack of motivation is important and is often associated with dysfunction in the frontal lobe and limbic system.25

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Anxiety often coexists with depression in PD, but anxiety also may fluctuate in conjunction with motor symptoms. Patients often experience more anxiety in the medication “off ” state compared to the medication “on” state. Generalized anxiety disorder and panic disorder are the most common anxiety disorders in PD.26 Comorbid anxiety could also lead to a fear of walking or fear of falling. Other psychiatric symptoms include psychosis and hallucinations. Psychosis occurs in as many as 20% to 40% of treated PD patients, with visual hallucinations being the most common symptom.27 It is the single greatest risk factor for nursing home placement in PD.28 Hallucinations may result from PD medications, underlying disease, or a combination of the two. Of the common agents for PD, dopamine agonists are more likely to lead to hallucinations than levodopa,28 though hallucinations may occur with any of the anti-​ parkinsonian medications including amantadine and anticholinergics (including those used for bladder control). Some patients retain insight into their hallucinations and are not overly bothered by them. When insight is lost, hallucinations become problematic, especially when accompanied by delusions. Delusions in PD are usually paranoid in nature and may include spousal infidelity, intruders in the home, or others stealing from the patient. Cognitive dysfunction is also another common non-​motor symptom of PD. Mild cognitive dysfunction may be present at the time of PD diagnosis29,30 and predicts progression to dementia,31 with more than 80% of PD patients eventually developing dementia.32 Consistent risk factors for developing dementia in PD include advanced age and severity of PD motor symptoms. Later age at onset of PD, severe motor disease, longer duration of PD symptoms, depression, hallucinations, early occurrence of levodopa-​related psychosis, smoking, poor cognitive test scores, and severe gait and postural reflex disturbances are other reported risk factors.33 The earliest manifestations of cognitive dysfunction in PD include problems with executive function (decision making or multitasking) and visuospatial dysfunction, with memory retrieval problems developing later. PD with dementia is clinically defined as the development of cognitive disability at least 1  year after the onset of parkinsonian features; however, dementia beginning within the first year of the onset of motor parkinsonism has the same pathologic substrate. Sleep disturbances are present in 40% to 90% of PD patients.34 The most common sleep disturbance is sleep fragmentation. There are several reasons for this including nocturia, vivid dreams, and wearing off of medications during the night, which causes symptomatic rigidity, off-​period dystonic cramps, pain, or difficulty turning in bed. Patients with PD commonly experience obstructive sleep apnea and have an increased risk of rapid eye movement sleep behavior disorder (RBD) and restless leg syndrome (RLS). RBD is characterized by violent behaviors during rapid eye movement sleep, such as shouting, boxing, kicking, or acting out dreams. RBD may precede the onset of motor symptoms in PD; 33% to 45% of patients with idiopathic RBD will subsequently develop a neurodegenerative disease within a mean of 5 years from diagnosis.35 Patients with RBD may injure themselves or their bed partner. Restless leg syndrome is characterized by uncomfortable and unpleasant sensations, coupled with an urge to move the legs. These symptoms typically occur when sitting or lying down and are relieved by movement, such as walking or stretching.36 This disorder, like many of the other sleep disorders, can contribute to poor sleep quality and excessive daytime sleepiness. Excessive daytime somnolence affects between 33% and 76% of PD patients.37–​39 Most often, excessive daytime sleepiness is multifactorial. Depression, sleep disorders such as RLS or RBD, and medication effects all can contribute to daytime sleepiness. Sleepiness is a well-​known side effect of dopamine agonists, and some patients on this class of medications may even have sudden onset of sleep 14 | M o v e m e n t D i s o r de r s

episodes or “sleep attacks,” leading to increased risk of injury when driving. Levodopa also may cause excessive sleepiness but this seems to occur less frequently than with dopamine agonists. Autonomic symptoms are also common in PD. These symptoms include sexual dysfunction, orthostatic hypotension, impaired temperature regulation, constipation, dysphagia, and urinary difficulties. Sexual dysfunction in PD commonly manifests as decreased interest and drive, which may be due to depression or the motor symptoms. Those on dopamine agonist therapy may have hypersexuality instead. Many male PD patients have erectile dysfunction and female patients often experience vaginal tightness, dryness, and an inability to achieve orgasm.40,41 Erectile dysfunction also occurs in patients with multiple system atrophy. Orthostatic hypotension (OH) is defined as a drop in systolic blood pressure upon standing by 20 mmHg or increase in pulse by 10 beats per minute. However, the increase in heart rate usually does not occur in PD due to the autonomic dysfunction. Similar to erectile dysfunction, orthostatic hypotension is one of the common symptoms in multiple system atrophy. However, erectile dysfunction and OH are usually more severe in multiple system atrophy, and multiple system atrophy is typically unresponsive to levodopa. In PD, OH is often a side effect of the dopaminergic medications, especially the dopamine agonists or amantadine. Gastrointestinal symptoms such as constipation, sialorrhea (drooling), and dysphagia are all common non-​motor manifestations of PD. The etiology behind many of these symptoms is complex, but neuropathological changes in the dorsal nucleus of vagus may cause decreased input to the autonomic nervous system as well as neuropathological changes to enteric neurons in the enteric nervous system.42 Urinary symptoms relating to bladder dysfunction include urinary frequency, urgency, hesitancy, and incontinence.

D ISE AS E P RO GR E SSION Parkinson disease is a progressive neurodegenerative disease, but there is marked variability in the rate of progression among patients with PD. There are no symptoms or signs that currently allow clinicians to predict progression in any given individual. However, some studies have suggested that disease progression varies for different subtypes of PD. Patients with a tremor-​predominant picture tend to have slower progression and less neuropsychologic impairment.43–​45 compared to those with an akinetic-​rigid or postural instability/​gait disorder type. Younger onset patients also tend to progress more slowly46,47 but are more likely to develop early levodopa-​ related motor complications (fluctuations and dyskinesias).48 No medication or treatment strategy has been proven to unequivocally slow down the progression of disease, but because the motor symptoms in PD respond well to medications, many patients are able to live their lives with minimal functional impairment for a substantial period of time.

L A BORATORY   T E STS Laboratory testing and neuroimaging are typically unhelpful in the diagnosis of PD.49 However, magnetic resonance imaging (MRI) of the brain may be helpful to exclude a secondary cause of parkinsonism, such as significant vascular changes, tumor, or hydrocephalus. Occasionally, brain MRI may also reveal radiologic findings suggestive of atypical parkinsonism, such as thinning of the anteroposterior diameter of the midbrain with enlargement of the posterior third ventricle in progressive supranuclear palsy50 or atrophy of the brainstem and cerebellum in multiple system atrophy.51

The United States Food and Drug Administration has approved the use of striatal dopamine transporter imaging using 123I-​ioflupane dopamine transporter single photon emission tomography as a diagnostic tool for differentiating patients with parkinsonism from essential tremor.52 However, a normal scan does not exclude subsequent development of parkinsonism. These scans also cannot differentiate PD from other parkinsonian syndromes, limiting its overall utility. The diagnostic accuracy of these scans is no better than a careful history and a thorough neurological examination.53 For patients under the age of 40 who present with parkinsonian symptoms, the possibility of Wilson’s disease should be considered. This treatable condition, if caught early, can be excluded with a serum ceruloplasmin, 24-​hour urinary copper, and ophthalmology referral to look for Kayser-​Fleischer rings.

TA BL E 2.4 . Features Suggesting a Diagnosis Other Than

Parkinson Disease History of encephalitis History of repeated head injury History of recurrent strokes with stepwise progression of parkinsonism History of oculogyric crisis Current or recent use of dopaminergic blockers or depletors within the last 6–​12 months Brain imaging finding of a structural abnormality that may underlie symptoms Presence of a supranuclear gaze palsy Frequent falls early in the course of the disease or at presentation Dementia preceding or occurring concurrently with parkinsonism Unexplained cerebellar signs

D IA GNOSIS AN D D IFFER ENTIAL D IA GNOSIS

Autonomic nervous system dysfunction early in the disease course (i.e. urinary incontinence, urinary retention requiring catheterization, persistent erectile failure, symptomatic orthostatic hypotension) Unexplained spasticity, hyper-​reflexia or Babinski responses

The diagnosis of PD is currently made on the basis of clinical symptoms. It is generally accepted that bradykinesia plus tremor or rigidity should be present. As mentioned earlier in this chapter, the fourth cardinal manifestation, postural instability, is generally not present in early PD. An excellent response to dopaminergic therapy (levodopa or a dopamine agonist) is an important supportive feature of the clinical diagnosis. However, when patients have mild symptoms that do not interfere with daily activities, it may not be necessary to initiate dopaminergic therapy purely to establish a diagnosis. Other clinical features that are supportive of the diagnosis of idiopathic PD include asymmetric onset with persistent asymmetry (i.e., the initially symptomatic side remains more severely affected as the disease progresses) and presence of a rest tremor.54 When patients have a poor response to levodopa, an alternative diagnosis should be considered. Some clinical features that may be helpful for distinguishing other forms of parkinsonism from PD,49 if present in early stages of disease, are listed in Table 2.4. The major diagnostic considerations in a patient presenting with parkinsonism are listed in Table 2.5). The atypical parkinsonian syndromes (multiple system atrophy, progressive supranuclear palsy, corticobasal degeneration, and dementia with Lewy bodies) are neurodegenerative disorders that may be indistinguishable from PD in the early stages of disease. Multiple system atrophy commonly presents with parkinsonism, accompanied by dysautonomia.55 Patients may also have cerebellar involvement and pyramidal signs. Progressive supranuclear palsy is characterized by vertical supranuclear palsy and early postural instability.56 Unlike idiopathic PD, bradykinesia and rigidity in progressive supranuclear palsy are typically symmetric and rest tremor is rare. Corticobasal degeneration is characterized by severe asymmetric bradykinesia and rigidity. More distinctive features of corticobasal degeneration include ideomotor apraxia, alien limb phenomenon, aphasia, and loss of cortical sensory function.57 Dementia with Lewy bodies (DLB) is the second most common cause of neurodegenerative dementia after Alzheimer disease. In addition to parkinsonism, these patients also have visual hallucinations and fluctuating cognition, and may have repeated falls, syncope, autonomic dysfunction, neuroleptic sensitivity, delusions, hallucinations in nonvisual modalities, sleep disorders, and depression.58 Dementia with Lewy bodies is similar pathologically to PD with dementia. Clinically, DLB is arbitrarily distinguished from PD with dementia when dementia occurs concomitantly with or before the development of parkinsonian signs, but some consider these two conditions the same.

Presence of apraxia (inability to carry out learned motor skills to command or in imitation) Cortico-​sensory deficits (impaired sensation despite intact primary sensory systems such as impaired ability to identify objects in hand with eyes closed with intact perception of pinprick, touch) Abrupt onset of symptoms or sustained spontaneous remission of parkinsonian symptoms Strictly unilateral features after three years Symmetrical motor signs

These atypical parkinsonian disorders are poorly responsive or unresponsive to levodopa, which distinguishes them from idiopathic PD. Other neurodegenerative disorders that may include parkinsonism include:  Alzheimer disease, frontotemporal dementia, Huntington’s disease, Parkinsonism-​dementia-​ALS complex of TA BL E 2.5 .  Differential Diagnosis of Parkinson Disease

Neurodegenerative causes • Alzheimer disease • Cortical-​basal ganglionic degeneration • Dementia with Lewy bodies • Frontotemporal dementia • Huntington’s disease • Multiple System Atrophy • Parkinsonism-​dementia-​ALS complex of Guam • Progressive Supranuclear Palsy • Spinocerebellar ataxias Symptomatic • Drug-​induced (neuroleptics, other dopamine receptor antagonists) • Infectious (post-​encephalitic, Creutzfeldt-​Jakob disease) • Metabolic (Wilson’s disease, neurodegeneration with brain iron accumulation, hepatocerebral degeneration, parathyroid disorders) • Neoplastic • Post-​traumatic • Toxic (Carbon monoxide, manganese, MPTP) • Vascular Other • Essential Tremor • Normal Pressure Hydrocephalus

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Guam, and the spinocerebellar ataxias. These are usually distinguishable from PD based on the presence of other clinical features. Other causes of parkinsonism include drugs, toxins, infection, metabolic derangements, neoplasm, trauma, and vascular disease. Of these secondary causes, drug-​ induced parkinsonism occurs most frequently, and dopamine blocking agents such as antipsychotics and antiemetics are the most common offenders.59 When the offending agent is withdrawn parkinsonism commonly diminishes, but this may take several months to a year. Some patients have persistent or progressive parkinsonism despite withdrawal of the offending drug, leading one to suspect that the drug may have exacerbated an underlying neurodegenerative parkinsonism. Wilson’s disease is an inborn error of copper metabolism60 and an important alternative diagnosis to consider. In this disorder, deposition of copper primarily in the liver and brain results in hepatic cirrhosis and basal ganglia dysfunction. If started early, treatment can reverse this process and prevent disability. Other disorders to consider in the differential of PD include normal pressure hydrocephalus, vascular parkinsonism, and primary progressive freezing gait, which present with gait abnormalities that can resemble parkinsonism. Essential tremor may also occasionally be confused with PD, especially in patients who have a prominent tremor.

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2 Pa r k i n s o n D i s e a s e :   Pat h o ph y s i o l o g y, G e n e t i c s , C l i n i c a l M a n i f e s tat i o n s , a n d   C o u r s e | 17

3 | PARKINSON DISEASE: CURRENT TREATMENTS AND PROMISING CLINICAL TRIALS T H I E N T HIE N L IM A N D HU B E RT H.  FERN A N DEZ

INTRODU CTION Although Parkinson disease (PD) is now considered a neurodegenerative disorder involving several neurotransmitters, affecting almost all organ systems, with motor and non-​motor features, including cognitive impairment, behavioral dysfunction, autonomic, gastrointestinal, urinary, sleep, and dermatological disorders, its diagnosis remains largely based on the presence of cardinal motor features. PD often presents asymmetrically with a combination of resting tremor, rigidity, bradykinesia, and postural instability. The treatment of PD remains a challenging task often requiring a multidisciplinary approach involving neurologist, psychiatrist, physical therapist, occupational therapist, neuropsychologist, and speech and swallow clinician. In some cases, treatment may require a neurosurgeon, PD nurse specialist, gastroenterologist, urologist, or dermatologist, among others. Although current available drug treatments can provide significant symptomatic benefit, none has been definitively or consistently proven to be neuroprotective. Therefore, treatment of PD often focuses primarily function. The goals and treatment strategies vary for each patient and require individualized discussion between patient and caregiver. Because PD is a progressive neurodegenerative disorder, medications often need to be modified and titrated over time. In general, the overall treatment strategy is to optimize functional improvement and minimize side effects.

CURRE NT TRE ATM E NT O P TIONS T R E AT M E N T O F   M O T O R SYMPTOMS IN PD

Levodopa has remained unchallenged as the most efficacious medication to reduce motor impairment in PD since its introduction in 1969. Once levodopa is absorbed in the gut and crosses the blood-​ brain barrier, it gets converted to dopamine to replenish the main neurotransmitter implicated in PD. However, not all motor features respond uniformly (e.g., the response to tremor is variable, and the response to postural instability is often insufficient), and compared with all other pharmacological options, it has a higher propensity to cause motor fluctuations (such as wearing-​off) and dyskinesias. Within 4 to 6 years of initiating therapy, 40% of patients treated with levodopa develop motor fluctuations, dyskinesias or both.1 The most popular hypothesis explaining this phenomenon is that levodopa, because of its short half-​life, delivers nonphysiologic, pulsatile dopaminergic stimulation, resulting in motor fluctuations. Therefore, strategies that provide a more physiologic “continuous dopaminergic stimulation” continue to be explored for their potential to prevent or alleviate these motor fluctuations.2

1 8 | M o v e m e n t D i s o r de r s

These motor complications can be challenging to control and may rapidly become a major source of disability to PD patients. Therefore, in the hopes of delaying these motor complications, some clinicians utilize alternative treatments (such as dopamine agonists, monoamine oxidase B [MAO-​B] inhibitors, and amantadine), to “spare” or minimize levodopa use, especially among younger patients in whom the frequency of developing motor fluctuations and dyskinesias is higher.3 However, dopa-​induced dyskinesias may reflect severity of PD and not cumulative treatment with levodopa.4 Regardless of when levodopa is initiated, almost all patients will eventually require levodopa. In the earlier stages of PD, levodopa, despite its short half-​life, often provides a long duration of motor response, requiring less frequent dosing intervals. However, as the disease progresses, its duration of effect starts to approximate its pharmacokinetic properties. The first and most common type of motor fluctuation is “end-​of-​dose wearing-​off,” when the motor improvements provided by levodopa no longer “connect” from one dose to the next. There are numerous choices available to treat wearing-​off. The most common pharmacological strategy to treat wearing-​off is to either increase levodopa dose, shorten the dosing interval, or both. Some clinicians add a longer-​acting levodopa (Sinemet CR or Madopar HBS). However, due to its erratic absorption in the gut, this technique is less commonly used, except to control nocturnal or early morning akinesia, when given at bedtime. Another option to treat wearing-​off would be to add a dopamine agonist (which has a longer half-​life than levodopa). The recent introduction of extended-​ release formulations of dopamine agonists provide ease of administration and the ability to maintain therapeutic plasma levels for up to 24 hours. One other method to control wearing-​off would be to add a selective MAO-​B inhibitor, such as selegiline or rasagiline. Catechol-​ O-​methyltransferase (COMT) inhibitors, such as entacapone, also can be combined with levodopa to increase its duration of action, thereby reducing wearing-​off. Tolcapone, another COMT-​inhibitor, has greater potency than entacapone but is typically relegated as a second choice because of required liver function monitoring due to potential hepatotoxicity. COMT and MAO-​B inhibitors act by inhibiting the breakdown of levodopa peripherally (entacapone and tolcapone) or centrally (tolcapone) or dopamine centrally (for MAO-​B inhibitors), thereby maximizing levodopa absorption, passage across the blood brain barrier and prolonging its duration of effect. Drug-​ specific side effects of COMT inhibitors include diarrhea and orange colored urine. Combination tablets containing levodopa, carbidopa, and entacapone are available, providing an easier and more convenient mode of administration. Initiating levodopa-​carbidopa-​entacapone among dopaminergic-​naïve PD patients did not delay the induction of dyskinesias compared to starting with levodopa-​carbidopa alone.5 However, early initiation of levodopa-​ carbidopa-​ entacapone was

associated with a shorter time to onset and an increased frequency of dyskinesias compared with levodopa-​carbidopa alone. Apomorphine was approved by the US FDA in 2004 as an acute, intermittent, subcutaneous injection for the treatment of wearing-​off and unpredictable on-​off episodes. Although it has a reliable and quick onset of action (typically within 10 minutes), it lasts for only for 60 to 90 minutes. Therefore, it is best utilized as a “rescue therapy” for wearing-​off, unpredictable off, or sudden off periods, while maintaining the PD regimen. The best tolerated dose is between 4 to 10 mg. In other parts of the world, apomorphine is also available as a continuous subcutaneous infusion. Apart from the motor symptoms of wearing-​off, PD patients can also experience behavioral, sensory, or autonomic symptoms of wearing-​off. Examples of these symptoms include anxiety, pain, depression, panic attacks, sweating, abdominal bloating, dyspnea, and urinary urgency. The treatment of these non-​motor wearing-​off symptoms are similar to the treatment strategies for motor wearing-​ off symptoms (Table 3.1). The majority of patients develop dyskinesias after years of disease progression (Table 3.2). However, these dyskinesias are often more noticed and bothersome to caregivers than to PD patients. Once dyskinesias cause social or functional impairment, there are several strategies to overcome it. Reducing levodopa dose is the most commonly employed strategy, but this can result in increased wearing-​off episodes. Reducing the individual levodopa doses while increasing its frequency of administration may alleviate dyskinesias and prevent wearing off but may lower patient compliance of medication administration. Adding a dopamine agonist to minimize wearing off as levodopa dose is lowered is often easier in theory than in practice. The only drug that has consistently been shown to reduce dyskinesias without requiring levodopa dose adjustment is amantadine, a N-​methyl-​D-​aspartate antagonist.6–​8 Studies have demonstrated that amantadine reduced dyskinesia severity by 60% without exacerbation of motor function.9 However, the efficacy of amantadine may be time-​limited for only 8 months.10 Moreover, amantadine may cause pedal edema, psychosis, livedo reticularis, anticholinergic side effects,

and myoclonus. Clozapine also may decrease the severity of dyskinesias. However, randomized, placebo-​controlled clinical trials have not confirmed this approach, and clozapine requires regular blood count monitoring because of its rare potential (less than 1%) to cause agranulocytosis. In one report, PD patients who experienced peak-​ dose dyskinesia improved with levetiracetam.11 Levodopa-​carbidopa intestinal gel administered through a percutaneous gastro-​jejunostomy tube, from an external pump source, is another alternative for continuous delivery of levodopa for the treatment of wearing off. This highly effective strategy improves Parkinson motor and quality of life scale scores, and reduces wearing off without increasing dyskinesias.12,13 The target population for this treatment is similar to that of the deep brain stimulation (DBS) population, but could potentially extend to those with mild cognitive impairment and minor co-​morbidities that would otherwise be surgical contraindications. The drawbacks include the invasiveness of the tube placement, inconvenience of an external pump, device, associated tube complications, and expense. A Phase 3 clinical trial on carbidopa-​levodopa intestinal gel (Duodopa) showed that it reduced “off ” time by an additional 1.91 hours (p  =  .0015) compared with improvement in “off ” time and increased “on” time without troublesome dyskinesia by 1.86 hours (p = .0059) compared to standard treatment.14

T R E AT M E N T O F   N O N -​M O T O R SYMPTOMS IN PD

Non-​motor symptoms have been consistently shown to be even more disabling to patients with PD as compared with motor symptoms. Common non-​motor symptoms in PD include cognitive impairment, depression, anxiety, sleep disorders, psychosis, autonomic dysfunction, and gastrointestinal/​urinary symptoms. About 40% of patients with PD have dementia in cross-​sectional epidemiologic studies.16 The risk increases to 80% when PD patients are followed for 15 years of their disease.17 The presence of dementia prevents the optimal use of drugs in PD, and often limiting the

TA B L E   3. 1 . Therapeutic Options in the Treatment of Motor Fluctuations MOTOR COMPLICATIONS

TREATMENT OPTIONS

COMMENTS

Wearing-​off

Increase levodopa dose amount

Inexpensive approach but can precipitate dyskinesias in some patients

Increase the levodopa dose frequency

Inexpensive approach but may be inconvenient for patients

Add COMT inhibitors or MAO-​B inhibitors

Reduces “off” time by about 1–​1.5 hours

Add dopamine agonist

Side effects of weight gain, leg swelling, impulse control behavior disorders, “sleep attacks” will need to be weighed against expected benefits

Add amantadine

Efficacious in some cases; potential side effects need to be weighed against benefits

DBS STN

Improvement in “off” time of up to 4 to 6 hours will need to be weighed against the invasiveness of the procedure. Vigilance for potential surgical contraindications is required.

Subcutaneous apomorphine

Available as a subcutaneous injection or continuous infusion in some countries.

Levodopa/​carbidopa intestinal gel

Invasiveness and cost will need to be weighed against the benefits of providing about 2 hours of improvement in “off” time.

See ref. 15.

3 Pa r k i n s o n D i s e a s e :   C u r r e n t T r e at m e n t s a n d P r o m i s i n g C l i n i c a l   T r i a l s | 19

TAB L E 3. 2 . Therapeutic Options in Treatment of Dyskinesias DYSKINESIAS

TREATMENT OPTIONS

COMMENTS

Peak-​dose dyskinesia

Add amantadine

Intrinsic anti-​dyskinetic effect without needing levodopa reduction. However, benefit may last < 8 months and vigilance is required for potential side effects.

Reduce levodopa dose

Risk of increased OFF time may be compensated by increasing the number of levodopa doses

Discontinue MAO-​B inhibitors or COMT inhibitors then adjust levodopa approproptriately

May increase risk of wearing off

Add clozapine (usual dose from 12.5 mg to 75 mg/​day)

Need for monitoring of white cell count (due to the < 1% risk of agranulocytosis)

Deep brain stimulation surgery (subthalamic nucleus or globus pallidus interna)

STN DBS has the advantage of reduction of total dopaminergic burden. GPi DBS has an intrinsic anti-​dyskinetic effect.

Diphasic dyskinesia

Increasing the dose and frequency of levodopa

There is a risk of converting diphasic dyskinesia into peak dose dyskinesia.

Off-​period and early morning dystonias

Refer to strategies of “wearing-​off” Addition of levodopa or dopamine agonist Addition of long acting levodopa, e.g., Sinemet CR or Madopar HBS

Effective for early morning akinesia when given the night prior

Deep brain stimulation surgery

Freezing of gait

Botulinum toxin injection for dystonia

Botulinum toxin is more practical for focal dystonias.

Use of visual and auditory cues

May not respond to dopaminergic strategies

Reduction in dopaminergic therapy (for ON freezing)

May worsen wearing-​off

See ref. 16.

clinician’s option to levodopa. The only FDA-​ approved drug for dementia in PD is rivastigmine. Its effect is modest with transient worsening of PD symptoms.18 About 50% of PD patients experience an episode of hallucination or delusion during their lifetime. More often, psychosis may be exacerbated by electrolyte imbalance, infection, or polypharmacy (especially with PD medications). Of course, assessment and potential withdrawal of other contributing drugs should be withdrawn like anticholinergics used for voiding difficulties, narcotics, benzodiazepines, diphenhydramine, and others. If psychosis persists, the the most common strategy is to “peel off ” PD medications in the following order: other anticholinergics, amantadine, MAO-​B inhibitors, dopamine agonists, and COMT inhibitors, until the psychosis improves. If psychosis still persists, then levodopa, the most efficacious agent with the widest therapeutic window, should be reduced to a minimum. If the PD medication is at the minimum tolerable, and the patient’s psychosis persists, the addition of an atypical antipsychotic should be considered. Clozapine remains the gold standard treatment for psychosis in PD without worsening parkinsonism. However, clozapine requires weekly white blood cell counts in view of the risk of agranulocytosis ( 30 years of age) disease characterized by autonomic failure (urinary incontinence, with erectile dysfunction in males, or significant orthostatic drop in blood pressure as previously outlined) plus either a) parkinsonism poorly responsive to levodopa or b) cerebellar dysfunction. Possible MSA requires, again, the clinical picture of a sporadic progressive adult onset (>30 years of age) disease characterized by a) parkinsonism or b) a cerebellar syndrome, plus at least one feature of autonomic dysfunction (unexplained urinary urgency, frequency, incomplete bladder emptying, erectile dysfunction in males, or significant orthostatic hypotension that does not meet the level defined in probable MSA). Possible MSA also requires at least one additional feature from a list that includes the presence of the Babinski sign plus hyperreflexia or stridor. In the case of possible MSA-​P, this list also includes rapidly progressive parkinsonism, poor response to levodopa, postural instability

TA B L E   4. 1 .  Common Differential Diagnosis for MSA DIFFERENTIAL DIAGNOSIS BASED

DIFFERENTIAL DIAGNOSIS BASED

DIFFERENTIAL DIAGNOSIS BASED

ON PARKINSONISM

ON CEREBELLAR DYSFUNCTION

ON DYSAUTONOMIA

Idiopathic Parkinson Disease

Spinocerebellar ataxias

Pure autonomic failure

Progressive Supranuclear Palsy

Alcohol abuse

Paraneoplastic syndrome

Cerebrovascular disease

Friedreich’s Ataxia

Diabetes

Corticobasal degeneration

Fragile X tremor ataxia syndrome (FXTAS) Thiamine deficiency Multiple sclerosis Paraneoplastic cerebellar degeneration

4 Mult i ple S y s t e m At r o ph y | 27

within 3  years of onset, cerebellar dysfunction in the form of gait ataxia, cerebellar dysarthria, limb ataxia, cerebellar oculomotor dysfunction, dysphagia within 5  years of motor onset, atrophy on MRI of the putamen, middle cerebellar peduncle, pons, or cerebellum, or hypometabolism on FDG-​PET in the putamen, brainstem, or cerebellum. In the case of MSA-​C, this list includes parkinsonism, atrophy on MRI of the putamen, middle cerebellar peduncle or pons, hypometabolism on FDG-​PET in the putamen, or presynaptic nigrostriatal dopaminergic denervation on SPECT or PET. Other clinical findings that support a diagnosis of MSA include cranial dystonia, disproportionate anterocollis, camptocormia and/​or Pisa syndrome, contractures of the hands and feet, inspiratory sighs, severe dysphonia, severe dysarthria, new or increased snoring, emotional incontinence, and jerky myoclonic postural or action tremor.6 Features that do not support a diagnosis of MSA include a classic “pill-​rolling” rest tremor, clinically significant neuropathy, non–​ medication-​related hallucinations, late onset of disease (over age 75), positive family history of ataxia or parkinsonism, dementia, or white matter lesions on MRI suggestive of multiple sclerosis.6

D IA GNOSTIC STU D I ES As MSA is a clinical diagnosis, there is no single diagnostic test. However, several investigations may be of use in the evaluation of the suspected MSA patient and the more commonly used and readily available studies will be reviewed herein. In MSA-​P, MRI scanning (Figure 4.1) is helpful to rule out mimickers of MSA such as stroke and multiple sclerosis. It may also reveal supportive findings of MSA such as atrophy of the pons, putamen, middle cerebellar peduncle, or the cerebellum.38 The putaminal rim sign (in which the dorsolateral border of the putamen has hyperintense signal along with putaminal hypointensity on T2-​weighted sequences) and the “hot-​cross-​bun sign” (cruciform hyperintensity of the pons on T2-​weighted sequences) have both been found to be have high specificity but low sensitivity for MSA. In MSA-​C, atrophy of the putamen, middle cerebellar peduncle, or pons may be seen (Figure 4.2). In MSA-​P, diffusion-​weighted imaging sequence of the MRI shows increased diffusivity seen in the putamen and it helps to differentiate MSA-​C from idiopathic PD. Increased diffusivity in the middle cerebellar peduncle can help to differentiate MSA-​P from PD and PSP.37 Hyperechogenicity in the lentiform nucleus may have some diagnostic value.37 Hypometabolism on FDG PET scans may be seen in the putamen, brainstem, or cerebellum in MSA patients.6 Urodynamic studies and postvoid residuals may be helpful to evaluate for alternative explanations of bladder dysfunction.

Figure 4.1  An example of “hot-crossed bun sign” on MRI of patients with

Multiple System Atrophy.

Genetic testing to exclude diseases such as the spinocerebellar ataxias, Friedreich’s ataxia, or fragile X tremor ataxia syndrome can be done in select cases of MSA. If there is a suspicion of a paraneoplastic process, paraneoplastic antibody panels can be obtained and thiamine levels can be measured for suspected thiamine deficiency. Rarer autoimmune causes such as anti-​GAD antibody ataxia, post-​Epstein Barr virus cerebellitis, or Hashimoto’s thyroiditis can be searched for with the appropriate serologic tests.39

MANA G EM E NT AND TREATM ENT To date, no disease-​modifying therapies are known to exist and treatment is focused on symptom management. Monoamine oxidase inhibitors may provide some theoretical neuroprotection to patients with PD in slowing down disease progression, but this was not true for MSA and especially MSA-​P.40 For parkinsonian symptoms, levodopa or dopamine agonists can be considered and levodopa may be transiently beneficial in 40% of MSA patients.30 One of levodopa’s main drawbacks is its potential to worsen orthostatic hypotension. Deep brain stimulation has not been helpful in patients with MSA, in general. Physiotherapy and supportive therapies remain the mainstay of treatment for those with disabling ataxia, as there are no recognized pharmacologic treatments for the cerebellar dysfunction. Orthostatic hypotension can be clinically managed with nonpharmacologic

Figure 4.2  An example of a normal brain structure on the right compared with atrophy of the cerebellum and midbrain structures.

28 | M o v e m e n t D i s o r de r s

methods like increasing fluid and salt intake, avoiding heavy meals, avoiding being recumbent during the day, having a mild head-​up tilt to the bed for nighttime sleep, and the use of compression garments.41 Reducing or avoiding medications that worsen orthostatic hypotension such as antihypertensives and nitrates is also important. Medication options for the treatment of orthostatic hypotension include midodrine, fludrocortisone, and pyridostigmine.39,42,43 Supine hypertension is a common complication of orthostatic hypotension treatment. In February of 2014, the FDA approved droxidopa (l-​ threo-​ 3,4-​ dihydroxyphenylserine) for the treatment of neurogenic orthostatic hypotension in PD. This synthetic amino acid is converted centrally and peripherally to norepinephrine. A recently published randomized study, which included patients with MSA, showed benefit with less supine hypertension.44 Although nonpharmacologic methods of treating bladder dysfunction include intermittent self-​catheterization, anticholinergic medications such as oxybutynin and trospium can help to reduce detrusor hyperreflexia.33,45 Alpha-​adrenergic blockers such as prazosin can also improve voiding function.46 Phosphodiesterase inhibitors such as sildenafil can be helpful for erectile dysfunction, but their vasodilatory effects can worsen orthostatic hypotension.47 Onabotulinum toxin injections to the detrusor muscles may be of benefit without worsening orthostatic hypotension. Botulinum toxins can be helpful in treating dystonias including camptocormia associated with MSA. Physical, occupational, and speech therapy assist patients in optimizing overall function.

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35. Beck, R., Betts, C., & Fowler, C. (1994). Genitourinary dysfunction in multiple system atrophy: clinical features and treatment in 62 cases. J Urol, 151(5), 1336–​1341. 36. Goldstein, D., Pechnik, S., Holmes, C., Eldadah, B., & Sharabi, Y. (2003). Association between supine hypertension and orthostatic hypotension in autonomic failure. Hypertension, 42(2), 136–​142. 37. Stankovic, I., Krismer, F., Jesic, A., et al. (2014). Cognitive impairment in multiple system atrophy:  a position statement by the Neuropsychology Task Force of the MDS Multiple System Atrophy (MODIMSA) study group. Move Disord, 29(7), 857–​867. 38. Brooks, D., & Seppi, K. (2009). Proposed neuroimaging criteria for the diagnosis of multiple system atrophy. Mov Disord, 24(7), 949–​964. 39. Fanciulli, A., & Wenning, G. (2015). Multiple-​system atrophy. N Engl J Med, 372(3), 249–​263. 40. Poewe, W., Seppi, K., Fitzer-​Attas, C. J., Wenning, G. K., Gilman, S., Low, P. A., et al. (2014). Efficacy of rasagiline in patients with the parkinsonian variant of multiple system atrophy:  A  randomised, placebo-​controlled trial. Lancet Neurol, 14(2), 145–​152. 41. Low, P., & Singer, W. (2008). Management of neurogenic orthostatic hypotension: An update. Lancet Neurol, 7(5), 451–​458.

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42. Freeman, R. (2008). Current pharmacologic treatment for orthostatic hypotension. Clin Autonom Res, 18(Suppl 1), 14–​18. 43. Singer, W., Sandroni, P., Opfer-​Gehrking, T., et al. (2006). Pyridostigmine treatment trial in neurogenic orthostatic hypotension. Arch Neurol, 63(4), 513–​518. 44. Biaggioni, I., Freeman, R., Mathias, C. J., Low, P., Hewitt, L. A., Kaufmann, H., et  al. (2015). Randomized withdrawal study of patients with symptomatic neurogenic orthostatic hypotension responsive to droxidopa. Hypertension, 65(1), 101–​107. 45. Halaska, M., Ralph G., Wiedemann, A., et al. (2003). Controlled, double-​ blind, multicentre clinical trial to investigate long-​term tolerability and efficacy of trospium chloride in patients with detrusor instability. World J Urol, 20(6), 392–​399. 46. Sakakibara, R., Hattori, T., Uchiyama, T., et  al. (2000). Are alpha-​blockers involved in lower urinary tract dysfunction in multiple system atrophy? A comparison of prazosin and moxisylyte. J Auton Nerv Syst, 79(2–​3), 191–​195 47. Hussain, I., Brady, C., Swinn, M., Mathias, C., & Fowler, C. (2001). Treatment of erectile dysfunction with sildenafil citrate (Viagra) in parkinsonism due to Parkinson’s disease or multiple system atrophy with observations on orthostatic hypotension. J Neurol Neurosurg Psychiatry, 71(3), 371–​374.

5 | PARKINSON SYNDROMES: PROGRESSIVE SUPRANUCLEAR PALSY V I KAS KO TA GA L A N D P R AVE E N D AYA L U

D EFINITION

Variable neuronal loss is also reported in the basal ganglia and thalamus, particularly the ventral anterior (VA) and ventral lateral In 1955, a 52 year-​old resident of Toronto developed the unusual clini- (VL) thalamic nuclei. Cell loss is also seen in the nucleus basalis of cal syndrome of clumsiness, visual impairment, and memory difficul- Meynert, superior colliculus, trochlear and oculomotor nuclei, perities. He sought the professional opinion of his good friend, Dr. Clifford aqueductal grey, pedunculopontine nucleus, medullary tegmentum, Richardson, head of Neurology at Toronto General Hospital. Over inferior olives, and the cervical spinal cord.3 Tau-​based neurofibrillary tangles and neuropil threads are the the coming 4  years he developed an unusual constellation of neurological exam findings including vertical supranuclear opthalmoparesis, pathological hallmark of PSP. Intraneuronal tau inclusions, detected dystonic neck rigidity, pseudobulbar palsy, dysarthria, and dementia. using silver staining or immunohistochemistry, predominate in the Within a few years, Richardson would identify three additional patients striatum, globus pallidus, premotor cortex, as well as the numerous aforementioned brainstem regions. Inclusions tend to be more with similar neurologic features.1 In 1963, Richardson along with neuropathologist Jerzy Olszewski coil shaped in the cortex and globose or spherically shaped in the and neurology resident John Steele presented the clinical-​pathological brainstem. Supplementary western blot studies have also revealed findings of six such patients at the annual meeting of the American abundant insoluble tau in subcortical white matter structures not Neurological Association. They suggested that patients displaying associated with intraneuronal inclusions, though the pathological these neurologic features may be suffering from a discrete, and hereto- significance of this finding is not well understood.5 Tufted astrocytes are a unique histopathological feature of PSP fore unrecognized, clinical entity different from the well-​characterized like astrocytic plaques seen in neurodegenerative diseases of the time, including paralysis agitans and differ from the more crown-​ and olivo-​pontocerebellar degeneration. Richardson initially named Corticobasal degeneration. They are seen most commonly in the putathe new disease entity “heterogeneous system degeneration” though men and prefrontal cortex.6 Tau-​based inclusions in oligodendrocytes soon it became known as Steele-​Richardson-​Olszewski syndrome. take the form of either “coiled bodies” or interfascicular threads and In 1963 itself, Richardson would propose the name of Progressive can be detected using immunohistochemistry in cerebral, subcortical, and cerebellar white matter.3 Supranuclear Palsy. To fulfill the National Institute for Neurological Disorders and Today, progressive supranuclear palsy (PSP) is recognized as a form of atypical sporadic parkinsonism characterized by its unique Stroke neuropathological criteria for typical PSP, high-​density neuaxial motor features, onset in middle age, and its inexorably pro- rofibrillary tangles must be identified in at least two of the following gressive disease course. Additional phenotypes have been identi- regions: globus pallidus, subthalamic nucleus, substantia nigra, and fied, confounding clinical diagnosis. For example, some patients pons. In addition, low-​density neurofibrillary tangles must be identihave a milder course characterized by levodopa-​responsive appen- fied in at least one of the following regions: the striatum, oculomodicular bradykinesia and tremor followed by the later onset of gait tor complex, medulla, and dentate gyrus.4 The presence of astrocytic difficulties and oculomotor features. The term “PSP-​parkinsonism” involvement is considered a supportive feature. Progressive supranuclear palsy and other tauopathies overlap (PSP-​P) has been suggested to differentiate such patients from the more classic Richardson variant.2 Histopathologically, PSP features significantly in clinical and postmortem pathological features, sugcharacteristic intracellular tau deposition in specific subcortical gesting a continuum of tau disorders rather than discrete disease nuclei and cortical structures involved in balance, oculomotor con- processes. This pathological overlap is reflected in the evolving trol, and frontally mediated cognitive function. Synonyms: Steele-​ inclusiveness of the term “progressive supranuclear palsy.” When Richardson-​ Olszewski syndrome, Richardson’s syndrome, and presenting with overlapping features of PSP, tauopathies such as corticobasal degeneration, frontotemporal lobar dementia (FTLD), PSP-​parkinsonism. and motor neuron disease can be considered variants of “atypical PSP” that manifest with a greater degree of cortical tau burden NE UROPATHO L O GY and less severe brainstem tau density compared with conventional Macroscopically, early PSP is characterized by atrophy in several key PSP. Conversely, overlap with PSP can also be seen in patients who mesencephalic structures including the cerebral peduncles, supe- initially mimic idiopathic Parkinson disease (PD) but who later rior cerebellar peduncles, and subthalamic nucleus. Enlargement develop severe oculomotor or gait difficulties. These patients may of the third and fourth ventricles and the aqueduct of Sylvius often be characterized either as PSP-​P or alternatively as pure akinesia accompany these changes. Loss of neuromelanin is seen in both the with gait freezing (PAGF), the latter of which may represent a varisubstantia nigra and locus ceruleus, consistent with associated mono- ant of “atypical PSP” with more extensive pathology in deep brain aminergic cell loss. Atrophy can also be seen in the globus pallidus structures including the globus pallidus, brainstem, and diencephalon relative to the cortex.3 and along the primary motor cortex in Brodmann’s area 4.3,4 5 P r o g r e s s i v e Sup r a n ucle a r   Pa l s y | 3 1

S CI ENTIFI C FU N DAM E NTAL S GENETICS OF PROGRESSIVE S U P R A N U C L E A R   PA L S Y

The vast majority of PSP cases occur sporadically. Nevertheless there do exist several PSP kindreds with identified genetic mutations. A single family was identified to have an mutation in an unknown gene on chromosome 1q13.1.7 Other kindreds have shown an autosomal dominant mode of inheritance due to various mutations within the microtubule-​ associated protein tau (MAPT) gene on chromosome 17q21.3.8 Mutations in the MAPT gene more typically confer an increased risk for the development of PSP rather than mediating a direct causative effect. The MAPT gene spans 150 kb and in the wild type setting, expresses tau, an essential protein involved in microtubule stabilization in the peripheral and central nervous system. In 1999, Baker et al. identified a series of single nucleotide polymorphisms occurring more commonly in PSP than in controls. The genomic region associated with a high risk for PSP expands far outside of the MAPT locus, consistent with the phenomenon of linkage disequilibrium. We now recognize two non-​recombinant haplotypes, H1 and H2, that span a region estimated to be as large as 1.8 million base pairs.9 The H1 haplotype is seen commonly in Caucasians, in whom its estimated prevalence is between 70% and 80%. Among those with PSP, 90% of individuals carry at least one copy of the H1 haplotype.9 Within the H1 clade, the H1c sub-​haplotype confers an even greater risk for developing PSP and has been specifically investigated to look for a causative mutation. A recent Genome-​wide association study comparing autopsy-​confirmed cases of PSP to controls has revealed three other genes associated with an increased risk for PSP including STX6, a SNARE protein involved in vesicular membrane fusion; MOBP, a myelin protein expressed in brainstem structures; and EIF2AK3, a component of the endoplasmic reticulum’s unfolded protein response.10 An elevated 4R:3R ratio of tau isoforms may also be suggestive of PSP, distinguishing it from other tauopathies including Alzheimer’s disease, which shows a relatively even ratio of 4R:3R isoforms, and FTLD, which shows an elevated 3R:4R ratio.9 M I T O C H O N D R I A L PAT H O L O G Y A N D P R O G R E S S I V E S U P R A N U C L E A R   PA L S Y

Pathological tau accumulation in PSP may also occur secondary to antecedent changes in mitochondrial ATP production. Postmortem immunochemical studies have shown a mitochondrial metabolic deficit in PSP, though it remains unclear whether this is a result of the underlying disease process or a downstream effect.8 Annonaceae plants, which contain potent mitochondrial complex 1 inhibitors, have been associated with PSP in Guadalupe and in New Caledonia.11,12 When administered in vivo, a similar toxin can induce neurodegeneration in the basal ganglia and brainstem.13 Depleting ATP may lead to impaired trafficking of tau to axonal regions thereby promoting its accumulation in the cell bodies. Alternatively, impaired functioning of mitochondrial complex 1 may lead to an increase in reactive oxygen species, which in turn promote the nonspecific activation of many kinase systems contributing to tau phosphorylation. Hyperphosphorylated tau is more likely to aggregate and may further worsen mitochondrial energy demands.8

EP IDE MIOL OGY The prevalence of PSP is 6.4 cases per 100,000 with an age adjusted incidence rate of 1.14-​1.21 per 100,000 person years, making it the 32 | M o v e m e n t D i s o r de r s

second most common cause of idiopathic parkinsonism.14,15 The typical age of onset is in the sixth or seventh decade of life with a median time to diagnosis in one series of 3.5 years16 and an estimated disease duration between 8 and 10 years.16,17 Other series describe a shorter disease duration of less than 6 years, though their estimates may be influenced by referral bias.

C L INI CA L F E ATU R ES Early in the disease course, PSP can be difficult to parse from other similar neurodegenerative disorders. As the disease advances, though, its distinctive features become apparent. Interestingly, as astutely noted by British neurologist A. J. Larner,18 the first clinical description of PSP may in fact have been by Charles Dickens in 1857, predating Clifford Richardson’s report by nearly 100 years. In Dickens’s Magazine “Household Words,” the author relates an encounter with: A chilled, slow, earthy, fixed old man. A  cadaverous man of measured speech. An old man who seemed as unable to wink, as if his eyelids had been nailed to his forehead. An old man whose eyes—​two spots of fire—​had no more motion that [sic] if they had been connected with the back of his skull by screws driven through it, and rivetted and bolted outside, among his grey hair. He had come in and shut the door, and he now sat down. He did not bend himself to sit, as other people do, but seemed to sink bolt upright, as if in water, until the chair stopped him. (p. 194). DI CK E NS C , C O L L INS W.  The lazy tour of two idle apprentices.

In: No thoroughfare and other stories. Stroud: Alan Sutton; 1990 (p 128–​227)

This passage evokes many of the key clinical features of PSP including a) bradykinesia, b) speech and/​or language difficulties, c) facial hypomimia with a prominent lid-​retraction and a “staring” appearance, d) axial rigidity, and e) postural instability. In addition to these disease features, patients with PSP also develop highly characteristic supranuclear oculomotor palsy leading to limited volitional vertical eye movements, particularly downgaze, which is distinctly different from the common aging-​associated loss of volitional upgaze. Patients will often develop slow-​to-​initiate and hypometric saccades prior to exhibiting a complete limitation in range of vertical gaze. Horizontal gaze impairment also may occur later in the disease course. Oculocephalic maneuvers should facilitate an increased range of eye movements in the vertical plane compared to voluntary gaze, implying intact oculomotor neurons within and distal to cranial nerve nuclei. The gaze deficits in PSP point to dysfunction in the visual centers of the midbrain tectum including the rostral medial longitudinal fasciculus and superior colliculus, as well as the cortically based frontal and supplementary eye fields. Inappropriate vertical optokinetic responses with normal horizontal responses may help in differentiating PSP from PD early in the disease course. Eyelid retraction is a common feature of PSP which, coupled with facial hypokinesia, leads to a typical staring or “surprised” appearance that is seen more frequently in PSP compared with other parkinsonian syndromes. Apraxia of eyelid opening can cause a mild “stickiness” of lid closure during blinking, or be severe enough to cause functional blindness. This may reflect either a praxis difficulty or a dystonia involving levator palpebrae superioris.

Communication difficulties and dysphagia occur frequently in PSP and may profoundly impair quality of life. Cortically based language impairment is a more common early feature of corticobasal degeneration (CBD) than PSP. Nevertheless, both disorders can display apraxia of speech, characterized by slow speech and impaired pronunciation, as well as a progressive nonfluent aphasia, characterized by agrammatic language with impaired comprehension of spoken and written language.19 Much like PD, persistent hypophonia is common in PSP. However, dysarthria in PSP is usually more complex, with a mix of spastic, ataxic, and hypokinetic features.20 Dysphagia is also common, and often manifests with a paucity of spontaneous swallows and a longer time needed to complete a swallow.21 Overstuffing the mouth during meals is said to be a characteristic feature of PSP, but there are little data on the specificity and sensitivity of this finding. Rigidity preferentially involving the neck and torso rather than the limbs is a distinctive feature of PSP that may help differentiate it from PD clinically. Among PSP subtypes, axial rigidity is more commonly seen in the Richardson syndrome variant (RS) and relatively less frequent in PSP-​P. Likewise, asymmetric or unilateral bradykinesia, rigidity, and tremor are more likely to be seen in PSP-​P than in RS. Distinguishing early PSP-​P from idiopathic PD can be challenging. Although even PSP-​P patients may respond to L-​dopa, this response may be milder and less sustained in PSP-​P.2 Nevertheless, there may exist considerable overlap between the two disorders early in the disease course, making a definitive diagnosis challenging. Early and severe gait and balance difficulties help distinguish PSP from other parkinsonian and neurodegenerative disorders. Postural instability in PSP may have several causes, including selective neuronal loss in the cholinergic pedunculopontine nucleus (PPN),22 as well as a lower threshold for loss of balance mediated through comorbid axial rigidity and loss of ocular motility. The tendency of PSP patients to fall backward rather than forward may reflect vestibulospinal tract degeneration.23 The prevalence of cognitive impairment in early PSP ranges from 40% to 62%.24 Cognitive symptoms include both a frontal syndrome with impaired verbal fluency and perseveration as well as a subcortico-​ frontal syndrome consisting of impaired attention and executive dysfunction.24,25 Pseudobulbar affect is common in PSP and most likely reflects loss of corticopontine connections. Among neuropsychiatric symptoms, apathy is the most frequent, with a reported prevalence of 91% in one series.26 Other common features include depression, anxiety, and disinhibition. Most patients with PSP will also experience sleep difficulties. Compared with PD, PSP patients show a similar rate of sleep-​disordered breathing, a lower prevalence of REM sleep behavior disorder, and an increased prevalence of periodic leg movements of sleep and impaired sleep efficiency.27 Clinical research criteria for the diagnosis of PSP were drafted by the National Institute for Neurological Disorders and Stroke as well as the Society for PSP in 1996. Clinical criteria for possible “possible PSP” include onset after age 40, progressive clinical course, and either vertical supranuclear gaze palsy or the combination of slowed vertical saccades and postural instability in the first year of symptoms without an alternative explanation. The diagnosis of “probable PSP” requires the presence of a supranuclear gaze palsy, prominent postural instability, and the presence of falls within 1 year of symptom onset.28 The same diagnostic criteria list both supportive criteria (which include symmetric akinesia, poor response to levodopa, early dysphagia) and exclusion criteria (including markedly asymmetric parkinsonian signs, hallucinations unrelated to dopaminergic therapy, and alien limb phenomenon). Several clinical scales exist which can be used to track disease severity and progression.

NAT U RAL H ISTORY AND S U RVIVAL Progressive supranuclear palsy progresses at a more rapid rate on average than idiopathic Parkinson disease. Gait and balance impairment worsen with time, and patients require a walker or even a wheelchair relatively early in the course. Injuries from falls are common. Dysphagia can lead to aspiration pneumonia, choking, malnutrition, or dehydration; sometimes a percutaneous feeding tube is required. Dementia and behavior changes contribute heavily to morbidity. Such problems accrue more rapidly in PSP than in PD, resulting also in higher rates of institutionalization. Natural history studies of PSP have been complicated by limited postmortem data as well as prospective study design, which can lead to the erroneous inclusion of misdiagnosed patients in a PSP cohort. Nath et al.29 reported baseline clinical findings on 187 PSP subjects identified through an epidemiological study in the United Kingdom. The most common reason given for a referral from a general practitioner was “parkinsonism” followed by “balance disorder.” Nearly 70% of the cohort reported falls as their first symptom. Overall, 88% of all subjects reported falls at some point during the disease process with 70% of the total cohort reporting that they usually fell backward. Among the 75 subjects who died during follow-​up, the mean disease duration was 5.7 years, although this number does not account for the longer duration of survival among the majority of subjects in the cohort. The median time to onset of clinical symptoms was as follows: falls, 0 years; diplopia, 1 year; speech problems, 1.75 years; eyelid apraxia, 3.0  years; swallowing difficulties, 3.58  years, and placement of a percutaneous gastric feeding tube, 5.0 years. A retrospective study conducted by O’Sullivan et  al. looked at the natural history of 110 subjects with autopsy-​confirmed PSP.16 Of these, 69 were determined to have Richardson syndrome based on retrospective chart review with 29 subjects having PSP-​P and the remainder having an indeterminate subtype. The mean age of onset and mean time-​to-​diagnosis among the two subtypes respectively was 66.5 years & 3.1 years (RS) and 63.2 years & 4.0 years (PSP-​P). Mean disease duration among subtypes was 6.3 years (RS) and 11.7 years (PSP-​P). Not surprisingly, patients with PSP-​P were far more likely to have a positive response to levodopa treatment (65.5% vs. 17.0%), although levodopa-​responsiveness was not found to impact survival. The authors compared all 110 subjects with PSP to a similar cohort of 83 subjects with multiple system atrophy (MSA) and determined that regular falls, unintelligible speech, and cognitive impairment all occurred earlier in the disease course of PSP subjects.

D IFF ER E NTIAL DIA G NOSIS The differential diagnosis for PSP includes parkinsonian syndromes such as PD, MSA, and dementia with Lewy bodies (DLB); progressive tauopathies including CBD, FTLD, PAGF, and progressive non-​fluent aphsasia; vascular parkinsonism; normal pressure hydrocephalus; as well as other more rare neurodegenerative disease including Creutzfeldt-​Jakob disease, Whipple disease, motor-​neuron disease, neuroacanthocytosis, late onset Niemann-​Pick disease Type C, and progressive external opthalmoplegia. Mass lesions that compress the midbrain tectum also can manifest similar vertical ophthalmoplegia, hypokinesia, and cognitive impairment. As mentioned previously, early PSP-​P can appear similar to idiopathic PD because both syndromes can present with unilateral parkinsonism that may be respond to levodopa. However, early postural instability and falls, impaired vertical gaze, and dysphagia are uncommon in PD and may manifest soon after symptom onset in PSP. 5 P r o g r e s s i v e Sup r a n ucle a r   Pa l s y | 33

Clinical history and exam features can help differentiate PSP from other forms of atypical parkinsonism. On average, MSA may occur nearly a decade earlier than PSP (mean age of onset, MSA: 56.8 years, PSP:  65.6  years).16 Autonomic symptoms and cerebellar ataxia are more prevalent in MSA than in PSP. Similarly, early cognitive impairment is more common in PSP along with the other classic disease features of postural instability and vertical gaze impairment. The presence of early cognitive impairment with hallucinations and REM sleep behavior disorder coupled with mild parkinsonism are more suggestive of the diagnosis of DLB than PSP. Both MSA and DLB are less likely to manifest with the profound facial hypokinesia and oculomotor features of PSP. It may be more challenging to differentiate PSP from other neurodegenerative tauopathies including CBD, PAGF, and progressive nonfluent aphasia. Some question whether these disorders, instead of representing discrete diagnostic entities, are better understood as variant subtypes of progressive tauopathy. Alternatively, in an era where we increasingly recognize the presence of comorbid neurodegenerative pathologies in clinicopathological correlative studies, the overlap between PSP and other tauopathies may simply reflect the co-​occurrence of discrete disease entities with similar cellular substrates. The term “atypical PSP” has been coined to refer to forms of PSP that may overlap with other tauopathies though there are no well-​established clinical or pathological diagnostic criteria. Corticobasal degeneration, a tauopathy manifesting with asymmetric rigidty, dystonia, cortical sensory loss, apraxia, and alien limb phenomena, is termed “corticobasal syndrome” (CBS) when suspected clinically. One of the more common postmortem mimics of CBD among clinically diagnosed CBS is PSP. Postmortem findings of “PSP-​CBS” suggest a pathological variant of PSP with additional tau pathology in frontal and parietal association cortices.3 “PSP-​PAGF” is another distinct syndrome with progressive freezing of gait and axial rigidity in the first 5 years of symptoms, with late-​onset cognitive and ocular motility features. “PSP-​FTLD” refers to those patients with clinically diagnosed PSP who develop profound frontal cognitive syndromes. Minimal existing postmortem evidence suggests this overlap may be due to more aggressive tau deposition and synaptic loss in PSP-​FTLD compared with conventional PSP.3

ADDITIONA L T ESTING The diagnosis of PSP is made on clinical grounds. Though there do not exist well-​validated criteria for the use of ancillary clinical laboratory or imaging testing, a growing body of research suggests several findings can alter the index of clinical suspicion in a given patient. Conventional brain imaging, including head CT or brain MRI, can be useful in excluding alternative structural abnormalities such as infarcts, hydrocephalus, or intracranial masses. Tectal and tegmental atrophy of the midbrain has been recognized a hallmark of PSP for decades and may be apparent on conventional MRI imaging. The “hummingbird” sign was first described in 199430 and refers to the appearance of the brainstem on sagittal MRI where, due to atrophy of the midbrain, enlargement of the 3rd ventricle, and relative sparing of the pons, it takes the shape of a hummingbird. When viewed axially, the same midbrain atrophy and third ventricle enlargement have been termed the “morning glory flower” sign. Attempts to validated these two signs against a postmortem cohort of subjects with parkinsonian disorders during life suggested a high degree of specificity for both radiologic findings with a more limited sensitivity of (approximately 50%) in pathologically confirmed PSP.31 34 | M o v e m e n t D i s o r de r s

Flourodeoxyglucose positron emission tomography studies have shown a pattern of frontal, striatal, thalamic, and midbrain hypometabolism helpful in differentiating PSP from PD.32 Thalamic and frontal hypometabolism may be more prevalent in Richardson syndrome than in PSP-​P wherein putaminal hypometabolism is the predomaint feature.32 Dopamine transporter single photon emission computed tomography may be useful in distinguishing PSP patients from otherwise healthy individuals but does not effectively differentiate PSP from other parkinsonian disorders.33 Cerebrospinal fluid levels of tau are largely within the normal range in PSP, failing to differentiate it significantly from CBD.34 However, not all tau isoforms are presents in equal proportion among tauopathies. One post-​mortem study found a lower amount of the 33kDa tau isoform in PSP compared with CBD.35 A  follow-​up CSF study suggested that a high ratio of 33kDa/​55kDa tau isoforms could reliably distinguish PSP from CBD.36 Although this finding is promising, tau isoform ratio testing is not readily available for commercial testing and is unlikely to alter clinical management. In clinical practice, an aggressive levodopa trial remains an important diagnostic test, even in patients whose history and examination strongly raise suspicion for PSP. Levodopa should be titrated at least as high as 900mg daily before concluding that the patient has not responded. This is a critical step because some patients with Parkinson disease may mimic features of PSP.

MANA G EM E NT AND TREATM ENT No disease modifying therapy exists for PSP. Clinical strategies tend to focus on the management of specific symptoms and prevention of complications. A  trial of levodopa may provide some relief of global or appendicular bradykinesia although this benefit tends to be modest, short lasting, and is more common in PSP-​P than in axial predominant RS. There has been considerable interest in cholinergic therapies because of profound PPN degeneration seen in PSP. Unfortunately, several trials have failed to show a significant benefit from acetylcholinesterase inhibitors in both motor and cognitive domains.37,38 Physical therapy may be useful for improvement of gait and balance, although multi-​arm, prospective studies proving efficacy are lacking. Modifying activities and the home environment, as well as judicious use of gait assist devices, can help prevent falls. Referral to a speech language pathologist for management of dysphagia is often indicated once a patient or family begins to notice aspiration events, but may be worth considering for early swallowing problems such as increased difficulty finishing meals or weight loss. Placement of a PEG tube for enteral feedings later in the disease course can be considered if consistent with the patient’s goals of care. Diplopia might respond to prism lenses, and apraxia of eyelid opening might benefit from botulinum toxin.39

F U T U R E DIRE C TIONS Deep brain stimulation of the PPN has been attempted for PSP with modest early results.40 Combined PPN-​subthalamic nucleus stimulation has also been attempted in severe Parkinson disease aimed at improving gait and postural instability.41 Because of challenges related to the precision of target localization as well as the possibility of perioperative or stimulation-​based impairment to adjacent structures, PPN DBS is currently only being performed at a limited group of surgical centers.

Recent gains made in neurodegenerative disease research centered on tau regulation in Alzheimer’s dementia may pay crucial dividends in PSP. A recent double-​blinded, placebo-​controlled clinical trial testing Davunetide (AL-​108), an anti-​tau therapy, showed no benefit relative to placebo.42 Nevertheless, this large-​scale effort involving over 300 participants serves as a proof-​of-​concept for future international multicenter trials testing novel therapeutic agents in PSP. The same study also uncovered a significant association between 12-​month changes in CSF neurofilament light chain and changes in ocular motility and atrophy of the superior cerebellar peduncles, raising the possibility that it may have utility as a secondary outcome in PSP clinical trials moving forward. Abnormal acetylation of tau at lysine residue 280 has also been noted to be a unique feature of tau-​based neurodegenerative diseases. Postmortem immunohistochemistry studies reveal that across tauopathies the distribution of lysine 280 acetylation correlates well with the regional burden of hyperphosphorylated tau, suggesting that it may contribute to the generation of toxic, hypefibrillary tau, and might serve as a potential therapeutic target.43

CONC LUSION Progressive Supranuclear Palsy is one of several tau-​based neurodegenerative diseases. Though disease modifying therapies are not currently available, increased understanding of the genetics and molecular pathogenesis of all tauopathies, including Alzheimer’s disease and frontotemporal lobar dementia, is likely to contribute significantly toward knowledge of therapeutic targets and the development of disease modifying treatments for PSP.

REFE RE NC ES 1. Williams, D. R., Lees, A. J., Wherrett, J. R., & Steele, J. C. (2008). J. Clifford Richardson and 50  years of progressive supranuclear palsy. Neurology, 70(7), 566–​573. doi: 10.1212/​01.wnl.0000286938.39473.0e 2. Williams, D. R., de Silva, R., Paviour, D. C., Pittman, A., Watt, H. C., Kilford, L., . . . Lees, A. J. (2005). Characteristics of two distinct clinical phenotypes in pathologically proven progressive supranuclear palsy: Richardson’s syndrome and PSP-​parkinsonism. Brain, 128(Pt 6), 1247–​1258. doi: 10.1093/​ brain/​awh488 3. Dickson, D.  W., Ahmed, Z., Algom, A.  A., Tsuboi, Y., & Josephs, K.  A. (2010). Neuropathology of variants of progressive supranuclear palsy. Curr Opin Neurol, 23(4), 394–​400. doi: 10.1097/​WCO.0b013e32833be924 4. Hauw, J.  J., Daniel, S.  E., Dickson, D., Horoupian, D.  S., Jellinger, K., Lantos, P. L., . . . Litvan, I. (1994). Preliminary NINDS neuropathologic criteria for Steele-​Richardson-​Olszewski syndrome (progressive supranuclear palsy). Neurology, 44(11), 2015–​2019. 5. Zhukareva, V., Joyce, S., Schuck, T., Van Deerlin, V., Hurtig, H., Albin, R., . . . Lee, V. M. (2006). Unexpected abundance of pathological tau in progressive supranuclear palsy white matter. Ann Neurol, 60(3), 335–​345. doi: 10.1002/​ ana.20916 6. Matsusaka, H., Ikeda, K., Akiyama, H., Arai, T., Inoue, M., & Yagishita, S. (1998). Astrocytic pathology in progressive supranuclear palsy: significance for neuropathological diagnosis. Acta Neuropathol, 96(3), 248–​252. 7. Ros, R., Gomez Garre, P., Hirano, M., Tai, Y. F., Ampuero, I., Vidal, L., . . . de Yebenes, J. G. (2005). Genetic linkage of autosomal dominant progressive supranuclear palsy to 1q31.1. Ann Neurol, 57(5), 634–​641. doi: 10.1002/​ ana.20449 8. Stamelou, M., de Silva, R., Arias-​Carrion, O., Boura, E., Hollerhage, M., Oertel, W.  H., .  .  . Hoglinger, G.  U. (2010). Rational therapeutic approaches to progressive supranuclear palsy. Brain, 133(Pt 6), 1578–​ 1590. doi: 10.1093/​brain/​awq115 9. Pittman, A. M., Fung, H. C., & de Silva, R. (2006). Untangling the tau gene association with neurodegenerative disorders. Hum Mol Genet, 15(Spec No 2), R188–​195. doi: 10.1093/​hmg/​ddl190 10. Hoglinger, G. U., Melhem, N. M., Dickson, D. W., Sleiman, P. M., Wang, L. S., Klei, L., . . . Schellenberg, G. D. (2011). Identification of common

variants influencing risk of the tauopathy progressive supranuclear palsy. Nat Genet, 43(7), 699–​705. doi: 10.1038/​ng.859 11. Angibaud, G., Gaultier, C., & Rascol, O. (2004). Atypical parkinsonism and Annonaceae consumption in New Caledonia. Mov Disord, 19(5), 603–​604. doi: 10.1002/​mds.20104 12. Caparros-​Lefebvre, D., & Elbaz, A. (1999). Possible relation of atypical parkinsonism in the French West Indies with consumption of tropical plants:  A  case-​control study. Caribbean Parkinsonism Study Group. Lancet, 354(9175), 281–​286. 13. Champy, P., Hoglinger, G.  U., Feger, J., Gleye, C., Hocquemiller, R., Laurens, A., .  .  . Ruberg, M. (2004). Annonacin, a lipophilic inhibitor of mitochondrial complex I, induces nigral and striatal neurodegeneration in rats: Possible relevance for atypical parkinsonism in Guadeloupe. J Neurochem, 88(1), 63–​69. 14. Mazorra, L., & Cadogan, M.  P. (2012). Progressive supranuclear palsy. J Gerontol Nurs, 38(3), 8–​11. doi: 10.3928/​00989134-​20120207-​07 15. Schrag, A., Ben-​Shlomo, Y., & Quinn, N. P. (1999). Prevalence of progressive supranuclear palsy and multiple system atrophy:  a cross-​sectional study. Lancet, 354(9192), 1771–​1775. 16. O’Sullivan, S.  S., Massey, L.  A., Williams, D.  R., Silveira-​Moriyama, L., Kempster, P. A., Holton, J. L., . . . Lees, A. J. (2008). Clinical outcomes of progressive supranuclear palsy and multiple system atrophy. Brain, 131 (Pt 5), 1362–​1372. doi: 10.1093/​brain/​awn065 17. Golbe, L.  I., Davis, P.  H., Schoenberg, B.  S., & Duvoisin, R.  C. (1988). Prevalence and natural history of progressive supranuclear palsy. Neurology, 38(7), 1031–​1034. 18. Larner, A. J. (2002). Did Charles Dickens describe progressive supranuclear palsy in 1857? Mov Disord, 17(4), 832–​833. doi: 10.1002/​mds.10170 19. Josephs, K.  A., & Duffy, J.  R. (2008). Apraxia of speech and nonfluent aphasia: a new clinical marker for corticobasal degeneration and progressive supranuclear palsy. Curr Opin Neurol, 21(6), 688–​692. doi: 10.1097/​ WCO.0b013e3283168ddd 20. Kluin, K. J., Foster, N. L., Berent, S., & Gilman, S. (1993). Perceptual analysis of speech disorders in progressive supranuclear palsy. Neurology, 43(3 Pt 1), 563–​566. 21. Litvan, I., Sastry, N., & Sonies, B.  C. (1997). Characterizing swallowing abnormalities in progressive supranuclear palsy. Neurology, 48(6), 1654–​1662. 22. Zweig, R.  M., Whitehouse, P.  J., Casanova, M.  F., Walker, L.  C., Jankel, W. R., & Price, D. L. (1987). Loss of pedunculopontine neurons in progressive supranuclear palsy. Ann Neurol, 22(1), 18–​ 25. doi:  10.1002/​ ana.410220107 23. Liao, K., Wagner, J., Joshi, A., Estrovich, I., Walker, M.  F., Strupp, M., & Leigh, R.  J. (2008). Why do patients with PSP fall? Evidence for abnormal otolith responses. Neurology, 70(10), 802–​809. doi:  10.1212/​ 01.wnl.0000304134.33380.1e 24. Brown, R.  G., Lacomblez, L., Landwehrmeyer, B.  G., Bak, T., Uttner, I., Dubois, B., . . . Leigh, N. P. (2010). Cognitive impairment in patients with multiple system atrophy and progressive supranuclear palsy. Brain, 133(Pt 8), 2382–​2393. doi: 10.1093/​brain/​awq158 25. Soliveri, P., Monza, D., Paridi, D., Carella, F., Genitrini, S., Testa, D., & Girotti, F. (2000). Neuropsychological follow up in patients with Parkinson’s disease, striatonigral degeneration-​type multisystem atrophy, and progressive supranuclear palsy. J Neurol Neurosurg Psychiatry, 69(3), 313–​318. 26. Litvan, I., Mega, M.  S., Cummings, J.  L., & Fairbanks, L. (1996). Neuropsychiatric aspects of progressive supranuclear palsy. Neurology, 47(5), 1184–​1189. 27. Sixel-​ Doring, F., Schweitzer, M., Mollenhauer, B., & Trenkwalder, C. (2009). Polysomnographic findings, video-​based sleep analysis and sleep perception in progressive supranuclear palsy. Sleep Med, 10(4), 407–​415. doi: 10.1016/​j.sleep.2008.05.004 28. Litvan, I., Agid, Y., Calne, D., Campbell, G., Dubois, B., Duvoisin, R. C., . . . Zee, D. S. (1996). Clinical research criteria for the diagnosis of progressive supranuclear palsy (Steele-​Richardson-​Olszewski syndrome): Report of the NINDS-​SPSP international workshop. Neurology, 47(1), 1–​9. 29. Nath, U., Ben-​Shlomo, Y., Thomson, R.  G., Lees, A.  J., & Burn, D.  J. (2003). Clinical features and natural history of progressive supranuclear palsy: A clinical cohort study. Neurology, 60(6), 910–​916. 30. Iwata, M. (1994). Humming-​bird appearance of mid-​brain in MRI of progressive supranuclear palsy. Annual Report of the Research Committee of CNS Degenerative Diseases. The Minister of Health and Welfare of Japan, 48–​50. 31. Massey, L.  A., Micallef, C., Paviour, D.  C., O’Sullivan, S.  S., Ling, H., Williams, D. R., . . . Jager, H. R. (2012). Conventional magnetic resonance imaging in confirmed progressive supranuclear palsy and multiple system atrophy. Mov Disord, 27(14), 1754–​1762. doi: 10.1002/​mds.24968

5 P r o g r e s s i v e Sup r a n ucle a r   Pa l s y | 35

32. Srulijes, K., Reimold, M., Liscic, R.  M., Bauer, S., Dietzel, E., Liepelt-​ Scarfone, I., . . . Maetzler, W. (2012). Fluorodeoxyglucose positron emission tomography in Richardson’s syndrome and progressive supranuclear palsy-​parkinsonism. Mov Disord, 27(1), 151–​155. 33. Kim, Y. J., Ichise, M., Ballinger, J. R., Vines, D., Erami, S. S., Tatschida, T., & Lang, A. E. (2002). Combination of dopamine transporter and D2 receptor SPECT in the diagnostic evaluation of PD, MSA, and PSP. Mov Disord, 17(2), 303–​312. 34. Urakami, K., Wada, K., Arai, H., Sasaki, H., Kanai, M., Shoji, M., .  .  . Nakashima, K. (2001). Diagnostic significance of tau protein in cerebrospinal fluid from patients with corticobasal degeneration or progressive supranuclear palsy. J Neurol Sci, 183(1), 95–​98. 35. Arai, T., Ikeda, K., Akiyama, H., Nonaka, T., Hasegawa, M., Ishiguro, K., .  .  . Mochizuki, A. (2004). Identification of amino-​ terminally cleaved tau fragments that distinguish progressive supranuclear palsy from corticobasal degeneration. Ann Neurol, 55(1), 72–​79. doi: 10.1002/​ana.10793 36. Borroni, B., Gardoni, F., Parnetti, L., Magno, L., Malinverno, M., Saggese, E., . . . Di Luca, M. (2009). Pattern of Tau forms in CSF is altered in progressive supranuclear palsy. Neurobiol Aging, 30(1), 34–​40. doi: 10.1016/​ j.neurobiolaging.2007.05.009 37. Foster, N.  L., Aldrich, M.  S., Bluemlein, L., White, R.  F., & Berent, S. (1989). Failure of cholinergic agonist RS-​ 86 to improve cognition

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and movement in PSP despite effects on sleep. Neurology, 39(2 Pt 1), 257–​261. 38. Litvan, I., Phipps, M., Pharr, V.  L., Hallett, M., Grafman, J., & Salazar, A. (2001). Randomized placebo-​controlled trial of donepezil in patients with progressive supranuclear palsy. Neurology, 57(3), 467–​473. 39. Boghen, D. (1997). Apraxia of lid opening:  A  review. Neurology, 48(6), 1491–​1494. 40. Hazrati, L.  N., Wong, J.  C., Hamani, C., Lozano, A.  M., Poon, Y.  Y., Dostrovsky, J. O., . . . Moro, E. (2012). Clinicopathological study in progressive supranuclear palsy with pedunculopontine stimulation. Mov Disord, 27(10), 1304–​1307. doi: 10.1002/​mds.25123 41. Khan, S., Gill, S.  S., Mooney, L., White, P., Whone, A., Brooks, D.  J., & Pavese, N. (2012). Combined pedunculopontine-​subthalamic stimulation in Parkinson disease. Neurology, 78(14), 1090–​1095. doi:  10.1212/​ WNL.0b013e31824e8e96 42. Boxer, A. L., Lang, A. E., Grossman, M., Knopman, D. S., Miller, B. L., Schneider, L.  S., .  .  . Morimoto, B.  H. (2014). Davunetide in patients with progressive supranuclear palsy: A randomised, double-​blind, placebo-​controlled phase 2/​3 trial. Lancet Neurol, 13(7), 676–​685. doi: 10.1016/​s1474-​4422(14)70088-​2 43. Irwin, D. J., Cohen, T. J., Grossman, M., Arnold, S. E., Xie, S. X., Lee, V. M., & Trojanowski, J. Q. (2012). Acetylated tau, a novel pathological signature in Alzheimer’s disease and other tauopathies. Brain, 135(Pt 3), 807–​818. doi: 10.1093/​brain/​aws013

6 | PARKINSON SYNDROMES: CORTICOBASAL SYNDROME S AMI B AR M A D A

D EFINITION Corticobasal syndrome (CBS) is a clinically and pathologically heterogenous condition marked most often by asymmetric parkinsonism and apraxia, with or without cognitive dysfunction. Synonyms: corticobasal disease; cortical basal degeneration.

INTRODU CTION Although most patients with parkinsonism present with the classic triad of bradykinesia, tremor, and rigidity that is the hallmark of idiopathic Parkinson’s disease, many will exhibit additional signs or symptoms that cannot be explained by this condition alone. In these patients, often lumped under the diagnostic category of “atypical parkinsonism syndromes” or “parkinsonism-​plus,” the classic triad is supplemented by myriad deficits, including but not limited to oculomotor dysfunction, apraxia, myoclonus, and cognitive decline.1 Distinguishing among these conditions is not purely academic, because the underlying pathology and disease mechanisms may be completely different and therefore may indicate a distinct approach to treatment in each case. Here, we will focus upon corticobasal syndrome, a clinically and pathologically heterogenous condition that is increasingly recognized as a major cause of motor, language, and cognitive deficits in patients with atypical parkinsonism.

instead may emerge gradually over time; in a small minority of patients, these symptoms will never emerge.7 Cognitive decline in CBS is variable, affecting between 35% to 70% of patients at the time of diagnosis, but eventually cognitive deficits can be seen in nearly 100% of affected individuals. Disinhibition, apathy, social withdrawal, agitation, aphasia, and executive dysfunction are prominent in CBS patients, resembling the type of cognitive symptoms noted in the behavioral variant of frontotemporal dementia.8 The unique symptoms that comprise CBS are a direct result of neuronal dysfunction and neurodegeneration in specific regions of the central nervous system (CNS).9,10 Even so, the precise cause of the neuronal loss in these areas may vary considerably, such that multiple molecular pathologies may result in CBS11 (Figure 6.1). In this respect, CBS differs fundamentally from one of the most common neurologic disorders, cerebral ischemia or stroke. The symptoms of ischemia involving the cerebral arteries are diverse, and depend primarily upon the areas of the CNS most affected, but the underlying pathology is the same:  interruption of blood flow to neurons.12 Conversely, CBS is a clinical syndrome comprised of stereotyped symptoms, and a host of different insults can result in a similar picture. In the section that follows, I will discuss the genetic and molecular causes that precipitate this condition.

N E URO BIOL O G Y OF  D IS E ASE MOLECULAR, GENETIC, AND N E U R O PAT H O L O G I C C O R R E L AT E S IN CBS

CLINI C AL P RES E NTATION As its name implies, the corticobasal syndrome is a collection of signs and symptoms that are often observed in conjunction with one another. Asymmetry is one of the defining features of CBS,2–​4 and although patients rarely present with wholly unilateral symptoms, most of the deficits are limited to one side of the body or are at least more pronounced on one side. Apraxia is also a common and characteristic finding in CBS.2–​4 At its most fundamental level, apraxia is a disorder of voluntary action,5 manifesting as clumsiness or freezing despite normal strength, and is primarily unilateral. Apraxia has several manifestations, including ideomotor apraxia (the inability to plan or perform voluntary actions) and ideational apraxia (the inability to perform multistep actions or grasp the meaning of the actions).6 People with CBS also may develop alien limb phenomenon, involving abnormal, unconscious movement of an arm or leg. In each case, there is a fundamental disconnect between the planning and execution stages of motor function. In addition to parkinsonism, patients with CBS may display gait instability, dystonia, myoclonus, dysautonomia, limb or oculomotor apraxia, cortical sensory loss, and cognitive dysfunction.2–​4 Interestingly, although CBS is considered to be an atypical parkinsonism syndrome, the extrapyramidal symptoms, including bradykinesia, tremor, and rigidity, may not be present at the time of diagnosis, and

The first neuropathological descriptions of patients with CBS noted neuronal loss in focal regions of the cortex and substantia nigra, in combination with cortical and subcortical neuronal inclusions and astrocytic plaques that are rich in the microtubule binding protein tau.13 This distinctive pathology was described as corticobasal degeneration (CBD), and was initially presumed to represent the neuropathologic correlate of CBS. With the growing realization of CBS as a clinical entity, however, postmortem studies demonstrated that CBD was not invariably associated with CBS;7,14 in fact, at best only half of patients diagnosed clinically with CBS exhibited CBD on autopsy. The positive predictive value of a diagnosis of CBS for CBD neuropathology is only 25%, but doubles if a neurologist specializing in movement disorders makes the diagnosis. Moreover, the accuracy of a clinical diagnosis of CBD using criteria for CBS is especially poor at early stages of disease, when CBS is often confused for progressive supranuclear palsy (PSP), a related atypical parkinsonism syndrome that shares some characteristics with CBS but exhibits unique neuropathology.7,14 In addition to CBD, several other pathologies can be responsible for the clinical presentation of CBS (see Figure 6.1). Most often, these include distinct neurodegenerative diseases such as Alzheimer’s disease, frontotemporal lobar dementia, PSP, or Lewy-​body dementia.15,16

6 Pa r k i n s o n S y n d r o m e s :   C o r t i c o b a s a l S y n d r o m e | 3 7

Genes

Proteins

Pathology

Diseases

MAPT

Tau

CBD

PD

LRRK2

α-syn

FTLD-tau

DAT

FUS

FUS

LBD

PSP

FTLD-FUS

CBS

FTLD-TDP

bvFTD

GRN TDP43

TDP43

C9ORF72

PPA FTD-MND

Figure 6.1  Heterogeneity of CBS genetics, neuropathology, and clinical

presentation. The figure depicts the disconnect between genetic causes of CBS (far left), the proteins affected by the mutations (middle left), the neuropathological entities related to each protein (middle right), and the range of clinical presentations for each (far right). As the scale increases from single molecules to human beings, the complexity and potential combinations increase exponentially. α-​syn, alpha-​synuclein; bvFTD, behavioral variant of frontotemporal dementia; C9ORF72, chromosome 9 open reading frame 72; CBD, corticobasal degeneration; CBS, corticobasal syndrome; DAT, dementia of the Alzheimer’s type; FTD-​MND, frontotemporal dementia with motor neuron disease; FTLD-​FUS, frontotemporal lobar degeneration with FUS deposits; FTLD-​tau, frontotemporal lobar degeneration with tau deposits; FTLD-​TDP, frontotemporal lobar degeneration with TDP43 deposits; FUS, fused in sarcoma; GRN, progranulin; LBD, Lewy-​body dementia; LRRK2, leucine-​rich repeat kinase 2; MAPT, microtubule associated protein tau; PD, Parkinson’s disease; PPA, primary progressive aphasia; PSP, progressive supranuclear palsy; TDP43, transactive response element DNA/​RNA binding protein, 43 kDa. Refs: 8, 14, 15, 19–​24.

In some cases, Creutzfeldt-​Jacob disease17 and stroke18 can result in CBS. Even inflammatory conditions such as antiphospholipid antibody syndrome have been implicated in the development of CBS,19 confirming the importance of localization over pathologic subtype in the development of CBS. Corticobasal degeneration, on the other hand, has been observed in patients with PSP, FTD, progressive nonfluent aphasia, and posterior cortical atrophy.9,15,20 Thus, CBS is a clinical diagnosis that exhibits little correlation with the pathologic entity of CBD. Genetic studies have uncovered several important genes and protein products that are integrally involved in the pathogenesis of CBS. Although there are no specific genes that have been directly associated with CBS or CBD, several different mutations can cause the clinical picture of CBS and/​or the pathologic changes characteristic of CBD (see Figure 6.1). Mutations in the genes encoding tau (MAPT),21 progranulin (GRN),22 and leucine-​rich repeat kinase 2 (LRRK2)23 most often cause FTD or PD, but have also been linked to CBS in some patients. Moreover, pathogenic mutations in TARDBP,24 FUS,24 or C9ORF7225 have been associated with CBS in rare cases. Such mutations result in a diverse array of pathologies, including neuronal inclusions rich in tau, α-​synuclein, FUS, and TDP43. Taken together, these observations underscore the conclusion that CBS has many causes, implying that neuronal dysfunction and loss within a conserved network of brain regions, regardless of origin, are the defining features that lead to CBS. SELECTIVE NEURONAL SUSCEPTIBILITY IN CBS

One of the key features of CBS that distinguishes it from related conditions is apraxia,5 or the inability to perform a task despite intact strength, sensation, coordination, and understanding. As discussed, CBS affects the brain regions and pathways that control voluntary

38 | M o v e m e n t D i s o r de r s

actions. These areas include the frontoparietal cortices, especially the dorsolateral prefrontal cortex (DLPFC) and the pre-​supplemental motor area (pre-​SMA).10,26 The latter region is responsible for the decision to act, or volition, which we perceive as conscious intention, and lesions here can result in contralateral alien limb phenomena and apraxia.5 The pre-​SMA is one among many regions that collectively make up a network controlling the execution of willed action, and connections between this region and the DLPFC, basal ganglia, insular cortex, and pre-​motor area are essential for awareness and control of movement.27 Disruptions to this network are characteristic of CBS, and often can be detected antemortem using sensitive measures of neuronal connectivity and regional brain atrophy. For instance, resting and active state functional connectivity, as gauged by functional MRI,27 have confirmed disruptions in the pre-​SMA–​frontal cortex circuit. Studies incorporating voxel-​based morphometry5,9,26 demonstrated selective and asymmetric degeneration of the frontal cortices, supplemental motor area, DLPFC, insula, and striatum. Interestingly, although asymmetry of atrophy was a prominent finding in CBS, many patients with CBD showed no significant asymmetry.9 In addition, diffusion-​tensor imaging, focusing on the white matter tracts connecting separate brain regions, showed reduced fractional anisotropy and increased mean diffusivity in the corpus collosum, cingulum, superior cerebellar peduncles, pre-​motor and prefrontal white matter in CBS.28 These results suggest CBS is associated with degeneration or disconnection of the pre-​SMA, DLPFC, insula, and striatum, the same network of brain regions controlling volition and planned movement. Although this core network appears to be most affected in CBS, the mechanism by which genetic and environmental factors cause selective degeneration of these regions in CBS remain unclear. As mentioned previously and shown in Figure 6.1, mutations in several different genes may lead to CBS in a subset of patients. However, even family members with identical mutations do not always develop CBS, and may remain asymptomatic or exhibit signs and symptoms of a clinically and pathologically distinct neurodegenerative disorder. On the other hand, patients from unrelated families carrying unique mutations might present with equivalent clinical pictures and demonstrate indistinguishable pathologic changes on autopsy. Initial studies have hinted that the pre-​SMA, DLPFC, insula, and striatum—​the same assembly of regions targeted in CBS—​express elevated levels of a tau splice isoform harboring four microtuble repeat regions (4R tau).29 This, in turn, may make these regions more susceptible to inborn genetic mutations, age-​dependent changes, or accumulating environmental insults that impact the maintenance of protein homeostasis. Neurons are among the most long-​lived cells in the body, and thus even relatively small perturbations in their ability to maintain protein homeostasis could, in the long term, result in the deposition of misfolded and neurotoxic proteins such as tau. In addition, local dysfunction of astrocytes and other supporting glia in susceptible regions of the CNS might account for the selective vulnerability of the core network in CBS.30 Investigations into the glial contributions to CBS are preliminary, but have raised the intriguing possibility that regional specialization of glia, not just neurons, may underlie the pattern of neuronal dysfunction and degeneration that characterizes CBS. PROGRESSION OF DISEASE IN CBS

How does CBS originate, why does it involve a select network of brain regions, and why does it present clinically with a stereotyped

Neurotoxicity threshold Misfolding threshold

Misfolded proteins

(A) Neuron #

set of signs and symptoms? Although we do not yet have definitive answers for these questions, recent studies have highlighted the potential pathways by which the pathologic changes evident in CBS might initiate and spread within the CNS, eventually resulting in the outward presentation of parkinsonism, apraxia, and cognitive dysfunction. The primary insult that triggers the dysfunction and death of neurons in CBS may not be a single event, but one of several potential factors. For instance, genetic mutations (see Figure 6.1), as-​yet unknown environmental exposures, progressive and age-​related deficiencies in cellular protein turnover mechanisms (i.e., the ubiquitin proteasome system), or stochastic events such as the misfolding and aggregation of unstable proteins might underlie the beginning of neurodegeneration, either by themselves or in combination with one another. The latter two mechanisms may also exhibit feed-​forward kinetics, because misfolded proteins are normally degraded by the proteasome, and some misfolded proteins can directly inhibit the proteasome,31 resulting in even greater levels of abnormal protein isoforms. Studies have shown that many of the disease-​related proteins in CBS, including amyloid-​ß, α-​synuclein, tau, and TDP43, are capable of misfolding and, once the concentration of misfolded protein reaches a critical level, catalyzing the further misfolding of their “normal” counterparts.32–​35 This self-​templated conversion is a fundamental tenant of prions, the infectious proteinacious particles that are responsible for Creutzfeld-​Jacob disease (CJD), fatal familial insomnia, and kuru. Interestingly, CJD can sometimes present with a CBS-​like clinical picture.17 These findings offer a potential explanation for the age-​ dependent onset of neurodegenerative conditions such as CBS (Figure 6.2). In younger neurons, cellular mechanisms responsible for the maintenance of protein homeostasis function efficiently enough to keep the level of misfolded proteins to a minimum. However, the combination of genetic mutations—​causing amino acid changes that subtly destabilize proteins—​and age-​related deficiencies in protein clearance mechanisms eventually lead to an accumulation of misfolded proteins. Once a critical or threshold concentration is reached, the proteins themselves catalyze additional misfolding, inhibit the proteasome, or both, leading to a rapid rise in protein misfolding. One result of this cascade is the apparent precipitation of misfolded proteins into macroscopic aggregates or inclusion bodies that are characteristic findings in all neurodegenerative diseases, including CBS. In addition, through unknown pathways, the accumulation of misfolded proteins triggers neuronal dysfunction and ultimately cell death In CBS, the initial pathology primarily involves the network comprised of the pre-​SMA, DLPFC, insula, and striatum. The high degree of interconnectedness among these brain regions, as evidenced by functional studies in humans,27 as well as their elevated level of 4R tau expression,29 might contribute to their shared susceptibility. Investigations involving in vitro and in vivo (animal) models of neurodegenerative disorders have shown that the major disease-​related proteins in CBS—​amyloid-​ß, α-​synuclein, tau, TDP43, and the prion protein—​are capable of spreading through the CNS via synaptic connections between neurons,36 propagating neurotoxicity in their wake. If the original event (the equivalent of the index case) were to occur within the pre-​SMA, DLPFC, insula, or striatum, disease would spread preferentially within this network. What follows clinically is parkinsonism, apraxia, and cognitive deficits, because these regions are required for proper motor control, the coordination of voluntary movement, and executive functioning.

Time (B)

Normal protein

Misfolded protein

Protein aggregate

Figure 6.2  A model for the onset and progression of CBS. (A) Hypothetical

relationship between protein misfolding (dark line, beginning at bottom) and neuron number (lighter line, beginning at top) over time. Two thresholds are apparent from this diagram: a “protein misfolding threshold,” representing the critical concentration of misfolded proteins required to achieve self-​ templated conversion of normal isoforms to disease-​associated misfolded conformers; and the “neurotoxicity threshold,” the point at which enough misfolded protein has accumulated to cause neuronal dysfunction and death. (B) Schematic diagram illustrating the steps involved in disease progression, and potential therapeutic strategies. (1) Protein misfolding occurs stochastically or may be induced by disease-​associated mutations. (2) In healthy, young neurons, soluble misfolded protein is degraded by the ubiquitin-​proteasome system. (3) Over time, the proteasome becomes inefficient or enough misfolded protein has accumulated to stimulate self-​templated misfolding, resulting in the formation of insoluble protein aggregates. Deposition of misfolded proteins and neurotoxicity can potentially be reduced by induction of autophagy (4) or by functional disaggregages (5) capable of refolding disease-​associated protein conformers.

F U T U R E DIRE C TIONS I M P L I C AT I O N S F O R   T R E AT M E N T   I N   C B S

Our understanding of the neuropathologic events leading to CBS has changed significantly in the past decade, affecting how we approach treatment for this disorder. Currently, treatment options are limited to symptomatic management of parkinsonism in CBS using dopamine precursors or direct dopamine agonists, which have limited or no efficacy.37 Additional strategies include occupational and physical therapy for gait difficulties, selective serotonin reuptake inhibitors for behavioral changes, botulinum toxin injections and benzodiazepines for dystonia, and cholinesterase inhibitors and NMDA-​ receptor blockers for cognitive dysfunction.38 There is no definitive evidence that these treatments slow or prevent the progression of disease, however. The development of a truly effective strategy in CBS is complicated by the lack of a defined molecular pathology responsible for neurodegeneration. Even if a tau-​or TDP43-​specific treatment option were to be made available, the difficulty in accurately identifying the relevant neuropathology antemortem precludes patient selection for

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enrollment in clinical trials and, eventually, treatment outside of the research setting. Biomarkers capable of specifically labeling ongoing pathologic processes in vivo, such as radiotracers that avidly bind tau or TDP43 inclusions, are sorely needed. Moreover, once the relevant pathology has been detected, candidate treatments must be capable of preventing neuronal dysfunction and death. However, recent studies have demonstrated the broad therapeutic potential of autophagy induction and protein disaggregases, raising the possibility that a novel class of therapies might act through conserved mechanisms that are shared among many neurodegenerative conditions (see Figure 6.2). Autophagy is an essential cellular pathway capable of degrading long-​lived, aggregated proteins and entire organelles, and is absolutely necessary for maintaining neuronal health.39 Importantly, upregulation of autophagy through genetic or pharmacologic means protects against neurodegeneration in multiple cellular and animal models of neurodegenerative diseases (reviewed in ref. 39), including Alzheimer’s disease, Huntington’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis. Ongoing studies are now aimed at optimizing candidate small molecule inducers of autophagy for their use in humans with neurodegenerative disease. Other potential strategies take advantage of specialized enzymes termed “disaggregases” that are able to disassemble protein aggregates and refold pathologic conformers into their functional, nontoxic isoforms.40 Although such approaches may ultimately prove effective, lingering questions include the delivery method for the protein complexes and their long-​ term effects upon neuronal health and disease progression.

CONC LUSIONS Corticobasal syndrome is a clinical condition marked by parkinsonism, apraxia, and cognitive dysfunction. The clinical heterogeneity of CBS is mirrored by similar diversity at the cellular and molecular level. In most cases, however, CBS is characterized by dysfunction in a core network of brain regions including the pre-​SMA, DLPFC, insula, and striatum. The combination of genetic, age-​dependent, and ill-​defined environmental factors result in the selective degeneration of neurons within this network, but once disease begins, it appears to spread among the interconnected nodes of the network through a prion-​like mechanism. Novel therapies, if they are to be effective, must be capable of preventing neurotoxicity through multiple mechanisms by acting upon a common pathway that is shared amongst the disparate causes of CBS. Protein misfolding, the accumulation and deposition of misfolded proteins, and self-​templated renewal of abnormal protein isoforms are conserved pathways implicated in neurodegeneration in CBS, and therefore represent potential targets for newly developed therapeutic strategies.

REFE RE NC ES 1. Ahlskog, J. (2000). Diagnosis and differential diagnosis of Parkinson’s disease and parkinsonism. Parkinsonism Relat Disord, 7(1), 63–​70. 2. Sorbi, S., Hort J, Erkinjuntti, T., et al. (2012). EFNS-​ENS Guidelines on the diagnosis and management of disorders associated with dementia. Eur J Neurol, 19(9), 1159–​1179. 3. Chang, K-​H., Chuang, C-​C., Lyu, R-​K, et al. (2007). Clinical characteristics of corticobasal syndrome amongst Chinese in Taiwan. Parkinsonism Relat Disord, 13(4), 219–​223. 4. Gibb, W. R., Luthert, P. J., & Marsden, C. D. (1989). Corticobasal degeneration. Brain, 112(Pt 5), 1171–​1192. 5. Burrell, J. R., Hornberger, M., Vucic, S., Kiernan, M. C., & Hodges, J. R. (2014). Apraxia and motor dysfunction in corticobasal syndrome. PLoS One, 24, 9(3), e92944.

40 | M o v e m e n t D i s o r de r s

6. Grijalvo-​Perez, A., & Litvan, I. (2014). Corticobasal degeneration. Semin Neurol, 34(02), 160–​173. 7. Mathew, R., Bak, T. H., & Hodges, J. R. (2012). Diagnostic criteria for corticobasal syndrome:  a comparative study. J Neurol Neurosurg Psychiatr, 83(4), 405–​410. 8. Rankin, K. P., Mayo, M. C., Seeley, W. W., et al. (2011). Behavioral variant frontotemporal dementia with corticobasal degeneration pathology: Phenotypic comparison to bvFTD with Pick’s Disease. J Mol Neurosci, 45(3), 594–​608. 9. Lee, S. E., Rabinovici, G. D., Mayo, M. C., et al. Clinicopathological correlations in corticobasal degeneration. Ann Neurol, 70(2), 327–​340. 10. Kouri, N., Murray, M. E., Hassan, A., et al. (2011). Neuropathological features of corticobasal degeneration presenting as corticobasal syndrome or Richardson syndrome. Brain, 134(11), 3264–​3275. 11. Boeve, B.  F., Huisman, M.  H. B., de Jong, S.  W., et  al. (2011). The multiple phenotypes of corticobasal syndrome and corticobasal degeneration: Implications for further study. J Mol Neurosci, 45(3), 350–​353. 12. Moustafa, R.  R., & Baron, J-​C. (2009). Pathophysiology of ischaemic stroke: Insights from imaging, and implications for therapy and drug discovery. Br J Pharmacol, 153(S1), S44–​S54. 13. Rebeiz, J. J., Kolodny, E. H., & Richardson, E. P. (1968). Corticodentatonigral degeneration with neuronal achromasia. Arch Neurol, 18(1), 20–​33. 14. Ouchi, H., Toyoshima Y, Tada, M., et al. (2013). Pathology and sensitivity of current clinical criteria in corticobasal syndrome. Mov Disord, 29(2), 238–​244. 15. Josephs, K.  A., Petersen, R.  C., Knopman, D.  S., et  al. (2006). Clinicopathologic analysis of frontotemporal and corticobasal degenerations and PSP. Neurology, 66(1), 41–​48. 16. Boeve, B. F. (2005). Corticobasal degeneration:  The Syndrome and the Disease. In Current Clinical Neurology:  Atypical Parkinsonian Disorders, pp. 309–​334. I. Litvan, Ed. Humana Press Inc., Totawa NJ. 17. Lee, W., Simpson, M., Ling, H., Mclean, C., Collins, S., & Williams, D. R. (2013). Characterising the uncommon corticobasal syndrome presentation of sporadic Creutzfeldt-​Jakob disease. Parkinsonism Relat Disord, 19(1), 81–​85. 18. Miyaji, Y., Koyama, K., Kurokawa, T., Mitomi, M., MD YS, Kuroiwa, Y. (2013). Vascular corticobasal syndrome caused by unilateral internal carotid artery occlusion. J Stroke Cerebrovasc Dis, 22(7), 1193–​1195. 19. Lee, D.  W., Eum, S.  W., Moon, C.  O., Ma, H.  I., & Kim, Y.  J. (2014). Corticobasal syndrome associated with antiphospholipid syndrome without cerebral infarction. Neurology, 82(8):730–​731. 20. Boeve, B. F., Chakrabarti, S., Maraganore, D. M., et al. (1999). Pathologic heterogeneity in clinically diagnosed corticobasal degeneration. Neurology, 53(4), 795–​795. 21. Kouri, N., Carlomagno, Y., Baker, M., et  al. (2013). Novel mutation in MAPT exon 13 (p.N410H) causes corticobasal degeneration. Acta Neuropathol, 127(2), 271–​282. 22. van Swieten, J. C., & Heutink, P. (2008). Mutations in progranulin (GRN) within the spectrum of clinical and pathological phenotypes of frontotemporal dementia. Lancet Neurol, 7(10), 965–​974. 23. Zimprich A, Biskup S, Lichtner, et al. (2004). Mutations in LRRK2 cause autosomal-​dominant parkinsonism with pleomorphic pathology. Neuron, 44(4), 601–​607. 24. Huey, E. D., Ferrari, R., Moreno, J. H., et al. (2011). FUS and TDP43 genetic variability in FTD and CBS. Neurobiol Aging, 33(5), 1016.e9–​1016.e17. 25. Lindquist, S. G., Lindquist, S.  G., Duno, M., et  al. (2013). Corticobasal and ataxia syndromes widen the spectrum of C9ORF72 hexanucleotide expansion disease. Clin Genet, 83(3), 279–​283. 26. Whitwell, J. L., Jack, C. R., Boeve, B. F., et al. (2010). Imaging correlates of pathology in corticobasal syndrome. Neurology, 75(21), 1879–​1887. 27. Wolpe, N., Moore JW, Rae, C.  L., et  al. (2014). The medial frontal-​ prefrontal network for altered awareness and control of action in corticobasal syndrome. Brain, 137(1), 208–​220. 28. Whitwell, J. L., Schwarz, C. G., Reid, R. I., et al. (2014). Diffusion tensor imaging comparison of progressive supranuclear palsy and corticobasal syndromes. Parkinsonism Relat Disord, 20(5), 493–​498. 29. Trabzuni D, Wray S, Vandrrrovcova, J., et  al. (2012). MAPT expression and splicing is differentially regulated by brain region:  relation to genotype and implication for tauopathies. Hum Mol Genet, 21(18):4094–​4103. 30. Ferrer I, López-​González I, Carmona, M., et  al. (2014). Glial and neuronal tau pathology in tauopathies:  Characterization of disease-​specific phenotypes and tau pathology progression. J Neuropathol Exp Neurol, 73(1), 81–​97. 31. Ciechanover, A., & Brundin, P. (2003). The ubiquitin proteasome system in neurodegenerative diseases: sometimes the chicken, sometimes the egg. Neuron, 40(2), 427–​446.

32. Stöhr, J., Watts, J. C., Mensinger, Z. L., et al. (2012). Purified and synthetic Alzheimer’s amyloid beta (Aβ) prions. Proc Natl Acad Sci USA, 109(27), 11025–​11030. 33. Sydow, A., & Mandelkow, E-​ M. “Prion-​ like” propagation of mouse and human tau aggregates in an inducible mouse model of tauopathy. Neurodegener Dis, 7(1–​3), 28–​31. 34. Masuda-​Suzukake, M., Nonaka T, Hosokawa, M., et al. (2013). Prion-​like spreading of pathological -​synuclein in brain. Brain, 136(4):1128–​1138. 35. Nonaka, T., Masuda-​Suzukake, M., Arai, T., et al. (2013). Prion-​like properties of pathological TDP-​43 aggregates from diseased brains. Cell Rep, 4(1), 124–​134. 36. Aguzzi, A., & Rajendran, L. (2009). The transcellular spread of cytosolic amyloids, prions, and prionoids. Neuron, 64(6), 783–​790.

37. Armstrong, M. J. (2014). Diagnosis and treatment of corticobasal degeneration. Curr Treat Options Neurol, 16(3), 282. 38. Seltman, R. E., & Matthews, B. R. (2012). Frontotemporal lobar degeneration:  Epidemiology, pathology, diagnosis and management. CNS Drugs, 26(10), 841–​870. 39. Wong, E., & Cuervo, A.  M. (2010). Integration of clearance mechanisms:  The proteasome and autophagy. Cold Spring Harb Perspect Biol, 2(12), a006734. 40. Jackrel, M. E., DeSantis, M. E., Martinez, B. A., et al. (2014). Potentiated Hsp104 variants antagonize diverse proteotoxic misfolding events. Cell, 16, 156(1–​2):170–​182.

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7 | H UNTINGTON DISEASE: ETIOLOGY, GENETICS, AND CLINICAL MANIFESTATIONS RO G E R L . A L B IN A N D HE N RY L . PA UL SON

D EF INITION Huntington disease (HD) is an autosomal dominant neurodegenerative disease characterized by prominent neuropsychiatric manifestations and caused by a polyglutamine (polyQ)-​encoding CAG repeat expansion in the HTT gene. It is important to distinguish manifest HD from the premanifest or presymptomatic mutant allele carrier state. A  diagnosis of HD is a clinical judgment that a mutant allele carrier exhibits clinical features of HD. The conventional definition of disease manifestation is an examining clinician’s judgment that the patient has a movement disorder, typically involuntary movements (see later). Mutant allele carriers without such features are not typically designated as suffering from HD. Synonyms: Huntington chorea, Huntington’s disease, Huntington’s chorea.

NEUROB IO L OGY Nine diseases comprise the polyQ disease family; HD; spinocerebellar ataxias 1, 2, 3, 6, 7, 17; dentatorubral-​pallidoluysian atrophy (DRPLA); and spinobulbar muscular atrophy. In each, the causative mutation is expansion of a normally polymorphic CAG trinucleotide repeat (encoding glutamine) within protein coding sequences of these unrelated genes.1 Expansion of the CAG/​polyQ domain beyond disease-​specific thresholds results in neurodegeneration. Other common features of polyQ diseases include variable age of onset with mid-​ life onset being most typical, phenotypic intergenerational anticipation correlated with increasing CAG/​polyQ repeat number, pathology largely restricted to the central nervous system, and autosomal dominant inheritance (with the exception of X-​linked SBMA). The threshold for development of HD is 39 to 40 repeats, and the normal range of polyQ repeats is 26 or fewer. Individuals with 36 to 39 repeats exhibit reduced penetrance, and individuals with “intermediate size” repeats of 27 to 35 do not manifest HD but their children are at significantly increased risk for developing HD due to intergenerational repeat expansion.2 The latter phenomenon underlies anticipation, earlier onset of manifest disease in succeeding generations, characteristic of polyQ diseases. Repeat numbers may contract or expand during intergenerational transmission, with an overall tendency to expand, particularly when a male is the affected parent. There is a strong relationship between repeat number and age of onset. Longer repeat numbers are associated with earlier age of onset, accounting for approximately 50% of the variance in age of onset.3 The most common repeat expansions, however, 39 to the low 40s, are associated with considerable variation in age of onset; thus typical repeat numbers have little value in predicting the age of onset of individuals. The different members of the polyQ family are distinguished by varied regional and subregional patterns of neuropathology, giving 42 | Movement Disorders

rise to distinctive clinical features. For example, HD is characterized by prominent early striatal pathology (later).4 An attractive model accounting for both the common features of polyQ diseases and their neuropathological and clinical differences is that the expanded polyQ domain is the primary driver of neurodegeneration, whereas the specific biology of each mutant protein determines the patterns of neurodegeneration.5 Each polyQ disease protein has a distinct normal function and is embedded in distinctive networks of interacting protein partners. Alterations of normal polyQ protein functions and their interactions with other proteins likely cause distinctive regional pathologies. The HD gene codes for the protein Huntingtin (Htt), a large (~350 kD) cytosolic protein expressed in all neurons and many peripheral tissues.6 Encoded by the first exon of the HTT gene, the polyQ domain resides near the N-​terminus of Htt. The normal functions of Htt are still uncertain, but increasing evidence suggests that it participates in vesicular and cytoskeletal transport as well as selective autophagy. Htt interacts with numerous proteins linked to diverse functions from endocytosis to gene regulation.7 Knockout experiments indicate that Htt is essential for normal brain development, but which functions of Htt are critical for brain development remain unknown.8 The dominant nature of HD suggests that mutant Htt (mHtt) causes so-​called "gain of function effects” in which mHtt has acquired new, toxic properties. The toxic protein species may be N-​terminal fragments of mHtt containing the expanded polyQ domain. Whatever the toxic species, a number of pathogenetic mechanisms may cause neuronal dysfunction and neurodegeneration in HD.9 Proposed proximate mechanisms include transcriptional dysregulation, mitochondrial dysfunction, abnormal axonal transport, proteosomal dysfunction, abnormal lipid metabolism, dysregulation of neuronal calcium homeostasis, and excitotoxicity. All of these proposed mechanisms receive support from the large body of work investigating the pathogenesis of HD, and many of these proposed proximate mechanisms overlap. A likely conclusion is that mHtt perturbs a variety of important cellular processes. Further complicating understanding of HD pathogenesis is the hypothesis that mHtt also causes partial loss of function (haploinsufficiency) that may contribute to HD pathogenesis.10 There is suggestive evidence that some effects of the expanded CAG mutation in HTT cause toxicities at the RNA level11 or through unconventional translation across different reading frames of the repeat expansion.12 The complexity of mHtt protein and potential HTT transcript pathogenic effects indicates that no single pathogenic pathway is solely responsible for neuronal death and dysfunction in HD. Accordingly, finding the proverbial “magic bullet” therapuetic agent targeting a key node in a proximate mechanism of neurodegeneration will be difficult. As in all polyQ diseases, HD exhibits distinctive regional and subregional pathology. The striatum was identified in historic pathologic studies as the most prominently affected brain region in HD. Analysis

of striatal pathology indicates differential effects of mHtt on striatal neuron subpopulations. Striatal interneurons expressing somatostatin-​ neuropeptide Y and nitric oxide synthase are spared in HD.13 Other striatal interneuron subpopulations are affected in HD. Parvalbumin expressing interneurons degenerate and striatal cholinergic interneurons exhibit sparing of perikarya but loss of terminals and markers of functional activity.14,15 The great majority of striatal neurons are projection neurons sending efferents to different downstream components of the basal ganglia. Striatal projection neurons degenerate in HD but in a specific temporal sequence that correlates with the motor phenotype of HD.16 Early, preferential loss of some striatal projection neuron subpopulations correlates with chorea and characteristic saccadic eye movement abnormalities. Mood disorders in HD also may correspond with specific aspects of striatal pathology.17 Neocortex is also affected significantly in HD. Some data suggest that neocortical atrophy proceeds in tandem with striatal atrophy.18 As in the striatum, there is evidence for differential involvement of different cortical neuron populations in HD. Differential changes in cortical pathology may also correlate with clinical features of HD.17 At the cellular level, neuronal intranuclear and cytoplasmic aggregates contain mHtt, ubiquitin, and other proteins.19 The presence of aggregates supports the concept that polyQ expansion promotes abnormal folding of mHtt, causing aggregation and tissue accumulation.

CLINICA L P RESENTATION Huntington disease is a true neuropsychiatric disorder. The clinical triad of HD is 1) progressive movement disorder; 2) progressive cognitive disturbance culminating in dementia; and 3) various behavioral disturbances that often precede diagnosis and can vary depending on the state of disease. E P I D E M I O L O G Y A N D N AT U R A L H I S T O RY

Manifest HD prevalence is approximately 10 to 15 per 100,000 in populations of European descent.20,21 Prevalence is much lower in non-​European populations. Individuals at risk for HD constitute a larger group and there may be as many as 150,000 at risk individuals in the USA. Although HD is a rare disease, its impact is out of proportion to its prevalence. Because it usually strikes adults in their prime working years, the economic impact is substantial. Often, HD has a negative impact on the life trajectories of unaffected siblings and children of HD patients. Although the great majority of HD patients will have a family history, a small but significant fraction appear sporadically, primarily because of intergenerational repeat instability during mutant allele transmission from a parent with an intermediate size or reduced penetrance allele. Manifest HD is defined conventionally by the presence of a movement disorder, usually chorea (see Movement Disorder section). In some patients, other motor abnormalities may lead to a diagnosis of HD. This is a conservative approach because cognitive or behavioral features often precede the motor features of HD (see later). In the earlier stages of HD, motor abnormalities may be subtle and fluctuate depending on the state of arousal of the patient. Median age of diagnosis is approximately 40  years of age with a wide range in ages of onset. Onset before age 20 or after age 65 is relatively rare, but very young and elderly new-​onset HD patients are seen in tertiary referral clinics. Death generally occurs 15 to 20 years after diagnosis.22 A common cause of death in those with

advanced HD is aspiration pneumonia, reflecting severe dysphagia and general immobility.23 MOVEMENT DISORDER

Chorea is the classic motor sign of HD. Chorea often begins as fleeting, suppressible movements, particularly of the digits, that may appear as fidgetiness. With disease progression, chorea becomes more overt as it involves larger muscle groups. Patients often incorporate chorea into purposeful movements. Motor impersistence, the inability to sustain voluntary muscular effort, is common in HD and often goes hand in hand with chorea. Chorea is usually not greatly disabling and is not usually a major target of treatment. Flailing and continual chorea, amounting to ballism, can be disabling and/​or physically harmful, requiring treatment (see ­chapter 8 for management and treatment). Dystonia is seen in most persons with HD but is especially prominent in younger-​onset individuals. As “typical” adult-​onset HD progresses, chorea can evolve into a more complicated constellation of movement disorders that increasingly include dystonia.24 Overt bradykinesia is common in HD, especially in earlier-​onset disease. The juvenile-​onset form of disease that manifests initially with bradykinesia, rigidity, and little or no chorea has been given its own name, the “Westphal variant.” Very early onset cases also have a high incidence of epilepsy. The distinctive phenotype of very early-​onset HD probably reflects the effects of the mutant allele on developing brains. It is better to think of motor signs in HD as spanning a spectrum—​earlier-​ onset cases tending to have more bradykinesia and dystonia and later-​ onset cases tending to have more chorea. In most adult-​onset HD patients, chorea will gradually progress and then begin to subside as dystonia and bradykinesia become more prominent motor features. The combination of chorea, bradykinesia, and dystonia sometimes leads to unusual gait patterns that leave patients prone to falls. Tics, similar to facial and head tics seen in Tourette syndrome, are also seen in HD.25 Axial ataxia and marked postural instability are common in those with more advanced HD. Eye movement abnormalities are an early and persistent feature of HD. Patients with HD often manifest difficulty maintaining fixation and develop slowed initiation and velocity of saccades.26,27 As saccadic dysfunction worsens, patients with HD need to thrust their head or blink to break fixation and move their eyes to gaze at a new target. Hyperactive deep tendon reflexes are a common examination finding in HD. In summary, HD manifests a wide range of movement disorders and other neurologic features, partly reflecting changing disease features over time. The progressive movement disorder and increasingly widespread failure of the motor system contribute greatly to physical disability and decreased life expectancy of individuals with HD. In particular, difficulties with dysphagia, dysarthria, and frequent falls become debilitating.

COGNITIVE DISORDER

Large-​scale observational studies of premanifest HD gene carriers make it clear that subtle cognitive impairment is among the earlier manifestations of HD and is associated with progressive caudate atrophy.28,29 At diagnosis, most subjects with HD have significant cognitive impairments readily measurable by neuropsychological testing. These early deficits do not impede most activities of daily living, but individuals with demanding jobs often find work increasingly difficult. The cognitive impairment progresses slowly to frank dementia in most persons with HD. Huntington disease results in a largely “subcortical” dementia characterized by slowness in initiating thought processes, difficulties

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with executive function, and problems with attentional and sequencing tasks.30,31 Although episodic memory is impaired, memory in general is relatively well preserved. In contrast to Alzheimer disease or frontotemporal dementias, language function is relatively well preserved. An intriguing feature of the cognitive impairments in HD is the lack of insight patients often exhibit regarding their own symptoms.32 Lack of insight is a typical sign of impaired frontal lobe function and may reflect early dysfunction of striatal neurons receiving frontal lobe inputs. B E H AV I O R A L D I S O R D E R

The behavioral problems of HD are usually the most troublesome for patients, families, and physicians. These range from affective illness, most notably depression and apathy, to delusional behaviors. The behavioral disorders of HD evolve often during the course of illness. Most HD gene carriers will experience some behavioral symptoms before establishing the diagnosis.33–​35 These may include depression, obsessive-​ compulsive behaviors, irritability, and behavioral outbursts.33–​35 Family members often comment that patients’ personalities change in the years leading up to diagnosis, although this may be apparent only in retrospect. Depression is particularly common in those with HD; between 30% and 50% of patients will develop depressive symptoms. Depression often responds well to treatment, with conventional antidepressants commonly being the first agents tried. There is often superimposed and difficult to treat apathy. Personality changes are associated with agitation, anxiety, alcohol abuse, marital problems, and antisocial behavior. Obsessive-​compulsive behaviors may overlap with features of cognitive rigidity and perseveration secondary to frontostriatal circuit dysfunction. The severity of psychiatric symptoms varies greatly in HD patients and does not correlate with dementia and chorea. An important cautionary note is the high rate of suicide in patients with HD.23,36 The risk is significantly higher for those with HD gene-​positive status, including both those with diagnosed HD and those who are premanifest mutant allele carriers. The risk may also be high for family members who are not carriers of the gene, underscoring the tremendous stress and burden placed on families with HD.

LAB ORATORY  TEST When the characteristic motor disorder is present in an individual from a well-​characterized HD pedigree, diagnosis of manifest HD is straightforward and can be made on the basis of clinical assessment. The existence of rare genetic phenocopies of HD (see Differential Diagnosis section), underscores the importance of certainty that the family in question exhibits HD. Documented molecular or autopsy confirmation of HD in any family member is sufficient to establish the nature of the disease in the family; genetic testing of all individuals suspected to exhibit HD is not necessary. Circumstances arise where information about the family history is limited or absent. Early death of a parent or adoption without knowledge of a biological parent’s history of HD are examples. Absence of an apparent family history of HD may be secondary to covert adoption, nonpaternity, or repeat expansion from a parent with a nonpenetrant allele. Genetic testing is invaluable in these situations. Molecular testing is useful also when diagnosis is confounded by a possible tardive movement disorder. Regardless of the specific situation in which either clinical diagnosis or molecular diagnosis is established, a diagnosis of HD should be accompanied by discussion of its genetics. Clinicians need to be sensitive to the fact that a diagnosis of HD carries considerable implications for patients’ families 44 | M o v e m e n t D i s o r d e r s

and if possible, family members should be made aware of genetic counseling services. A related but different situation is use of molecular diagnosis for presymptomatic detection of mutant alleles. Such testing should only be offered with specific safeguards ensuring that only psychologically stable individuals undergo testing with careful counseling prior to testing and appropriate follow-​up evaluations. Consensus guidelines describe the appropriate procedures.37 This approach is successful in the sense that there are very few severe adverse outcomes of presymptomatic testing.38 Uptake of presymptomatic testing by the at risk population, however, has been modest, with only a small fraction of those eligible pursuing testing. An extension of presymptomatic testing is prenatal testing. Traditional prenatal testing may be problematic because a positive test automatically identifies the at-​risk parent as a mutant allele carrier. Pre-​implantation genetic diagnosis can avoid this problem but is costly and has lower pregnancy completion rates.

D I F F ERENTIAL DIA G NOSIS Huntington disease is a distinctive phenotype, but HD mimics are encountered occasionally in clinical practice. The differential diagnosis list of choreiform disorders is extensive.39 Many can be excluded based on the history or features of the physical examination. In doubtful cases, genetic testing is invaluable for identifying or excluding HD. Sporadic and treatable causes of chorea include acute drug side effects, tardive chorea, thyrotoxicosis, polycythemia vera, and systemic lupus erythematosis. In younger onset patients, especially those with a dystonic-​rigid phenotype and/​or psychiatric problems, Wilson disease is always a consideration. Sporadic chorea may occasionally be seen as a consequence of a paraneoplastic disorder or Sydenham chorea. More difficult to evaluate are inherited neurodegenerative disorders that mimic HD.40 These include other dominant disorders such as the polyQ diseases DRPLA and SCA17; Huntington’s disease-​ like 2 (another expanded repeat disorder); inherited prion disease, and members of the neurodegeneration with brain iron accumulation spectrum. Dominant hexanucleotide repeat expansions within the C90rf72 gene usually associated with familial frontotemporal dementia or amyotrophic lateral sclerosis are described recently as causing HD phenocopies.41 Recessive and X-​linked disorders in the neuroacanthocytosis family also can mimic HD, and there are reports of another recessive disorder, Friedreich ataxia, mimicking HD. Genetic testing is available for all of these diseases. HD is by far the most common of these diseases, and a reasonable strategy is to test first for the presence of an HD mutation. If HD molecular testing is negative, more extensive molecular testing is pursued. Establishing an accurate diagnosis is crucial for patients and their families. The clinical implications are vastly different for a dominant versus a recessive disorder, and appropriate presymptomatic testing in family members can be pursued only with an accurate diagnosis.

M ANA G EM ENT AND TREAT M ENT See ­chapter 8.

F U T U RE D IRECTIONS The last 2 decades have seen an explosion of research on HD and other polyQ diseases. Some major emergent themes point to important research directions for the near future.

An impressive body of work indicates the pleiotropic nature of cellular events initiated by mHtt. This suggests that conventional therapeutic approaches attempting to target a single proximate pathway of pathogenesis will not be successful. The major general alternative approach is to reduce the amount of mHtt, either by reducing mHtt production or by increasing mHtt catabolism. There has been a recrudescence of interest in “knockdown” approaches using gene therapy methods or antisense oligonucleotides to reduce mHtt production. Some of this work has entered nonhuman primate trials with promising results and the first clinical trial of antisense oligonucleotides in humans with HD began in 2015. Given the widely dispersed pathology in HD, a major challenge for knockdown approaches is delivering treatment throughout the very large human brain. A theoretically attractive alternative to knockdown approaches is harnessing the intrinsic cellular mechanisms used to degrade misfolded proteins to reduce mHtt concentration. Exciting basic research on proteosomal function, autophagy, and the unfolded protein response has helped to clarify mechanisms of disease protein degradation. Evaluating potential therapies depends not only on suitable candidates emerging from the laboratory but also the capability to perform critical proof of principle and pivotal trials. An important emergent theme of neurodegenerative disease research generally is that symptomatic disease represents advanced stages of processes occurring over many prior years. Volumetric imaging data emerging from major studies of presymptomatic HD indicates that such changes begin decades prior to manifest HD. In manifest HD, secondary pathologic processes may obscure responses to interventions effective in premanifest subjects. This concept poses a major obstacle to developing appropriate trial methods for evaluating potential therapies. As with the development of therapies for multiple sclerosis, development of imaging methods or other biomarker methods assessing disease progression is likely to be crucial for evaluating novel therapies. Similarly, response biomarkers to assess intervention effects will also be crucial. Development of such biomarkers is a major focus of research in the field.

REFERENCES 1. Williams, A.  J., & Paulson, H.  L. (2008). Polyglutamine neurodegeneration:  protein misfolding revisited. Trends Neurosci, 31(10), 521–​528. doi:10.1016/​j.tins.2008.07.004 2. Semaka, A., Creighton, S., Warby, S., & Hayden, M. R. (2006). Predictive testing for Huntington disease: Interpretation and significance of intermediate alleles. Clin Genet, 70(4), 283–​294. 3. Stine, O. C., Pleasant, N., Franz, M. L., Abbott, M. H., Folstein, S. E., & Ross, C.  A. (1993). Correlation between the onset age of Huntington’s disease and length of the trinucleotide repeat in IT-​15. Hum Mol Genet, 2(10), 1547–​1549. 4. Vonsattel, J. P., & DiFiglia, M. J. (1998). Huntington disease. J Neuropathol Expl Neuol, 57(5), 369–​384. 5. Orr, H. T., & Zoghbi, H. Y. (2007). Trinucleotide repeat disorders. Ann Rev Neurosci, 30, 575–​621. 6. Zheng, Z., & Diamond, M.  I. (2012). Huntington disease and the huntingtin protein. Prog Mol Biol Transl, 107,189–​214. doi:10.1016/​ B978-​0-​12-​385883-​2.00010-​2 7. Truant, R., Atwal, R., & Burtnik, A. (2006). Hypothesis: Huntingtin may function in membrane association and vesicular trafficking. Biochem Cell Biol, 84(6):912–​917. 8. Duyao, M.  P., Auerbach, A.  B., Ryan, A., Persichetti, F., Barnes, G.  T., McNeil, S.  M., Ge, P., Vonsatte, J.  P., Gusella, J.  F., Joyner, A.  L., et  al. (1995). Inactivation of the mouse Huntington’s disease gene homolog Hdh. Science, 269(5222), 407–​410. 9. Imarisio, S., Carmichael, J., Korolchuk, V., Chen, C.  W., Saiki, S., Rose, C., Krishna, G., Davies, J.  E., Ttofi, E., Underwood, B.  R., & Rubinsztein, D.  C. (2008). Huntington’s disease:  From pathology and

genetics to potential therapies. Biochem J, 412(2):191–​209. doi:10.1042/​ BJ20071619 10. Zuccato, C., Valenza, M., & Cattaneo, E. (2010). Molecular mechanisms and potential therapeutical targets in Huntington’s disease. Physiol Rev, 90(3), 905–​981. doi:10.1152/​physrev.00041.2009 11. Baez-​Coronel, M., Porta, S., Kagerbauer, B., Mateu-​Huertas, E., Pantano, L., Ferrer, I., Guzmn, M., Estivill, X., & Mart, E. (2012). A pathogenic mechanism in Huntington’s disease involves small CAG-​repeated RNAs with neurotoxic activity. PLoS Genetics, 8(2), e1002481. doi:10.1371/​journal.pgen.1002481. 12. Banez-​Coronel, M., Ayhan, F., Tarabochia, A.  D., Zu, T., Perez, B.  A., Pletnikova, O., Borchelt, D. R., Ross, C. A., Margolis, R. L., Yachnis, A. T., Troncoso, J. C., & Ranum, L. P. (2015). RAN translation in Huntington disease. Neuron, 88(4), 667–​677. doi:10.1016/​j.neuron.2015.10.038. 13. Ferrante, R.  J., Kowall, N.  W., Beal, M.  F., Martin, J.  B., Bird, E.  D., & Richardson, E. P. (1987). Morphologic and histochemical characteristics of a spared subset of striatal neurons in Huntington’s disease. J Neuropathol Exp Neurol, 146(1), 12–​27. 14. Ferrante, R.  J., Beal, M.  F., Kowall, N.  W., Richardson, E.  P., & Martin, J. B. (1987). Sparing of acetylcholinesterase-​containing striatal neurons in Huntington’s disease. Brain Res, 411(1), 162–​66. 15. Reiner, A., Shelby, E., Wang, H., Demarch, Z., Deng, Y., Guley, N. H., Hogg, V., Roxburgh, R., Tippett, L. J., Waldvogel, H. J., Faull, R. L. (2013). Striatal parvalbuminergic neurons are lost in Huntington’s disease: Implications for dystonia. Mov Disord, 28(12),1691–​1699. doi:10.1002/​mds.25624 16. Deng, Y. P., Albin, R. L., Penney, J. B., Young, A. B., Anderson, K. D., Reiner. A. (2004). Differential loss of striatal projection systems in Huntington’s disease:  A  quantitative immunohistochemical study. J Chem Neuroanat, 27(3), 143–​164. 17. Waldvogel, H.  J., Thu, D., Hogg, V., Tippett, L., & Faull, R.  L. (2012). Selective neurodegeneration, neuropathology and symptom profiles in Huntington’s disease. Adv Exp Med Biol, 769, 141–​152. 18. Macdonald, V., & Halliday, G. (2002). Pyramidal cell loss in motor cortices in Huntington’s disease. Neurobiol Dis, 10(3), 378–​386. 19. DiFiglia, M., Sapp, E., Chase, K. O., Davies, S. W., Bates, G. P., Vonsattel, J. P., & Aronin, N. (1997). Aggregation of huntingtin in neuronal intranuclear inclusions and dystrophic neurites in brain. Science, 277(5334), 1990–​1993. 20. Fisher, E.  R., & Hayden, M.  R. (2013). Multisource ascertainment of Huntington disease in Canada:  Prevalence and population at risk. Mov Disord, 29(1), 105–​114. doi:10.1002/​mds.25717. 21. Evans, S. J., Douglas, I., Rawlins, M. D., Wexler, N. S., Tabrizi, S. J., & Smeeth, L. (2013). Prevalence of adult Huntington’s disease in the UK based on diagnoses recorded in general practice records. J Neurol Neurosurg Psychiatry, 84(10), 1156–​ 1160. doi:10.1136/​ jnnp-​2012-​304636 22. Roos, R. A., Hermans, J., Vegter-​van der Vlis, M., van Ommen, G. J., & Bruyn, G. W. (1993). Duration of illness in Huntington’s disease is not related to age at onset. J Neurol Neurosurg Psychiatry, 56(1), 98–​100. 23. Srensen, S.  A., & Fenger, K. (1992). Causes of death in patients with Huntington’s disease and in unaffected first degree relatives. J Med Genet, 29(12), 911–​914. 24. Feigin, A., Kieburtz, K., Bordwell, K., Como, P., Steinberg, K., Sotack, J., Zimmerman, C., Hickey, C., Orme, C., & Shoulson, I. (1995). Functional decline in Huntington’s disease. Mov Disord, 10(2), 211–​214. 25. Kumar, R., & Lang, A. E. (1997. Tourette syndrome. Secondary tic disorders. Neurol Clin, 15(2), 309–​331. 26. Lasker, A. G., Zee, D. S., Hain, T. C., Folstein, S. E., & Singer, H. S. (1988). Saccades in Huntington’s disease:  Slowing and dysmetria. Neurology, 38(3), 427–​431. 27. Lasker, A. G., Zee, D. S., Hain, T. C., Folstein, S. E., & Singer, H. S. (1987). Saccades in Huntington’s disease:  Initiation defects and distractibility, Neurology, 37(3), 364–​370. 28. Stout, J.  C., Paulsen, J.  S., Queller, S., Solomon, A.  C., Whitlock, K.  B., Campbell, J. C., Carlozzi, N., Duff, K., Beglinger, L. J., Langbehn, D. R., Johnson, S.  A., Biglan, K.  M., & Aylward, E.  H. (2011). Neurocognitive signs in prodromal Huntington disease. Neuropsychology, 25(1),1–​14. doi:10.1037/​a0020937 29. Aylward, E.  H., Nopoulos, P.  C., Ross, C.  A., Langbehn, D.  R., Pierson, R. K., Mills, J. A., Johnson, H. J., Magnotta, V. A., Juhl, A. R., & Paulsen, J. S. (2011). PREDICT-​HD Investigators and Coordinators of Huntington Study Group. Longitudinal change in regional brain volumes in prodromal Huntington disease. J Neurol Neurosurg Psychiatry, 82(4), 405–​410. doi:10.1136/​jnnp.2010.208264 30. Dumas, E.  M., van den Bogaard, S.  J., Middelkoop, H.  A., & Roos, R. A. (2013). A review of cognition in Huntington’s disease. Frontiers in Biosciences, 5,1–​18. ñ

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31. Paulsen, J.  S. (2011). Cognitive impairment in Huntington dis ease: Diagnosis and treatment. Curr Neurol Neurosci Rep, 11(5), 474–​483. doi:10.1007/​s11910-​011-​0215-​x 32. Hoth, K. F., Paulsen, J. S., Moser, D. J., Tranel, D., Clark, L. A., Bechara,A. (2007). Patients with Huntington’s disease have impaired awareness of cognitive, emotional, and functional abilities. J Clin Exp Neuropsychol, 29(4), 365–​376. 33. Duff, K., Paulsen, J. S., Beglinger, L. J., Langbehn, D. R., Stout, J. C.; Predict-​ HD Investigators of the Huntington Study Group. (2007). Psychiatric symptoms in Huntington’s disease before diagnosis:  The predict-​ HD study. Biol Psychiatry, 62(12), 1341–​1346. 34. Duff, K., Paulsen, J. S., Beglinger, L. J., Langbehn, D. R., Wang, C., Stout, J.  C., Ross, C.  A., Aylward, E., Carlozzi, N.  E., Queller, S.; Predict-​HD Investigators of the Huntington Study Group. (2010). “Frontal” behaviors before the diagnosis of Huntington’s disease and their relationship to markers of disease progression:  Evidence of early lack of awareness. J Neuropsychiatry Clin Neurosci, 22(2),196–​207. doi:10.1176/​appi. neuropsych.22.2.196 35. Beglinger, L.  J., Paulsen, J.  S., Watson, D.  B., Wang, C., Duff, K., Langbehn, D. R., Moser, D. J., Paulson, H. L., Aylward, E. H., Carlozzi, N.  E., Queller, S., & Stout, J.  C. (2008). Obsessive and compulsive symptoms in prediagnosed Huntington’s disease. J Clin Psychiatry, 69(11):1758–​1765. 36. Farrer, L.  A. (1986). Suicide and attempted suicide in Huntington disease:  Implications for preclinical testing of persons at risk. Am J Med Genet, 24(2), 305–​311. 37. MacLeod, R., Tibben, A., Frontali, M., Evers-​Kiebooms, G., Jones, A., Martinez-​Descales, A., Roos, R.  A.; Editorial Committee and Working Group ‘Genetic Testing Counselling’ of the European Huntington Disease Network. (2013). Recommendations for the predictive genetic

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test in Huntington’s disease. Clin Genet, 83(3), 221–​ 231. doi:10.1111/​ j.1399-​0004.2012.01900.x 38. Paulsen, J.  S., Nance, M., Kim, J.  I., Carlozzi, N.  E., Panegyres, P.  K., Erwin, C., Goh, A., McCusker, E., & Williams, J.  K. (2013). A review of quality of life after predictive testing for and earlier identification of neurodegenerative diseases. Prog Neurobiol, 110:2–​28. doi:10.1016/​ j.pneurobio.2013.08.003 39. Walker, R. H. (2011). Differential diagnosis of chorea. Curr Neurol Neurosci Rep, 11(4):385–​395. doi:10.1007/​s11910-​011-​0202-​2. PMID:21465146 40. Wild, E. J., & Tabrizi, S. J. (2007). Huntington’s disease phenocopy syndromes. Curr Opinion Neurol, 20(6), 681–​687. 41. Hensman Moss, D. J., Poulter, M., Beck, J., Hehir, J., Polke, J. M., Campbell, T., Adamson, G., Mudanohwo, E., McColgan, P., Haworth, A., Wild, E.  J., Sweeney, M.  G., Houlden, H., Mead, S., Tabrizi, S.  J. (2014). C9orf72 expansions are the most common genetic cause of Huntington disease phenocopies. Neurology, 82(4), 292–​299.

A DD ITIONA L RESO U RCES 1. Huntington’s Disease Society of America: Http://​www.hdsa.org/​ 2. Huntington Society of Canada: Http://​www.huntingtonsociety.ca/​ 3. Huntington’s Disease Association (Great Britain): Http://​hda.org.uk/​ 4. National Institute of Neurologic Disease and Stroke:  Http://​www.ninds. nih.gov/​ 5. ClinicalTrials.gov: Http://​clinicaltrials.gov/​ 6. Hereditary Disease Foundation: Http://​www.hdfoundation.org/​home.php 7. HD Lighthouse: Http://​www.hdlf.org/​welcome/​ 8. HD Buzz: Http://​en.hdbuzz.net/​

8 | H UNTINGTON DISEASE: TREATMENT AND CURRENT CLINICAL TRIALS CH AR L E S S .   VE N U T O A N D K A R L K IEB U RTZ

D EF INITION See ­chapter 7. Synonyms: Huntington’s disease, Huntington disease, Huntington’s chorea.

approaches to treatment may vary among centers. Recent reviews of the evidence for drug treatments in HD are available and offer some guidance in pharmacologic management.2,3 More recently, symptom-​ specific algorithms also have been proposed.4–​6

G ENERAL MANA GE MENT AND TREATM ENT AP P ROACH ES

P RINCIP L ES OF   P H ARM ACOL O GIC T H ERAP Y

Huntington disease (HD) pathogenesis is characterized by significant neuronal dysfunction and cell death most prominently in the striatum and globus pallidus, producing a gradual decline in motor, cognitive, and behavioral functioning that diminishes quality of life and leads to eventual premature death (see ­chapter 7 for disease neurobiology). Given the genetic and progressive nature of HD, patients are generally classified as being in either a premanifest or manifest stage of disease. Premanifest HD is traditionally defined as testing positive for the characteristic mutation, but without the emergence of substantial motor signs, whereas manifest HD is marked by the presence of overt HD features. On average, symptoms develop during the third to fifth decade of life with choreic movements being the classic motor feature at onset. As disease progresses, dystonia and bradykinesia become more prominent and cognitive function declines. Psychiatric changes, particularly mood disorders, may be present in both the premanifest and manifest states. Death usually occurs 15 to 20 years after symptomatic onset. A juvenile form of the disease is also well-​known (Westphal variant) and is associated with an akinetic-​rigid motor syndrome and cognitive impairment before the age of 20. No effective treatment for delaying, altering, or halting the onset or progression of disease is currently available. Instead, pharmacologic measures are based on symptomatic management, and thus target the manifest HD population. The goals of symptomatic therapy should be to maximize function and improve quality of life. Development of disease modifying therapies are more challenging because the clinical manifestations of disease can be variable among patients and will require predictable metrics of either onset of clinical manifestations or disease progression. Management of HD typically entails both pharmacologic and nonpharmacologic care. Regarding the latter, genetic counseling, physical therapy, nutritional support, psychological therapy, and other supportive care for the patient and family should be offered because of the profound effects of the disease (Table 8.1). For pharmacologic therapy, evidence-​based treatment guidelines for chorea have been published by the American Academy of Neurology.1 However, many of the medications historically used for HD have not been rigorously tested in clinical trials. Therefore, anecdotal clinical experience generally governs the choice of medication(s) and the

HYPERKINETIC MOTOR DYSFUNCTION

Involuntary hyperkinetic motor symptoms are the classic movement disorder in HD. With progressing illness, dystonia and akinetic-​rigid parkinsonian features predominate and chorea becomes less prominent. Although the hyperkinetic involuntary movements may be marked and may appear physically unsettling, it is often the parkinsonism that disrupts activities and ability to function. It is therefore important to continually reassess the need for treatment of chorea throughout the course of disease. Pharmacotherapy for chorea may be warranted if movements become embarrassing to the patient, cause physical injury or loss of balance, or interfere with routine daily activities or sleep. Chorea is believed to be the result of dysfunctional striatal cholinergic systems and a loss of inhibitory GABAergic neurons leading to the equivalent of excessive activity of striatal dopaminergic neurons. Pharmacologic interventions for hyperkinesias often involve antidopaminergic modulation targeted at returning the functional balance between GABA-​ mediated inhibitions in striatum and overacting dopaminergic systems. Anxiety and stress often compound involuntary motor disturbances, so treatment with anxiolytics also may be beneficial, but care must be taken that postural stability is not further impaired. Nevertheless, benzodiazepines such as clonazepam and lorazepam may be considered as primary, secondary, or adjunctive antichoreic therapy. Historically, reducing choreatic hyperkinesias was treated with high potency conventional antipsychotic agents such as haloperidol, fluphenazine, and pimozide.7–​14 The dosage needed for ameliorating chorea with these drugs is often lower than what is required for their antipsychotic effects, and it is therefore recommended to start on the lower end of the dosing spectrum and adjust as needed (Table 8.2). Despite lower doses usually being required, the side-​effect profile of typical antipsychotic agents remains important to consider upon their initiation. The risk of parkinsonism is significant with the high potency D2 dopamine receptor antagonists, particularly haloperidol and fluphenazine. Parkinsonism, akathisia, and acute dystonia are side effects that may warrant the use of lower potency antipsychotics such as thioridazine and thiothixene; however, these agents carry their own side effects including sedation and hypotension. Tiapride

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TAB L E   8. 1 . Nonpharmacologic Supportive Care

for Consideration in Huntington Disease EXAMPLES OF ASPECTS OF DISEASE SUPPORTIVE CARE

REQUIRING SUPPORTIVE CARE

Physical Therapy and Occupational Therapy

-​Gait and balance issues and preventing falls are of concern, particularly with dystonic and akinetic-​rigid motor symptoms. -​The combination of motor and cognitive impairments diminishes the ability to function, eventually leading to permanent disability. Therefore, the functional capacity of a patient should be assessed throughout the course of disease at regular intervals.

Dietary Support

-​Significant weight loss is observed throughout the course of disease and may be due to hyperkinetic movements, dysphagia, and other underlying biologic mechanisms. -​High calorie diets are often recommended, especially during the middle stages of disease. -​Enteral feeding may be required as disease progresses and swallowing becomes more difficult.

Speech Therapy

-​Dysarthria presenting as slurred speech, along with disordered inspiration and expiration causing dysrhythmic patterns may make it difficult to understand the patient. Cognitive impairment may further disrupt communication.

Genetic Counseling

-​Presymptomatic genetic counseling, confirmatory genetic testing, and family planning are important aspects of care for the entire family and should be accompanied with psychological support when offered.

Psychological Counseling

-​The pathogenesis of the disease leading to depression, apathy, aggression, irritability, and other behavioral disturbances in the individual patient that may require nonpharmacologic psychological support ancillary to pharmacologic management. -​Psychosocial impacts of the disease on the entire family are well recognized due its genetic nature and the overall burden of the illness.

and sulpiride are additional neuroleptics commonly used for chorea reduction in HD, but are not available for use in the United States.6,15,16 Atypical antipsychotics also have been considered for the treatment of involuntary motor dysfunction in HD. Moderate reductions in chorea were observed in several open-​label studies with olanzapine when low to moderate doses (5–​10 mg/​day) were tested for behavioral and motor effects.17 Titrating doses of olanzapine beyond 10 mg per day appear to be more efficacious and generally safe and well-​tolerated in HD patients; however, its use has not been formally tested in a controlled setting.18,19 Case reports and series with

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other atypical antipsychotics (risperidone, aripiprazole, quetiapine, and ziprasidone) for chorea have reported a favorable response.20–​24 Generally, the dosages with reported beneficial effects have been titrated upward to moderate and high levels approaching the suggested maximum dosage limits of the respective agent (Table 8.2). Tetrabenazine is currently the only pharmacologic agent tested in well-​controlled clinical trials and with FDA approval for symptomatic treatment of chorea associated with HD. It is hypothesized to work primarily through the depletion of presynaptic dopamine storage via inhibition of vesicular monoamine transporter 2 (VMAT2), an integral membrane protein that transports and concentrates monoamines into presynaptic vesicles. Its approval was based on a 12-​week randomized, placebo-​controlled trial demonstrating a reduction in baseline chorea by more than 20% and with approximately 45% of subjects on tetrabenazine experiencing more than minimal clinical reduction of chorea (compared with 6.9% of those on placebo).25 Follow-​up studies have demonstrated tetrabenazine to be generally safe and well tolerated over extended periods of time (studied out to 80 weeks), although its benefits may wane as disease progresses into more dystonic and rigid symptoms.26 Determining the optimal dose of tetrabenazine often requires dosage adjustment throughout treatment. Initially, a dose of 12.5 mg should be taken once daily (in the morning is recommended), which may be increased at weekly intervals by 12.5 mg to the maximum recommended dose of 100 mg/​day. However, if a dose of greater than 50 mg per day is required, it is recommended for the patient to be genotyped for CYP2D6 metabolizer status due to its extensive hepatic metabolism mediated by this isoenzyme. If a patient is determined to be a “poor metabolizer” as indicated by CYP2D6 genotype, the recommended maximum daily dose should not exceed 50 mg. Concomitant medications should also be taken into account when determining the appropriate dosage of tetrabenazine, because potential drug-​drug interactions could result in elevated levels of tetrabenazine.27 During treatment with tetrabenazine, depression has been reported to occur in approximately 15% of patients and is likely a result of presynaptic depletion of serotonin and norepinephrine. Because HD patients are at increased risk for depression, they must be carefully assessed prior to therapy and closely monitored throughout treatment. Other adverse effects reported include anxiety, drowsiness, fatigue, pseudoparkinsonism, akathisia, and gastrointestinal disturbances. If necessary, abrupt discontinuation of tetrabenazine appears to be safe and without consequences of withdrawal effects.28 Amantadine, which may act as an N-​methyl-​D-​aspartic acid (NMDA) noncompetitive receptor antagonist, can also alleviate chorea in HD patients. Therapeutic dosages studied have ranged between 300 and 400 mg orally per day, as well as 200 mg via intravenous infusion.29–​31 The literature supporting the use of amantadine has been inconsistent, and it is difficult to determine a priori if a patient will respond to treatment. Adverse effects associated with amantadine, including sedation, depression, anxiety, dizziness, and psychosis, are of particular concern in the HD population. HYPOKINETIC MOTOR DYSFUNCTION

The progression of HD is characterized by increasing motor impairment due to reduction of voluntary movements and dystonic features. Bradykinesia, rigidity, and incoordination increasingly interfere with daily function and eventually become so disabling that multidisciplinary fulltime care is needed. In the Westphal variant form of HD, the hypokinetic symptoms described pervade the

TA B L E   8.2 . Selection of Drugs for the Treatment of Chorea in Huntington Disease SUGGESTED ANTICHOREATIC DRUG

DOSAGES: (MG/​D AY)

COMMENTS

Initial: 12.5 mg Therapeutic: 12.5–​100 mg

Only FDA-​approved agent for HD chorea

Fluphenazine

Initial: 0.5–​1 mg Therapeutic: 6–​8 mg

Haloperidol

Initial: 0.5 -​1 mg Therapeutic: 1.5–​10 mg

Evidence for haloperidol and fluphenazine exists in small placebo-​controlled studies. Sulpiride has been reported in case-​reports, yet is frequently used outside the United States.

Pimozide

Initial: 2 mg Therapeutic: 12–​16 mg

Sulpiride

Initial: 100–​200 mg Therapeutic: 200–​1200 mg

VMAT2 Inhibitor

Tetrabenazine

Typical Antipsychotics

Atypical Antipsychotics

Aripiprazole

Initial: 2.5–​5 mg Therapeutic: 5–​20 mg

Olanzapine

Initial: 2.5–​5 mg Therapeutic: 5–​30 mg

Risperidone

Initial: 0.25–​0.5 mg Therapeutic: 1–​6 mg

Only case reports support the use of aripiprazole and risperidone. Olanzapine has been studied in open-​label studies.

Other

Amantadine

Therapeutic: 300–​400 mg 200 mg (intravenous infusion)

clinical presentation of disease. Sparse reports of the antiparkinsonian drugs levodopa and pramipexole suggests transient relief of akinetic-​rigid symptoms.32–34 However, it is important to note that levodopa and dopamine agonists have the potential to cause dyskinesias closely resembling chorea with HD. B E H AV I O R A L D I S T U R B A N C E S

Behavioral and psychiatric symptoms in HD are common and may occur at any stage of the disease; however, depression, irritability, and apathy are often present early in the course of disease. Increasing evidence suggests that subtle behavioral changes precede the onset of classic HD motor symptoms and may be detected a decade before diagnosis during the premanifest stage of disease.35,36 Other prevailing psychiatric manifestations include anxiety, psychosis, agitation, and obsessive-​compulsive symptoms. The ability to effectively manage this component of disease is important because the associated symptoms are often distressing and can have important consequences for quality of life and ability to function. In general, the approaches to treatment of behavioral symptoms should be guided by prevailing symptoms as well as the side effect profiles of pharmacologic agents under consideration. Similar to other neurodegenerative diseases, rates of depression in HD are high with prevalence rates estimated between 30% and 50%, and suicide rates 4 to 5 times that found among the general

Mixed results from small double-​blind placebo-​controlled studies

population.37 The etiology of depression is likely multifactorial, arising in part from environmental factors such as grief in dealing with a terminal illness, frustrations due to increasing disability, and drug-​ induced mood changes. However, biochemical changes in the brain are also likely to be predisposing factors leading to depression. The literature examining antidepressant use in HD is made up of low-​level evidence through case reports and uncontrolled clinical trials. Therefore, selecting an antidepressant should be based on expected tolerability and response, as well as the patient’s willingness to remain adherent to the medication. A  trial with either selective serotonin reuptake inhibitors (SSRIs) or serotonin-​norepinephrine reuptake inhibitors (SNRIs) may be a good starting point due to their relatively mild side effect profile and once daily dosing. However, potential drug-​ drug interactions must be considered with these agents. For example, fluoxetine and paroxetine are strong inhibitors of CYP2D6 and therefore may require reduction of tetrabenazine dosing. Many tricyclic antidepressants provide less selective pharmacologic actions that may produce more unwanted effects (e.g., anticholinergic and cardiovascular effects). Other frequently encountered neuropsychiatric disorders in HD include irritability, agitation, aggressiveness, psychosis, and obsessive-​compulsive disorders that are often disruptive. Selective serotonin reuptake inhibitors, antipsychotics, and anticonvulsants may act as mood stabilizers, but only low-​level evidence supports their use. Although selecting an agent is often empirical, the presence

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TA B L E   8. 3 . Selection of Drugs for the Treatment of Behavioral Disturbances in Huntington Disease PHARMACOLOGIC CLASS

EXAMPLES

BEHAVIORAL INDICATIONS*

Selective Serotonin Reuptake Inhibitors

citalopram, escitalopram, fluoxetine, paroxetine, sertraline

Depression, anxiety, obsessive compulsive disorder

Serotonin/​Norepinephrine Reuptake Inhibitors

venlafaxine

Depression, anxiety, obsessive compulsive disorder

Anticonvulsants

carbamazepine

Aggression, agitation, irritability

Antipsychotics

olanzapine, risperidone,

Aggression, agitation, irritability, psychosis

Benzodiazepines

alprazolam, clonazepam, lorazepam

Anxiety, insomnia

Others

buspirone

Anxiety, depression

Antidepressants

Anxiolytics

*Dosage may be selected based on those used in the general population.

of comorbid psychiatric disorders may make one agent more appropriate than another. For example, the presence of anxiety and depression may be optimally treated with an SSRI or benzodiazepine, whereas a patient with more severe irritability and aggression could be better suited to receive treatment with an antipsychotic or antiepileptic. A  selection of medications to consider for the variety of psychiatric symptoms encountered in the HD setting is provided in Table 8.3.

COGNITIVE DECLINE

There are no therapeutic interventions known to improve cognitive function in HD patients. Cholinesterase inhibitors have been studied for treating cognitive impairment in HD based on their approval in Alzheimer’s disease. However, neither rivastigmine nor donepezil have demonstrated significant effects for improving or delaying cognitive dysfunction.38,39 The psychostimulant, modafinil, demonstrated

TAB L E   8. 4 .  Prospective Longitudinal Observational Studies of Huntington Disease START–​END STUDY NAME

POPULATION(S) OF INTEREST

DATES

DATA COLLECTED

SAMPLE SIZE

PREDICT-​HD51

-​Pre-​manifest HD (mutation carriers)

2002–​2013

-​Annual motor, cognitive, and neuropsychiatric measures -​Biological specimens (CSF, blood) -​ MRI

1,500

BIOHD52

-​Premanifest and manifest HD -​Controls (i.e. members of non-​HD families)

2003–​2020

-​Motor, cognitive, and neuropsychiatric measures -​Biological specimens (blood, urine) -​ Neuroimaging

1,800

*REGISTRY53

-​Pre-​manifest and manifest HD -​HD family members without mutation -​Controls (i.e. members of non-​HD families)

2004–​2014

-​Motor, cognitive, and neuropsychiatric measures -​Biological specimens (blood, urine) -​ MRI

10,000

*COHORT54

-​Premanifest and manifest HD -​At-​risk individuals (family history of HD but mutation status unknown) -​HD family members without mutation -​Controls (i.e., spouse or caregiver)

2006–​2020

-​Annual motor, cognitive, and neuropsychiatric measures -​Biological specimens (blood, urine)

5,000

TRACK-​HD55

-​Premanifest and early manifest HD (TFC 11-​13; mutation carriers) -​ Controls

2008–​2011

-​Annual motor, cognitive, and neuropsychiatric measures -​Biological specimens -​ MRI

349 (analyzed)

*REGISTRY and COHORT registries to be combined and transitioned to Enroll-​HD study. MRI = Magnetic resonance imaging; TFC = total functional capacity score.

50 | M o v e m e n t D i s o r d e r s

improvements in alertness but without improvements in cognitive function or mood and had deleterious effects on visual recognition and working memory.40 Additional drugs from various pharmacologic classes, including SNRIs, SSRIs, glutamate antagonists, N-​methyl-​D-​ aspartate receptor antagonists, and nutritional supplements also have failed to show significant cognitive benefit.

CURRENT CLINICA L  TRIA L S Clinical research in HD is presently aimed at identifying new symptomatic interventions as well as progression of disease. Although randomized, placebo-​controlled interventional studies bring new drugs to market most directly, the value of carefully designed and conducted longitudinal observational studies to drug development should not be underestimated. Characterizing the changes in disease over time not only leads to a better understanding of the neurobiology of the disease, but also helps identify the measures of disease progression and prediction of symptom onset. Future HD clinical trials, especially those designed to slow onset of clinical manifestions, require development of validated, sensitive outcomes. A selected summary of these studies are provided in Table 8.4. Current investigations include studies of symptomatic and disease modifying treatments (Table 8.5). These studies employ pharmacologic and surgical interventions. Direct strategies aimed at

surgically restoring damaged neurons in the striatum using intracerebral fetal neural grafting have shown intermittent efficacy, lasting approximately 2 years until benefits begin deteriorating.41–​45 Investigators in Europe intend to further evaluate intracerebral grafting through a phase 2 randomized, delayed wash-​in clinical trial, in which all subjects will eventually have the surgical procedure performed.46 However, these types of interventions only target striatum and do not address the substantial ongoing pathologic changes in other brain areas. Pharmacologic therapies address motor, behavioral, and cognitive symptoms, as well as disease modifying effects. Symptomatic therapy to improve voluntary motor function would represent a considerable advance in the treatment of HD, as these symptoms closely relate to functional disability. Pridopidine is a pharmacologic agent in the later stages of development intended to improve voluntary and involuntary psychomotor activity. It belongs to a novel class of drugs known as “dopamine stabilizers” wherein its mechanism of action is influenced by prevailing dopaminergic activity. A phase 3 trial with pridopidine reported a favorable trend of voluntary motor functions after 26 weeks but failed to meet its prespecified primary outcome. However, significant improvements were noted in total motor scores that took into account voluntary and involuntary motor symptoms.47 Pridopidine continues to be assessed in open-​label extension studies of the phase 2 and phase 3 clinical trials from North America and Europe, respectively.

TAB L E   8. 5 .  Huntington Disease Experimental Therapeutics* COMPOUND

PHARMACOLOGIC CLASS

PHASE

PRIMARY OUTCOME

SEN0014196 (Siena Biotech)

Sirtuin 1 inhibitor

1

Safety, tolerability, and pharmacokinetics

PBF-​999

Phosphodiesterase 10 inhibitor

1

Safety

PF-​0254920

Phosphodiesterase 10A inhibitor

2

Safety, tolerability, change in Total Motor Score over 28 days

OMS643762

Phosphodiesterase 10 inhibitor

2

Safety, tolerability

BN82451

Antioxidant, cyclooxygenase inhibitor, mitochondria protective

2

Safety

Laquinimod

Immunomodulator

2

Change in Total Motor Score after 12 months

PB2 (Prana Biotech)

Metal ligand

2

Safety, tolerability

Epigallocatechin gallate

Nutritional supplement

2

Change in UHDRS-​Cog over 12 months

delta-​9 tetrahydrocannabinol and cannabidiol

Cannabinoid

2

Change in UHDRS after 4 and12 weeks treatment

Pridopidine

Dopamine “stabilizer”

2

Safety, tolerability

Memantine

NMDA receptor antagonist

2

TRACK-​HD assessment battery after 6 months treatment

Creatine monohydrate

Nutritional supplement

3

Change in TFC over 3 years

Olanzapine, tiapride, tetrabenazine

Antipsychotics and monoamine depletor

3

Change in Independence Scale after 12 months treatment

SD-​809

VMAT-​2 inhibitor

3

Change in Total Maximal Chorea Score after 12 weeks

*Based on a search through ClinicalTrials.gov using search term “Huntington disease,” and limited to interventional studies that were active or recently completed (accessed September 25, 2014).

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Mutated huntingtin could lead to mitochondrial dysfunction with either bioenergetic deficiency or free radical toxicity with subsequent selective neostriatal neurodegeneration. Evidence from cell culture studies, animal models and postmortem brain tissue from HD patients linking mutated huntingtin to mitochondrial dysfunction and oxidative stress suggests these processes may occur early and facilitate downstream neurodegenerative changes in the striatum. In HD transgenic mice, various interventions believed to enhance mitochondrial function and suppress oxidative injury have been shown to have neuroprotective effects, increasing survival and delaying striatal atrophy. In light of these findings, two large, phase 3, double-​blind, placebo controlled clinical trials were to test the effects of the nutritional supplements coenzyme Q10 and creatine monohydrate. Both studies were designed to each enroll over 600 early symptomatic HD patients to determine if either treatment retards progression of functional decline. However, both were stopped early due to futility. Another target for intervention is the aberrant accumulation of transition metals that may contribute to neuronal toxicity in HD. Elevated levels of ferritin iron, zinc, and copper have been observed in basal ganglia structures of HD patients, and accumulating evidence suggests that metal dysregulation occurs prior to clinical manifestations.48 Metals such as iron and zinc may enhance formation of reactive oxygen species, whereas copper interactions with mutant huntingtin may promote its accumulation and toxic effects. Furthermore, clioquinol, an antibacterial and metal-​binding compound, may improve motor function and survival as well as reduce striatal atrophy and huntingtin aggregate accumulation in mice models expressing the toxic N-​terminal fragments of HTT.49 Early-​phase clinical trials in early to mid-​stage HD patients are testing the safety and early efficacy of a metal-​protein attenuating agent structurally related to clioquinol, which has previously demonstrated signals of cognitive improvement for Alzheimer’s patients.50

REFERENCES 1. Armstrong, M.  J., & Miyasaki, J.  M. (2012). Evidence-​ based guideline: Pharmacologic treatment of chorea in Huntington disease: Report of the guideline development subcommittee of the american academy of neurology. Neurology, 79(6), 597–​603. doi: 10.1212/​WNL.0b013e318263c443 2. Venuto, C. S., McGarry, A., Ma, Q., & Kieburtz, K. (2012). Pharmacologic approaches to the treatment of Huntington’s disease. Mov Disord, 27(1), 31–​41. doi: 10.1002/​mds.23953; 10.1002/​mds.23953 3. Mestre, T., Ferreira, J., Coelho, M.  M., Rosa, M., & Sampaio, C. (2009). Therapeutic interventions for symptomatic treatment in Huntington’s disease. Cochrane Database Syst Rev, 8(3), CD006456. 4. Groves, M., van Duijn, E., Anderson, K., Craufurd, D., Edmondson, M.  C., Goodman, N., van Kammen, D.  P., & Goodman, L. (2011). An international survey-​based algorithm for the pharmacologic treatment of irritability in Huntington’s disease. PLoS Currents, 3, RRN1259. 5. Anderson, K., Craufurd, D., Edmondson, M. C., Goodman, N., Groves, M., van Duijn, E., van Kammen, D. P., & Goodman, L. (2011). An international survey-​ based algorithm for the pharmacologic treatment of obsessive-​compulsive behaviors in Huntington’s disease. PLoS Currents, 3, RRN1261. 6. Burgunder, J. M., Guttman, M., Perlman, S., Goodman, N., van Kammen, D.  P., & Goodman, L. (2011). An international survey-​based algorithm for the pharmacologic treatment of chorea in Huntington’s disease. PLoS Currents, 3, RRN1260. 7. Sallee, F.  R., Nesbitt, L., Jackson, C., Sine, L., & Sethuraman, G. (1997). Relative efficacy of haloperidol and pimozide in children and adolescents with Tourette’s disorder. Am J Psychiatry, 154(8), 1057–​1062. 8. Girotti, F., Carella, F., Scigliano, G., Grassi, M. P., Soliveri, P., Giovannini, P., et al. (1984). Effect of neuroleptic treatment on involuntary movements

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and motor performances in Huntington’s disease. J Neurol Neurosurg Psychiatry, 47(8), 848–​852. 9. Barr, A.  N., Fischer, J.  H., Koller, W.  C., Spunt, A.  L., & Singhal, A. (1988). Serum haloperidol concentration and choreiform movements in Huntington’s disease. Neurology, 38(1), 84–​88. 10. Terrence, C. F. (1976). Fluphenazine decanoate in the treatment of chorea: A double-​blind study. Curr Ther Res Clin Exp, 20(2), 177–​183. 11. Whittier, J.  R., & Korenyi, C. (1968). Effect of oral fluphenazine on Huntington’s chorea. Int J Neuropsychiatry, 4(1), 1–​3. 12. Korenyi, C., & Whittier, J.  R. (1967). Drug treatment in 117 cases of Huntington’s disease with special reference to fluphenazine (prolixin). Psychiatr Q, 41(2), 203–​210. 13. Arena, R., Iudice, A., Virgili, P., Moretti, P., & Menchetti, G. (1980). Huntington’s disease: Clinical effects of a short-​term treatment with pimozide. Adv Biochem Psychopharmacol, 24, 573–​575. 14. Siegmund, R., Schmeisser, G., & Heidrich, R. (1982). Therapeutic experiences in the treatment of hyperkineses with the neuroleptic pimozide (antalon, orap) in the frame of Huntington chorea. [Therapeutische Erfahrungen bei der Behandlung von Hyperkinesen mit dem Neuroleptikum Pimozid (AntalonR, OrapR) im Rahmen der Chorea Huntington] Psychiatr Neurol Med Psychol, 34(5), 307–​308. 15. Quinn, N., & Marsden C. D. (1984). A double blind trial of sulpiride in Huntington’s disease and tardive dyskinesia. J Neurol Neurosurg Psychiatry, 47, 844–​847. 16. Reveley, M. A., Dursun, S. M., & Andrews, H. (1996). A comparative trial use of sulpiride and risperidone in Huntington’s disease:  a pilot study. J Psychopharmacol, 10(2): 162–​165. 17. Squitieri, F., Cannella, M., Piorcellini, A., Brusa, L., Simonelli, M., & Ruggieri, S. (2001). Short-​term effects of olanzapine in Huntington disease. Neuropsychiatry Neuropsychol Behav Neurol, 14(1), 69–​72. 18. Bonelli, R. M., Mahnert, F. A., & Niederwieser, G. (2002). Olanzapine for Huntington’s disease:  An open label study. Clin Neuropharmacol, 25(5), 263–​265. 19. Paleacu, D., Anca, M., & Giladi, N. (2002). Olanzapine in Huntington’s disease. Acta Neurologica Scandinavica, 105(6), 441–​444. 20. Dallocchio, C., Buffa, C., Tinelli, C., & Mazzarello, P. (1999). Effectiveness of risperidone in Huntington chorea patients. J Clin Psychopharmacol, 19(1), 101–​103. 21. Brusa, L., Orlacchio, A., Moschella, V., Iani, C., Bernardi, G., & Mercuri, N.  B. (2009). Treatment of the symptoms of Huntington’s disease: Preliminary results comparing aripiprazole and tetrabenazine. Mov Disord, 24(1), 126–​129. doi: 10.1002/​mds.22376 22. Lin W.  C., & Chou Y.  H. (2008). Aripiprazole effects on psychosis and chorea in a patient with Huntington’s disease. Am J Psychiatry, 165: 1207–​1208. 23. Bonelli, R. M, Niederwiese,r G. (2002). Quetiapine in Huntington’s disease: A first case report. J Neurol, 249(8): 1114–​1115. 24. Bonelli R. M., Mayr, B. M., Niederwieser, G., Reisecker, F., & Kapfhammer, H. P. (2003). Ziprasidone in Huntington’s disease: The first case reports. J Psychopharmacol, 17(4): 459–​460. 25. Huntington Study Group. (2006). Tetrabenazine as antichorea therapy in Huntington disease: A randomized controlled trial. Neurology, 66(3), 366–​372. doi: 10.1212/​01.wnl.0000198586.85250.13 26. Frank, S. (2009). Tetrabenazine as anti-​chorea therapy in Huntington disease:  An open-​label continuation study. Huntington study Group/​ TETRA-​HD investigators. BMC Neurology, 9, 62. doi:  10.1186/​ 1471-​2377-​9-​62 27. Xenazine (tetrabenazine) package insert. Deerfield, IL:  Lundbeck, Inc; September 2009. 28. Frank, S., Ondo, W., Fahn, S., Hunter, C., Oakes, D., Plumb, S., et  al. (2008). A study of chorea after tetrabenazine withdrawal in patients with Huntington disease. Clin Neuropharmacol, 31(3), 127–​133. doi: 10.1097/​ WNF.0b013e3180ca77ea 29. Lucetti, C., Del Dotto, P., Gambaccini, G., Dell’Agnello, G., Bernardini, S., Rossi, G., et al. (2003). IV amantadine improves chorea in Huntington’s disease: An acute randomized, controlled study. Neurology, 60(12), 1995–​1997. 30. O’Suilleabhain, P., & Dewey, R. B., Jr. (2003). A randomized trial of amantadine in Huntington disease. Arch Neurol, 60(7), 996–​998. doi: 10.1001/​ archneur.60.7.996 31. Heckmann, J. M., Legg, P., Sklar, D., Fine, J., Bryer, A., & Kies, B. (2004). IV amantadine improves chorea in Huntington’s disease: An acute randomized, controlled study. Neurology, 63(3), 597–​ 598; author reply 597–​598.

32. Low, P. A., Allsop, J. L., & Halmagyi, G. M. (1974). Huntington’s chorea: The rigid form (westphal variant) treated with levodopa. Med J Austral, 1(11), 393–​394. 33. Racette, B. A., & Perlmutter, J. S. (1998). Levodopa responsive parkinsonism in an adult with Huntington’s disease. J Neurol Neurosurg Psychiatry, 65(4), 577–​579. 34. Bonelli, R. M., Niederwieser, G., Diez, J., Gruber, A., & Koltringer, P. (2002). Pramipexole ameliorates neurologic and psychiatric symptoms in a westphal variant of Huntington’s disease. Clin Neuropharmacol, 25(1): 58–​60. 35. Marshall, J., White, K., Weaver, M., Flury Wetherill, L., Hui, S., Stout, J. C., et al. (2007). Specific psychiatric manifestations among preclinical Huntington disease mutation carriers. Arch Neuro, 64(1), 116–​121. doi: 10.1001/​archneur.64.1.116 36. Duff, K., Paulsen, J. S., Beglinger, L. J., Langbehn, D. R., Stout, J. C., Predict-​ HD Investigators and Huntington Study Group, (2007). Psychiatric symptoms in Huntington’s disease before diagnosis: The Predict-​HD study. Biol Psychiatry, 62(12): 1341–​1346. 37. Paulsen, J. S., Nehl, C., Hoth K. F., Kanz, J. E., Benjamin, M., Conybeare, R., McDowell, B., Turner, B., The Huntington Study Group. (2005). Depression and stages of Huntington’s disease. J Neuropsychiatry Clin Neurosci, 17(4): 496–​502. 38. Fernandez, H. H., Friedman, J. H., Grace, J., & Beason-​Hazen S. (2000). Donepezil for Huntington’s disease. Mov Disord, 15(1): 173–​176. 39. Cubo, E., Shannon, K. M., Tracy, D., Jaglin, J. A., Bernard, B. A., Wuu, J., & Leurgans, S. E. (2006). Effect of donepezil on motor and cognitive function in Huntington disease. Neurology, 67(7), 1268–​1271. doi: 10.1212/​ 01.wnl.0000238106.10423.00 40. Blackwell, A. D., Paterson, N. S., Barker, R. A., Robbins, T. W., & Sahakian, B. J. (2008). The effects of modafinil on mood and cognition in Huntington’s disease. Psychopharmacology, 199(1), 29–​36. doi: 10.1007/​ s00213-​008-​1068-​0 41. Philpott, L. M., Kopyov, O. V., Lee, A. J., Jacques, S., Duma, C. M., Caine, S., et al. (1997). Neuropsychological functioning following fetal striatal transplantation in Huntington’s chorea: Three case presentations. Cell Transplant, 6(3), 203–​212. 42. Bachoud-​Levi, A. C., Remy, P., Nguyen, J. P., Brugieres, P., Lefaucheur, J. P., Bourdet, C., et al. (2000). Motor and cognitive improvements in patients with Huntington’s disease after neural transplantation. Lancet, 356(9246), 1975–​1979. 43. Hauser, R. A., Furtado S., Cimino C.R., et al. (2002). Bilateral human fetal striatal transplantation in Huntington’s disease. Neurology, 58(5), 687–​695. 44. Bachoud-​Levi, A. C., Gaura, V., Brugieres, P., Lefaucheur, J. P., Boisse, M. F., Maison, P., et al. (2006). Effect of fetal neural transplants in patients with Huntington’s disease 6 years after surgery: A long-​term follow-​up study. Lancet Neurol, 5(4), 303–​309. doi: 10.1016/​S1474-​4422(06)70381-​7 45. Cicchetti, F., Saporta, S., Hauser, R. A., Parent, M., Saint-​ Pierre, M., Sanberg, P. R., et al. (2009). Neural transplants in patients with Huntington’s disease undergo disease-​like neuronal degeneration. Proc Natl Acad Sci USA, 106(30), 12483–​12488. doi: 10.1073/​pnas.0904239106 46. Assistance Publique-​Hopitaux de Paris. MIG-​HD: Multicentric intracerebral grafting in Huntington’s disease. Bethesda, MD: ClinicalTrials.gov. National

Library of Medicine. ClinicalTrials.gov identifier: NCT00190450. Available at: http://​clinicaltrials.gov/​ct2/​show/​NCT00190450. Accessed July 12, 2012. 47. de Yebenes, J. G., Landwehrmeyer, B., Squitieri, F., Reilmann, R., Rosser, A., Barker, R. A., et al; MermaiHD study investigators. (2011). Pridopidine for the treatment of motor function in patients with Huntington’s disease (MermaiHD): A phase 3, randomised, double-​ blind, placebo-​controlled trial. Lancet Neurol, 10(12), 1049–​1057. doi: 10.1016/​S1474-​4422(11)70233-​2; 10.1016/​S1474-​4422(11)70233-​2 48. Bartzokis, G., Lu, P. H., Tishler, T. A., Fong, S. M., Oluwadara, B., Finn, J. P., et al. (2007). Myelin breakdown and iron changes in Huntington’s disease: Pathogenesis and treatment implications. Neurochem Res, 32(10), 1655–​1664. doi: 10.1007/​s11064-​007-​9352-​7 49. Nguyen, T., Hamby, A., & Massa, S. M. (2005). Clioquinol down-​regulates mutant huntingtin expression in vitro and mitigates pathology in a Huntington’s disease mouse model. Proc Natl Acad Sci USA, 102(33), 11840–​11845. doi: 10.1073/​pnas.0502177102 50. Lannfelt, L., Blennow, K., Zetterberg, H., Batsman, S., Ames, D., Harrison, J. et al; PBT2-​201-​EURO study group. (2008). Safety, efficacy, and biomarker findings of PBT2 in targeting abeta as a modifying therapy for alzheimer’s disease: A phase IIa, double-​blind, randomised, placebo-​controlled trial. Lancet Neurol, 7(9), 779–​786. doi: 10.1016/​S1474-​4422(08)70167-​4 51. Paulsen, J. S., Hayden, M., Stout, J. C., Langbehn, D. R., Aylward, E., Ross, C. A., et al. Predict-​HD Investigators of the Huntington Study Group. (2006). Preparing for preventive clinical trials: The predict-​HD study. Arch Neurol, 63(6), 883–​890. doi: 10.1001/​archneur.63.6.883 52. Assistance Publique—​Hopitaux de Paris. Study of Biomarkers that predict the evolution of Huntington’s disease (BIOHD). Bethesda, MD: ClinicalTrials.gov. National Library of Medicine. ClinicalTrials.gov identifier: NCT01412125. Available at: http://​clinicaltrials.gov/​ct2/​show/​ NCT01412125. Accessed September 25, 2012. 53. Orth, M., European Huntington’s Disease Network, Handley, O. J., Schwenke, C., Dunnett, S., Wild, E. J. et al. (2011). Observing Huntington’s disease: The European Huntington’s Disease Network’s REGISTRY. J Neurol Neurosurg Psychiatry, 82(12), 1409–​ 1412. doi: 10.1136/​jnnp.2010.209668 54. Dorsey, E. R., & Huntington Study Group COHORT Investigators. (2012). Characterization of a large group of individuals with Huntington disease and their relatives enrolled in the COHORT study. PloS One, 7(2), e29522. doi: 10.1371/​journal.pone.0029522 55. Tabrizi, S. J., Reilmann, R., Roos, R. A., Durr, A., Leavitt, B., Owen, G. et al; TRACK-​HD investigators. (2012). Potential endpoints for clinical trials in premanifest and early Huntington’s disease in the TRACK-​HD study: Analysis of 24 month observational data. Lancet Neurol, 11(1), 42–​53. doi: 10.1016/​S1474-​4422(11)70263-​0

A DD ITIONA L RESO U RCES http://​www.hdsa.org/​ http://​clinicaltrials.gov/​ct2/​results?term=HD&Search=Search (for HD trials) http://​www.huntington-​study-​group.org/​ (Huntington Study Group)

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9 | E SSENTIAL TREMOR ARI F DALVI, K E L LY E .   LY ON S , A N D RA JESH PA H WA

D EF INITION Essential tremor (ET) is an idiopathic postural or kinetic tremor varying from 4 to 12 hertz that may affect the limbs, voice, head and neck, or trunk. Synonyms: essential tremor; familial tremor, hereditary tremor. Essential tremor is the most common pathological tremor in humans.1 Analogous to the term “essential hypertension,” the term “ET” was coined to describe tremor as an isolated symptom without a secondary etiology. However, recent observations suggest that it may be a neurodegenerative process with additional symptoms developing over time, with specific genetic etiologies in a small number of cases.2

PAT HOLOGY AN D PATH O P H YSIOL O G Y OF ESSENTIAL  TRE M OR Identified pathological processes underlying ET have been fairly limited and the findings have not been consistent. In one report,3 33 brains of patients with ET and 21 controls were examined. Two broad categories of pathology were seen. The first was the presence of prominent cerebellar changes seen in about 75% of the ET brains. These changes included a significant decline in the number of Purkinje cells and a marked increase in the number of swollen Purkinje cell axons, called “torpedoes.” The remaining 25% of brains showed Lewy bodies (hyaline intracellular inclusions within neurons) confined, for the most part, to the locus coeruleus. Other brainstem structures, including the substantia nigra and dorsal vagal nucleus, that contain Lewy bodies in Parkinson’s disease (PD) were minimally affected. These two pathological subtypes were mutually exclusive, with the former type called “cerebellar ET” and the latter the “Lewy body variant of ET.” The presence of two distinct pathological subtypes casts doubt on the concept of ET as a homogenous clinicopathological entity.4 It remains to be established how Lewy bodies in locus coeruleus could lead to a kinetic tremor. Norepinephrine is the principal neurotransmitter in the locus coeruleus, and axons from the locus coeruleus project to cerebellar Purkinje cells. A  locus coeruleus lesion may thus cause reduced stimulatory output from the locus coeruleus to the inhibitory Purkinje cells with a net reduction in γ-​aminobutyric acid (GABA)-​ mediated output from the Purkinje cells.4 In contrast, other studies have not identified increased Lewy bodies in ET autopsied cases compared with control cases.5 In a series of 24 ET cases and 21 controls, 12.5% of the ET cases had Lewy bodies (1 in the locus coeruleus; 1 neocortical; 1 neocortical, locus coeruleus, and substantia nigra) compared with 9.5% in controls (1 neocortical), a nonsignificant difference. In addition, 30% of persons over the age of 65 years have Lewy bodies at autopsy, suggesting that some Lewy bodies may relate to the aging process.5,6 In terms of pathophysiology, ET may be considered a cerebellar disorder. Pathological changes in ET either occur in the cerebellum 54 | Movement Disorders

itself or in neurons that synapse with the Purkinje cells of the cerebellum. Functional imaging studies corroborate the idea of cerebellar dysfunction in ET.7,8 The location of the central oscillator in ET is a matter of debate. The cerebellum and the olivopontocerebellar pathways are favored as the likely location. However, the ventral intermediate nucleus (Vim) of the thalamus may be an alternative site. Of note the Vim is the preferred surgical target for ET.9

G ENETICS OF   ESSENTIA L   TREM OR Essential tremor is often inherited in a manner that suggests an autosomal dominant genetic pattern. The incidence of inherited essential tremor ranges from 17% to 100% depending on the study methodology and defining characteristics used in the study.10 Two loci with linkage to ET have been reported on chromosome 3q13 (ETM1) and 2p22-​25 (ETM2),11,12 with additional linkage suggested at 6p23.13 However, a putative gene remains to be found. In a population-​based twin study, high concordance was observed among elderly monozygotic twins, suggesting that the ET phenotype has a high heritability and is a good candidate for linkage studies.14 Recently, a large sample of familial ET in Iceland revealed an association with the LINGO1 gene using genome wide association methods. The LINGO1 gene is required for proper myelination and is also important in regulating central nervous ​system axon regeneration and oligodendrocyte maturation.15 A subsequent study has replicated this finding in a Caucasian population in North America, with young-​onset ET patients more likely to have this association.16 Abnormalities in the number of triplet repeats in the Fragile X gene (FMR1) have also been identified in the setting of ET.17 The normal number of CAG repeats in this region is less than 50. When more than 200 repeats occur the presentation includes a learning disability, and Fragile X syndrome is the most common cause of inherited mental retardation. Patients with a repeat number between 55 and 200 show a postural tremor that is identical to ET. In addition, they also show mild ataxia of gait and cognitive impairment that may be mild but may progress to the level of dementia. This presentation is referred to as the Fragile X-​associated tremor/​ataxia syndrome.18

E P I DE M IOL O G Y O F   ESSENTIA L   TREM OR Essential tremor is one of the most common movement disorders and also one of the most common neurological disorders among adults.19 The study of the epidemiology of ET has been limited by several methodological issues that may have led to an underestimation of its prevalence. Many patients with mild tremor remain undiagnosed due to the belief that tremor is a normal age-​related condition.20 It is estimated that up to 90% of patients with ET do

not see a physician for tremor21 despite the finding from population-​ based studies that test-​detectable tremor may occur in as high as 98% of an older population.22 Patients who are socially or functionally impacted by the tremor are most likely to seek help and be identified. Another issue is the difficulty of case definition in a monosymptomatic disorder. Unlike PD, which has more than one cardinal feature, the defining feature of ET is action (postural or kinetic) tremor. However, an action tremor may be seen in some cases of PD and other disorders of the central and peripheral nervous system. ET also must be distinguished from enhanced physiological tremor. Consensus criteria have been defined for ET23,24 that improve case identification, but these also rely on a clinical diagnosis in the absence of a biomarker. Population-​based studies attempt to eliminate biases involved with patient selection and referral. A large population-​based study from central Spain examined 5,278 subjects and found 256 prevalent ET cases. A follow-​up evaluation of 3,942 individuals revealed 83 incident ET cases.20 The adjusted annual incidence rate (per 100,000 person-​years) in the population aged 65  years and older was 616 (95% CI: 447 to 784). Of note 64 of the 83 incident cases (77%) had not been previously diagnosed, suggesting that epidemiological results from studies that are not population based may significantly underestimate the prevalence and incidence of ET. A pooled analysis of 28 population-​based epidemiological studies in ET from nine countries calculated a crude prevalence across all ages of 0.4%. Prevalence increased markedly with age, and was found to be 4.6% in those aged 65 or over, and 21.7% in those aged 95 or over. Greater than a third of the studies showed gender differences, with the prevalence being greater among men.25 A bimodal pattern has been reported for ET with a smaller peak in the second decade and a larger peak in the sixth decade.26 Retrospective studies from subspecialty movement disorder clinics indicate that childhood-​onset ET is usually hereditary, begins at a mean age of 6 years, and affects boys three times as often as girls.27 A study of ethnic differences in ET examined a random sample of 2,117 Medicare recipients residing in Washington Heights-​Inwood, NY. Prevalence was higher in Whites than African Americans and intermediate in Hispanics.28

CLINICA L PRESENTATION OF ESSENTIAL  TRE MOR The most common clinical presentation of ET is that of a monosymptomatic tremor disorder.29 The tremor is an action tremor with mixed postural and kinetic elements. Postural tremor is most commonly seen in the hands when they are held outstretched. Holding objects in the hands may enhance tremor, which is more likely with heavier objects. The kinetic tremor is brought out by actions such as pouring a cup of water, eating with utensils or handwriting. Having the patient draw an Archimedes spiral can help demonstrate ET and help distinguish ET from PD. The typical spiral in ET is tremulous and jagged but not micrographic in contrast to PD wherein tighter spiraling is more prominent. There may be a significant positional component to the tremor. For example, a patient may have a mild tremor when the hands are held outstretched in front but the tremor may increase when the hands are held in front of the chest with the elbows bent. There may also be a component of terminal or intention tremor. This refers to the increase in tremor on finger to nose testing as the fingertip approaches the intended target at the terminus of the action.30 Although the hands are most commonly affected, many patients may have head tremor as well. The upper limbs are affected in about

95% of patients, followed by head (34%), lower limbs (20%), voice (12%), and face and trunk (5%).31 Occasionally the tremor may present as an isolated head tremor. In this case ET will need to be distinguished from cervical dystonia or spasmodic torticollis. In the latter syndrome there is a distinct directional component to the head tremor. In addition sustained abnormal posturing of the head is a hallmark of cervical dystonia. Asymmetric hypertrophy of the cervical muscles, especially the sternocleideomastoid, may be observed in cervical dystonia that is very unusual in ET.32 Given that head tremor may precede by many years the dystonic component of cervical dystonia, some investigators refer to pure head tremor as probable ET rather than definite ET.33 Some patients may also present with a voice tremor. This is best demonstrated by asking the patient to sustain a note for a minute that reveals a wavering voice. At times the voice tremor of ET may be confused with spasmodic dysphonia. However, in the latter case the voice is strained and tight, not breathy like in ET. It is important to note that laryngeal tremor and spasmodic dysphonia can coexist.34 Videostroboscopic examination of the vocal cords can help distinguish the two presentations when a clinical diagnosis is difficult. Isolated essential voice tremor is more common in women. One third to one half of affected individuals have a family history of tremor. Videostroboscopic examination reveals a kinetic laryngeal tremor extending beyond the larynx to involve the phonatory apparatus globally.35

DIA G NOSTIC CRITERIA AND RATIN G SCA L ES F OR   ESSENTIA L   TRE M OR Although the diagnosis of ET is clinical, no universally accepted criteria exist for the diagnosis. The Movement Disorder Society has proposed consensus criteria for ET.24 More recently, core and secondary criteria have been proposed to facilitate diagnosis. Core criteria include bilateral action tremor of the hands and forearms, absence of other neurological signs, and isolated head tremor without signs of dystonia. Secondary criteria include long duration (greater than 3 years), positive family history, and a beneficial response to alcohol.23 The most widely used clinical rating scale is the Fahn, Tolosa, Marin tremor rating scale (TRS).36 The TRS quantifies rest, postural, and action/​intention tremors, and the severity in various body parts is rated from 0 (none) to 4 (severe). The scale is divided into three parts assessing tremor location/​severity, ability to perform specific motor tasks/​functions, and patient-​reported disability due to tremor. Although useful, the interobserver variability of the TRS is fair, and thus it is important to maintain the same observer to assess for change in tremor severity.37 The Tremor Research Group developed the TRG Essential Tremor Rating Assessment Scale (TETRAS), which has an ET-​specific rating scale that can be completed in less than 10 minutes. This rating requires only a pen and paper and includes objective tremor measurement anchors that improve inter-​and intrarater reliability.38 TETRAS has 12 items assessing activities of daily living and 9 performance items to measure tremor in the limbs, head, voice, face, and trunk. The scale was found to be valid and highly reliable in terms of both intra-​and interrater assessments.

CO G NITIVE S Y M P TO M S ASSOCIATE D W IT H  ESSENTIA L   TRE M OR In the realm of movement disorders, more attention is now being focused on the non-​motor aspects of various disorders including ET. As the most 9 E s s e n t i a l   T r e m o r | 55

common of the movement disorders, ET has been found to carry with it risk for cognitive deficits. A population-​based, case-​control study of cognitive function in ET revealed that Mini Mental State Examination scores declined at a rate that was seven-​times faster in ET cases compared with controls over a 3-​year follow-​up.39 Several studies have found executive functioning deficits in ET.40,41 The study by Gasparini and colleagues41 was especially intriguing because it found a continuum of normals, familial ET, ET with a family history of PD, and patients with PD, suggesting a common dysregulation of dopamine pathways. Patients with ET may also show changes in personality. A cross-​ sectional study that used the Tridimensional Personality Questionnaire showed that patients with ET had higher scores in comparison with controls in the domain of harm avoidance, implying a personality with increased levels of pessimism, fearfulness, and shyness. Tremor severity and harm avoidance scores were not correlated, suggesting that the personality profile was a primary feature of the disease rather than a reactive psychological consequence of severe and disabling tremor.42 The term “essential tremor plus” has been used analogous to the Parkinson-​plus syndromes as has the term “indeterminate tremor syndrome” to describe a category of ET in which additional signs and symptoms are noted in addition to the primary presentation of tremor.43

PHARMACOLOGY OF ESSENTIAL  TRE M OR Although no curative treatment for ET is available, medications may reduce the adverse impact of ET on quality of life. The goals of treatment are to improve function in activities such as eating, drinking, writing, and typing, as well as to reduce social embarrassment. Pharmacological treatment of tremor is based on mechanisms that include reducing the sympathetic drive that may exacerbate tremor, increasing GABAergic inhibition of the central oscillators that drive tremor, and membrane stabilizing effects. Propranolol, primidone, and alcohol are the prototypical drugs that respectively represent the three mechanisms. In practice, the discovery of drugs for tremor has often been a matter of serendipity. Other comorbidities such as diabetes, cardiac failure, glaucoma, and renal failure should be kept in mind when tailoring the choice of drug to a particular patient. The American Academy of Neurology (AAN) has published a practice parameter for the therapy of ET that can serve as a guideline.44 Key pharmacotherapeutic agents are reviewed below. B E TA -​A D R E N E R G I C B L O C K E R S

Propranolol was one of the earliest agents shown to be effective in ET and continues to remain a mainstay of treatment.45 It is the only medication that has been approved by the FDA for the treatment of ET. Controlled studies demonstrated that about 50% to 70% of patients obtained substantial relief.46,47 The starting dose of propranolol should be 20 to 80 mg/​day. The dosage range in the AAN practice parameter is 60 to 800 mg/​day.44 A dose-​response study showed that optimum tremor control was achieved at doses ranging from 160 to 320 mg/​day. Doses above 320 mg/​day did not confer additional benefit.48 The long-​ acting form of propranolol (propranolol-​LA) has also been used successfully and may help with compliance when high doses are required.49 It can be initiated at 80 mg/​day and increased in 80 mg increments up to 320 mg/​day if tolerated. Other beta-​blockers that have been used include atenolol, metoprolol, nadolol, sotalol, timolol and arotinolol. However a recent evidence-​based review suggested that clinical evidence for their use when compared with placebo or propranolol is 56 | M o v e m e n t D i s o r d e r s

lacking.50 Contraindications to the use of beta-​blockers include moderate to severe asthma, presence of heart block and concurrent calcium-​channel blockers. They should be used with caution in diabetics because they can mask the sympathetic response to hypoglycemia.50 Caution should be exercised in elderly patients, as orthostatic hypotension tends to be more common in this age group. Initial doses should be lower and the dose titration should proceed more slowly. PRIMIDONE

Primidone has been shown to have an efficacy in ET that is equivalent to propranolol.51 Doses used in ET are lower than typical antiepileptic doses. The initial dose is 25 mg at bedtime (half of a 50 mg tablet) with a titration in 50 mg increments each week up to 250 mg/​day. Initially the entire dose may be given at bedtime, as drowsiness is the most common side effect. However, part of the dose may be moved to daytime hours if needed once the patient has shown good tolerance to the side effects. In a double-​blind study, two doses of primidone at 250 mg/​day and 750 mg/​day were compared after 1 year of treatment. Both doses were effective and the effect size was similar. However, the drop-​out rate due to side effects was significantly lower on the lower dose.52 Primidone is metabolized to phenobarbital and phenylethylmalonamide. Of note, primidone was superior to phenobarbital and placebo, suggesting that it has a direct effect rather than working through its metabolites.53 Combination therapy with propranolol and primidone may provide benefit in cases that have suboptimal tremor control wtih either drug alone.54 GABAPENTIN

Though gabapentin is a structural analog of GABA it has no affinity for the GABA receptor, and the mechanism of action in ET is unclear. Results from randomized, controlled trials are mixed. One study showed gabapentin at a dose of 1200 mg/​day to be equivalent to propranolol at a dose of 120 mg/​day with both drugs superior to placebo.55 Other studies have either shown mixed results56 or failed to support this initial observation.57 Gabapentin is generally initiated with 100 to 300mg at bedtime and slowly increased up to 600mg three times daily. It is typically well-​tolerated. with the most common side effects being lethargy, somnolence, fatigue, dizziness, anxiety, decreased libido, shortness of breath, and nausea.

T O P I R A M AT E

Topiramate is an agent with multiple mechanisms of action that include glutamate antagonist and GABA-​agonist activities. In a controlled study topiramate at a mean dose of 333 mg/​day was found to be superior to placebo. Significant adverse events that required discontinuing topiramate were nausea, paresthesia, and concentration/​ attention difficulty.58 A multicenter study confirmed this finding with a target dose of topiramate of 400 mg/​day when used as monotherapy or as an adjunct to one previously used anti-​tremor medication.59 Topiramate should be avoided in patients with glaucoma or those who are at risk for nephrolithiasis and should be used with caution in the elderly, as it imposes a risk of cognitive side effects. The most common side effects are weight loss, decreased appetite, paresthesias, cognitive issues, fatigue, nausea, taste perversion, and somnolence. BENZODIAZEPINES

Alprazolam, clonazepam, and lorazepam may suppress tremor through their GABA-​agonist activity. They can be especially useful in

anxious patients due to their anxiolytic properties. In a double-​blind study, alprazolam was shown to be effective in ET with doses ranging from 0.75 to 2.75 mg/​day.60 The efficacy of clonazepam and lorazepam for ET has not been demonstrated in controlled studies. The benzodiazepines are best used as third-​line agents due to the potential for tolerance and addiction. Rapid withdrawal should be avoided when these drugs need to be discontinued.

the pons, and therefore, the Vim is a relay station in a cerebellar-​ motor cortical loop of activity. It is believed that oscillatory neural activity in this loop (originating in the olivocerebellar network) causes ET, and interruption of this abnormal network oscillation will halt tremor.69 A novel target area for surgical intervention for tremor is the area below the ventrolateral thalamus and posterior to the subthalamic nucleus. This area includes the prelemniscal radiations and zona incerta (ZI), and has been called the “posterior subthalamic area.”70 BOTULINUM TOXIN The ZI was named by Forel as a “region of which nothing certain can 71 A number of patients with head tremor may have cervical dystonia. be said” or a “zone of uncertainty.” The ZI is a sparse nucleus with diffuse connectivity, most important of which for tremor is the conThe efficacy of botulinum toxin has been unequivocal in this connection from primary motor cortex, basal ganglia, and cerebellum, dition. There is limited information from small trials about efficacy with output to the ventrolateral thalamus. The ZI was shown to be 61 in patients with head tremor without cervical dystonia. The use of botulinum toxin in hand tremor is limited by lack of efficacy as dem- involved in the pathogenesis of some forms of tremor. Stimulation ZI provokes a rest tremor in people who onstrated by functional rating scales, as well as a tendency to impair with 5 to 40 Hz to caudal 72 do not have tremor. Plaha and colleagues used this finding to 62 motor dexterity. hypothesize that parkinsonian rest tremor occurs when the ventrolateral thalamus generates a five-​per-​second rebound burst firing in response to oscillatory input from the ZI. This hypothesis may I N V E S T I G AT I O N A L   A G E N T S explain the mechanism of action of anticholinergic drugs for tremor, The beneficial effect of alcohol for ET has been known from the earli- since acetylcholine enhances thalamic rebound burst firing. Bilateral est descriptions. However, limitations to the use of alcohol as treat- caudal ZI stimulation effectively suppresses the postural and kinetic ment for ET include the short duration of response, development of component of ET, with a low incidence of stimulation related comtolerance to the antitremor effect, and the risk of alcoholism.63 As an plications. Clinical benefit persisted for a follow-​up period of up to attempt to capture the antitremor effect of alcohol while avoiding its 7 years.73 intoxicating effects, 1-​octanol is under investigation. It is an 8-​carbon The most widely accepted surgical treatment of choice for ET alcohol currently used as a food-​flavoring agent shown to inhibit is Vim DBS. Lyons and Pahwa reviewed 8 outcome studies of DBS tremor in animal models of ET. In a small pilot trial a single dose of for ET,74 covering 158 patients implanted unilaterally and 68 with 1-​octanol significantly decreased tremor amplitude for up to 90 min- bilateral DBS. Across studies, over 33  months of mean follow-​up, utes without causing intoxication as a side effect.64 Sodium oxybate is activities of daily living improved on average by 46%. There was a currently approved by the FDA for the treatment of excessive daytime reduction in overall tremor of 48%, including 73% for hand tremor. sleepiness and cataplexy associated with narcolepsy. A  small open-​ Head tremor improved only 35% in unilaterally implanted patients, label study showed beneficial effects of sodium oxybate for ethanol-​ but 81% in bilateral patients, and the same was generally true for responsive ET and myoclonus.65 Sodium oxybate has a high potential voice tremor. Thus head and voice tremor require bilateral DBS for for abuse and can only be prescribed through a specific risk manage- maximum benefit. Regarding adverse events, the authors reported ment program. that complications were rare and generally led to no permanent deficits. One meta-​ analysis of the complications of DBS75 for 1,154 S URGICA L TREATMENT patients showed the following common adverse events:  mental staOF ESSENTIAL  TRE M OR tus or behavioral changes (16.6%), infection (2.2%), speech disturbance (2.0%), symptomatic intracerebral hemorrhage (2.0%), seizures Surgical treatment is an option for intractable tremor.9 The surgical (1.0%), misplaced electrodes (1.6%), and asymptomatic intracerebral modalities used and the surgical targets also provide insight into hemorrhage (1.2%). Hardware-​related adverse events occurred in the neurobiology of tremor. Most pathological tremors are believed 8.7% of patients. to be generated within the central nervous system.7 However, the exact mechanisms and location of these central oscillators are still unclear, and differences exist in the pathophysiological mecha- A DVANCES IN  I M A G IN G TEC H NIQ UES nism of tremor due to PD and ET.66 Regardless of etiology, a sur- F OR   TREM OR D IAG NOSIS gical intervention in the motor thalamus is most effective in the vast majority of pathological tremors, which may be explained by The diagnosis of ET remains in the clinical domain. Imaging studies its central position between subcortical and cortical tremor net- in the form of a brain MRI are usually performed during the initial works.67 The two surgical methods of modifying tremor include evaluation. These techniques help exclude structural etiologies for thalamotomy and deep brain stimulation (DBS). The target for tremor such as stroke or multiple sclerosis. However, they are unhelpboth is the ventral intermediate (Vim) nucleus of the thalamus.67 ful in distinguishing ET from PD. Single photon emission computed Due to the irreversible nature of the radiofrequency lesion used in tomography (SPECT) techniques represent an advance in the ability thalamotomy and the high risk of hypophonia, dysarthria, and cog- to distinguish ET from parkinsonism. In cases of diagnostic uncernitive deficits following bilateral ablation, DBS has become the pre- tainty between degenerative parkinsonism and non-​ degenerative ferred surgical modality.68 The precise mechanism of action of DBS tremor disorders, baseline SPECT imaging with the dopamine transremains to be elucidated and may differ with different disease states porter ligand [(123)I]ioflupane has shown 78% sensitivity and 97% as well as with surgical targets. The Vim receives inputs predomi- specificity with reference to clinical diagnosis at 3 years, versus 93% nantly from the cerebellar deep nuclei, and projects to the primary and 46%, respectively, for baseline clinical diagnosis.76 However, these motor cortex. The motor cortex projects back to the cerebellum via scans may provide no advantage over clinical diagnosis and may miss 9 E s s e n t i a l   T r e m o r | 57

a clinically treatable condition.77 Furthermore, these SPECT scans do not differentiate between PD and atypical parkinsonism.

FU TURE DIRECTIONS A great deal of research is needed in order to identify the cause and provide more effective treatments and ultimately the cure for ET. Most studies suggest that the cerebellum is involved in the pathophysiology of ET and a majority of cases appear to have an autosomal dominant inheritance pattern; however, the actual cause of ET and a gene responsible for the majority of cases have not been identified. Without a definitive cause of ET, it has been difficult to develop new, more effective treatments. At this time, the pharmacological treatments used in ET were developed for other purposes and later found to benefit ET. However, it is estimated that only about 50% to 60% of ET patients receive benefit from the current medications, and the benefit obtained is often not sufficient to completely resolve the tremor and consequent disability. Deep brain stimulation has been shown to result in significant improvements in tremor, but not all patients are candidates for DBS. Further development of neuroimaging and other techniques to aid in the diagnosis of ET is critical, as an early and accurate diagnosis is required to obtain valid, reliable and accurate research results and to provide the highest possible level of care.

REFERENCES 1. Louis, E. D., Thawani, S. P., Andrews, H. F. (2009). Prevalence of essential tremor in a multiethnic, community-​based study in northern Manhattan, New York, N.Y. Neuroepidemiology, 32(3), 208–​214. 2. Deuschl, G., & Elble, R. (2009). Essential tremor—​neurodegenerative or nondegenerative disease towards a working definition of ET. Mov Disord, 24(14), 2033–​2041. 3. Louis, E. D., Faust, P. L., Vonsattel, J. P., Honig, L. S., Rajput, A., Robinson, C.  A., Rajput, A., Pahwa, R., Lyons, K.  E., Ross, G.  W., Borden, S., Moskowitz, C. B., Lawton, A., & Hernandez, N. (2007). Neuropathological changes in essential tremor: 33 cases compared with 21 controls. Brain, 130(Pt 12), 3297–​3307. 4. Louis, E. D. Essential tremor: Evolving clinicopathological concepts in an era of intensive post-​mortem enquiry. Lancet Neurol, 9(6), 613–​622. 5. Adler, C.  H., Shill, H.  A., & Beach, T.  G. (2011). Essential tremor and Parkinson’s disease: Lack of a link. Mov Disord, 26(3), 372–​377. 6. Rajput, A.  H., Adler, C.  H., Shill, H.  A., & Rajput, A. (2012). Essential tremor is not a neurodegenerative disease. Neurodegener Dis Manag, 2(3), 259–​268. 7. Bucher, S. F., Seelos, K. C., Dodel, R. C., Reiser, M., & Oertel, W. H. (1997). Activation mapping in essential tremor with functional magnetic resonance imaging. Ann Neurol, 41(1), 32–​40. 8. Louis, E. D., Shungu, D. C., Chan, S., Mao, X., Jurewicz, E. C., 7 Watner, D. (2002). Metabolic abnormality in the cerebellum in patients with essential tremor:  A  proton magnetic resonance spectroscopic imaging study. Neurosci Lett, 333(1), 17–​20. 9. Benabid, A.  L., Pollak, P., Gervason, C., Hoffmann, D., Gao, D.  M., Hommel, M., Perret, J. E., & de Rougemont, J. (1991). Long-​term suppression of tremor by chronic stimulation of the ventral intermediate thalamic nucleus. Lancet, 337(8738), 403–​406. 10. Louis, E.  D., & Ottman R. (1996). How familial is familial tremor? The genetic epidemiology of essential tremor. Neurology, 46(5), 1200–​1205. 11. Gulcher, J. R., Jónsson, P., Kong, A., Kristjánsson, K., Frigge, M. L., Kárason, A., Einarsdóttir, I. E., Stefánsson, H., Einarsdóttir, A. S., Sigurthoardóttir, S., Baldursson, S., Björnsdóttir, S., Hrafnkelsdóttir, S.  M., Jakobsson, F., Benedickz, J., & Stefánsson, K. (1997). Mapping of a familial essential tremor gene, FET1, to chromosome 3q13. Nat Genet, 17(1), 84–​87. 12. Higgins, J. J., Loveless, J. M., Jankovic, J., & Patel, P. I. (1998). Evidence that a gene for essential tremor maps to chromosome 2p in four families. Mov Disord, 13(6):972–​977. 13. Shatunov, A., Sambuughin, N., Jankovic, J., Elble, R., Lee, H. S., Singleton, A. B., Dagvadorj, A., Ji, J., Zhang, Y., Kimonis, V. E., Hardy, J., Hallett, M., &

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Goldfarb, L.  G. (2006). Genomewide scans in North American families reveal genetic linkage of essential tremor to a region on chromosome 6p23. Brain, 129(Pt 9), 2318–​2331. 14. Lorenz, D., Frederiksen, H., Moises, H., Kopper, F., Deuschl, G., & Christensen, K. (2004). High concordance for essential tremor in monozygotic twins of old age. Neurology, 62(2), 208–​211. 15. Stefansson, H., Steinberg, S., Petursson, H., Gustafsson, O., Gudjonsdottir, I.  H., Jonsdottir, G.  A., Palsson, S.  T., Jonsson, T., Saemundsdottir, J., Bjornsdottir, G., Böttcher, Y., Thorlacius, T., Haubenberger, D., Zimprich, A., Auff, E., Hotzy, C., Testa, C.  M., Miyatake, L.  A., Rosen, A.  R., Kristleifsson, K., Rye, D., Asmus, F., Schöls, L., Dichgans, M., Jakobsson, F., Benedikz, J., Thorsteinsdottir, U., Gulcher, J., Kong, A., & Stefansson, K. (2009). Variant in the sequence of the LINGO1 gene confers risk of essential tremor. Nat Genet, 41(3), 277–​279. 16. Clark, L. N., Park, N., Kisselev, S., Rios, E., Lee, J. H., & Louis, E. D. (2020). Replication of the LINGO1 gene association with essential tremor in a North American population. Eur J Hum Genet, 18(7), 838–​843. 17. Leehey, M.  A., Munhoz, R.  P., Lang, A.  E., Brunberg, J.  A., Grigsby, J., Greco, C., Jacquemont, S., Tassone, F., Lozano, A. M., Hagerman, P. J., & Hagerman, R. J. (2003). The fragile X premutation presenting as essential tremor. Arch Neurol, 60(1), 117–​121. 18. Leehey, M.  A. (2009). Fragile X-​ associated tremor/​ ataxia syndrome: Clinical phenotype, diagnosis, and treatment. J Investig Med, 57(8), 830–​836. 19. Benito-​ León, J. (2009). How common is essential tremor? Neuroepidemiology, 32(3), 215–​216. 20. Benito-​León, J., Bermejo-​Pareja, F., Louis, E.  D; Neurological Disorders in Central Spain (NEDICES) Study Group. (2005). Incidence of essential tremor in three elderly populations of central Spain. Neurology, 64(10), 1721–​1725. 21. Louis, E. D., Ottman, R., & Hause, W. A. (1998). How common is the most common adult movement disorder? Estimates of the prevalence of essential tremor throughout the world. Mov Disord, 13(1), 5–​10. 22. Louis, E.  D., Wendt, K.  J., & Ford, B. (2000). Senile tremor. What is the prevalence and severity of tremor in older adults? Gerontology, 46(1),12–​16. 23. Bain, P., Brin, M., Deuschl, G., Elble, R., Jankovic, J., Findley, L., Koller, W. C., & Pahwa, R. (2000). Criteria for the diagnosis of essential tremor. Neurology, 54(11 Suppl 4), S7. 24. Deuschl, G., Bain, P., & Brin, M. (1998). Consensus statement of the Movement Disorder Society on Tremor. Ad Hoc Scientific Committee. Mov Disord, 13(Suppl 3), 2–​23. 25. Louis, E. D., & Ferreira, J. J. (2010). How common is the most common adult movement disorder? Update on the worldwide prevalence of essential tremor. Mov Disord, 25(5), 534–​541. 26. Lou, J. S., & Jankovic, J. (1991). Essential tremor: clinical correlates in 350 patients. Neurology, 41(2 (Pt 1)), 234–​238. 27. Ferrara, J., & Jankovic, J. (2009). Epidemiology and management of essential tremor in children. Paediatr Drugs, 11(5), 293–​307. 28. Louis, E. D., Marder, K., Cote, L., Pullman, S., Ford, B., Wilder, D., Tang, M.  X., Lantigua, R., Gurland, B., & Mayeux, R. (1995). Differences in the prevalence of essential tremor among elderly African Americans, whites, and Hispanics in northern Manhattan, NY. Arch Neurol, 52(12), 1201–​1205. 29. Elble, R. J. (2002). Essential tremor is a monosymptomatic disorder. Mov Disord, 17(4), 633–​637. 30. Dalvi, A.​, & Premkumar, A. (2011). Tremor:  etiology, phenomenology, and clinical features. Dis Mon, 57(3), 109–​126. 31. Elble, R. J. (2000). Diagnostic criteria for essential tremor and differential diagnosis. Neurology, 54(11 Suppl 4), S2–​6. 32. Pal, P.  K., Samii, A., Schulzer, M., Mak, E., & Tsui, J.  K. (2000). Head tremor in cervical dystonia. Can J Neurol Sci, 27(2), 137–​142. 33. Jankovic, J. (2002). Essential tremor:  A  heterogenous disorder. Mov Disord, 17(4), 638–​644. 34. Wolraich, D., Vasile Marchis-​Crisan, C., Redding, N., Khella, S.  L., & Mirza, N. (2010). Laryngeal tremor: co-​occurrence with other movement disorders. ORL J Otorhinolaryngol Relat Spec, 72(5), 291–​294. 35. Sulica, L., Louis, E.  D. (2010). Clinical characteristics of essential voice tremor: A study of 34 cases. Laryngoscope, 120(3), 516–​528. 36. Fahn, S., Tolosa, E., & Marin, C. (1993). Clinical rating scale for tremor. In J. Jankovic, & E. Tolosa (Eds.), Parkinson’s disease and movement disorders (2nd ed., pp. 225–​234). Baltimore: Williams & Wilkins. 37. Stacy, M. A., Elble, R. J., Ondo, W. G., et al. (2007). Assessment of interrater and intrarater reliability of the Fahn-​Tolosa-​Marin Tremor Rating Scale in essential tremor. Mov Disord, 22, 833–​838. 38. Elble, R., Comella, C., Fahn, S., et al. (2012). Reliability of a new scale for essential tremor. Mov Disord, 27, 1567–​1569.

39. Louis, E.  D., Benito-​ León, J., Vega-​ Quiroga, S., Bermejo-​ Pareja, F; Neurological Disorders in Central Spain (NEDICES) Study Group. (2010). Faster rate of cognitive decline in essential tremor cases than controls: a prospective study. Eur J Neurol, 17(10), 1291–​1297. 40. Benito-​León, J., Louis, E. D., Bermejo-​Pareja, F; Neurological Disorders in Central Spain (NEDICES) Study Group. (2006). Population-​based case-​control study of cognitive function in essential tremor. Neurology, 66(1), 69–​74. 41. Gasparini, M., Bonifati, V. Fabrizio, E., Fabbrini, G., Brusa, L., Lenzi, G. L., & Meco, G. (2001). Frontal lobe dysfunction in essential tremor: A preliminary study. J Neurol, 248(5), 399–​402. 42. Chatterjee, A., Jurewicz, E. C., Applegate, L. M., & Louis, E. D. (2004). Personality in essential tremor: further evidence of non-​motor manifestations of the disease. J Neurol Neurosurg Psychiatry, 75(7), 958–​961. 43. Louis, E. D. (2009). Essential tremors: a family of neurodegenerative disorders? Arch Neurol, 66(10), 1202–​1208. 44. Zesiewicz, T.  A., Elble, R., Louis, E.  D., Hauser, R.  A., Sullivan, K.  L., Dewey, R.  B., Jr., Ondo, W.  G., Gronseth, G.  S., Weiner, W.  J; Quality Standards Subcommittee of the American Academy of Neurology. (2005). Practice parameter: Therapies for essential tremor: Report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology, 64(12), 2008–​2020. 45. Winkler, G. F., & Young, R. R. (1974). Efficacy of chronic propranolol therapy in action tremors of the familial, senile or essential varieties. N Engl J Med, 290(18), 984–​988. 46. Tolosa, E. S., & Loewenson, R. B. (1975). Essential tremor: treatment with propranolol. Neurology, 25(11), 1041–​1044. 47. Calzetti, S., Findley, L. J., Perucca, E., & Richens, A. (1983). The response of essential tremor to propranolol: Evaluation of clinical variables governing its efficacy on prolonged administration. J Neurol Neurosurg Psychiatry, 46(5), 393–​398. 48. Koller, W.  C. (1986). Dose-​response relationship of propranolol in the treatment of essential tremor. Arch Neurol, 43(1), 42–​43. 49. Kolle,r W.  C. (1985). Long-​ acting propranolol in essential tremor. Neurology, 35(1), 108–​110. 50. Ferreira, J. J., & Sampaio, C. (2007). Essential tremor. BMJ Clin Evid, 05 1206. 51. Koller, W.  C., & Royse, V.  L. (1986). Efficacy of primidone in essential tremor. Neurology, 36(1), 121–​124. 52. Serrano-​Dueñas, M. (2003). Use of primidone in low doses (250 mg/​day) versus high doses (750 mg/​day) in the management of essential tremor. Double-​blind comparative study with one-​year follow-​up. Parkinsonism Relat Disord, 10(1), 29–​33. 53. Sasso, E., Perucca, E., & Calzetti, S. (1988). Double-​blind comparison of primidone and phenobarbital in essential tremor. Neurology, 38(5), 808–​810. 54. Lyons, K. E., Pahwa, R., Comella, C. L., Eisa, M. S., Elble, R. J., Fahn, S., Jankovic, J., Juncos, J. L., Koller, W. C., Ondo, W. G., Sethi, K. D., Stern, M. B., Tanner, C. M., Tintner, R., & Watts, R. L. (2003). Benefits and risks of pharmacological treatments for essential tremor. Drug Saf, 26(7), 461–​481. 55. Gironell, A., Kulisevsky, J., Barbanoj, M., López-​Villegas, D., Hernández, G., & Pascual-​Sedano, B. (1999). A randomized placebo-​controlled comparative trial of gabapentin and propranolol in essential tremor. Arch Neurol, 56(4):475–​480. 56. Ondo, W., Hunter, C., Vuong, K. D., Schwartz, K., & Jankovic, J. (2000). Gabapentin for essential tremor: a multiple-​dose, double-​blind, placebo-​ controlled trial. Mov Disord, 15(4), 678–​682. 57. Pahwa, R., Lyons, K., Hubble, J. P., Busenbark, K., Rienerth, J. D., Pahwa, A., & Koller, W. C. (1998). Double-​blind controlled trial of gabapentin in essential tremor. Mov Disord, 13(3), 465–​467.

58. Connor, G.  S., Edwards, K., & Tarsy, D. (2008). Topiramate in essential tremor: findings from double-​blind, placebo-​controlled, crossover trials. Clin Neuropharmacol, 31(2), 97–​103. 59. Ondo, W.  G., Jankovic, J., Connor, G.  S., Pahwa, R., Elble, R., Stacy, M. A., Koller, W. C., Schwarzman, L., Wu, S. C., Hulihan, J. F; Topiramate Essential Tremor Study Investigators. Topiramate in essential tremor:  a double-​blind, placebo-​controlled trial. Neurology, 66(5), 672–​677. 60. Huber, S. J., & Paulson, G. W. (1988). Efficacy of alprazolam for essential tremor. Neurology, 38(2), 241–​243. 61. Pahwa, R., Busenbark, K., Swanson-​ Hyland, E.  F., Dubinsky, R.  M., Hubble, J. P., Gray, C., & Koller, W. C. (1995). Botulinum toxin treatment of essential head tremor. Neurology, 45(4), 822–​824. 62. Jankovic, J., Schwartz, K., Clemence, W., Aswad, A., & Mordaunt, J. (1996). A randomized, double-​blind, placebo-​controlled study to evaluate botulinum toxin type A in essential hand tremor. Mov Disord, 11(3), 250–​256. 63. Schroeder, D., & Nasrallah, H. A. (1982). High alcoholism rate in patients with essential tremor. Am J Psychiatry, 139(11), 1471–​1473. 64. Bushara, K. O., Goldstein, S. R., Grimes, G. J., Jr, Burstein, A. H., Hallett, M. (2004). Pilot trial of 1-​octanol in essential tremor. Neurology, 62(1), 122–​124. 65. Frucht, S. J., Houghton, W. C., Bordelon, Y., Greene, P. E., & Louis, E. D. (2005). A single-​blind, open-​label trial of sodium oxybate for myoclonus and essential tremor. Neurology, 65(12), 1967–​1969. 66. Pedrosa, D. J., Reck, C., Florin, E., Pauls, K. A., Maarouf, M., Wojtecki, L., Dafsari, H.  S., Sturm, V., Schnitzler, A., Fink, G.  R., & Timmermann, L. (2012). Essential tremor and tremor in Parkinson’s disease are associated with distinct ‘tremor clusters’ in the ventral thalamus. Exp Neurol, 237(2), 435–​443. 67. Schuurman, P. R., Bosch, D. A., Merkus, M. P., & Speelman, J. D. (2008). Long-​term follow-​up of thalamic stimulation versus thalamotomy for tremor suppression. Mov Disord, 23(8), 1146–​1153. 68. Novak, K. E., Dalvi, A., Nenonene, E. K., & Bernstein, L. P. (2011). Surgical treatment of tremor. Dis Mon, 57(3), 142–​159. 69. Deuschl, G., & Bergman, H. (2002). Pathophysiology of nonparkinsonian tremors. Mov Disord, 17(Suppl 3), S41–​48. 70. Blomstedt, P., Sandvik, U., Fytagoridis, A., & Tisch, S. (2009). The posterior subthalamic area in the treatment of movement disorders: Past, present, and future. Neurosurgery, 64(6), 1029–​1038. 7 1. Mitrofanis, J. (2005). Some certainty for the “zone of uncer tainty”? Exploring the function of the zona incerta. Neuroscience, 130(1), 1–​1 5. 72. Plaha, P., Filipovic, S., & Gill, S. S. (2008). Induction of parkinsonian resting tremor by stimulation of the caudal zona incerta nucleus:  a clinical study. J Neurol Neurosurg Psychiatry, 79(5), 514–​521. 73. Plaha, P., Javed, S., Agombar, D., O’ Farrell, G., Khan, S., Whone, A., & Gill, S. (2011). Bilateral caudal zona incerta nucleus stimulation for essential tremor: outcome and quality of life. J Neurol Neurosurg Psychiatry, 82(8), 899–​904. 74. Lyons, K.  E., & Pahwa, R. (2008). Deep brain stimulation and tremor. Neurotherapeutics, 5(2), 331–​338. 75. Videnovic, A., & Metman, L.  V. (2008). Deep brain stimulation for Parkinson’s disease: prevalence of adverse events and need for standardized reporting. Mov Disord, 23(3), 343–​349. 76. Cummings, J. L., Henchcliffe, C., Schaier, S., Simuni, T., Waxman, A., & Kemp, P. (2011). The role of dopaminergic imaging in patients with symptoms of dopaminergic system neurodegeneration. Brain, 134(Pt 11), 3146–​3166. 77. De la Fuente-​Fernandez, R. (2012). Role of DaTSCAN and clinical diagnosis in Parkinson disease. Neurology, 78(10), 696–​701.

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10 | T HE NEUROBIOLOGY OF DYSTONIA H . A. J I N N A H, C E C IL IA N .   P R U D E N TE, SA MU EL J.   ROSE, A N D EL L EN J.   H ESS

D EF INITION Dystonia is a movement disorder characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive movements, postures, or both. Dystonic movements are typically patterned, twisting, and may be tremulous. Dystonia is often initiated or worsened by voluntary action and associated with overflow muscle activation. Related terms & synonyms:  dystonia, torsion dystonia, dystonia musculorum, torticollis, blepharospasm, writer’s cramp, musician’s dystonia, Meige syndrome, spasmodic dysphonia.

INTRODU CTION The dystonias are a group of disorders characterized by the core defect of over-​activity of muscles needed for movement. This overactivity emerges as excessive muscular force needed to generate a movement, extraneous activation of nearby muscles, and sometimes simultaneous activation of antagonistic muscles. The muscles involved determine the ultimate appearance of the abnormal movements. In its mildest forms, the dystonic movements appear as exaggerations of otherwise normal movement. In more severe forms, the movements appear stiff, cramped, or twisting. The most severe movements appear as fixed abnormal postures. A recent consensus committee provided the following formal definition for the dystonias1: Dystonia is a movement disorder characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive movements, postures, or both. Dystonic movements are typically patterned, twisting, and may be tremulous. Dystonia is often initiated or worsened by voluntary action and associated with overflow muscle activation.

review focuses on the biological basis for this heterogeneous group of disorders.

M O L ECU L AR AND B IOC HEM ICA L B ASIS F OR  DY STONIA A C Q U I R E D V E R S U S I N H E R I T E D PAT H W AY S

Multiple molecular mechanisms cause dystonia, both inherited and acquired. The best-​characterized acquired molecular causes of dystonia involve exposure to certain toxins or drugs. Toxins that can cause dystonia include 3-​ nitropropionic acid, carbon disulfide, carbon monoxide, cyanide, manganese, and others. These toxins most likely cause dystonia by damaging neural circuitry involved in the control of movement. Some medications may also cause dystonia as a side effect. The most commonly implicated drugs are dopamine receptor

TA BL E 10.1 . Classification of the Dystonias According

to Clinical Features DIMENSION FOR CLASSIFICATION

SUBGROUPS

Age at onset

Infancy (birth to 2 years) Childhood (3–​12 years) Adolescence (13–​20 years) Early adulthood (21–​40 years) Late adulthood (40 years and older)

Dystonic movements may emerge at any age, and in any region of the body. Some begin abruptly and remain static, others are progressive or intermittent. Dystonic movements may be slow and torsional, rapid and jerky, or semi-​rhythmical resembling oscillations associated with the tremor.2–​6 If dystonic movements are the only clinical problem, the disorder is called “isolated dystonia.” However, they often are combined with other neurological or medical problems, and then are called “combined dystonia.” These many different clinical manifestations of dystonic movements are classified according to four dimensions (Table 10.1) that include the age at onset, the region of the body affected, their temporal aspects, and whether they are combined with additional clinical problems.1 In addition to the many varied clinical appearances of dystonic movements, there also are many different etiologies.7 The many causes are grouped according to whether there is evidence for a genetic or acquired cause, and whether there is evidence for any overt neuropathological defects in the nervous system (Table 10.2). This 60 | Movement Disorders

Body distribution

Focal (one isolated region) Segmental (2 or more contiguous regions) Multifocal (2 or more noncontiguous regions) Hemidystonia (half the body) Generalized (trunk plus 2 other sites)

Temporal pattern

Disease course (static vs. progressive) Short-​term variation (persistent, action-​specific, diurnal, paroxysmal)

Associated features

Isolated (with or without tremor) Combined (with other neurological or systemic features)

TABLE 10.2 . Classification of the Dystonias According to Etiology DIMENSION FOR CLASSIFICATION

SUBGROUPS

Nervous system pathology

Degenerative Structural (typically static) No evidence for degenerative or structural lesions

Heritability

Inherited (autosomal dominant, autosomal recessive, mitochondrial, etc.) Acquired (brain injury, drugs/​toxins, vascular, neoplastic, etc.)

Idiopathic

Sporadic Familial

antagonists. In these cases, dystonia results from a functional disturbance of motor pathways, not overt structural pathology. Multiple genes also are linked with different types of dystonia.8,9 The majority of these genes are associated with combined dystonia syndromes in which dystonic movements are part of a more complex clinical disorder.7 A smaller number of genes are associated with isolated dystonia syndromes. All together, these genes involve diverse molecular pathways.9–​11 They affect numerous cellular processes including basic metabolism, cell growth and development, intracellular and intercellular signaling, the nucleus and nuclear envelope, the mitochondria and lysosomes, and cell survival. Basic concept

The broad array of molecular defects associated with dystonia means that there is no single biochemical pathway or cellular process that causes all forms of dystonia. However, it is likely that certain subgroups of the dystonias share a common biochemical or cellular pathogenesis, and that these different pathways converge onto a common final pathway to produce dystonic movement (Figure 10.1). In fact, the growing list of molecular defects associated with dystonia already has revealed several common themes. Identification of these common pathways is of great interest, because targeted interventions of shared pathways hold the greatest promise for developing novel therapies, regardless of the triggering molecular defect.12,13 Some of the most well-​recognized molecular and biochemical themes are summarized in the following text. D O PA M I N E S I G N A L I N G

The best evidence connecting abnormal dopamine signaling with dystonia comes from a group of disorders known as the dopa-​ responsive dystonias.14 These disorders are most often caused by mutations in genes required for dopamine biosynthesis. The most well known is the GCH1 gene that encodes the enzyme GTP-​ c yclohydrolase, which is associated with childhood-​ onset focal or generalized dystonia. This enzyme is required for the synthesis of tetrahydropterin, a cofactor needed by tyrosine hydroxylase in the synthesis of dopamine. In affected individuals, dystonic movements can be eliminated by administering levodopa, the precursor for dopamine. This observation illustrates that reduced dopamine may cause dystonic movements. Dystonia also occurs in several other disorders involving other steps in the synthesis of tetrahydropterin, or in the synthesis and metabolism of dopamine more directly. Included are defects in Dystonia

A

B

C

D

Etiology

Etiol 1 Etiol 2 Etiol 3

Etiol 1 Etiol 2 Etiol 3

Etiol 1 Etiol 2 Etiol 3

Molecular

Shared molecular pathway

Mol 1

Mol 3

Mol 1

Mol 2

Mol 3

Shared cellular pathway

Cell 1

Cell 2

Cell 3

Cellular

Mol 2

Shared anatomic pathway

Anatomic

Systems

Shared systems biology

Disorder

Dystonia

Figure 10.1  Shared biological pathways. Panel A shows the basic conceptual representation for the pathogenesis of any disease. Right: Concept applied to

dystonia, where different etiologies could converge onto a shared molecular pathology. Further, different molecular pathologies could converge on a common cellular and systems output, manifesting in dystonia. 

1 0 Th e N e u r o b i o l o gy o f D y s t o n i a | 61

sepiapterin reductase, pyruvoyl-​tetrahydropterin synthase, tyrosine hydroxylase, aromatic amino acid decarboxylase, the vesicular monoamine transporter, and the dopamine reuptake transporter (Figure 10.2). In these disorders, dystonia is typically combined with additional neurological features, which presumably result from simultaneous dysfunction of other monoamine pathways. Dopamine dysfunction also is implicated in dystonic disorders that are indirectly associated with dopamine signalling. Mutations in GNAL, which encodes a G-​protein involved in dopamine receptor signaling, are associated with adult-​onset focal and segmental dystonia.15,16 Individuals with mutations in the HPRT1 gene encoding the purine recycling enzyme hypoxanthine-​guanine phosphoribosyltransferase have severe generalized dystonia combined with other clinical features in Lesch-​Nyhan disease.17–​19 The dystonia in this disorder is associated with developmental dysfunction of nigrostriatal dopamine pathways.20 Patients with dystonia due to mutations in the TOR1A gene encoding torsinA causing DYT1 dystonia exhibit subtle morphological changes in nigrostriatal dopamine neurons,21 an abnormality that has been replicated in the associated knock-​in

GTP GCH-1 PTPS SPR

DAT

DHPR PCD

Tyrosine TH

D2DAR

L-DOPA AADC Dopamine VMAT2

mouse model.22 Mouse models for DYT1 dystonia also show a prominent defect in dopamine release.22–​24 Dystonic movements may also occur in Parkinson disease, a disorder caused by degeneration of dopamine neurons.25–​30 The dystonic movements typically occur in two different situations. First, approximately 15% of patients with Parkinson disease may present with dystonic posturing of an arm or leg, especially when the disorder emerges before 40  years of age.28 More commonly, dystonic movements emerge later in the course of the disease, as a complication of treatment with levodopa. Here, dystonic movements tend to occur when dopamine levels wane at the end of a dose cycle.26,29,31 Dystonic movements associated with dopamine neuron loss also can be seen in nonhuman primates exposed to the neurotoxin, MPTP.32,33 Dystonic movements sometimes occur in response to dopamine receptor antagonists34 as an acute reaction to a recent dose (acute dystonic reaction), or as a long-​term consequence of chronic therapy (tardive dystonia). Other evidence implicating dopamine pathways in dystonia comes from positron emission tomography studies of different types of dystonia, which have revealed decrements in D2-​ like dopamine receptors.35,36 Recent imaging studies also have shown abnormally low dopamine release in spasmodic dysphonia37 or writer’s cramp.38 Some studies have linked blepharospasm or cervical dystonia with the genes encoding dopamine receptors,39–​41 although this relationship has been questioned.42,43 The exact mechanisms by which abnormal dopamine signaling cause dystonia remain unclear.44 In some cases the mechanism appears to involve insufficient dopamine signaling. Thus dystonic movements can be eliminated with levodopa in patients with classic dopa-​responsive dystonia and Parkinson disease. However, low dopamine levels cannot explain all cases, because levodopa is not always effective. Disorders not responsive to levodopa include some patients with defects in proteins involved in dopamine metabolism, Lesch-​ Nyhan disease, patients with mutations in TOR1A or GNAL, tardive dystonia, spasmodic dysphonia, and writer’s cramp. In these disorders, there may be some additional pathogenic process, or early dopamine loss may trigger maladaptive plastic changes in the brain that cannot be readily reversed by replacing dopamine. ION CHANNELS AND ION HANDLING

D1DAR

D2DAR GNAL

Figure 10.2  Dopamine dysfunction in dystonia. The schematic shows a typical

dopamine synapse with the pathways for dopamine synthesis and metabolism. Both presynaptic and postsynaptic mechanisms are known. Genes that play a role in dopamine synthesis and transport and implicated in dystonia are depicted in red. GTP-​cyclohydrolase 1 (GCH1), 6-​pyrovoyl-​tetrahydrobiopterin synthase (PTPS), and sepiapterin reductase (SPR) are necessary for synthesizing the tyrosine hydroxylase (TH) cofactor tetrahydropterin (BH4). Dihydropteridine reductase (DHPR) and pterin-​4α-​carbinolamine dehydrate (PCD) are involved in BH4 recycling. TH converts tyrosine to levodopa (L-​DOPA). Aromatic acid decarboxylase (AADC) converts L-​DOPA to dopamine. The vesicular monoamine transporter-​2 (VMAT2) packages dopamine into synaptic vesicles and the dopamine transporter (DAT) clears dopamine from the synaptic cleft. 

62 | M o v e m e n t D i s o r d e r s

Disruption of ion transport also appears to be a shared molecular theme in dystonia, although the disorders are different from those involved in dopamine signaling. Most notably, abnormal calcium homeostasis is implicated in dystonic patients and animal models of dystonia. First, dystonia is an occasional feature of episodic ataxia type 2 and spinocerebellar ataxia type 6 in humans. These disorders are caused by mutations in the CACNA1A gene, which encodes the pore forming α1 subunit of the Cav2.1 (P/​Q-​type) voltage-​gated calcium channel.45 Though cerebellar ataxia is the dominant phenotype of these disorders, the presence of dystonia in many patients establishes a role for Cav2.1 channel function in dystonia too.46 Dystonic movements are even more prevalent in mutant mice with different mutations in the Cacna1a gene including the tottering, leaner, rocker, and engineered knock-​out lines.47 Other inherited disorders further implicate dysfunction of transport of other ions. For instance, mutations in ATP1A3 gene encoding the α3 subunit of the Na+-​K+-​ATPase cause rapid-​onset dystonia-​ parkinsonism.48 Additionally, mutations in ANO3, encoding anoctamin 3, cause tremor-​dominant cervical dystonia. This protein is believed to act as a calcium-​gated chloride channel.49 Whether these perturbations to ion transport converge on a common brain region or neurochemical system is still not known, though work from several animal models has implicated abnormal cerebellar signaling.50–​52

T R A N S P O R T A N D M E TA B O L I S M O F   H E AV Y   M E TA L S

Another theme that spans several unrelated dystonias involves the processing of heavy metals. The best recognized is Wilson’s disease, which involves the uptake and transport of copper.53 Affected patients suffer toxicity due to copper accumulation. Also well recognized is a group of disorders known as neurodegeneration with brain iron accumulation.54 Most recently, dystonia has been linked with mutations in the SLC30A10 gene, which encodes a manganese transporter, leading to manganese accumulation.55 For all of these disorders, toxicity from excess accumulation of heavy metals causes symptoms. For reasons that are not entirely understood, the basal ganglia appear to be particularly vulnerable, with pathology often visible using structural imaging of the brain. Thus this common molecular theme may share a causal mechanism that involves toxic degeneration of a specific brain region.

Controls

Writer’s cramp

Figure 10.3  Neuroimaging of human dystonia. This is an example of an

MITOCHONDRIAL DYSFUNCTION A N D E N E R G Y M E TA B O L I S M

Another shared theme is mitochondrial dysfunction.56 Dystonia occurs in inherited disorders affecting mitochondria such as Leber’s optic neuropathy, Leigh’s syndrome, the Mohr-​Tranebjaerg dystonia-​ deafness syndrome, or defects in mitochondrial polymerase gamma. In most cases, dystonia is generalized and accompanied by other neurological defects.7 In other cases, dystonia is the initial problem,57,58 the main problem,59,60 or limited to one part of the body.60–​63 In addition to inherited diseases, dystonia is a prominent feature following exposure to the mitochondrial toxin 3-​nitroproionic acid in children64 and nonhuman primates.65 Subtle defects in mitochondrial complex I have also been reported for adult-​onset isolated focal dystonias.66,67 The mechanisms responsible for dystonia due to mitochondrial dysfunction are not known. In some cases, there is overt pathology of the basal ganglia. Other cases without overt pathology may involve energy limitation, because dystonia also is observed in other disorders that influence energy production. Examples include pyruvate decarboxylase deficiency, glutaric aciduria, and mutations affecting the GLUT1-​encoded glucose transporter.68–​70

ANATOMICA L BASIS F OR  D Y STONIA A fundamental question for any neurological disorder is: What region of the nervous system is responsible for the problem? Knowing the anatomical basis for dystonia is a prerequisite for guiding molecular or cellular studies, and for developing novel medical or surgical interventions targeting the relevant regions. Surprisingly, the areas of the nervous system responsible for dystonia have not yet been entirely worked out.71,72 More than one region may be responsible. BASAL GANGLIA

Strong evidence links dystonia with dysfunction of the basal ganglia and its connections.73–​75 The basal ganglia are the most commonly implicated areas in autopsy studies of acquired dystonias.76,77 In structural neuroimaging studies, lesions in individuals with dystonia are most commonly found in the basal ganglia or its connections.78–​81 Even when overt structural abnormalities are absent, subtle structural abnormalities of the basal ganglia can be found using voxel based morphometry or diffusion tensor imaging, or functional abnormalities can be found via positron emission tomography (PET) or functional MRI

fMRI-​related blood oxygen level-​dependent (BOLD) signal in the brains of healthy controls (N = 17) and individuals with writer’s cramp (N = 17) during tactile stimulation of the right index finger. As is often the case with other forms of dystonia, the individuals with writer’s cramp showed broader bilateral increases in task-​related activity in many regions of the cerebral cortex (visual cortical areas, anterior insula, intraparietal sulcus), basal ganglia (putamen, caudate nucleus, internal globus pallidus), cerebellum (hemispheres, posterior vermis, deep nuclei), and thalamus. This figure was modified from Peller, M., et al. (2006). The basal ganglia are hyperactive during the discrimination of tactile stimuli in writer’s cramp. Brain, 129, 2697–​2708.

(fMRI).71,72,82 An example of a PET study showing multiple regions of abnormality in writer’s cramp is shown in Figure 10.3. Additional evidence implicating the basal ganglia has been provided by functional studies. Neurosurgical interventions demonstrate that dystonia improves following lesions or deep brain stimulation of the internal segment of the globus pallidus.83–​85 Furthermore, physiological recordings during surgery for deep brain stimulation have suggested altered neuronal activity in the basal ganglia.86,87 The link between dopamine function and certain forms of dystonia further implicates the basal ganglia in dystonia. Rodent and primate studies have shown that lesions and pharmacological manipulations of the basal ganglia can induce dystonia.88–​92 Chronic administration of levodopa also causes dystonic and other dyskinetic movements in nonhuman primates treated with MPTP93,94 or rodents treated with 6-​hydroxydopamine.95,96 CEREBELLUM

Similar evidence links dystonia with dysfunction of the cerebellum.71,97–​100 Autopsy studies in cervical dystonia have suggested that subtle abnormalities in cerebellar Purkinje cells may be associated with dystonia,101,102 and structural neuroimaging studies have linked different dystonias with abnormalities of cerebellar circuits.71,103,104 Furthermore, tumors of the posterior fossa that impinge on the cerebellum are sometimes associated with cervical dystonia.105–​107 Functional imaging studies of both acquired and inherited forms of dystonia have repeatedly revealed abnormalities in the cerebellum and its connections.72,108–​113 These cerebellar abnormalities originally were interpreted as secondary compensatory changes to causal pathology in the basal ganglia, but more recent reinterpretations suggest the cerebellar abnormalities may sometimes be causal.108,114 Functional studies also implicate the cerebellum. For example, this region has been implicated by neurosurgical interventions 1 0 Th e N e u r o b i o l o gy o f D y s t o n i a | 63

involving dentatectomy115,116 or deep brain stimulation of regions of the thalamus receiving cerebellar afferents.117–​120 Human physiological studies also have revealed several abnormalities in functions intrinsic to the cerebellum, such as eyeblink conditioning, saccadic adaptation, and movement time estimation.97,121,122 The best evidence implicating the cerebellum in dystonia comes from animal studies.50,52,71,123–​129 Generalized dystonia in the dt mutant rat arises from abnormal Purkinje neuron output, and removal of this aberrant output eliminates dystonia.125,126 Paroxysmal dystonia in tottering mutant mice similarly arises from dysfunctional Purkinje neurons and surgical removal of the cerebellum or selective genetic deletion of cerebellar Purkinje neurons eliminates their dystonia.50,130–​ 132 Furthermore, pharmacological stimulation of the cerebellum can induce dystonic movements even in normal mice.51,128,129 OTHER REGIONS

Several other regions of the nervous system also have been implicated in dystonia. The thalamus has been implicated in dystonia by lesion and neuroimaging studies71,72,112 and neurosurgical studies that target the thalamus with lesions or deep brain stimulation.117–​119 Considering that the thalamus serves as a relay for signals from the basal ganglia or cerebellum to the cerebral cortex, abnormalities of the thalamus are not surprising. Several cortical areas have been linked with dystonia including the primary motor cortex, premotor cortex, supplementary motor area, cingulate gyrus, and primary somatosensory area.71,72,112 Interestingly, the primary somatosensory cortex is frequently involved, and there are several reports of patients with dystonia due to isolated lesions of the parietal cortex.104,133–​138 One study surveying neurological problems in 32 patients with isolated parietal strokes reported dystonia in 84%.139 Involvement of the sensory and parietal cortex may be attributed to faulty processing of sensory information or distortion of body perception. Dysfunction of the midbrain and brainstem also has been associated with dystonia in neuropathological, imaging and physiological studies.71 Additionally, experimental manipulations of various midbrain or brainstem areas can induce abnormal movements resembling dystonia in animals.140–​145 It is important to note, however, that abnormalities in these regions can present a challenge for interpreting the functional anatomy of dystonia because of the close proximity of multiple nuclei and fibers of passage. Finally, some forms of dystonia also have been associated with abnormalities of the spinal cord103,105 or peripheral nerves.146 The mechanism may involve disruption of sensory feedback from muscles to the brain or distortion of signals from the brain to the muscles.

(A) Normal

THE NETWORK MODEL

In view of evidence pointing to several regions of the nervous system, dystonia is viewed as a network disorder rather than one linked with pathology of a single region.71,100 The network model posits that dysfunction of different regions or “nodes” in the network may cause dystonia. Alternatively, dystonia may arise from combined dysfunction of multiple nodes, or from aberrant communication between them (Figure 10.4). Which of these possibilities best applies to dystonia remains unclear, and there is evidence that supports each. Observations from clinical and animal studies indicating that dystonia may arise from focal lesions or manipulations of the basal ganglia or cerebellum support the idea that dysfunction of a single node can cause dystonia. These observations imply that different types of dystonia do not always share the same neuroanatomical pathogenesis, a fact that may explain some of the heterogeneity of clinical manifestations. There also is evidence that dystonia may result from simultaneous dysfunction of more than one node. An example is the two-​hit rat model for blepharospasm. combining partial injury to nigral neurons with partial injury to the nerve to the orbicularis oculi muscles results in blepharospasm, when neither abnormality alone is sufficient.147 Other studies have shown that subclinical lesions of the basal ganglia exacerbate dystonia in rodent models in which dystonia is triggered by cerebellar dysfunction.52,131 Furthermore, evidence in rodents and nonhuman primates demonstrate that the basal ganglia and cerebellum are anatomically interconnected,148,149 providing pathways whereby the function/​dysfunction of one region may influence another region. The idea that dystonia is a network disorder provides a broad conceptual paradigm that accommodates results from prior clinical and animal studies that have pointed either to the basal ganglia, cerebellum, or other regions. Future research must focus on the neurobiological defects that occur in different regions, and whether some of the differences in the clinical expression of dystonia can be explained by differences in the anatomical substrates. A  better understanding of these issues is critical for targeting new therapies to appropriate clinical populations based on different anatomical and physiological causes.

P HY SIO L O G ICAL B ASIS F OR   DY STONIA The core functional defect underlying all forms of dystonia is excessive muscle contraction. This excess contraction is not due to

(B) Independent nodes

normal movements

dystonia

(C) Communication

dystonia

dystonia

(D) Two-hit hypothesis

dystonia

Figure 10.4  The network model for dystonia. Normal movements are known to require integrated function of distinct motor systems including the motor cortex,

basal ganglia, cerebellum, and brainstem (A). Dystonia may arise from dysfunction of one, or another node in the network (B). Dystonia may alternatively require abnormal communication between nodes (C), or dysfunction of more than one node (D). The source of dysfunction in any part of the network is depicted red. Downstream effects from the initial dysfunction are represented in gray. 

64 | M o v e m e n t D i s o r d e r s

autonomous muscle activity as it is in myotonia, or to autonomous motor neuron activity as it is in neurotonia. In dystonia, excess muscle contraction arises primarily from abnormal signals in central nervous system. The core physiological defects causing dystonia remain unclear, but many studies of multiple different types of dystonia have repeatedly identified three common themes. They include loss of inhibition, abnormal sensorimotor integration, and maladaptive plasticity.74,150 LOSS OF INHIBITION

One common physiological finding in dystonia involves a change in the balance between inhibitory and excitatory processes, in favor of excitation.151 A loss of inhibition has been documented for many different types of dystonia including childhood-​onset generalized dystonias and adult-​onset focal dystonias. A loss of inhibition also has been observed at multiple levels of the nervous system including the spinal cord,152,153 brainstem,154 and cerebral cortex.155 The occurrence of this physiological abnormality across so many different types of dystonia and different levels of the nervous system has led to belief that it is a core physiological defect underlying dystonia. The loss of inhibition provides an intuitive mechanism to explain the excessive contraction of muscles in dystonia. A  loss of “surround inhibition” also provides an intuitive explanation for spread of contractions to nearby and even antagonistic muscles.156 Although loss of inhibitory processes is a common finding, whether it plays a causal role in dystonia remains unclear. Loss of inhibition has been documented also for other neurological disorders such as Parkinson disease and stroke, as well as pseudo-​dystonic movements in psychiatric conversion disorders.157,158 These findings have raised the possibility that loss of inhibition is a nonspecific consequence of motor dysfunction, rather than a cause, so further studies are needed.

ABNORMAL SENSORIMOTOR I N T E G R AT I O N

Another common physiological finding in dystonia involves abnormal sensory thresholds, or impaired central processing of sensory information.159,160 These abnormalities again have been documented using many different experimental paradigms across many different types of dystonia. For example, patients with different types of dystonia display abnormal somatosensory thresholds for both spatial161 and temporal162 discrimination tasks. There also is strong evidence showing abnormal proprioceptive feedback in different types of dystonia.163–​165 Cortical sensorimotor maps are often enlarged and distorted in dystonia,166,167 and affected patients display abnormalities of perception regarding the positioning of body parts in space.168,169 Abnormalities of sensorimotor integration also provide an intuitively attractive physiological mechanism to explain dystonia. From an engineering perspective, all motor control systems must have some mechanism to provide feedback regarding a motor command, to ensure it is executed properly. Without this feedback, errors cannot be corrected. With incorrect feedback, motor control centers are likely to attempt to make corrections that are not appropriate, causing the intended movement to be abnormal. Although abnormalities in sensory feedback or sensorimotor integration are common in dystonia, whether they are a cause or consequence is not yet firmly established. Altered sensory discrimination thresholds and cortical sensory or motor maps also occur in other motor disorders, and even after intensive training or exercise.170–​172 These findings raise the possibility that they may be a consequence of dystonia, not a cause.

MALADAPTIVE PLASTICITY

Neural plasticity refers to the ability of the nervous system to modify the effectiveness of neural transmission. It underlies many aspects of nervous system function, such as learning and memory. The changes may reflect alterations in the strength of existing synapses, modifications to neuronal excitability, formation of new synapses, or even remodeling of axonal and dendritic connectivity. Plasticity is nearly always regarded as a useful function, but maladaptive plasticity refers to abnormal plastic mechanisms that lead to counterproductive outcomes. A number of noninvasive physiological measures have demonstrated that plasticity is abnormal in individuals with many different types of dystonia.150,173 Maladaptive plasticity is not seen among patients with pseudo-​dystonic movements due to psychiatric disorders, making it less likely that it is a consequence of the movements.158 Maladaptive plasticity also provides an intuitively attractive physiological mechanism to explain many types of dystonia, particularly those that result from repetitive movements, such as writing, or intensive training, such as musician’s dystonia. It seems feasible that highly repetitive movements may induce plastic changes that are not beneficial. Although this mechanism may be relevant to task-​specific dystonias, it is not clear that it is relevant to other forms of dystonia that do not involve highly repetitive movements.174 I N T E G R AT I N G S H A R E D PHYSIOLOGICAL THEMES

Which of the three common themes is most important in the physiology of human dystonia remains unclear. Different physiological processes may be more relevant for different types of dystonia, or combined defects may be required to cause dystonia. These themes also may not be independent. For example, a loss of inhibitory processes may contribute to defects in sensorimotor integration or maladaptive plasticity. There are several important related areas for future research. One involves delineating the relevance of the physiological abnormalities in different types of dystonia. Another involves determining the anatomical regions responsible for generating these physiological abnormalities.150 Finally, it would be useful to build a more complete picture of how specific molecular insults may alter neuronal processing in the responsible brain regions. The three common themes in the physiology of human dystonia have been explored largely through indirect and non-​invasive methods, such as transcranial magnetic stimulation. Studies in animals have permitted a more direct window to neurophysiological changes, even at the single cell level. Multiple studies of DYT1 mouse models have revealed abnormal physiological interactions in corticostriatal glutamatergic, nigrostriatal, and striatal intrinsic cholinergic pathways.22,23,175–​180 Other studies of the tottering mutant mouse and rapid-​onset dystonia parkinsonism have implicated abnormal activity of cerebellar Purkinje neurons.50,52,128,181,182 Here again, the relationships among these findings remain unexplored. Also unexplored is how these findings may relate to the themes uncovered in affected humans using more indirect methods. More importantly, deciphering causal abnormalities from secondary changes has been challenging, because abnormalities in one region of the network can be transmitted to other regions131

E X P ERIM ENTAL M O DE L S F OR   DY STONIA RESEARCH Direct studies of human subjects have provided enormous amounts of information regarding the molecular, anatomical, 1 0 Th e N e u r o b i o l o gy o f D y s t o n i a | 65

TAB L E   10. 3 . Criteria for Useful Animal Models

SIMPLE MODELS

for Dystonia

A major advantage of mammalian cell culture models is the ability to examine the consequences of specific manipulations in a precisely controlled environment. Multiple cell culture models have been developed to explore the cellular pathogenesis of specific molecular triggers known to cause dystonia. Invertebrate models involving the roundworm (Caenor­habditis elegans) and the fruit fly (Drosophila melanogaster) have been developed for DYT1 dystonia, dopa-​responsive dystonia, and rapid-​onset dystonia-​parkinsonism.183 These relatively simple models have been useful for exploring the pathogenesis of known genetic causes for dystonia.

RELIABILITY

THE MODEL PROVIDES CONSISTENT RESULTS

Validity

face validity

The model exhibits a motor syndrome that meets typical criteria used to define dystonia in humans.

etiologic validity

The model was derived from a cause known to cause dystonia in humans.

predictive validity

The model predicts a key feature of human dystonia, such as treatment response.

P R I M AT E   M O D E L S

and physiological basis for dystonia. However, many experiments needed to elucidate the pathogenesis of dystonia cannot be performed with human subjects. As a result, surrogate experimental models are important in dystonia research. It often is incorrectly believed that a good experimental model must replicate all features of the human disease, from original cause to clinical manifestations. In reality, experimental models are judged instead by their reliability and validity (Table 10.3). Reliability refers to the ability of the model to generate reproducible results under different conditions. Validity is established in three different ways. Models with etiological validity are based on a cause known to provoke dystonia in humans. Examples include cell or animal models with a specific gene defect known to cause dystonia in humans. Models with face validity must have a movement disorder that resembles a specific type of dystonia. Examples here include primates or rodents with overt dystonic movements (Figure 10.5). Models with predictive validity reproduce an outcome in humans with dystonia, such as response to treatment.

A

B

Nonhuman primate models are attractive because their motor behavior and nervous systems resemble those of humans. Dystonia has been reported with a variety of manipulations in a number of different primate species.90 Some examples are listed in Table 10.4. For example, dystonic limb movements have been reported following lesions or transient pharmacological inactivation of the posterior putamen184 or the internal segment of the globus pallidus.185 Similarly, abnormal movements of the head and neck resembling cervical dystonia have been reported following manipulations of different areas in the midbrain.140,141,186,187 Dystonic movements also have been reported following exposure to the toxins MPTP,32,33,94 manganese,188 and 3-​nitropropionic acid.65 A model of focal hand dystonia was described in owl monkeys trained to perform a task involving opening and closing the hand.189 The monkeys performed up to 3,000 cycles in training periods lasting up to 2 hours. After 5 weeks, three of four monkeys were reported to develop abnormal movements resembling hand dystonia. This paradigm is suggestive of task-​specific dystonias that develop in humans following over-​use.

C

D

E

Figure 10.5  Some examples of dystonic movements in different species. Panel A shows extreme lateral tilting of the head resembling human torticollis induced by

electrolytic lesion of the brainstem reticular formation in a rhesus monkey, modified from the original report.186 Panel B shows lateral tilting of the head induced by injection of kainic acid into the right mesencephalic tegmental of a cat.187 Abnormal dystonic postures in rodents include an example of the dt sz hamster,193 the dt rat,123 and a mouse following injection of kainic acid into the cerebellum.123 

66 | M o v e m e n t D i s o r d e r s

F

ERENCES

YP

RE

PH

E

M

ENOT

PUL

OTOR

M

ATION

D

ANI

S

R

G

ETE

TAR

 S

S

G

ION

RE

P

ome Primate tudies eported to  how Dystonic Movements

ECIES

S

TAB L E   10. 4 .

red nucleus

electrolytic lesion

torticollis

194

Macaca mulatta

reticular formation

electrolytic lesion

torticollis

186

Macaca mulatta, Theropithecus gelada, Pan troglodytes

vestibular nuclei

physical lesion

torticollis, nystagmus

195

Macaca mulatta

tegmentum

electrolytic lesion

torticollis

187

Macaca fascicularis

substantia nigra, striatum

MPTP, L-DOPA

dystonia

196

Saimiri sciureus

substantia nigra, striatum

MPTP, L-DOPA

generalized dystonia, chorea

32

Macaca mulatta

globus pallidus, dentate nucleus

kainic acid, muscimol

limb dystonia

185

Macaca mulatta, Macaca fuscata

motor cortex

bicuculline, muscimol

limb dystonia

197

Aotus nancimaae

not applicable

repetitive hand tasks

limb dystonia

189, 198, 199

Macaca mulatta

striatum

quinolinic acid, apomorphine

dystonia and dyskinesia

184

Callithrix Jacchus

substantia nigra, striatum

MPTP, L-DOPA

trunk and limb dystonia

93

Macaca mulatta

globus pallidus, substantia nigra

manganese chloride

bradykinesia, rigidity, facial dystonia

188

Papio anubis

substantia nigra, striatum

MPTP

transient dystonia

33

Macaca fascicularis

substantia nigra, globus pallidus

bicuculline, muscimol

torticollis, limb dystonia

92

Macaca mulatta

thalamus

bicuculline

tonic or myoclonic dystonia

200

Cebus apella

striatum

3NPA

generalized dystonia

65

Macaca fascicularis

thalamus

bicuculline

tonic or myoclonic dystonia

201

Macaca fascicularis, Macaca mulata

interstitial nucleus of Cajal

muscimol

torticollis

140, 202

Macaca nemestrina, Macaca fascicularis

substantia nigra, striatum

MPTP

transient dystonia, Parkinsonism

94

Macaca mulata

striatum

3NPA

limb dystonia

203

Macaca nemestrina

substantia nigra

bicuculline, muscimol

torticollis

88

​

​

​

Macaca mulatta

​

​

​

​

D s t o n i a | 67 y

o

f

gy

ro io o l

e

b

e

u

10

N

Because of technical challenges and costs inherent in working with nonhuman primates, most research has focused on rodent models.89,91,190,191 The ability to manipulate genes and study large numbers of animals under different conditions has made it feasible to explore many issues that are not readily studied in primate models.

The rodent models can be divided into two broad categories. First are the etiological models, which are based on an established cause for human dystonia, and therefore have etiological validity. These models have been useful for exploring the biological consequences of known causes for dystonia, but they rarely exhibit dystonic movements (Table 10.5). Second are the phenotypic models, which exhibit abnormal movements resembling dystonia and

Th

RODENT MODELS

​

​

​

​

​

The term torticollis, which literally means twisted neck, historically was used often as a synonym for cervical dystonia. Abbreviations: 3NPA, 3-nitropropionic acid; L-DOPA, L-3,4-dihydroxyphenylalanine; MPTP, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine.

F

ERENCES

RE

E

YP

ENOT

L PH

AVIORA

B H E

D

ISEASE

HUM

AN

P

R

E

 S

ome tiological odent Models for Dystonia ROTEIN

G

ENE

TAB L E   10. 5 .

ATM

ATM

ataxia telangiectasia

supersensitive to amphetamine; stride length asymmetry

205

ATP1A3

α3 subunit of Na+-K+-ATPase

rapid-onset dystonia parkinsonism

Stress-induced motor coordination abnormalities

206

ATP7B

copper ATPase

Wilson disease

none reported

207

ATXN3

ataxin-3

Machado-Joseph disease

gait abnormalities, hypotonia, tremor, hypoactivity

208, 209

GCDH

glutaryl-CoA dehydrogenase

glutaric acidemia

diet-induced abnormal movements

210

GCH1

GTP cyclohydrolase

DOPA-responsive dystonia (DYT5a)

wasting syndrome after phenylalanine challenge

211

HD

huntingtin

Huntington disease

age-dependent hypoactivity or hyperactivity, tremor, and dyskinesias

212, 213

HPRT

hypoxanthine phosphoribosyl transferase

Lesch-Nyhan disease

amphetamine supersensitivity

214, 215

NPC1

NPC1 (endosomal cholesterol transporter)

Niemann-Pick C

hypoactivity, abnormal habituation, poor coordination, tremor, abnormal gait

216, 217

PARKIN

parkin

Parkinson disease

impaired beam walking

218

PNKD

pnkd protein

paroxysmal dyskinesias

caffeine-induced paroxysmal dyskinesias

219

PLP

proteolipid protein

Pelizaeus-Merzbacher disease

tremor

220, 221

PPT1

palmitoyl protein thioesterase

infantile neuronal ceroid lipofuscinosis

myoclonic jerks, hindlimb paralysis, seizures

222

PTPS

6-pyruvoyl-tetrahydrobiopterin synthase

dopa-responsive dystonia

hindlimb clasping

223

SGCE

epsilon sarcoglycan

Myoclonus dystonia (DYT11)

myoclonus, impaired beam walking

224

SNCA

alpha-synuclein

Parkinson disease

rigidity, dystonia, hindlimb freezing, loss of righting reflex, paralysis

225–227

TH

tyrosine hydroxylase

DOPA-responsive dystonia (DYT5b)

mild to marked hypoactivity, ptosis

228

TOR1A

torsin A

Oppenheim’s dystonia (DYT1)

subtle motor coordination deficits

191

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

204

​

abnormal rotarod performance and progressive ataxia

​

metachromatic leukodystrophy

​

arylsulfatase A

​

ASA

ent Disor

d

68 | M o v e

m

ers

LU

SIONS

D

CONC

Y

AN

UMM

AR

therefore have face validity (Table 10.6). These models have been useful for exploring the biological basis for dystonic movement, even though they may not have a precisely matched human counterpart. Studies of these models have been extremely useful for exploring the neurobiology of dystonia at the cellular, anatomical, physiological, pharmacological, and behavioral levels. Several of these findings have been described in the relevant sections earlier.

S

This table summarizes some of the mouse models of dystonia that were created by introducing a defect in a gene known to result in dystonic movements in humans. These models therefore have etiological validity, even though many do not exhibit overt dystonic movements.

The dystonias are a group of heterogeneous disorders defined by peculiar abnormal movements that are caused by excessive muscle activity originating from abnormal motor programming in the central nervous system. Although there are many different triggers, both inherited and acquired, it is likely that they produce similar defects in motor control through common molecular, anatomical, or

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ome maller Mammals eported to Have Dystonic Movements

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TAB L E   10. 6 .

rat

6OHDA lesion of nigrostriatal pathway and partial facial nerve lesion

phenotypic

sustained partial eyelid closure, increased blink rate, occasional spasms

147

cervical dystonia

cat

electrical stimulation, kainic acid, or 6OHDA in midbrain

phenotypic

sustained abnormal head/neck postures

187, 229

cervical dystonia

cat

bicuculline in putamen

phenotypic

sustained abnormal head/neck postures

230

cervical dystonia

cat

electrical stimulation of globus pallidus

phenotypic

sustained abnormal head/neck postures

231

cervical dystonia

rat

sigma receptor ligand in red nucleus

phenotypic

abnormal head/neck postures and occasionally the trunk and limbs

142, 232

dystonic cerebral palsy

rabbit

uterine ischemia during pregnancy

etiologic, phenotypic

motor impairments with increased tone suggestive of dystonia plus spasticity

233

focal dystonias

mouse

electrical stimulation or kainic acid injection into cerebellum

phenotypic

sustained but reversible abnormal postures of the trunk, limbs, neck or face

51

generalized dystonia

mouse

leaner mutant or knockout of Cacna1a gene

etiologic, phenotypic

sustained twisting and abnormal postures of entire body, ataxia

234

generalized dystonia

mouse

dystonia musculorum mutant (Bpag1 gene)

phenotypic

sustained twisting and abnormal postures of entire body

235, 236

generalized dystonia

mouse

MedJ mutant (Scna8 gene)

phenotypic

action-induced transient twisting movements of the trunk or limbs

237

generalized dystonia

rat

dt mutant model (Atcay gene)

phenotypic

sustained twisting and abnormal postures of entire body

124, 238

generalized dystonia

mouse or rat

systemic BayK 8644 injection

phenotypic

bradykinesia, akinesia, sustained but transient twisting movements and abnormal postures

239

generalized dystonia

mouse or rat

electrical stimulation or kainic acid injection into cerebellum

phenotypic

sustained but reversible abnormal postures of the trunk, limbs, neck and face

51, 127, 129

Huntington disease

mouse or rat

systemic or striatal 3NPA injection

etiologic, phenotypic

bradykinesia, akinesia, and progressive irreversible abnormal postures of the trunk and hind limbs

240

paroxysmal dystonia

mouse

tottering or rocker mutants of (Cacna1a gene)

phenotypic

attacks of transient twisting or 47 abnormal postures of the trunk, neck, limbs and/or face

paroxysmal dystonia

hamster

unknown gene

phenotypic

attacks of transient twisting or 241 abnormal postures of the trunk, neck, limbs and/or face

rapid onset dystonia-parkinsonism

rat

ouabain infusion into cerebellum

etiologic, phenotypic

bradykinesia, akinesia, abnormal trunk and limb postures

52

truncal dystonia

mouse

opisthtonus mutant (iptr1 gene)

phenotypic

severe truncal arching

242

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blepharospasm

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This table summarizes several of the small animal models described to have dystonic movements. These models may have face validity, depending on how well the motor phenotype was characterized. Some also have etiologic validity because they involve a trigger known to cause dystonia in humans. Abbreviations: 6OHDA, 6-hydroxydopamine; 3NPA, 3-nitropropionic acid.

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Our work in dystonia has been supported in part by grants from private foundations including the Bachmann-Strauss DystoniaParkinson Foundation, the Benign Essential Blepharospasm Research Foundation, Cure Dystonia Now, Dystonia Medical Research Foundation, and Tyler’s Hope for a Cure. It also has been supported in part by research grants from the NIH (U54 NS065701 and TR000146, R01 NS040470, R01 033592, R01 HD 053312) and Emory University Research Council grant UL1 RR025008.



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physiological mechanisms. Delineating these shared mechanisms is important for understanding how so many different causes can provoke a similar motor phenotype, and for identifying the most fruitful targets for therapeutic interventions.

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154. Berardelli, A., et al. (1985). Pathophysiology of blepharospasm and oromandibular dystonia. Brain, 108, 593–608. 155. Ridding, M. C., et al. (1995). Changes in the balance between motor cortical excitation and inhibition in focal, task specific dystonia. J Neurol Neurosurg Psychiatry, 59, 493–498. 156. Sohn, Y. H., & Hallett, M. (2004). Disturbed surround inhibition in focal hand dystonia. Ann Neurol, 56, 595–599. 157. Espay, A. J., et al. (2006). Cortical and spinal abnormalities in psychogenic dystonia. Ann Neurol, 59, 825–834. 158. Quartarone, A., et  al. (2009). Abnormal sensorimotor plasticity in organic but not in psychogenic dystonia. Brain, 132, 2871–2877. 159. Tinazzi, M., et  al. (2009). Sensory functions in dystonia: insights from behavioral studies. Mov Disord, 2009. 24, 1427–1436. 160. Patel, N., Jankovic, J., & Hallett, M. (2014). Sensory aspects of movement disorders. Lancet Neurol, 13, 100–112. 161. Molloy, F.  M., et  al. (2003). Abnormalities of spatial discrimination in focal and generalized dystonia. Brain, 126, 2175–2182. 162. Bradley, D., et al. (2009). Temporal discrimination threshold: VBM evidence for an endophenotype in adult onset primary torsion dystonia. Brain, 132, 2327–2335. 163. Bove, M., et  al. (2004). Neck proprioception and spatial orientation in cervical dystonia. Brain, 127, 2764–2778. 164. Kaji, R., et al. (1995). Tonic vibration reflex and muscle afferent block in writer’s cramp. Ann Neurol, 38, 155–162. 165. Shaikh, A. G., et al. (2013). Keeping your head on target. J Neurosci, 33, 11281–11295. 166. Nelson, A. J., Blake, D. T., & Chen, R. (2009). Digit-specific aberrations in the primary somatosensory cortex in Writer’s cramp. Ann Neurol, 66, 146–154. 167. Kanovsky, P., et  al. (2003). Abnormalities of cortical excitability and cortical inhibition in cervical dystonia:  Evidence from somatosensory evoked potentials and paired transcranial magnetic stimulation recordings. J Neurol, 250, 42–50. 168. Anastasopoulos, D., et al. (1998). What is straight ahead to a patient with torticollis? Brain, 121, 91–101. 169. Anastasopoulos, D., et  al. (1997). Perception of spatial orientation in spasmodic torticollis. Part I:  The postural vertical. Mov Disord, 12, 561–569. 170. Zeuner, K. E., et al. (2002). Sensory training for patients with focal hand dystonia. Ann Neurol, 51, 593–598. 171. Zatorre, R. J., Fields, R. D. & Johansen-Berg, H. (2012). Plasticity in gray and white: neuroimaging changes in brain structure during learning. Nat Neurosci, 15, 528–536. 172. Draganski, B., & May, A. (2008). Training-induced structural changes in the adult human brain. Behav Brain Res, 192, 137–142. 173. Quartarone, A., Siebner, H.  R., &. Rothwell, J.  C. (2006). Task-specific hand dystonia: Can too much plasticity be bad for you? Trends Neurosci., 29, 192–199. 174. Kojovic, M., et  al. (2013). Secondary and primary dystonia: Pathophysiological differences. Brain, 2013. 136, 2038–2049. 175. Sciamanna, G., et  al. (2012). Cholinergic dysfunction alters synaptic integration between thalamostriatal and corticostriatal inputs in DYT1 dystonia. J Neurosci, 32, 11991–2004. 176. Sciamanna, G., et  al. (2012). Cholinergic dysregulation produced by selective inactivation of the dystonia-associated protein torsinA. Neurobiol Dis, 47, 416–427. 177. Martella, G., et al. (2009). Impairment of bidirectional synaptic plasticity in the striatum of a mouse model of DYT1 dystonia: role of endogenous acetylcholine. Brain, 132, 2336–2349. 178. Pisani, A., et al. (2006). Altered responses to dopaminergic D2 receptor activation and N-type calcium currents in striatal cholinergic interneurons in a mouse model of DYT1 dystonia. Neurobiol Dis, 24, 318–325. 179. Dang, M. T., et al. (2012). An anticholinergic reverses motor control and corticostriatal LTD deficits in Dyt1 DeltaGAG knock-in mice. Behav Brain Res, 226, 465–472. 180. Zhao, Y., DeCuypere, M., & LeDoux, M.  S. (2008). Abnormal motor function and dopamine neurotransmission in DYT1 DeltaGAG transgenic mice. Exp Neurol, 210, 719–730. 181. Chen, G., et al. (2009). Low-frequency oscillations in the cerebellar cortex of the tottering mouse. J Neurophysiol, 101, 234–245. 182. Campbell, D. B., Hess, E. J. (1998). Cerebellar circuitry is activated during convulsive episodes in the tottering (tg/tg) mutant mouse. Neurosci., 85, 773–783. 183. Caldwell, K.  A., et  al. (2013). Invertebrate models of dystonia. Curr Neuropharmacol, 11, 16–29.

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123. Raike, R. S., Jinnah, H. A., & Hess, E. J. (2005). Animal models of generalized dystonia. NeuroRx, 2, 504–512. 124. Xiao, J., & Ledoux, M. S. (2005). Caytaxin deficiency causes generalized dystonia in rats. Brain Res Mol Brain Res, 141, 181–192. 125. LeDoux, M. S., Lorden, J. F., & Ervin, J. M. (1993). Cerebellectomy eliminates the motor syndrome of the genetically dystonic rat. Exp Neurol, 120, 302–310. 126. LeDoux, M. S., Lorden, J. F., & Meinzen-Derr, J. (1995). Selective elimination of cerebellar output in the genetically dystonic rat. Brain Res., 697, 91–103. 127. Alvarez-Fischer, D., et  al. (2012). Prolonged generalized dystonia after chronic cerebellar application of kainic acid. Brain Res., 1464, 82–88. 128. Fan, X., et  al. (2012). Selective and sustained AMPA receptor activation in cerebellum induces dystonia in mice. J Pharmacol Exp Ther, 340, 733–741. 129. Pizoli, C. E., et al. (2002). Abnormal cerebellar signaling induces dystonia in mice. J Neurosci, 22, 7825–7833. 130. Raike, R.  S., et  al. (2013). Stress, caffeine and ethanol trigger transient neurological dysfunction through shared mechanisms in a mouse calcium channelopathy. Neurobiol Dis, 50, 151–159. 131. Neychev, V., et al. (2008). The basal ganglia and cerebellum interact in the expression of dystonic movement. Brain, 131, 2499–2509. 132. Campbell, D. B., & Hess, E. J. (1999). L-type calcium channels contribute to the tottering mouse dystonic episodes. Mol Pharmacol, 55, 23–31. 133. Coria, F., Blanco Martin, A. I., & Rivas Vilas, M. D. (2000). Pseudodystonic hand posturing contralateral to a metastasis of the parietal association cortex. Neurologia, 15, 362–365. 134. Burguera, J. A., Bataller, L., & Valero, C. (2001). Action hand dystonia after cortical parietal infarction. Mov Disord, 16, 1183–1185. 135. Jacob, P. C., Chand, R. P. (1995). Blepharospasm and jaw closing dystonia after parietal infarcts. Mov Disord, 10, 794–795. 136. Khan, A. A., & Sussman, J. D. (2004). Focal dystonia after removal of a parietal meningioma. Mov Disord, 19, 714–716. 137. Kim, J. W., & Lee, P. H. (2007). Dystonic head tremor associated with a parietal lesion. Eur J Neurol, 14, e32–33. 138. Krauss, J. K., et al. (1991). Hemidystonia due to a contralateral parietooccipital metastasis:  disappearance after removal of the mass lesion. Neurology, 41, 1519–1520. 139. Ghika, J., Ghika-Schmid, F., & Bogousslasvky, J. (1998). Parietal motor syndrome: a clinical description in 32 patients in the acute phase of pure parietal strokes studied prospectively. Clin Neurol Neurosurg, 100, 271–282. 140. Klier, E. M., et al. (2002). Midbrain control of three-dimensional head orientation. Science, 295, 1314–1316. 141. Holmes, A.  L., et  al. (2012). Superior colliculus mediates cervical dystonia evoked by inhibition of the substantia nigra pars reticulata. J Neurosci, 32, 13326–13332. 142. Nakazawa, M., et  al. (1999). Possible involvement of a o- receptor subtype in the neck dystonia in rats. Pharmacol Biochem Behav, 62, 123–126. 143. Corneil, B. D., Olivier, E., & Munoz, D. P. (2002). Neck muscle responses to stimulation of monkey superior colliculus. II. Gaze shift initiation and volitional head movements. J Neurophysiol, 88, 2000–2018. 144. Fukushima, K. (1987). The interstitial nucleus of Cajal and its role in the control of movements of the head and eyes. Prog Neurobiol, 29, 107–192. 145. Matsumoto, R. R., & Pouw, B. (2000). Correlation between neuroleptic binding to sigma(1) and sigma(2) receptors and acute dystonic reactions. Eur J Pharmacol, 401, 155–160. 146. Jankovic, J. (2009). Peripherally induced movement disorders. Neurol Clin, 27, 821–832. 147. Schicatano, E.  J., Basso, M.  A. & Evinger, C. (1997). Animal model explains the origins of the cranial dystonia benign essential blepharospasm. J Neurophysiol, 77, 2842–2846. 148. Bostan, A. C., Dum, R. P., & Strick, P. L. (2010). The basal ganglia communicate with the cerebellum. Proc Natl Acad Sci USA, 107, 8452–8456. 149. Hoshi, E., et al. (2005). The cerebellum communicates with the basal ganglia. Nature Neurosci., 8, 1491–1493. 150. Quartarone, A., & Hallett, M. (2013). Emerging concepts in the physiological basis of dystonia. Mov Disord, 28, 958–967. 151. Hallett, M. (2011). Neurophysiology of dystonia: The role of inhibition. Neurobiol Dis, 42, 177–184. 152. Nakashima, K., et al. (1989). Reciprocal inhibition between forearm muscles in patients with writer’s cramp and other occupational cramps, symptomatic hemidystonia and hemiparesis due to stroke. Brain, 112, 681–697. 153. Priori, A., et  al. (1995). Physiological effects produced by botulinum toxin treatment of upper limb dystonia. Changes in reciprocal inhibition between forearm muscles. Brain, 118, 801–807.

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211. Hyland, K., et  al. (2003). The HPH-1 mouse:  a model for dominantly inherited GTP-cyclohydrolase deficiency. Ann Neurol, 54(suppl 6), S46–S48. 212. Carter, R.  J., et  al. (1999). Characterization of progressive motor deficits in mice transgenic for the human huntington’s disease mutation. J Neurosci, 19, 3248–3257. 213. Reddy, P. H., et al. (1998). Behavioural abnormalities and selective neuronal loss in HD transgenic mice expressing mutated full-length HD cDNA. Nature Genet, 20, 198–202. 214. Jinnah, H.  A., Gage, F.H., Friedmann, T. (1991). Amphetamine-induced behavioral phenotype in a hypoxanthine-guanine phosphoribosyltransferasedeficient mouse model of Lesch-Nyhan syndrome. Behav Neurosci, 105, 1004–1012. 215. Jinnah, H. A., Langlais, P. J., & Friedmann, T. (1992). Functional analysis of brain dopamine systems in a genetic mouse model of Lesch-Nyhan syndrome. J Pharmacol Exp Ther, 263, 596–607. 216. Morris, J.  D., et  al. (1982). Lysosome lipid storage disorder in NCTRBALB/c mice:  I.  Description of the disease and genetics. Am J Pathol, 108, 140. 217. Voikar, V., Rauvala, H., & Ikonen, E. (2002). Cognitive deficit and development of motor impairment in a mouse model of Niemann-Pick type C disease. Behav Brain Res, 132, 10-Jan. 218. Goldberg, M.  S., et  al. (2003). Parkin-deficient mice exhibit nigrostriatal deficits but not loss of dopaminergic neurons. J Biol Chem, 278, 43628–43635. 219. Lee, H. Y., et al. (2012). Dopamine dysregulation in a mouse model of paroxysmal nonkinesigenic dyskinesia. J Clin Invest, 122, 507–518. 220. Eicher, E. M., & Hoppe, P. C. (1973. Use of chimeras to transmit lethal genes in the mouse and to demonstrate allelism of the two X-linked male lethal genes jp and msd. J Exp Zool, 183, 181–184. 221. Meier, H., & MacPike, A. D. (1970). A neurological mutation (msd) of the mouse causing a deficiency of myelin synthesis. Exp Brain Res, 1970. 10, 512–525. 222. Gupta, P., et  al. (2001). Disruption of PPT1 or PPT2 causes neuronal ceroid lipofuscinosis in knockout mice. Proc Natl Acad Sci USA, 98, 13566–13571. 223. Sato, K., et al. (2008). Differential involvement of striosome and matrix dopamine systems in a transgenic model of dopa-responsive dystonia. Proc Natl Acad Sci USA, 105, 12551–12556. 224. Yokoi, F., et  al. (2006). Myoclonus, motor deficits, alterations in emotional responses and monoamine metabolism in epsilon-sarcoglycan deficient mice. J Biochem, 140, 141–146. 225. Giasson, B. I., et al. (2002). Neuronal alpha-synucleinopathy with severe movement disorder in mice expressing A53T human alpha-synuclein. Neuron, 34, 521–533. 226. Gomez-Isla, T., et  al. (2003). Motor dysfunction and gliosis with preserved dopaminergic markers in human a-synuclein A30P transgenic mice. Neurobio. Aging 2003. 24, 245–258. 227. Lee, M.  K., et  al. (2002). Human alpha-synuclein-harboring familial Parkinson’s disease-linked Ala-53 ---> Thr mutation causes neurodegenerative disease with alpha-synuclein aggregation in transgenic mice. Proc Natl Acad Sci USA, 99, 8968–8973. 228. Althini, S., et al. (2003). Normal nigrostriatal innervation but dopamine dysfunction in mice carrying hypomorphic tyrosine hydroxylase alleles. J Neurosci Res, 72, 444–453. 229. Malouin, F., & Bedard, P. J. (1983). Evaluation of head motility and posture in cats with horizontal torticollis. Exp Neurol, 81, 559–570. 230. Yamada, H., Fujimoto, K. I., & Yoshida, M. (1995). Neuronal mechanism underlying dystonia induced by bicucullin injection into the putamen of the cat. Brain Res, 677, 333–336. 231. Filion, M., & Hebert, R. (1983). Redundancy in ascending and descending pathways mediating head turning elicited by entopenducular stimulation in the cat. Neuroscience, 10, 169–176. 232. Matsumoto, R. R., et al. (1990). Drug specificity of pharmacological dystonia. Pharmacol Biochem Behav, 36, 151–155. 233. Derrick, M., et al. (2004). Preterm fetal hypoxia-ischemia causes hypertonia and motor deficits in the neonatal rabbit: a model for human cerebral palsy? J Neurosci, 24, 24–34. 234. Fletcher, C.  F., et  al. (2001). Dystonia and cerebellar atrophy in Cacna1a null mice lacking P/Q calcium channel activity. FASEB J., 15, 1288–1290. 235. Duchen, L. W., Falconer, D. S., & Strich, S. J. (1963). Dystonia musculorum, a hereditary neuropathy of mice affecting mainly sensory pathways. J Physiol, 165, 7. 236. Brown, A., et al. (1995). The mouse dystonia gene is a neural isoform of bullous pemphigoid antigen 1. Nature Genet., 10, 301–306.

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184. Burns, L. H., et al. (1995). Selective putaminal excitotoxic lesions in nonhuman primates model the movement disorder of Huntington disease. Neurosci., 64, 1007–1017. 185. Mink, J.  W., & Thach, W.  T. (1991). Basal ganglia motor control. III. Pallidal ablation: normal reaction time, muscle cocontraction, and slow movement. J Neurophysiol, 65, 330–351. 186. Foltz, E. L., Knopp, L. M., & Ward, A. A. (1959). Experimental spasmodic torticollis. J Neurosurg, 16, 55–67. 187. Malouin, F., & Bedard, P. J. (1982). Frontal torticollis (head tilt) induced by electrolytic lesion and kainic acid injection in monkeys and cats. Exp Neurol, 78, 551–560. 188. Olanow, C. W., et al. (1996). Manganese intoxication in the rhesus monkey:  a clinical, imaging, pathologic, and biochemical study. Neurology, 46, 492–498. 189. Byl, N. N., Focal hand dystonia may result from aberrant neuroplasticity. Adv Neurol, 94, 19–28. 190. Jinnah, H. A., et al. (2008). Animal models for drug discovery in dystonia. Expert Opin. Drug Discovery, 3, 83–97. 191. Oleas, J., et  al. (2013). Engineering animal models for dystonia:  What have we learned?. Mov Disord, 28, 990–1000. 192. Peller, M., et  al. (2006). The basal ganglia are hyperactive during the discrimination of tactile stimuli in writer’s cramp. Brain, 129, 2697–2708. 193. Richter, A., & Loscher, W. (1998). Pathology of idiopathic dystonia:  Findings from genetic animal models. Prog. Neurobiol., 54, 633–677. 194. Carpenter, M. B. (1956). A study of the red nucleus in the rhesus monkey; anatomic degenerations and physiologic effects resulting from localized lesions of the red nucleus. J. Comp. Neurol, 105, 195–249. 195. Tarlov, E. (1969). The postural effect of lesions of the vestibular nuclei: a note on species differences among primates. J Neurosurg, 31, 187–195. 196. Clarke, C.  E., et  al. (1989). Drug-induced dyskinesia in primates rendered hemiparkinsonian by intracarotid administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). J Neurol Sci, 90, 307–314. 197. Matsumura, M., et al. (1991). Behavioral deficits induced by local injection of bicuculline and muscimol into the primate motor and premotor cortex. J Neurophysiol, 65, 1542–1553. 198. Byl, N. N., Merzenich, M. M. & Jenkins, W. M. (1996). A primate genesis model of focal dystonia and repetitive strain injury: I. Learning-induced dedifferentiation of the representation of the hand in the primary somatosensory cortex in adult monkeys. Neurology, 47, 508–520. 199. Byl, N. N. (2003). What can we learn from animal models of focal hand dystonia? Rev Neurol (Paris), 159, 857–873. 200. Guehl, D., et al. (2000). Bicuculline injections into the rostral and caudal motor thalamus of the monkey induce different types of dystonia. Eur J Neurosci, 12, 1033–1037. 201. Macia, F., et  al. (2002). Neuronal activity in the monkey motor thalamus during bicuculline-induced dystonia. Eur J Neurosci, 15, 1353–1362. 202. Farshadmanesh, F., et  al. (2007). Three-dimensional eye-head coordination after injection of muscimol into the interstitial nucleus of Cajal (INC). J Neurophysiol, 97, 2322–2338. 203. Cuny, E., et al. (2008). Sensory motor mismatch within the supplementary motor area in the dystonic monkey. Neurobiol Dis, 30, 151–161. 204. D’Hooge, R., et  al. (2001). Hyperactivity, neuromotor defects, and impaired learning and memory in a mouse model for metachromatic leukodystrophy. Brain Res., 907, 35–43. 205. Eilam, R., et  al. (1998). Selective loss of dopaminergic nigro-striatal neurons in brains of Atm-deficient mice. Proc Natl Acad Sci USA, 95, 12653–12656. 206. DeAndrade, M. P., et al. (2011). Characterization of Atp1a3 mutant mice as a model of rapid-onset dystonia with parkinsonism. Behav Brain Res, 216, 659–665. 207. Buiakova, O. I., et al. (1999). Null mutation of the murine ATP7B (Wilson disease) gene results in intracellular copper accumulation and late-onset hepatic nodular transformation. Hum Mol Genet, 8, 1665–1671. 208. Cemal, C. K., et al. (2002). YAC transgenic mice carrying pathological alleles of the MJD1 locus exhibit a mild and slowly progressive cerebellar deficit. Hum Mol Genet, 11, 1075–1094. 209. Ikeda, H., et al. (1996). Expanded polyglutamine in the Machado-Joseph disease protein induces cell death in vitro and in vivo. Nature Genet., 13, 196–202. 210. Zinnanti, W. J., et al. (2006). A diet-induced mouse model for glutaric aciduria type 1. Brain, 129, 899–910.

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11 |  DYSTONIA: DEFINITION, CLINICAL CLASSIFICATION, EPIDEMIOLOGY, CLINICAL MANIFESTATIONS, EVALUATION, AND CURRENT TREATMENT 

J E RI YVON N E W IL L IA M S A N D D AV ID G.   STA N DA ERT

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The word dystonia was coined by Hermann Oppenheim in 1911,1 as part of the term “dystonia musculorum deformans.” Oppenheim’s original description was based on four children with what we would now recognize as early-onset generalized dystonia. His description, as recently translated by Klein and Fahn,2 emphasized both abnormalities of posture and the activity-dependent nature of the symptoms. In the cases described, this was manifested by a marked worsening when walking or standing. He also noted progression over time, from a dynamic abnormality to a more fixed state. The modern concept of dystonia has its roots in the work of Marsden in the 1970s, who recognized the commonalities among diverse forms of dystonia, ranging from the generalized childhood disorder described by Oppenheim to the more focal abnormalities commonly seen in adults such as torticollis, blepharospasm, and writers’ cramp.3,4 An oft-cited definition is that proposed by Fahn and others at a consensus conference held in 1984: a syndrome consisting “of sustained muscle contractions, frequently causing twisting and repetitive movements, or abnormal postures.”5 Although valuable, this definition has several shortcomings, and recently an international consensus committee of dystonia experts has proposed an updated definition6: ​

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“Dystonia is a movement disorder characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive, movements, postures, or both. Dystonic movements are typically patterned, twisting, and may be tremulous. Dystonia is often initiated or worsened by voluntary action and associated with overflow muscle activation.” Synonyms: dystonia, primary dystonia, idiopathic dystonia, dystonia musculorum deformans, isolated dystonia.

Originally used to describe dystonias of unknown cause, the use of the term evolved over time to emphasize the “pure” dystonias, meaning dystonia without associated neurological findings such as paralysis or tremor. Many examples of “primary dystonia” were subsequently found to be caused by specific genetic mutations. The most recent classification system for dystonia, developed by an international consensus committee, abandons the concept of “primary dystonia” entirely.6 The new approach retains the longstanding clinical descriptors of age of onset and distribution of body parts affected, grouping these together under Axis I:  Clinical Characteristics. This Axis may also incorporate information on the temporal pattern of the disorder (static vs. progressive) and variability of symptoms (persistent vs. paroxysmal or action-induced). The prior concept of “primary dystonia,” emphasizing lack of other symptoms, is now largely supplanted by the descriptive term “isolated dystonia.” Axis II is devoted to description of the etiology of the disorder. Within the Axis II is included description of whether or not there is evidence of structural nervous system pathology (such as stroke, tumor, or neurodegeneration) and whether it is inherited (due to a known gene mutation), acquired (due to brain injury), or idiopathic (of unknown cause). Another classification method commonly encountered is the “DYT” numbering scheme used to designate different genetic forms of dystonia.8 The DYT numbers start with DYT1, now known to be caused by mutations of the gene coding for the protein torsinA, and extend at present to DYT28. Many, but not all, of the specific genes responsible for these “DYT” syndromes have been identified. Some of the DYT numbers have been assigned to forms of dystonia that are clearly hereditary, but the specific gene remains unknown. In other cases, it has been discovered that more than one kind of mutation can cause a single “DYT” disorder. An example of this is DYT5, originally used to designate genetic forms of dopa-responsive dystonia. It is now known that the phenomenology of dopa-responsive dystonia can be caused by mutations in several different parts of the dopamine signaling pathway, and the Human Genome Nomenclature Committee has recommended that the designation “DYT5” be abandoned. On the whole, the DYT scheme is best viewed as a kind of shorthand for those studying the genetic basis of dystonia, and for referring to specific gene mutations that can cause dystonia. It is not useful for the majority of cases of dystonia in which the cause is not known to be hereditary or the specific gene mutation is unknown.

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The classification of dystonia has undergone substantial evolution, as a result of growing knowledge of the underlying mechanisms. Most classifications schemes have taken a three-part approach, distinguishing the disorders by age of onset (early vs. late), the distribution of the body parts affected by the symptoms (commonly divided into focal, segmental, hemidystonia, or generalized) and the etiology of the disease. Although the clinical descriptors of age and distribution have proved relatively durable, classifications systems based on etiology have grown more complex. Particular controversy has arisen over the term “primary dystonia,” which is often found in the literature.7 ​

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Given the changing definitions of dystonia that have been applied over time, it should not be surprising that precise data on the 11 D stonia | 75 y

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The clinical features of dystonia are represented by an amalgamation of dystonic movements and postures to create sustained postural twisting (torsion dystonia). The speed of muscle contractions may be slow or rapid, but are sustained at the peak of movement. The muscle contractions tend to have a consistent directional character. Voluntary movements can exacerbate underlying dystonic symptoms. Conversely, specific voluntary movements or sustained postures that include touching specific body parts may temporarily ameliorate dystonia movements; this phenomenon is known as a sensory trick or “gestes antagonistes.” Overflow of movement to other body parts, during activation of the affected region, is also a feature of dystonia.6 Several specific dystonia syndromes that are commonly encountered are summarized below.

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The most common early-onset generalized dystonia is DYT1 dystonia (also called Oppenheim dystonia), which is caused by a deletion in the TOR1A gene that encodes the protein torsinA; this mutation is found in approximately 90% of Ashkenazi Jews with early-onset primary dystonia.12 Symptom onset typically occurs in childhood or adolescence and involves dystonic posturing of an upper or lower extremity. In one-third of patients, dystonic symptoms spread to other regions of the body within 5 years. Patients may report severe physical impairment, but no other neurologic symptoms develop during the course of the disease. Earlier age of onset and onset in the lower extremities correlates with increased morbidity and progression of the disorder.8 Patients with non-DYT1 generalized dystonia typically exhibit onset at a later age. In addition, the initial presentation of dystonia more often involves the cervical region when compared with predilection for limb dystonia in DYT1 dystonia. Slower progression ers

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is seen in patient with non-DYT1 early-onset generalized dystonia as well. Several different genetic mutations are known to produce generalized dystonia. In the presence of a clear familial pattern of inheritance, a vigorous search is warranted, guided by the clinical phenotype of the various DYT-designated disorders. In the absence of a clear familial pattern the only genetic form common enough to warrant diagnostic investigation is DYT6, caused by mutations of the THAP1 (thanatos associated protein) gene, which produce autosomal dominant disease.13 This type of dystonia was first discovered in Amish-Mennonite families with cranial or limb onset in childhood, but recent work has demonstrated that it may be found in patients of many backgrounds, may manifest as late as the fifth decade, and that a wide range of different mutations and modifications of the THAP1 gene can be responsible. Key features of this disorder include disabling dysphagia and dysarthria.14 A D U LT O N S E T F O C A L D Y S T O N I A S

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C E R V I C A L D Y S T O N I A ( S PA S M O D I C T O RT I C O L L I S ) This is the most common phenotype of focal dystonia in adults.11 The clinical presentation is characterized by abnormal head and neck postures in middle-aged patients. Women are more commonly affected with this disorder. Intermittent spasms of the neck muscles or abnormal head movements occur, due to contractions of the sternocleidomastoid, trapezius, and posterior cervical muscles. Horizontal twisting of the neck (torticollis), extension of the neck (retrocollis), flexion of the neck (anterocollis), or lateral flexion of the neck (laterocollis) may occur. These dystonic movements may occur simultaneously as well. Tremor also may accompany cervical dystonia, which must be distinguished from the clinical presentation of essential tremor. Head tremor in essential tremor differs from dystonic head tremor due to the absence of abnormal posturing. Cervical dystonia responds favorably to botulinum toxin injections. B L E P H A R O S PA S M ( C R A N I A L D Y S T O N I A ) This is a focal dystonia involving the eye muscles (orbicularis oculi, corrugator, procerus). Clinical features include increased blink rate, eye irritations, photophobia, and spasms of involuntary eye closure. Symptoms tend to involve both eyes, although onset may be unilateral in rare cases. Blepharospasm is frequently associated with oromandibular dystonia and responds robustly to botulinum toxin injections.15,16 OROMANDIBULAR DYSTONIA (CRANIAL DYSTONIA) Oromandibular dystonia is a form of dystonia characterized by involuntary movements of masticatory, pharyngeal, and lingual muscles. Symptoms include forceful contractions of the face, jaw, and tongue causing difficulty in opening and closing the mouth; this often leads to dysarthria, dysphagia, and difficulty chewing. Some may have involvement only of the tongue, so-called lingual dystonia that can interfere with speech or chewing. A related type of task specific dystonia affects the facial muscles and lips of musicians who play wind instruments (embouchure dystonia).15,17 ​

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incidence and prevalence of these disorders are difficult to come by. Generally speaking, the most common forms of dystonia seen by neurological practitioners are adult onset focal dystonias of unknown cause (Axis I: late adulthood, focal, static or progressive, persistent; Axis II: no evidence of structural lesion, idiopathic, sporadic). The prevalence of these in Rochester, Minnesota has been estimated as 30 per 100,000.9 A more recent meta-analysis of “primary” dystonia (used in this publication with a meaning similar to “isolated” dystonia under the newer classification scheme) yielded a worldwide estimate of 16.43 per 100,000, with higher prevalence in women than in men.10 A similar detailed analysis of cervical dystonia, a common form of focal dystonia, led to estimates of 2.8 to 18 cases per 100,000.11 This review also supported a gender bias, with a 2:1 female:male ratio. Generalized forms of dystonia are less common, are more often early in onset, and are more likely to be either due to an identifiable mutation (Axis I: childhood or adolescence, generalized, static or progressive, persistent; Axis II:  no evidence of structural lesion, inherited) or to at least demonstrate a familial pattern of inheritance (Axis II:  no evidence of structural lesion, idiopathic, familial). Because of the strong influence of genetics, the epidemiology of generalized dystonias is strongly dependent on the genetic background of the population surveyed. In the case of DYT1 dystonia, the prevalence is highest in those of Ashkenazi Jewish descent, with a disease frequency as high as 33 per 100,000. In non-Ashkenazi populations, the prevalence of DYT1 is much lower, between 3 and 10 per 100,000.8

L A RY N G E A L D Y S T O N I A ( S PA S M O D I C DYSPHONIA) Laryngeal dystonia is a focal type of dystonia that affects the laryngeal muscles. Onset occurs in adulthood and symptoms may be characterized by two forms:  adductor and abductor type. The most common form is the adductor type, which can be attributed to apposition of the

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X - L I N K E D D Y S T O N I A - PA R K I N S O N I S M   ( D Y T 3 ) This X-linked recessive syndrome, also known as Lubag dystonia, chiefly affects Filipino men in their fifth decade. There are reports of women affected with Lubag dystonia and they usually experience a more benign course. Key features of the disorder include progressive dystonia and parkinsonism. Unlike many of the other dystonia discussed here, DYT3 is associated with neurodegenerative change in the caudate and putamen. This disorder does not respond to dopaminergic medications, and patients succumb to illness by 10 to 12 years.26,27

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MYOCLONUS-DYSTONIA (DYT11, DYT15) This is an autosomal dominant disorder that slowly presents in childhood, adolescence, and adulthood. It is characterized by myoclonic jerks affecting the neck, arms, and axial muscles. Classically, dystonia accompanies the myoclonus, is mild in intensity, and significantly improves with alcohol intake although recent work has emphasized a broader phenotype.22

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PSYCHOGENIC DYSTONIAS As with all movement disorders, it is always important to consider the possibility that the condition may be psychogenic in origin. In dystonia, however, it is especially important not to make this diagnosis prematurely. Many patients with dystonia report frustration with having been labeled “psychogenic” early on, and struggling to get medical practitioners to reconsider this diagnosis. In general, psychogenic dystonia is over- rather than under-diagnosed. Clinical clues to psychogenic dystonia include abrupt onset, complaints of muscle weakness, sensory disturbances, fixed postures, distractibility, incongruency, bizarre movements, and the absence of a sensory trick. Ultimately, however, the only convincing evidence for a psychogenic origin is longitudinal clinical assessment and demonstration of a clear response to a psychological intervention.

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D O PA - R E S P O N S I V E D Y S T O N I A Dopa-responsive dystonia, or DRD, is a descriptive term that refers to forms of dystonia that demonstrate clinical improvement after treatment with levodopa or dopamine agonist drugs. As noted earlier, DRD was once designated “DYT5,” but this term has been abandoned because of the discovery of multiple different genes that can lead to a similar phenotype. The most common form of DRD, sometimes termed “Segawa disease,” is an autosomal dominant disorder caused by mutations in the GTP cyclohydrolase1 gene (GTPCH1).21 This enzyme is responsible for a key step in the synthesis of tetrahydrobiopterin, a cofactor for tyrosine hydroxylase, the rate-limiting enzyme in the synthesis of dopamine. Onset of Segawa disease is usually in childhood with progressive limb dystonia and parkinsonism. A  key feature that distinguishes this disorder from other dystonias is diurnal fluctuation with worsening of symptoms as the day goes on. Parkinsonian features may be the presenting manifestations when starting in adulthood. Whether primarily dystonic or parkinsonian, most of these patients exhibit a dramatic and sustained response to levodopa, without development of dyskinesias and motor fluctuations. Other genetic causes of DRD include defects in other components of the biopterin pathway and mutations of the gene encoding tyrosine hydroxylase itself. The clinical phenotype in some of these forms may be more severe, incorporating hypotonia and developmental delay.8 The response to levodopa may be less satisfactory, reflecting the effects of these mutations on a broad range of catecholamines rather than just dopamine synthesis.

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R A P I D - O N S E T D Y S T O N I A - PA R K I N S O N I S M (DYT12) This is an autosomal disorder present in adolescents and adults caused by a mutation in the ATP1A3 gene on chromosome 19. The striking feature of this disease is that the dystonic and parkinsonian symptoms are abrupt in onset and progress over hours to weeks. Dysphagia and dysarthria are typically present. Once the symptoms appear they are usually permanent, and the syndrome does not respond well to dopaminergic agents.28,29 ​

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HAND DYSTONIA (WRITER’S CRAMP) Writer’s cramp is a task-specific focal dystonia related to the act of writing. Common symptoms include excessive gripping of a writing utensil, impaired legibility of handwriting, tension and pain in the forearm, flexing of the wrist, elevation of the elbow, and occasional extension and rotation of the fingers. Onset typically occurs in adulthood. Handwriting may become shaky. Multiple blinded and placebo-controlled studies have demonstrated efficacy of botulinum toxin A in the treatment of writer’s cramp.19,20 Other task-specific dystonias affecting the hand may occur with a variety of specific triggering movements like typing or playing a specific musical instrument (like strumming a guitar).

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Paroxysmal nonkinesigenic dyskinesia is another rare disorder that consists of any combination of dystonic postures, chorea, athetosis, and ballism. The episodes may last from 2 minutes to 4 hours, may be unilateral or bilateral, and may be exacerbated by alcohol, caffeine, and fatigue. Mutations in the myofibrillogenesis regulator-1 (MR-1) protein have been implicated.25 ​

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vocal cords only during vocalization; this presents as a tight, strangledsounding voice quality. The abductor type is caused by abduction of the vocal cords during vocalization; this presents as a breathy, whispering voice.18

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PA R O X Y S M A L D Y S K I N E S I A W I T H   D Y S T O N I A Paroxysmal kinesigenic dyskinesia is a rare disorder often caused by mutations in the PRRT2 gene on chromosome 16.23,24 Clinical features involve any combination of dystonic postures, chorea, athetosis, and ballism. The episodes typically last seconds to less than 5 minutes, may be unilateral or bilateral, and may be precipitated by sudden movement, startle, or hyperventilation. Carbamazepine and phenytoin have been shown to be effective in the amelioration of symptoms.

The diagnosis of dystonia is based mostly on the clinical presentation and expert observation by a movement disorder–trained neurologist. The age of onset and anatomic distribution of dystonia are most helpful at establishing a diagnosis, but laboratory tests, genetic analysis, family history, electrophysiology testing (EMG, EEG), neuroimaging, and a trial of levodopa may be helpful as well. When there is a clear family history of dystonia, the laboratory test most likely to be useful involves genetic testing. Due to reduced penetrance and variable expression of disease, it is possible that genetic causes can be uncovered in patients who do not have a strong family history, but in the absence of a specific recognizable syndrome the cost of such testing is often prohibitive outside a research setting. To exclude structural and acquired forms of dystonia, one should consider the following high-yield laboratory tests as part of the diagnostic workup: complete blood count with peripheral smear, liver function tests, renal function tests, electrolytes, erythrocyte

carbamazepine have been shown to alleviate episodes of kinesigenic paroxysmal dystonia. BOTULINUM NEUROTOXINS Over the past three decades, botulinum neurotoxin therapy (BoNT) has become the mainstay treatment for patients with focal dystonias. The efficacy of BoNT in the treatment of cervical dystonia and blepharospasm has been demonstrated in multiple randomized, placebo-controlled trials.32 To date, there are five different formulations of BoNT type A  and one formulation of BoNT type B commercially available. The FDA has approved the use of BoNT type A  for blepharospasm and cervical dystonia. In addition, the FDA approved the BoNT type B formulation for treatment of cervical dystonia as well. The most recently FDA approved BoNT type A serotype, incobotulinumtoxinA, is unique in that it is free of complexing proteins and may be less likely to increase risk of antigenicity or treatment failure. More specifically, BoNT type B may provide benefit for patients who are refractory to previous treatments with BoNT type formulations.33 The most common side effect of BoNT for focal dystonias is localized weakness.

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sedimentation rate, antinuclear antibodies, serum ceruloplasmin, 24-hour urinary copper, and rapid plasma reagin. If there is suspicion of heredodegenerative disorders, then consider testing for lysosomal enzymes, serum and urine amino acids, oligosaccharides, and mucopolysaccharides. Obtaining a CT or MRI brain image may assist in excluding structural etiologies of dystonia, such as basal ganglia calcifications or necrosis.

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The primary goal of management and treatment is to provide symptomatic benefit.30 The different approaches to management and treatment can be divided into the following categories: pharmacological, toxin therapies, surgical, and therapy-based approaches. PHARMACOLOGICAL APPROACHES

ANTICHOLINERGIC THERAPY Anticholinergic medications (usually trihexyphenidyl or benztropine) block acetylcholine at muscarinic receptors in the central nervous system. Trihexyphenidyl was one of the first agents reported to have effectiveness in the treatment of dystonia.31 In contrast with adult patients, children and adolescents are often able to tolerate the drug at higher doses and can obtain a more robust response. The common side effects are those associated with cholinergic blockade (dry mouth, blurry vision, constipation, delayed gastric emptying, urinary retention, and confusion); the cognitive adverse effects may be particularly troublesome in older patients.

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OTHER PHARMACOLOGICAL APPROACHES A variety of other pharmacological agents have been used for the treatment of dystonia.30 Benzodiazepines (diazepam, lorazepam, or clonazepam) may provide modest amelioration of symptoms. Clonazepam has been shown to be especially useful in the treatment of myoclonic dystonia, blepharospasm, cervical dystonia, and secondary dystonia. Presynaptic GABA agonists such as baclofen have been used in the treatment of dystonia. Oral baclofen has been shown to improve symptoms of dystonia, especially in children and adolescents with primary generalized dystonia. Intrathecal baclofen has also been used in patients with severe generalized dystonia and concomitant spasticity. In a small open trial, clozapine was shown to be modestly effective in the treatment of generalized and segmental dystonia. In addition, clozapine has been reported to alleviate the symptoms of patients with tardive dystonia, as well. Tetrabenazine has been shown to improve symptoms of dystonia, especially in patients with tardive dystonia. Use of anticonvulsants has proved benefits for treatment of select types of dystonia. More specifically, phenytoin and

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D E E P B R A I N S T I M U L AT I O N When pharmacologic and chemodenervation therapies fail, deep brain stimulation (DBS) is a reversible and programmable option for treatment of patients with dystonia.34 Although not yet approved by the FDA, DBS is available in the United States under a humanitarian device exemption for treatment of primary dystonia. DBS appears to be particularly efficacious in the primary generalized dystonia population.35 In contrast to the immediate benefit derived from DBS in patients with Parkinson’s disease, the improvement in tonic features is more gradual in patients with dystonia. The main drawback to choosing DBS for dystonia is related to the adverse effects from surgery, including expensive costs, higher risk of infection, potential for hardware malfuncture, and need for battery changes. P H Y S I C A L A N D O C C U PAT I O N A L T H E R A P Y

Physical and occupational therapy serve as essential adjuvant therapy for the treatment of dystonia. Participation in regular therapy sessions may improve overall quality of life and functionality in patients with dystonia. Furthermore, physical and occupational therapy are useful for improving posture and preventing contractures in patients with dystonia. For example, neck braces may provide relief of pain and dystonic posturing in patients with cervical dystonia; these braces may serve as a sensory trick. Similar type braces have proven efficacious when applied to the hand in patients with writer’s cramp dystonia. CLINICAL TRIALS AND FUTURE THERAPIES

Currently, there is no cure for dystonia and the clinical focus is placed upon amelioration of dystonia-related symptoms. Various clinical trials and clinical research studies are currently underway to evaluate treatment and natural course of the disease. A complete description can be found at www.clinicaltrials.gov. Much of the current trial activity seeks to define the neural mechanisms of dystonia, and to correlate genetics, environment, and natural history. There is optimism that the recent genetic discoveries will lead to more specific, targeted therapies, but few of these have yet made it to the stage of interventional human trials. ​

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D O PA M I N E R G I C T H E R A P Y Levodopa, a first-line treatment used in the treatment of Parkinson’s disease, has also been used in the treatment of dystonia. Many experts in the field recommend that a levodopa trial should always be considered, especially in patients with early-onset segmental and generalized dystonia without an alternative diagnosis. Patients with Segawa disease (GTPCH deficiency) often exhibit marked amelioration of their symptoms using low doses of levodopa (100–200 mg/day). In a minority of cases, patients may require as high as 1,000mg per day of levodopa to experience alleviation of symptoms. The levodopa trial need not, however, be prolonged. Levodopa responsiveness can usually be identified within a matter of days to weeks, and if unsuccessful should be discontinued in favor of an alternative treatment.

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www.dystonia-foundation.org (Dystonia Medical Research Foundation) www.wemove.org (World Education and Awareness for Movement Disorders) http://rarediseasesnetwork.epi.usf.edu/dystonia (Dystonia Coalition) www.ninds.nih.gov/disorders/dystonias (National Institute of Neurological Disorders and Stroke) ​

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1. Oppenheim, H. (1911). Uber eine eigenartige Krampfkrankheit des kindlichen und jugendlichen Alters (Dysbasia lordotica progressiva, Dystonia musculorum deformans). Neurol Centrabl, 30, 1011, 1090–1097. 2. Klein, C., & Fahn, S. (2013). Translation of Oppenheim’s 1911 paper on dystonia. Mov Disord, 28(7), 851–862. doi: 10.1002/mds.25546 3. Marsden, C.  D. (1976). The problem of adult-onset idiopathic torsion dystonia and other isolated dyskinesias in adult life (including blepharospasm, oromandibular dystonia, dystonic writer’s cramp, and torticollis, or axial dystonia). Adv Neurol, 14, 259–276. 4. Marsden, C.  D., & Harrison, M.  J. (1974). Idiopathic torsion dystonia (dystonia musculorum deformans). A review of forty-two patients. Brain, 97(4), 793–810. 5. Fahn, S., Marsden, C. D., & Calne, D. B. (1987). Classification and investigation of dystonia. In: C. D. Marsden & S. Fahn (Eds.), Movement disorders (Vol. 2, pp. 332–358). London: Butterworths. 6. Albanese, A., Bhatia, K., Bressman, S. B., Delong, M. R., Fahn, S., Fung, V. S., Hallett, M., Jankovic, J., Jinnah, H. A., Klein, C., Lang, A. E., Mink, J. W., & Teller, J. K. (2013). Phenomenology and classification of dystonia: A consensus update. Mov Disord, 28(7), 863–873. doi: 10.1002/mds.25475 7. Bressman, S.  B., & Saunders-Pullman, R. (2013). Primary dystonia: Moribund or viable. Mov Disord, 28(7), 906–913. doi: 10.1002/mds.25528 8. Bressman, S.  B. (2012). Genetic forms of dystonia. In R. L.  Watts, D. G. Standaert, & J. A. Obeso (Eds.), Movement disorders (3rd ed., 555–570). New York: McGraw Hill. 9. Nutt, J. G., Muenter, M. D., Aronson, A., Kurland, L. T., & Melton, L. J., 3rd. (1988). Epidemiology of focal and generalized dystonia in Rochester, Minnesota. Mov Disord, 3(3), 188–194. doi: 10.1002/mds.870030302 10. Steeves, T. D., Day, L., Dykeman, J., Jette, N., & Pringsheim, T. (2012). The prevalence of primary dystonia: A systematic review and meta-analysis. Mov Disord, 27(14), 1789–1796. doi: 10.1002/mds.25244 11. Defazio, G., Jankovic, J., Giel, J.  L., & Papapetropoulos, S. (2013). Descriptive epidemiology of cervical dystonia. Tremor Other Hyperkinet Mov (N Y), 3. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3822401/ 12. Ozelius, L.  J., Hewett, J.  W., Page, C.  E., Bressman, S.  B., Kramer, P.  L., Shalish, C., de Leon, D., Brin, M. F., Raymond, D., Corey, D. P., Fahn, S., Risch, N. J., Buckler, A. J., Gusella, J. F., & Breakefield, X. O. (1997). The early-onset torsion dystonia gene (DYT1) encodes an ATP-binding protein. Nat Genet, 17(1), 40–48. doi: 10.1038/ng0997-40 13. Fuchs, T., Gavarini, S., Saunders-Pullman, R., Raymond, D., Ehrlich, M. E., Bressman, S. B., & Ozelius, L. J. (2009). Mutations in the THAP1 gene are responsible for DYT6 primary torsion dystonia. Nat Genet, 41(3), 286–288. doi: 10.1038/ng.304 14. LeDoux, M. S., Xiao, J., Rudzinska, M., Bastian, R. W., Wszolek, Z. K., Van Gerpen, J. A., Puschmann, A., Momcilovic, D., Vemula, S. R., & Zhao, Y. (2012). Genotype-phenotype correlations in THAP1 dystonia: Molecular foundations and description of new cases. Parkinsonism Relat Disord, 18(5), 414–425. doi: 10.1016/j.parkreldis.2012.02.001 15. LeDoux, M. S. (2009). Meige syndrome: What’s in a name? Parkinsonism Relat Disord, 15(7), 483–489. doi: 10.1016/j.parkreldis.2009.04.006 16. Marti, M. J., & Tolosa, E. S. (2012). Adult-onset idiopathic focal dystonia. In R. L. Watts, D. G. Standaert, & J. A. Obeso (Eds.), Movement disorders (3rd ed., 571–586). New York: McGraw Hill. 17. Frucht, S.  J. (2009). Embouchure dystonia—Portrait of a task-specific cranial dystonia. Mov Disord, 24(12), 1752–1762. doi:  10.1002/ mds.22550 18. Ludlow, C.  L. (2011). Spasmodic dysphonia:  A  laryngeal control disorder specific to speech. J Neurosci, 31(3), 793–797. doi:  10.1523/ JNEUROSCI.2758-10.2011 19. Dashtipour, K., & Pender, R. A. (2008). Evidence for the effectiveness of botulinum toxin for writer’s cramp. J Neural Transm, 115(4), 653–656. doi: 10.1007/s00702-007-0868-4 20. Hai, C., Yu-ping, W., Hua, W., & Ying, S. (2010). Advances in primary writing tremor. Parkinsonism Relat Disord, 16(9), 561–565. doi: 10.1016/ j.parkreldis.2010.06.013 21. Segawa, M. (2011). Dopa-responsive dystonia. Handb Clin Neurol, 100, 539–557. doi: 10.1016/B978-0-444-52014-2.00039-2

22. Carecchio, M., Magliozzi, M., Copetti, M., Ferraris, A., Bernardini, L., Bonetti, M., Defazio, G., Edwards, M. J., Torrente, I., Pellegrini, F., Comi, C., Bhatia, K. P., & Valente, E. M. (2013). Defining the epsilon-sarcoglycan (SGCE) gene phenotypic signature in myoclonus-dystonia: A reappraisal of genetic testing criteria. Mov Disord, 28(6), 787–794. doi: 10.1002/mds.25506 23. Cao, L., Huang, X.  J., Zheng, L., Xiao, Q., Wang, X.  J., & Chen, S.  D. (2012). Identification of a novel PRRT2 mutation in patients with paroxysmal kinesigenic dyskinesias and c.649dupC as a mutation hot-spot. Parkinsonism Relat Disord, 18(5), 704–706. doi:  10.1016/ j.parkreldis.2012.02.006 24. Youn, J., Kim, J. S., Lee, M., Lee, J., Roh, H., Ki, C. S., & Choa, J. W. (2014). Clinical manifestations in paroxysmal kinesigenic dyskinesia patients with proline-rich transmembrane protein 2 gene mutation. J Clin Neurol, 10(1), 50–54. doi: 10.3988/jcn.2014.10.1.50 25. Ghezzi, D., Viscomi, C., Ferlini, A., Gualandi, F., Mereghetti, P., DeGrandis, D., & Zeviani, M. (2009). Paroxysmal non-kinesigenic dyskinesia is caused by mutations of the MR-1 mitochondrial targeting sequence. Hum Mol Genet, 18(6), 1058–1064. doi:  10.1093/hmg/ ddn441 26. Goto, S., Lee, L.  V., Munoz, E.  L., Tooyama, I., Tamiya, G., Makino, S., Ando, S., Dantes, M. B., Yamada, K., Matsumoto, S., Shimazu, H., Kuratsu, J., Hirano, A., & Kaji, R. (2005). Functional anatomy of the basal ganglia in X-linked recessive dystonia-parkinsonism. Ann Neurol, 58(1), 7–17. doi: 10.1002/ana.20513 27. Herzfeld, T., Nolte, D., Grznarova, M., Hofmann, A., Schultze, J.  L., & Muller, U. (2013). X-linked dystonia parkinsonism syndrome (XDP, lubag):  Disease-specific sequence change DSC3 in TAF1/DYT3 affects genes in vesicular transport and dopamine metabolism. Hum Mol Genet, 22(5), 941–951. doi: 10.1093/hmg/dds499 28. Brashear, A., Sweadner, K., & Ozelius, L. (1993). Rapid-onset dystoniaParkinsonism. In R. A.  Pagon, M. P.  Adam, T. D.  Bird, C. R.  Dolan, C. T.  Fong, & K. Stephens (Eds.), GeneReviews. Seattle:  University of Washington. http://www.ncbi.nlm.nih.gov/books/NBK1115/ 29. de Carvalho Aguiar, P., Sweadner, K. J., Penniston, J. T., Zaremba, J., Liu, L., Caton, M., Linazasoro, G., Borg, M., Tijssen, M. A., Bressman, S. B., Dobyns, W. B., Brashear, A., & Ozelius, L. J. (2004). Mutations in the Na+/ K+ -ATPase alpha3 gene ATP1A3 are associated with rapid-onset dystonia parkinsonism. Neuron, 43(2), 169–175. doi: 10.1016/j.neuron.2004.06.028 30. Adam, O. R., & Jankovic, J. (2012). Treatment of dystonia. In R. L. Watts, D. G. Standaert, & J. A. Obeso (Eds.), Movement disorders (3rd ed., 587– 602). New York: McGraw Hill. 31. Fahn, S. (1983). High dosage anticholinergic therapy in dystonia. Neurology, 33(10), 1255–1261. 32. Hefter, H., Kupsch, A., Mungersdorf, M., Paus, S., Stenner, A., Jost, W., & Dysport Cervical Dystonia Study Group (2011). A botulinum toxin A treatment algorithm for de novo management of torticollis and laterocollis. BMJ Open, 1(2), e000196. doi: 10.1136/bmjopen-2011-000196 33. Jimenez-Shahed, J. (2012). A new treatment for focal dystonias: incobotulinumtoxinA (Xeomin(R)), a botulinum neurotoxin type A free from complexing proteins. Neuropsychiatr Dis Treat, 8, 13–25. doi:  10.2147/NDT. S16085 34. Vidailhet, M., Jutras, M.  F., Roze, E., & Grabli, D. (2013). Deep brain stimulation for dystonia. Handb Clin Neurol, 116, 167–187. doi: 10.1016/ B978-0-444-53497-2.00014-0 35. Mills, K. A., Starr, P. A., & Ostrem, J. L. (2014). Neuromodulation for dystonia:  target and patient selection. Neurosurg Clin N Am, 25(1), 59–75. doi: 10.1016/j.nec.2013.08.014

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12 |  PAROXYSMAL DYSKINESIAS AND OTHER PAROXYSMAL MOVEMENT DISORDERS 

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Paroxysmal dyskinesias are defined as a heterogeneous group of relatively rare neurological conditions manifested by recurrent episodes of involuntary movements that may include any combination of dystonia, chorea, ballism, or athetosis.1,2 Two pediatric cases of possible paroxysmal kinesigenic dyskinesia were published first in 1885 by Gowers, who viewed the condition as movement-induced seizures.3 The term “familial paroxysmal choreoathetosis” was first used by Mount and Reback in 1940 to describe a patient with familial form of periodic dystonia and chorea, with the attacks typically induced by alcohol, caffeine, or fatigue and lasting minutes to hours.4 The authors were first to recognize paroxysmal dyskinesias as forms of movement disorders rather than epilepsy, and the condition they described was later renamed “paroxysmal dystonic choreoathetosis of Mount and Reback.”5 In 1967, Kertesz first introduced the term “paroxysmal kinesigenic choreoathetosis” when describing a group of patients with childhood-onset, movement-induced, periodic choreoathetosis with episodes lasting for only seconds to minutes.6 In 1977, Lance reported a kindred with episodic choreoathetosis induced by prolonged exercise.7 Lance also provided the first comprehensive review of previously published cases and the first classification of paroxysmal dyskinesias. He separated paroxysmal choreoathetosis into three groups based primarily on duration of the attacks (brief, intermediate, and prolonged) and secondarily on precipitating events:  1)  paroxysmal kinesigenic choreoathetosis with movementinduced short attacks, 2)  paroxysmal dystonic choreoathetosis with long attacks not induced by movements, and 3) paroxysmal exerciseinduced dyskinesia with intermediate duration of the attacks. About two decades later, Demirkiran and Jankovic noted that each previously defined type of paroxysmal dyskinesia could manifest as either dystonia or chorea, or a combination of different forms of abnormal movements and proposed using the term “paroxysmal dyskinesia” instead of “choreoathetosis.”8 They classified paroxysmal dyskinesias based solely on precipitating factors of the attacks, namely:  1)  paroxysmal kinesigenic dyskinesia (PKD) replacing the term “paroxysmal kinesigenic choreoathetosis,” 2)  paroxysmal nonkinesigenic dyskinesia (PNKD) instead of “paroxysmal dystonic choreoathetosis of Mount and Reback,” 3)  paroxysmal exercise-induced dyskinesia (PED), and 4) paroxysmal hypnogenic dyskinesia (PHD). The last category of paroxysmal dyskinesias, manifested as attacks of involuntary movements in sleep, was first described in two families in 1969 by Horner and Jackson,9 but defined as “paroxysmal hypnogenic dyskinesia” only in 1981 by Lugaresi and Cirignotta.10 This condition is often considered a form of nocturnal epilepsy rather than a movement disorder, hence it is sometimes omitted from reviews of paroxysmal dyskinesias.

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The exact prevalence of paroxysmal dyskinesias is unknown, but the disorder is probably more frequent than initially thought. Many cases remain undiagnosed due to normal neurological examination between the paroxysms or are wrongly attributed to seizures or psychogenic (functional) disorders. Prevalence of the most common type of paroxysmal dyskinesia, PKD, was estimated at 1 in 150,000 individuals.11

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Primary, or idiopathic, paroxysmal dyskinesias are genetic disorders with predominantly autosomal dominant type of inheritance, although sporadic cases are not uncommon.2,12 PA R O X Y S M A L K I N E S I G E N I C DYSKINESIA

In 1997, paroxysmal familial infantile convulsions and choreoathetosis syndrome was described and linked to a locus on chromosome 16.13 Further studies identified two loci for PKD with or without infantile convulsions, termed “episodic kinesigenic dyskinesias” (EKD). EKD1, also classified as a form of dystonia and designated as DYT10, was linked to a locus on chromosome 16p11.2-q12.1. EKD1 is typically manifested by PKD and infantile convulsions (IC).14 EKD2, also designated as DYT19 and manifested by PKD without IC, was mapped to chromosome 16q13-q22.1.15 A few families with phenotype of PKD, designated as EKD3, also were described with no mutations on chromosome 16, thus indicating that other genes might be implicated in this condition.16 The major breakthrough in understanding the genetic mechanism of PKD occurred with the discovery of mutations in the PRRT2 gene in multiple families of different ethnic backgrounds affected by PKD with or without IC.17–26 PRRT2 (proline-rich transmembrane protein-2) is a member of the transmembrane protein family, highly expressed in the basal ganglia, that is thought to play an important role in calciuminduced neuronal exocytosis by interacting with the synaptosomeassociated protein 25kDa (SNAP25), a presynaptic membrane protein involved in synaptic vesicle fusion. PRRT2-positive PKD is usually inherited in an autosomal dominant pattern, although variable penetrance and denovo mutations in the PRRT2 gene have been reported.27–30 ​

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PA R O X Y S M A L N O N K I N E S I G E N I C DYSKINESIA

This disorder, also categorized among genetic dystonias as DYT8, has been associated with three distinct mutations in the PNKD gene,

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auses of  econdary Paroxysmal Dyskinesias

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Antiphospholipid syndrome, poststreptococcal autoimmune neuropsychiatric syndrome (PANDAS), voltage-gated potassium channel (VGPC) antibody encephalitis, celiac disease, Sjögren syndrome

Vascular CNS lesions

Stroke, transient ischemic attack, severe carotid stenosis or occlusion, moya-moya disease, arteriovenous malformation

Metabolic disorders

Hypoparathyroidism, pseudohypoparathyroidism, hyperglycemia, hypoglycemia, thyrotoxicosis, kernicterus, Wilson disease

Neurodegenerative disorders

Progressive supranuclear palsy, Fahr disease, neuroacanthocytosis

Infectious disorders

HIV encephalitis, subacute sclerosing panencephalitis, cytomegalovirus, meningovascular syphilis

Other disorders

Head injury, peripheral nervous system injury, perinatal hypoxic encephalopathy, migraine aura, primary CNS lymphoma

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Besides gene mutations, secondary, or symptomatic, PKD or PNKD can be caused by a variety of metabolic, immune, and neurodegenerative disorders as well as central nervous system (CNS) infections and vascular lesions (Table 12.1).48,49 Patients with multiple sclerosis can rarely present with PKD or PNKD precipitated by movement or hyperventilation and have lesions in the basal ganglia or spinal cord on neuroimaging.50,51 Many autoimmune movement disorders such as VGPC-antibody

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Mutations in three loci coding for nicotinic acetylcholine receptor subunits have been associated with autosomal dominant nocturnal frontal lobe epilepsy:  CHRNA4 gene on chromosome 20q13.2, CHRNB2 gene on chromosome 1, and a locus on chromosome 15q24.45,46 Others, however, believe that some people have nonepileptic PHD, and no clear genetic etiology has been identified.47

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encephalitis,52 celiac disease,53 PANDAS,54 antiphospholipid syndrome,55,56 and Sjögren syndrome57 are intermittent and episodic.58 Paroxysms resembling PKD can occur in hypoparathyroidism or pseudohypoparathyroidism, nonketotic hyperglycemia, hypothyroidism, hypoglycemia, and thyrotoxicosis. Head injury can be a cause of secondary PKD, PNKD, or PED, often with a lag period of several months.8 Radiculopathy or peripheral nerve injuries were identified as potential causative factors for paroxysmal dystonia in a few cases.48 Strokes and transient ischemic attacks involving basal ganglia or thalamus can cause PKD or PNKD. Orthostatic paroxysmal hemidystonia, probably caused by decreased cerebral blood flow because it is precipitated by arising from a sitting or supine position, was described in patients with severe bilateral carotid artery disease.59 Paroxysmal choreoathetosis induced by movement, sound, and photic stimulation was reported in a case of arteriovenous malformation in the parietal lobe.60 Moya-moya disease was associated with the attacks of paroxysmal dyskinesia induced by hyperventilation, stress, and exercise (Baik and Lee 2010).61 PNKD may be a manifestation of an aura of migraine headache.48 Cases of PKD or PNKD were reported in association with HIV encephalitis,62 subacute sclerosing panencephalitis,62a cytomegalovirus encephalitis, and meningovascular syphilis.48 PKD was described as a delayed symptom of cerebral palsy.63 Kernicterus was reported as a cause of PNKD.48 Other potential but rare causes of paroxysmal dyskinesias are progressive supranuclear palsy,64 primary CNS lymphoma,65 neuroacanthocytosis,66 Fahr disease,67 and Wilson disease.68 PED can be the first manifesting symptom of young-onset idiopathic Parkinson’s disease.69

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Mutations in the SLC2A1 on chromosome 1p35-p31.3 encoding GLUT1 were associated with PED with or without epilepsy and hemiplegic migraine (DYT18).42 Deficiency of GTP-cyclohydrolase 1 also was associated with PED responsive to levodopa.43 In addition to PED and dopa-responsive dystonia with or without diurnal variation, GTP-cyclohydrolase 1 deficiency was reported in association with restless legs syndrome, adult-onset parkinsonism, and possibly Tourette syndrome.43,44

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previously referred to as the “myofibrillogenesis regulator gene” (MR-1), on chromosome 2q33-35.31,32 The gene product is a homologue of the hydroxyacylglutathione hydrolase (HAGH), which participates in metabolic detoxification of methylglyoxal, a compound present in coffee and alcohol, and produced as a by-product of oxidative stress.31 More recent studies suggested that the gene product may be important for regeneration of glutathione in neurons, thus playing an important role in maintaining proper cellular redox status and protection against toxicity and other stress conditions that may occur in neurons.33 PNKD gene mutations demonstrate high penetrance,34 although some studies reported intrafamilial variability with incomplete penetrance in a few kindreds.35 Another locus for PNKD, associated with spastic paraparesis (“choreoathetosis/spasticity episodica”), also designated as DYT9, was linked to chromosome 1.36 Later, mutations in the SLC2A1 gene encoding glucose transporter (GLUT1), which facilitates transport of glucose into erythrocytes and across the blood-brain barrier, were identified as the cause of DYT9.37 GLUT1 deficiency is characterized by infantile onset seizures, delayed development, microcephaly, paroxysmal chorea, dystonia or ataxia, alternating hemiplegia, hypoglychorrhachia, and decreased erythrocyte glucose uptake.38,39 Other genetic paroxysmal dyskinesias manifested by the PNKD phenotype have been identified. Mutation on chromosome 2q31 was described in a Canadian family with PNKD, and designated as DYT20 (Spacey et  al 2006).40 Calcium-sensitive potassium channel (KCNMA1) gene mutation linked to chromosome 10q22 was identified in a large family of mixed European descent with PNKD and generalized epilepsy.41

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Paroxysmal dyskinesias may be classified according to etiology, precipitating factors, duration, and frequency of attacks (Tables 12.2 and 12.3).2

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Most cases of PKD are autosomal dominant disorders affecting males more than females, with the age at onset ranging between 1 and 20 years. Sporadic cases that account for about a quarter of all PKD patients have more variable age at manifestation. The attacks are typically precipitated by a sudden movement after a period of rest, sudden acceleration or change in direction of movement, startle, or rarely, by vestibular stimulation, and present most often as dystonia in one or more extremities, or less often as a combination of dystonia, chorea, and ballism.8,84 The attacks are short, lasting from a few seconds to a few minutes, and occurring up to 100 times per day. They are not associated with loss of consciousness, although some patients have trouble speaking during the attacks. Sensory aura such as numbness or paresthesia in the affected limb, or vague, abnormal sensation in the abdominal or head area was reported by 82% of patients just prior to the paroxysms.84 Frequency of the paroxysms often decreases in adulthood. Association with

lassification of Paroxysmal Dyskinesia Primary (idiopathic) a) Familial b) Sporadic Secondary

Precipitating factor

Paroxysmal kinesigenic dyskinesia (PKD) Paroxysmal non-kinesigenic dyskinesia (PNKD) Paroxysmal exertion-induced dyskinesia (PED) Paroxysmal hypnogenic dyskinesia (PHD)

Duration of attacks

Short—less than or equal to 5 minutes Long—longer than 5 minutes

Frequency of attacks

Frequent (up to 100/day) Infrequent (several/week-year)

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There has been a long-standing controversy related to classification of paroxysmal dyskinesias as a primary basal ganglia disorder versus some form of subcortical epilepsy. Supporters of the epileptogenic hypothesis of PKD base their theory on the observation that both PKD and epileptic seizures are paroxysmal events that often have an aura before the paroxysms, demonstrate marked response to anticonvulsants, and may be associated with infantile convulsions.13,70 Whereas the vast majority of PKD patients have normal EEG between the paroxysms and even during the attacks, reports of abnormal ictal EEG were previously described with the paroxysmal discharges arising from the supplementary sensory-motor cortex and concomitant discharges registered from the ipsilateral caudate nucleus.71 Interictal discharges from frontocentral area contralateral to the limbs affected by the paroxysmal dystonic posturing were reported in one teenage patient with infantile convulsions and choreoathetosis and confirmed PRRT2 gene mutation.70 Decreased postmovement inhibition of motor cortex in patients with PKD has been found in some cases.72 On the other hand, some authors argue that PKD is caused by basal ganglia dysfunction, partly based on response of symptoms to levodopa in some cases,73 neuroimaging evidence of interictal and ictal perfusion changes in the basal ganglia,74,75 and a high expression of PRRT2 protein in the basal ganglia. Some have suggested that paroxysmal dyskinesias result from decreased inhibition of the thalamic reticular nucleus by the medial globus pallidus and substantia nigra, thus producing hypersensitivity of the thalamus to superficial and deep sensory input.49 Basal ganglia dysfunction also was implicated in the pathophysiology of PNKD. Lombroso and Fischman reported decreased presynaptic dopa decarboxylase activity in the striatum together with what appeared to be an increased density of the postsynaptic dopamine D2 receptors, using positron emission tomography with different radioligands in a child with PNKD.76 Invasive EEG in that patient recorded discharges from the caudate nuclei coinciding with the attacks of dyskinesia, but no epileptiform cortical discharges were observed. Transgenic mice with PNKD mutations demonstrated nigro-striatal dopamine dysregulation manifested by reduced extracellular dopamine levels in the striatum and a proportional increase of dopamine release after administration of alcohol or caffeine.77 In PED, SPECT imaging revealed decreased ictal perfusion in the frontal cortex and basal ganglia, and increased perfusion in the cerebellum,78 a pattern of perfusion changes observed in primary or secondary dystonia but not during seizures, wherein cortical hyperperfusion is usually detected. In contrast, another study reported a patient with increased perfusion of somatosensory cortex during paroxysms of foot dystonia.79 PHD attacks closely resemble frontal lobe seizures, especially those arising from supplementary sensorimotor area, that often occur at night and present as short paroxysms of tonic posturing or proximal limb movements with preserved consciousness.80 EEG discharges arising from frontal lobes during attacks of PHD were reported in a few studies, hence supporting the hypothesis of epileptogenic nature of PHD,81 although ictal and interictal EEG can be normal. Clinical presentation of PHD paroxysms with dystonic limb posturing rather than clonic convulsions can possibly be explained by the spread of epileptiform activity from mesial frontal lobe to the basal ganglia. Coexistence of classic PHD attacks with daytime paroxysms of dyskinesia and with nocturnal tonic–clonic seizures often following a PHD episode were also described in some patients.82 Controversy around pathogenesis of PHD as a type of paroxysmal dyskinesia versus partial epilepsy remains unresolved and, in fact, might suggest that PHD

is a heterogeneous condition consisting of semiologically different epileptic and nonepileptic paroxysms in various combinations. Because of its episodic nature, paroxysmal dyskinesias have been proposed to represent channelopathies.83 This notion is supported by the finding of a locus for paroxysmal nonkinesigenic dyskinesia and spasticity (DYT9) in close proximity to the potassium channel gene on chromosome 1.36 Furthermore, one gene for PNKD was linked to the locus coding for calcium-sensitive potassium channel (KCNMA1) on chromosome 10q22.41 Besides, paroxysmal dyskinesias often co-occur with epilepsy, migraines, and episodic ataxia that were previously identified as channelopathies.83 Recent discoveries of the function of PRRT2 in PKD and MR-1 in PKND, protein products of genes mutated in these respective disorders, however, do not support the hypothesis of paroxysmal dyskinesia being channelopathies, although further studies are needed.

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TAB L E   12. 3 .

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PHD

Inheritance

AD, ¼ of cases are sporadic

AD, sometimes with incomplete penetrance

AD, some sporadic cases

Sporadic, ¼ cases are familial

Gender

M:F = 4:1

M:F = 2:1

M:F = 2:3

M:F = 7:3

Age at onset, years

1–20

Early childhood up to 20s

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Precipitating factors

Sudden movement, startle

Alcohol, caffeine, fatigue, emotions

Prolong exercise, muscle vibration

Sleep

Phenomenology of attacks

Dystonia; less commonly dystonia with chorea and ballism

Dystonia and/or choreoathetosis

Dystonia

Dystonia, chorea, ballism

Duration of attacks

Seconds to 5 minutes

2 minutes to 4 hours

5–30 minutes

30–45 seconds or 2–50 minutes

Frequency of attacks

Up to 100 per day

Few per week to few in a lifetime

1 to 2 per month

5 per year to 5 per night

Alleviating factors/ medications

Anticonvulsants

Sleep, benzodiazepines

Ketogenic diet in GLUT1 deficiency

Anticonvulsants, haloperidol, acetazolamide

Associated conditions

Infantile epilepsy, migraine

Spastic paraparesis, migraine

GLUT1 deficiency Epilepsy syndrome—developmental delay, hemolytic anemia, low CSF glucose

Genetics

1. EKD1—16p11.2-q12.1 (DYT10), 2. EKD2—16q13-q22.1 (DYT19), 3. EKD3.

1. MR-1—2q33-35 (DYT8), 2. CSE gene on chromosome 1 (DYT9), 3. 2q31 (DYT20), 4. KCNMA1 10q22

SLC2A1/GLUT1—1p35-p31.3 (DYT18)

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1. CHRNA4 (20q13.2), 2. CHRNB2 (chromosome 1), 3. locus on chromosome 15q24 



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AD, autosomal dominant; CHRNA4, alpha-4 subunit of the neuronal acetylcholine receptor; CHRNB2, beta-2 subunit of the neuronal acetylcholine receptor; CSE, choreoathetosis/spasticity episodica; EKD, episodic kinesigenic dyskinesia; F, female; GLUT1, glucose transporter 1; KCNMA1, calcium-sensitive potassium channel; M, male; MR-1, myofibrillogenesis regulator gene; SLC2A1, gene encoding GLUT1.

be delayed until the early 20s. The attacks are precipitated by alcohol, caffeine, fatigue, or emotions and last from 2 minutes to 4 hours, rarely longer than a day. Frequency varies from a few paroxysms per week to only a few in a lifetime. Phenomenologically, attacks present as dystonia or a combination of dystonia and choreoathetosis that can involve one limb and gradually spread to other extremities and face, sometimes causing inability to talk. Consciousness is always preserved. In about half of the patients, paroxysms might be preceded by sensory aura such as stiffness or numbness in the affected limb or, less often, internal feeling resembling anxiety.34 PNKD usually does not respond to anticonvulsants but the attacks can be alleviated by sleep or benzodiazepines, especially clonazepam. PNKD associated with MR-1 gene mutation has a more stereotypic phenotype, with earlier age at onset, mixed dystonia/choreoathetosis, duration of the attacks up to 1 hour, precipitation of the paroxysms by alcohol and caffeine, and good response to benzodiazepines.34 The phenotype of PNKD without MR-1 gene mutation is more variable in the age of onset, precipitants, clinical features, and response to medications.34 Association of PNKD with spastic paraparesis was reported in some cases by Auburger and later linked to SLC2A gene ​

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infantile convulsions, migraine including hemiplegic migraine, and episodic ataxia were also previously reported in PKD patients with PRRT2 mutations.13,22,24,84–88 Infantile convulsions and choreoathetosis syndrome is characterized by nonfebrile seizures in infancy that resolve by the age of 2 years followed by the development of PKD in young childhood. Phenotype can vary among the family members from pure PKD or infantile seizures to a combination of both.18,89 PRRT2-positive cases are more likely to have younger age of onset, longer duration of the attacks with bilateral involvement, premonitory sensation, and excellent response to low-dose carbamazepine.90,90a

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Paroxysmal nonkinesigenic dyskinesia is an autosomal dominant disorder affecting more males than females. Female patients have increased frequency of the attacks during menstruation or ovulation. The age at onset is usually early childhood but occasionally can

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on chromosome 1.36,37 Patients with PNKD also have higher prevalence of migraine than the general population.34

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EA-3 (with tinnitus and headache) was described in a Canadian Mennonite family with episodes of ataxia, vertigo, tinnitus, and headaches with no identified precipitants. Patients have interictal myokymia and sometimes residual ataxia between the paroxysms.102 Age at onset can vary from early childhood to adulthood. A candidate gene was identified on 1q42 chromosome.103

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EA-4 (with ocular motility dysfunction), or periodic vestibulocerebellar ataxia, manifests in early adulthood as recurrent attacks of ataxia, vertigo, tinnitus, and diplopia precipitated by fatigue or sudden change in head position, with episodes lasting minutes to hours.104,105 The episodes gradually become more frequent and might transform into progressive ataxia. The gene for EA-4 has not been identified. EA-5 (with vertigo and juvenile epilepsy) was described in a French Canadian family with attacks of ataxia and vertigo and interictal nystagmus, linked to CACNB4 gene on chromosome 2q22-23.106 The disorder was associated with juvenile epilepsy. ​

EA-6 (with episodes of ataxia from birth to 20 years) was initially described in 2005 in a patient with episodic ataxia, migraine, photophobia, alternating hemiplegia, and seizures who carried a mutation in SLC1A3 gene on chromosome 5p13 encoding glutamate transporter EAAT1.107 EA-6 can manifest as a milder phenotype with attacks of ataxia, nausea, vomiting, photophobia, phonophobia, vertigo, diplopia, and dysarthria.107a Attacks can be precipitated by exercise, fatigue, excitement, alcohol, or caffeine and last for 2 to 3 hours. Mild ataxia and nystagmus can persist between the attacks. ​

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Paroxysmal hypnogenic dyskinesia usually manifests in childhood or adolescence (sometimes even in adulthood) as paroxysms of dystonia, chorea, and/or ballism during non-REM sleep associated with sudden awakening. The attacks can occur from five per year to five per night and last 30 to 45 seconds.10 A small number of patients with longer paroxysms (2 to 50 minutes) resistant to medications has been described.10 During the episodes, patients have been observed to whistle, utter guttural sounds or incoherent words, and have a frightened facial expression. Ictal EEG may show normal awake pattern or epileptiform discharges arising from the frontal lobe, and the patients usually fall asleep following the paroxysms.81 Some patients also have daytime paroxysmal dyskinesia or tonic–clonic seizures following a nocturnal attack of dyskinesia. Most cases of PHD are sporadic but some patients report family history of epilepsy and parasomnias.97 Between the attacks, patients with all types of idiopathic paroxysmal dyskinesias have normal neurological examination. Patients with secondary types of paroxysmal dyskinesias may have interictal symptoms and neurologic deficits associated the underlying disorder. Secondary paroxysmal dyskinesias should be suspected in patients with older onset, longer duration of the attacks, abnormal neurological examination between attacks, and other atypical features (see Table 12.1).

EA-2 (with nystagmus) is characterized by paroxysms of ataxia and dysarthria of longer duration (hours to days) precipitated by exercise, fatigue, stress, and alcohol. There is no interictal myokymia in this type of EA, but the patients typically have nystagmus between the paroxysms. EA-2 is associated with P/Q type calcium channel (CACNA1A) gene mutations on chromosome 19p13.2.100,101

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PA R O X Y S M A L H Y P N O G E N I C DYSKINESIA

EA-1 (with interictal myokymia/neuromyotonia) typically manifests in childhood as recurrent attacks of ataxia lasting seconds to less than 2 minutes, often precipitated by startle or sudden movements. Between attacks, the patients have myokymia usually involving the face but no other neurological symptoms. Rarely, EA-1 patients also have PKD. EA-1 has been linked to the voltage-gated potassium channel (KCNA1) gene mutations on chromosome 12p13.99,100

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This condition usually has an autosomal dominant type of inheritance, with some sporadic cases described.91 It affects females more than males and it first manifests typically between the ages 2 and 30 years. The attacks are precipitated by prolonged exercise, can occur daily or a few per month and last for 5 to 30 minutes, occasionally up to 2 hours, and affect mainly legs. Rare precipitating factors are muscle vibration, passive movements, electric nerve stimulation, or cold. Paroxysmal leg dystonia is the most common presentation of PED. This type of paroxysmal dyskinesia can be associated with other manifestations of GLUT1 deficiency syndrome (see discussion earlier)—developmental delay, hemolytic anemia, and low CSF glucose. “Runner’s dystonia” is a sporadic variant of PED described in longdistance and marathon runners as paroxysmal leg or foot dystonia provoked by prolonged running.92 This disorder also shares some clinical features with other forms of isolated, idiopathic focal dystonia (such as sensory trick), PKD (good response to carbamazepine treatment), or peripherally-induced dystonia (history of injury to the affected limb prior to the onset of dystonia). A mixed phenotype combining characteristics of PKD and PNKD was described by Kinast in 1980.93 The attacks were described as brief and frequent, responding well to anticonvulsants, similar to PKD. However, the paroxysms were provoked by hyperventilation and not by sudden movements, thus resembling PNKD. PRRT2 mutations were also identified in some cases of paroxysmal exertioninduced dyskinesia,28,94 PNKD-like phenotype,28,95 or in a kindred with the clinical features of paroxysmal kinesigenic dyskinesia, paroxysmal exertion-induced dyskinesia, and non-kinesigenic paroxysmal dyskinesia.95a The combination of benign familial infantile seizures and PKD associated with mental retardation and episodic ataxia has been described in a consanguineous family.96

Episodic ataxias (EA) are rare familial disorders characterized by brief paroxysms of ataxia with usually normal interictal neurological examination except for myokymia/neuromyotonia, nystagmus, or mild ataxia in some types of EA. The disorders belong to the family of channelopathies, inherited in autosomal dominant fashion.98 Classification of episodic ataxias:

EA-7 (with episodes of ataxia in juveniles) was described in a family with paroxysms of ataxia, sometimes with dysarthria and weakness, triggered by exercise or emotions and linked to chromosome 19q13; however, no gene has been identified yet.108 ​

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motor area seizures may be triggered by movements and present as dystonic posturing of a limb without loss of consciousness, thus closely resembling PKD. Hyperventilation also can be a precipitating factor of both epileptic seizures and paroxysmal dyskinesias. Both conditions respond to anticonvulsants. EEG might help to differentiate paroxysmal dyskinesias from seizures; however, abnormal EEG was reported in paroxysmal dyskinesia and, on the other hand, epileptic seizures arising from deep temporal lobes and sometimes frontal lobes might not cause any abnormalities on scalp EEG. A case of frequent brief paroxysms of movement-induced dystonic posturing closely resembling PKD was recently reported in a patient who was found to have focal gliosis in the amygdala producing epileptic activity.115 Temporal lobectomy produced complete resolution of the paroxysms. Juvenile myoclonic epilepsy is another disorder manifesting as brief abnormal movements in the limbs, usually in the morning; however, it has a characteristic EEG pattern. PHD is often considered a type of nocturnal frontal lobe seizure. Eating reflex seizures and head nodding syndrome may resemble paroxysmal dyskinesia but probably represents a seizure disorder.116 Action dystonia is characterized by the appearance or exacerbation of dystonia during voluntary movements including specific tasks performed by the affected body part (task-specific dystonia such as writer’s cramp, musician’s dystonia). It might resemble PKD or PED; however, precipitation of dystonia by only certain tasks (in taskspecific dystonia), restriction of dystonia to a certain body part, relief from sensory tricks and no response to antiepileptics, as well as the lack of family history in most cases can help distinguish this condition from paroxysmal dyskinesia. Dopa-responsive dystonia (DRD) also manifests in childhood as lower limb dystonia exacerbated by exercise, similar to paroxysmal dyskinesia; however, it is characterized by diurnal fluctuation of the symptoms but not discrete paroxysms of dystonia. Dramatic response to levodopa is one of the most unique features of DRD. If the diagnosis is not certain, a trial of levodopa should be considered in any child or adolescent with paroxysmal or fluctuating dystonia. Tics can resemble short paroxysms of dyskinesia but they also have other characteristic features such as premonitory urge and ability to suppress the movements.117 Rarely, dopa-responsive dystonia and tics co-exist and may appear as paroxysmal disorders.44 Stereotypies are patterned, repetitive movements or vocalizations that might be involuntary or occurring in response to inner sensory stimulus.118 They can represent a normal phenomenon or a feature of different neurological and psychiatric disorders such as tardive dyskinesia, frontotemporal dementia, Tourette syndrome, autism, or mental retardation. Stereotypies, in contrast to paroxysmal dyskinesia, are not precipitated by a certain activity or other external factors and do not manifest as paroxysms of abnormal movements with asymptomatic intervals between them. Hyperekplexia is an exaggerated startle syndrome with complex movements with the onset in infancy that might resemble PKD; however, the attacks in hyperekplexia are precipitated by unexpected auditory or tactile stimuli but not movements.119 The culture-specific startle syndromes such as “Latah” in Indonesia and Malaysia may also resemble paroxysmal dyskinesias.120 Sandifer syndrome is an early childhood disorder characterized by prolonged paroxysms of head tilt following eating secondary to gastroesophageal reflux.121 Psychogenic movement disorders and nonepileptic pseudoseizures share certain clinical characteristics with paroxysmal dyskinesias, such as abrupt onset and fluctuation of the symptoms.122 Other features typical of psychogenic disorder, such as distractibility, suggestibility, inconsistency, and variability of clinical presentation from one paroxysm to another, can help differentiate it from an organic disease. Move

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Epilepsy. Preserved consciousness during the attacks, consistent precipitation of the paroxysms by certain factors, and positive family history of episodic involuntary movements are in favor of paroxysmal dyskinesias rather than seizures. On the other hand, supplemental

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Two autopsy reports on patients with PKD were published in the literature. Slight asymmetry of the substantia nigra was reported in one deceased patient114 and some melanin accumulation in macrophages in the locus coeruleus consistent with neuronal loss was found in another patient.6 Autopsies of two patients with PNKD reported no pathology.7

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History and the description of the paroxysms are often sufficient to diagnose paroxysmal dyskinesia. Observation of the attacks in the office or on home video can further support the diagnosis. Routine EEG or long-term video-EEG monitoring might be considered to exclude frontal lobe seizures. In more difficult cases, invasive EEG might be required. Brain MRI should be ordered in atypical cases of paroxysmal dyskinesia, including sporadic cases with later age at onset, residual neurological deficit between the attacks, or hyperventilation-induced paroxysms. Screening for metabolic causes of paroxysmal dyskinesia should include at least thyroid function tests, calcium level, and blood glucose obtained during the attacks. Lumbar puncture should be considered if there is any concern about GLUT1 deficiency syndrome. Fasting CSF glucose arms

HMN 2B

AD

HSPB1

608634

HMN 2C

AD

HSPB3

613376

HMN 2D

AD

FBXO38

615575

HMN 3 = DSMA3

AR

11q13

607088

HMN 4 = DSMA3

AR

11q13

HMN 5A = CMT2d

AD

GARS

600794

Arm predominant, distal

HMN 5B

AD

REEP1

614751

Arm predominant, distal

HMN 5C = Silver syndrome (SPG17)

AD

BSCL2

270685

Arm predominant, distal, with UMN signs

HMN 6 = DSMA1 = SMARD1

AR

IGHMBP2

604320

Infancy onset, respiratory distress with diaphragmatic paralysis, poor prognosis. Differs from SMA type I (distal weakness).

HMN 7A

AD

SLC5A7

158580

Laryngeal and distal arm involvement, early onset

HMN 7B

AD

DCTN1

607641

Laryngeal, facial and arm involvement, adult onset

DSMA 2 = SMA Jerash type = HMN 2J

AR

9p

605726

Juvenile onset with pyramidal features, multiple consanguinous families from Jordan

DSMA 4

AR

PLEKHG5

611067

Early, severe, distal and proximal weakness, family from Mali

DSMA 5

AR

DNAJB2

614881

Adult onset, slowly progressive, distal leg weakness, Moroccan Jewish Israeli family

SMA X1 = Kennedy disease

X linked

AR

313200

Discussed separately

X-linked infantile SMA with arthrogryphosis = SMA X2

X linked

UBA1

301830

Neonatal onset with arthrogryphosis, severe hypotonia and early death

X-linked HMN = SMA X3

X linked

ATP7A

300489

Juvenile to adult onset distal motor neuropathy. Allelic with Menkes syndrome

ALS4 = HMN with pyramidal features

AD

SETX

602433

Arm weakness with UMN signs. Allelic with ataxia with oculomotor apraxia type 2 (AOA2).

SMA Fickel type

AD

VAPB

182980

Adult-onset, slowly progressive, LMN only, prominent fasiculations

Congenital distal SMA

AD

TRPV4

600175

Early onset with contractures, non-progressive

Scapuloperoneal SMA = CMT2C

AD

TRPV4

181405

Progressive weakness of scapuloperoneal and laryngeal muscles

SMA with pontocerebellar hypoplasia = Pontocerebellar hypoplasia type 1

AR

VRK1

607596

Infantile onset, poor prognosis, clinically similar to SMA type I

Slowly progressive early adult onset

​

Slowly progressive juvenile onset with diaphragmatuc weakness

​

​

​

7q34-36 or HSPB1 or 8 ​

AD

​

HMN 1 = CMT2F

​

​

ALS = amyotrophic lateral sclerosis; CMT = Charcot-Marie-Tooth disease; DSMA = distal spinal muscular atrophy; HMN = hereditary motor neuropathy; SMA = spinal muscular atrophy; SMARD = SMA with respiratory distress.

​

​

dysphagia, choreoathetosis, and psychiatric manifestations. Imaging discloses cerebellar atrophy.38 Diagnosis is established by finding low Hexosaminidase A activity (with normal Hexosaminidase B activity) in serum or leucocytes, or alternatively by genetic testing. Tay-Sachs disease and LOTS are caused by mutations of the gene encoding the alpha subunit of the enzyme (HEXA). Hexosaminidase A comprises alpha and beta subunits, whereas Hexosaminidase B comprises beta subunits only. Mutations with residual enzyme activity are associated with LOTS, whereas mutations without residual activity cause the rapidly progressive early onset phenotype of Tay-Sachs disease. Mutations of the beta subunit (HEXB) cause Sandhoff disease, which is associated with a deficiency of both enzyme subtypes. Sandhoff disease is usually an early-onset disorder, although there do exist rare reports of an adult-onset phenotype with cerebellar and LMN deficits.39

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contribute to neurodegeneration and muscle atrophy.24 Experimental evidence suggests that exposure to the ligand (androgen) is necessary for disease expression, prompting a placebo-controlled trial of androgen deprivation (with leuprorelin) that suggests some benefit on functional and swallowing measures.25 AR accumulation in scrotal skin nuclei may serve as a biomarker of KD. Female carries of the AR gene CAG expansion may occasionally express symptoms of KD but manifestations tend to be minor (fasciculations, minimal weakness, elevated CK). Furthermore, homozygous expansion in females is only mildly symptomatic,26 supporting the role of androgen exposure in pathogenesis.

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Also known as late-onset Tay-Sachs disease (LOTS), this GM2 gangliosidosis presents with neurodegeneration that involves multiple systems.32 Manifestations include any combination of LMN loss involving extremities,33–35 UMN findings,36 ataxia, eye movement abnormalities (specifically multistep saccades37), speech alteration,

t

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Also known as adult-onset type IV glycogen storage disease, adult polyglucosan body disease is caused by a mutation of the glycogen brancher enzyme gene (GBE1). Presentation is typically after the age of 40 years with neurogenic bladder, gait change (from spasticity or weakness), mixed UMN and LMN signs, and mild cognitive loss.41,42 Periventricular lesions on brain MRI may result in a misdiagnosis of multiple sclerosis. Progression is slow over years, and survival is not shortened. GBE deficiency causes accumulation of PAS-positive material in nerve, muscle, grey and white matter, and various other tissues including apocrine sweat glands. Genetic testing the preferred method of diagnosis. Partial GBE deficiency causes this late-onset syndrome, whereas severe deficiency or absence of enzyme causes early forms that manifest with severe myopathy, cardiomyopathy, or hepatic changes. Inheritance is autosomal recessive, perhaps with a higher prevalence in individuals of Ashkenazi Jewish ancestry. ​

​

L AT E - O N S E T H E X O S A M I N I D A S E A DEFICIENCY

euro

A D U LT P O LY G L U C O S A N B O D Y D I S E A S E

Diseases

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Described are a few otherwise defined neurodegenerative disorders with LMN+/-UMN manifestations that feature in the differential diagnosis of ALS.

170 | M o o r

In its typical form, Alexander disease is a rare early-onset lethal leucodystrophy that is characterized by eosinophilic inclusions in astrocytes called Rosenthal fibers. After the identification of glial fibrillary acidic protein (GFAP) mutations causing Alexander disease, the phenotype was expanded to include an adult-onset form. Adult-onset Alexander disease may be the most common form of Alexander disease.40 It is characterized by progressive symptoms localizable to the lower brainstem and upper spinal cord, which typically appear markedly atrophic with signal change on MRI. Manifestations include pseudobulbar findings, dysarthria, dysphonia, vocal cord paralysis, spastic tetraparesis, ataxia, nystagmus, and saccadic pursuit. Forty percent of patients have palatal myoclonus. Bladder symptoms are common. LMN changes occur at cervical levels and may be associated with neck weakness. Age of onset varies from early adulthood to the eighth decade. Asymptomatic patients identified by radiological changes are reported. Rate of progression is generally slow, but varies extremely (duration 34 repeats) in ATXN2 cause a spinocerebellar ataxia accompanied by motor neuron loss. In multiple studies of sporadic ALS, intermediate-sized repeats (>29) have consistently been associated with a twofold increase in the risk of ALS.89–97 Efforts to link intermediate repeats and ALS pathogenesis have focused on interactions with FUS98 and TDP-4399 that exacerbate TDP-43 and FUS cellular pathology. ​

CHCHD10

G E N E S I M P L I C AT E D B Y   C A N D I D AT E GENE APPROACHES

​

​

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Although candidate gene studies had implicated cytoskeletal pathway genes in ALS (DCTN1, NEFH, spastin, and peripherin), the best evidence to date comes from the identification of mutations in profilin-1 (PFN1) in familial ALS.78 Although very few ALS patients with PFN1 mutations have been reported, all have had limb onset without cognitive impairment.78,79 Profilin 1 is important for axonal integrity and axonal transport, and the missense mutations described reduced actin binding and neurite outgrowth, as well as altered growth cone morphology and size.78 Interestingly, in vitro expression of mutated PFN1 results in aggregated cytosolic TDP-43, potentially linking the mechanism of PFN1 ALS to other forms of the disease.78

Overall, the contribution of common variation to ALS appears to be high: Two independent studies have recently demonstrated heritability between 12% and 20%.87,88 These studies have yielded important candidate risk factors (Table 27.2) and alleles influencing disease phenotypes or prognosis (Table 27.3), but in general these have been difficult to interpret due to problems with replication. Two methodologies have been utilized to look for more common risk factors: candidate gene investigations and genome-wide association studies. ​

​

​

​

​

RIS

​

​

​

UBQLN2 is the only known cause of X-linked ALS.71. The spectrum of ALS caused by UBQLN2 frequently includes FTD and several have shown juvenile onset.71 Although it is a rare cause of both familial and sporadic disease,72–75 this discovery has directed some attention toward the role of the ubiquitin-proteosome system in ALS. UBQLN2 functions to deliver ubiquitinated proteins to the proteasome, and the most clearly pathogenic ALS mutations disrupt the PXX domain, which is believed to regulate protein-protein interactions.71 Interestingly, UBQLN2 co-localizes with aggregated proteins in all forms of ALS, including those found in SOD1 and C9ORF72.71,76 Similar roles have been proposed of valosin-containing protein (VCP), mutations of which can also cause an ALS-like phenotype.77

S

A

F

isk actors reported for  L . This table highlights common low frequency variants that have been associated with risk

 R

TAB L E   27. 2

IO

A

LC T I

N

REP

IO

C T A

IFI

D NT E

OF

O

E

M TH D

ESS

C

PRO

E

T D

ISRUP

N/ D ​

NCT

IO

FU

N

EI

T

I

S

PRO

E

G N

E

A

for  L in at least one study, with a summary of replications attempts N

Proposed Risk factor genes identified in candidate SNP studies

Candidate variant assocation (CAG 29-32)

Yes

TREM2

triggering receptor on myeloid cells 2

microglial activation

Candidate variant association (p.R47H)

-

PFN1

profilin 1

regulates actin polymerization

Candidate variant association (p.E117G)

-

SMN1

survival motor neuron 1

snRNP and GEM formation, RNA processing

Candidate gene CNV association (1, 2, 3 copies)

Yes

PON1-3

paraoxonase 1–3

preventing lipid oxidation, detoxification of organophosphates

Candidate gene SNP association, sequencing

Mixed

HFE

hemachromatosis

regulation of iron metabolism

Candidate SNP association

Mixed

VEGF

vascular endothelial growth factor A

angiogenesis

Candidate gene association, sequencing

Mixed

APEX1

APEX nuclease

DNA damage repair

Candidate gene sequencing

Mixed

ANG

angiogenin

ribonucleolysis; angiogenesis

Candidate SNP association

Mixed

​

​

​

RNA translational regulation; endocytosis; ER stress

​

ataxin 2

​

ATXN2

​

Proposed Risk factor genes identified by genome- wide association studies (GWAS)

presynaptic protein with roles in glutamate neurotransmission

GWAS (SNP)

Mixed

ELP3

elongator protein 3

component of RNA polymerase

GWAS (microsatellites)

No

17q11.2

rs34517613 in LD with SARM1

unknown

GWAS (SNP)

No

DPP6

dipeptidyl-peptidase 6

regulates voltage-gated potassium channels

GWAS

No

FGGY

FGGY carbohydrate kinase domain containing

phosphorylates carbohydrates

GWAS, Candidate gene sequencing

No

ITPR2

inositol 1,4,5-trisphosphate receptor, type 2

GWAS (SNP)

No

NIPA1

non imprinted in Prader-Willi/Angelman syndrome 1

magnesium transport and early endosomes

Genome-wide CNV analysis

No

KIFAP3

kinesin-associated protein 3

linker between kinesins and chromosomes

GWAS

No

PLCD1

phospholipase C, delta 1

IP3/DAG signaling

GWAS

No

​

​

association suggests that the blockade of EPH4A expression or function might be a viable therapeutic target.

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PA R O X O N A S E Paraoxonase 1, 2, and 3 are enzymes encoded by a gene cluster on chromosome 7.  PON1 is important for detoxifying chemicals such as organophosphate pesticides. Given the hypothesized link between ALS and pesticide exposures, the paraoxonase locus has been extensively investigated as a genetic risk factor. Although an association

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27

Am

EPH4A EPH4A is a receptor for ephrins, a class of signaling molecules implicated in axonal repulsion as well as synapse formation. In a zebrafish model of SOD1 ALS, it was found that knockdown of EPH4A blocked SOD1 toxicity, nominating the receptor as a potential risk factor. In the same study, blood expression levels of EPH4A were inversely correlated with disease onset and survival in human ALS. Furthermore, two ALS patients were found to carry novel coding variants in EPH4A and each showed strikingly prolonged survival.106 If replicated, this

In

​

​

​

​

​

​

unc-13 homolog A ​

UNC13A

s | 211

phenotype. This table presents variants and genes that have been reported

S

A

 

TAB L E   27. 3 Genetic factors reported as modifiers of  L

D

CT

EFFE

PROPOSE

N

IO

A

I

LC T

REP

N

IO

O

A

C T

IFI

D NT E

I

ESS

C

PRO

E

T D

ISRUP

N/ D ​

NCT

IO

FU

N

EI

T

PRO

E

E

E

M TH D G N

OF

S

A

to influence the  L disease manifestation in carriers

Proposed modifiers of ALS phenotype

Mixed

earlier onset, shorter survival with common haplotype

UNC13A

unc-13 homolog A (C. elegans)

presynaptic protein with roles in glutamate neurotransmission

Candidate SNP association

Mixed

shorter survival

SMN2

survival motor neuron 2

snRNP and GEM formation, RNA processing

Candidate CNV association

Mixed

shorter survival

EPHA4

EPH receptor A4

neuronal developmental signaling

Candidate gene sequencing

No

longer survival times with disruptive mutations

NIPA1

non imprinted in Prader-Willi/Angelman syndrome 1

magnesium transport and early endosomes

Candidate gene repeat length association

No

earlier onset, shorter survival

HFE

hemachromatosis

regulation of iron metabolism

Candidate SNP association

Mixed

longer survival with H63D

KIFAP3

kinesin-associated protein 3

linker between kinesins and chromosomes

Candidate SNP association

Mixed

longer survival

VEGF

vascular endothelial growth factor A

angiogenesis

Candidate SNP association

Mixed

earlier onset

PPARGC1A

metabolic regulator peroxisome proliferatoractivated receptor gamma, coactivator 1 alpha

Candidate SNP association

-

earlier onset, shorter survival

Diseases

S

I

ESIS

E

E

E

O

O

M G N T C TH G N

K N O W N G E N E S S U G G E S T M U LT I P L E ROUTES TO MOTOR NEURONAL LOSS

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In other neurodegenerative diseases, the genetic landscape has greatly strengthened insights into disease pathogenesis. For example, in Alzheimer’s disease the known causative genes for early onset familial AD (PSEN1, PSEN2, and APP) are all directly involved in the metabolism of Aβ. This striking convergence on a single pathway has reinforced the importance of the amyloid beta pathway, a recognized pathological hallmark of disease. The spectrum of genes causing ALS includes functions in RNA processing, microtubule assembly/transport, endosomal transport, autophagy, and mitochondrial energy dynamics, to name a few (see gene functions column in Table 27.1). As such, genetic endeavors have not clearly delineated a single theme or biological pathway but have instead suggested that the destruction of motor neurons can result from failures in multiple disparate pathways. In this view, motor neurons are the Achilles heel of a complicated motor pathway. In sum, although there are several ways to draw links between the genes involved in ALS, how to draw these links remains unclear. That said, the identification of several RNA binding proteins (TDP-43, FUS/TLS, TAF15, EWSR1, hnRNPA2B1, and hnRNPA1) has rightly brought RNA biology (regulated expression, missplicing) to the forefront of investigation. Despite careful investigation, a unifying link between RNA mediated toxicity and ​

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Since 2007 when the first GWAS was published for ALS,113 multiple additional studies have endeavored to identify loci with common variants that influence risk for ALS. To date, only a single locus, 9p21, has been consistently replicated in well-powered studies.87,114,115 This region is explained by the C9ORF72 repeat expansion carried by a substantial number of subjects with sporadic ALS. Other loci identified in smaller studies include DPP6,116,117 ITPR2,118 FGGY,119 KIFAP3,120 ELP3,121 and UNC13A,122,123 but have failed to replicate in larger studies.87,124,125 Confidence in the future utility of GWAS for finding ALS risk genes has been fueled by studies in other neurological diseases (e.g., Alzheimer’s disease and schizophrenia), in which concerted efforts to increase sample sizes (and therefore power) have yielded impressive gains in the number of associated loci. Indeed, the largest meta-analysis of ALS to date (6,100 cases and 7,125 controls, which is still small by other disease standards) recently yielded a novel locus at 17q11.2 and a second suggestive association with 18q11.2.87

PA

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Y

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A

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with sporadic ALS was identified in six different populations,107–110 several GWAS studies and a large meta-analysis could not replicate the finding.111 More recently the burden of rare coding variants in the PON genes was also assessed in ALS and surprisingly revealed fewer mutations in patients compared with controls.112

​

Candidate SNP association

FRO

secreted growth factor

S

granulin

​

GRN

Two potential C9ORF72-specific therapies are under development. The first of these is an approach using antisense oligonucleotides to specifically bind C9ORF72 RNA containing the repeat expansion, thereby directing its degradation by cellular machinery. In patient-derived cell lines carrying C9ORF72 expansions, these molecules block formation of RNA foci, normalize transcriptome profiles, and eliminate the production of RAN translation products.19,140,141 Because ASOs have already been tried in humans, including for SOD1-related ALS,139 efforts to bring such drugs to clinical trials are currently underway. A small molecule approach targeting the repeats themselves has also been published, showing that small molecules can disrupt foci formation and RAN translation.25 In the future, biomarker profiles may identify other groups of patients for whom targeted therapies may be helpful. For example, miRNA signatures with associated therapeutic targets may be become equally compelling for drug development.142,143 Indeed, two groups have defined one particular miRNA, miR-155, as important in ALS.142,143 Koval and colleagues used an ASO approach to inhibit miR-155 and extend disease duration in animal models.143 The ability to extend RNA targeted therapeutic strategies to noncoding RNAs may open up novel targets beyond the defined dominantly inherited disease-causing mutations, and may apply more broadly to sporadic ALS. ​

​

ALS remains unsettled. For ALS there may be no clear genetic theme other than continuing to define the multiple sensitive pathways of the motor neuron. On the other hand, future studies and additional gene discoveries may yet uncover a more clearly unifying link. A L S I S L I K E LY T O B E A M U LT I S T E P DISEASE

ARE

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With an increasing number of genes identified in ALS and the development of targeted therapeutics, we anticipate that genetics will be increasingly incorporated into diagnosis and clinical care (Figure 27.4). The current diagnostic paradigm for ALS focuses on the use of laboratory testing, EMG/NCS, and imaging to exclude mimics of ALS (see Chapters X-Y). In most centers, genetic testing for known genes is applied to the minority of cases in which family history of ALS is evident. In these dominantly inherited ALS syndromes, genetic testing ​

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The genetics of ALS suggest that motor neurons are uniquely susceptible to many different types of insults. However, the late-onset nature of the disease emphasizes that motor neurons are resilient. This state is well illustrated by carriers of the highly penetrant SOD1 A4V mutation that survive 4 to 6 decades prior to symptom onset. This paradox supports a liability threshold model of disease, wherein there are many routes and insults (both genetic and environmental) that eventually lead to motor neuron death and the emergence of ALS symptoms.126 Some mutations (e.g., SOD1 p.Ala4Val) are sufficient on their own to cause disease in almost all carriers and therefore show up as familial ALS with clear Mendelian inheritance patterns. Others (e.g., TARDBP p.Ala382Thr) are frequently found in association with other ALS gene defects,127 suggesting that several gene defects with smaller effects sizes may be required. This does not even begin to address the environmental and behavioral factors that have been difficult to investigate in ALS but that undoubtedly contribute on their own or by interacting with genetic variation to trigger neurodegeneration. In fact, recent statistical modeling based on age-associated incidence of disease suggests that ALS is a multistep process, with an average of six insults or steps required for disease to occur.128

As the number of genes implicated in ALS has continued to expand, it is becoming increasingly clear that motor neuron loss manifesting as ALS is the final common pathway of a number of separate disorders that strike at the motor neuron. The heterogeneity of involved pathways across patients may help explain why many clinical trials directed broadly at “ALS” have failed. More success may come from defining groups of ALS patients with shared genetic or other molecular signatures and designing therapies targeting those specific abnormalities. The therapeutic toolbox for specifically targeting specific genes is expanding and includes small molecules, vaccination, passive immunization, viral delivery of RNAi, and antisense oligonucleotides (ASOs).129 Each of these options is increasingly viable and likely to be a component of one or more clinical trials in ALS in the near future. Patients with mutations in the same gene are currently the easiest subgroup to ascertain, and progress toward gene-specific therapies is being made for both SOD1 and C9ORF72. For SOD1, more than two decades of animal research has made it clear that mutations cause disease by a toxic gain-of-function rather than by impairing the superoxide dismutase enzymatic activity. Therefore, the most straightforward therapeutic approach for SOD1mediated ALS (clintrials.gov NCT00706147) is to reduce the levels of the SOD1 protein. There are now multiple efforts underway to lower SOD1 using small molecules,130,131 immunization,132 viral delivery of RNAi,133–137 and ASOs.138 The antisense oligonucleotide therapy recently completed a Phase I clinical trial.139 Although the amount of ASO given (clintrials.gov NCT02623699) in this trial was not expected to lower SOD1 levels or impact disease course, a follow-up clinical trial using this same approach is underway.

Current Paradigm

Future Paradigm

Patient presents with history and exam worrisome for ALS - Testing to exclude mimics: • EMG/NCS • Imaging • Lab evaluation • Selective genetic tests

- Testing to rule-in ALS: • Diagnostic biomarkers • Diagnostic genetic testing

Patient diagnosed with ALS

Patient treated for ALS

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Figure 27.4 Envisioned approach to the diagnosis and treatment of ALS

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patients. The insights from genetic studies in ALS are expected to soon revolutionize the clinical approach to ALS patients. Soon, instead of just clarifying the genetic cause in clearly familial cases, genetics will be utilized widely for diagnosis, prognosis, and even for the selection of personalized therapeutics.

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- Personalized drug regimen started based on: • ALS subtype • Stem-cell screening assays

- Consider riluzole - Supportive care - Symptom management

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- ALS subtype determined by: • Prognostic biomarkers • Genome/epi-genome - Patient’s stem-cell assayed for response to available treatments

s | 213

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1. Soong, B. W., Lin, K. P., Guo, Y. C., Lin, C. C., Tsai, P. C., Liao, Y. C., et al. (2014). Extensive molecular genetic survey of Taiwanese patients with amyotrophic lateral sclerosis. Neurobiol Aging, 35(10), 2423, e1–6. 2. Kenna, K. P., McLaughlin, R. L., Byrne, S., Elamin, M., Heverin, M., Kenny, E. M., et al. (2013). Delineating the genetic heterogeneity of ALS using targeted high-throughput sequencing. J Med Genet, 50(11), 776–783. 3. Cady, J., Allred, P., Bali, T., Pestronk, A., Goate, A., Miller, T.  M., et  al. (2014). ALS onset is influenced by the burden of rare variants in known ALS genes. Ann Neurol, 77(1), 100–113. 4. Renton, A.  E., Chio, A., & Traynor, B.  J. (2014). State of play in amyotrophic lateral sclerosis genetics. Nat Neurosci, 17(1), 17–23. 5. Metzker, M. L. (2010). Sequencing technologies—the next generation. Nat Rev Genet, 11(1), 31–46. 6. Consortium, E. P. (2012). An integrated encyclopedia of DNA elements in the human genome. Nature, 489(7414), 57–74. 7. Conte. A, Lattante, S., Luigetti, M., Del Grande, A., Romano, A., Marcaccio, A., et al. (2012). Classification of familial amyotrophic lateral sclerosis by family history: Effects on frequency of genes mutation. J Neurol Neurosurg Psychiatry, 83(12), 1201–1203. 8. Majounie, E., Renton, A. E., Mok, K., Dopper, E. G., Waite, A., Rollinson, S., et al. (2012). Frequency of the C9orf72 hexanucleotide repeat expansion in patients with amyotrophic lateral sclerosis and frontotemporal dementia: A cross-sectional study. Lancet Neurol, 11(4), 323–330.





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9. Al-Chalabi, A., & Lewis, C. M. (2011). Modelling the effects of penetrance and family size on rates of sporadic and familial disease. Hum Hered, 71(4), 281–288. 10. Renton, A. E., Majounie, E., Waite, A., Simon-Sanchez, J., Rollinson, S., Gibbs, J. R., et al. (2011). A hexanucleotide repeat expansion in C9ORF72 is the cause of chromosome 9p21-linked ALS-FTD. Neuron, 72(2), 257–268. 11. DeJesus-Hernandez, M., Mackenzie, I. R., Boeve, B. F., Boxer, A. L., Baker, M., Rutherford, N. J., et al. (2011). Expanded GGGGCC hexanucleotide repeat in noncoding region of C9ORF72 causes chromosome 9p-linked FTD and ALS. Neuron, 72(2), 245–256. 12. Byrne, S., Heverin, M., Elamin, M., Walsh, C., & Hardiman, O. (2014). Intermediate repeat expansion length in C9orf72 may be pathological in amyotrophic lateral sclerosis. Amyotroph Lateral Scler Frontotemporal Degener, 15(1–2), 148–150. 13. Nuytemans, K., Bademci, G., Kohli, M.  M., Beecham, G.  W., Wang, L., Young, J. I., et al. (2013). C9ORF72 intermediate repeat copies are a significant risk factor for Parkinson disease. Ann Hum Genet, 77(5), 351–363. 14. Harms, M.  B., Cady, J., Zaidman, C., Cooper, P., Bali, T., Allred, P., Cruchaga, C., Libby, R., Baughn, M., Pestronk, A., Goate, A., Ravits, R., & Baloh, R. H. (2013). Lack of C9ORF72 coding mutations supports a gain of function for repeats expansions in ALS. Neurobiol Aging, 24(9), 2234. 15. Debray, S., Race, V., Crabbe, V., Herdewyn, S., Matthijs, G., Goris, A., et al. (2013). Frequency of C9orf72 repeat expansions in amyotrophic lateral sclerosis: A Belgian cohort study. Neurobiol Aging, 34(12), 2890, e7–e12. 16. Ratti, A., Corrado, L., Castellotti, B., Del Bo, R., Fogh, I., Cereda, C., et al. (2012). C9ORF72 repeat expansion in a large Italian ALS cohort: Evidence of a founder effect. Neurobiol Aging, 33(10), 2528 e7–e14. 17. Lee, Y. B., Chen, H. J., Peres, J. N., Gomez-Deza, J., Attig, J., Stalekar, M., et al. (2013). Hexanucleotide repeats in ALS/FTD form length-dependent RNA foci, sequester RNA binding proteins, and are neurotoxic. Cell Rep, 5(5), 1178–1186. 18. Mori, K., Lammich, S., Mackenzie, I. R., Forne, I., Zilow, S., Kretzschmar, H., et al. (2013). hnRNP A3 binds to GGGGCC repeats and is a constituent of p62-positive/TDP43-negative inclusions in the hippocampus of patients with C9orf72 mutations. Acta Neuropathol, 125(3), 413–423. 19. Donnelly, C.  J., Zhang, P.  W., Pham, J.  T., Heusler, A.  R., Mistry, N.  A., Vidensky, S., et  al. (2013). RNA toxicity from the ALS/FTD C9ORF72 expansion is mitigated by antisense intervention. Neuron, 80(2), 415–428. 20. Xu, Z., Poidevin, M., Li, X., Li, Y., Shu, L., Nelson, D.  L., et  al. (2013). Expanded GGGGCC repeat RNA associated with amyotrophic lateral sclerosis and frontotemporal dementia causes neurodegeneration. Proc Natl Acad Sci U S A, 110(19), 7778–7783. 21. Ash, P. E., Bieniek, K. F., Gendron, T. F., Caulfield, T., Lin, W. L., DejesusHernandez, M., et  al. (2013). Unconventional translation of C9ORF72 GGGGCC expansion generates insoluble polypeptides specific to c9FTD/ ALS. Neuron, 77(4), 639–646. 22. Mori, K., Weng, S. M., Arzberger, T., May, S., Rentzsch, K., Kremmer, E., et al. (2013). The C9orf72 GGGGCC repeat is translated into aggregating dipeptide-repeat proteins in FTLD/ALS. Science, 339(6125), 1335–1338. 23. Gendron, T.  F., Bieniek, K.  F., Zhang, Y.  J., Jansen-West, K., Ash, P.  E., Caulfield, T., et  al. (2013). Antisense transcripts of the expanded C9ORF72 hexanucleotide repeat form nuclear RNA foci and undergo repeat-associated non-ATG translation in c9FTD/ALS. Acta Neuropathol, 126(6), 829–844. 24. Zu, T., Liu, Y., Banez-Coronel, M., Reid, T., Pletnikova, O., Lewis, J., et  al. (2013). RAN proteins and RNA foci from antisense transcripts in C9ORF72 ALS and frontotemporal dementia. Proc Natl Acad Sci U S A, 110(51), E4968–4977. 25. Su, Z., Zhang, Y., Gendron, T.  F., Bauer, P.  O., Chew, J., Yang, W.  Y., et al. (2014). Discovery of a biomarker and lead small molecules to target r(GGGGCC)-associated defects in c9FTD/ALS. Neuron, 83(5), 1043–1050. 26. Belzil, V. V., Bauer, P. O., Prudencio, M., Gendron, T. F., Stetler, C. T., Yan, I.  K., et  al. (2013). Reduced C9orf72 gene expression in c9FTD/ALS is caused by histone trimethylation, an epigenetic event detectable in blood. Acta Neuropathol, 126(6), 895–905. 27. Ciura, S., Lattante, S., Le Ber, I., Latouche, M., Tostivint, H., Brice, A., et al. (2013). Loss of function of C9orf72 causes motor deficits in a zebrafish model of amyotrophic lateral sclerosis. Ann Neurol, 74(2), 180–187. 28. Zhang, Y. J., Jansen-West, K., Xu, Y. F., Gendron, T. F., Bieniek, K. F., Lin, W.  L., et  al. (2014). Aggregation-prone c9FTD/ALS poly(GA) RANtranslated proteins cause neurotoxicity by inducing ER stress. 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provides important information for at-risk family members and, in some cases, influences clinical care and diagnosis. It has been apparent for some time that the presence of an SOD1 p.A4V mutation (and some other SOD1 mutations) portends a particularly aggressive disease course (about 1 year from onset to death), but beyond an understanding of disease course in a select number of patients, genetic information has not routinely been used to influence clinical decision making. As studies consistently show that approximately 10% of sporadic patients harbor mutations in known ALS genes,1–4 the role of genetic testing in sporadic patients is already expanding. The majority of mutations found in sporadic cases with European ancestry are in C9ORF72, leading some centers to routinely screen at least this single gene in all ALS patients. When present, this expansion portends an increased chance of FTD accompanying ALS and therefore allows for vigilant screening and earlier intervention. As the number of ALS genes increases and better genotype-phenotype correlations are recognized, genetic testing will be included earlier in the diagnostic algorithm, potentially obviating the need for some diagnostic procedures. For example, C9ORF72 testing followed by whole-exome sequencing could be used to rule-in known ALS-causing mutations, which would greatly increase the likelihood of an ALS diagnosis along with the appropriate signs and symptoms. This already occurs for some muscle diseases (e.g., myotonic dystrophy and fascioscapulohumeral muscular dystrophy) wherein the genotype–phenotype correlations are strong enough that a muscle biopsy is often no longer required to make the diagnosis. In addition to influencing the diagnosis of ALS, genetic findings from widespread testing will eventually provide improved prognostic information. To reach this stage, improved genotypephenotype correlations will have to be obtained for ALS. Eventually however, it may be possible to look at particular mutations, sets of mutations, or other biomarkers and predict rates of progression with implications for patient care decisions. Finally, the next and most important phase of incorporating this type of genetic testing into clinical evaluation will to be select an appropriate therapeutic based on the genetics, which might predict responders to a given therapeutic agent.

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53. Kwiatkowski, T.  J., Jr., Bosco, D.  A., Leclerc, A.  L., Tamrazian, E., Vanderburg, C. R., Russ, C., et al. ()2009. Mutations in the FUS/TLS gene on chromosome 16 cause familial amyotrophic lateral sclerosis. Science, 323(5918), 1205–1208. 54. Vance, C., Rogelj, B., Hortobagyi, T., De Vos, K.  J., Nishimura, A.  L., Sreedharan, J., et al. (2009). Mutations in FUS, an RNA processing protein, cause familial amyotrophic lateral sclerosis type 6. Science, 323(5918), 1208–1211. 55. Belzil, V. V., Valdmanis, P. N., Dion, P. A., Daoud, H., Kabashi, E., Noreau, A., et al. (2009). Mutations in FUS cause FALS and SALS in French and French Canadian populations. Neurology, 73(15), 1176–1179. 56. Damme, P. V., Goris, A., Race, V., Hersmus, N., Dubois, B., Bosch, L. V., et al. (2010). The occurrence of mutations in FUS in a Belgian cohort of patients with familial ALS. Eur J Neurol, 17(5), 754–756. 57. Waibel, S., Neumann, M., Rosenbohm, A., Birve, A., Volk, A.  E., Weishaupt, J. H., et al. (203). Truncating mutations in FUS/TLS give rise to a more aggressive ALS-phenotype than missense mutations: A clinicogenetic study in Germany. Eur J Neurol, 20(3), 540–546. 58. Suzuki, N., Aoki, M., Warita, H., Kato, M., Mizuno, H., Shimakura, N., et al. (2010). FALS with FUS mutation in Japan, with early onset, rapid progress and basophilic inclusion. J Hum Genet, 55(4), 252–254. 59. Tsai, C. P., Soong, B. W., Lin, K. P., Tu, P. H., Lin, J. L., & Lee, Y. C. (2011). FUS, TARDBP, and SOD1 mutations in a Taiwanese cohort with familial ALS. Neurobiol Aging, 32(3), 553, e13–21. 60. Zou, Z. Y., Cui, L. Y., Sun, Q., Li, X. G., Liu, M. S., Xu, Y., et al. (2013). De novo FUS gene mutations are associated with juvenile-onset sporadic amyotrophic lateral sclerosis in China. Neurobiol Aging, 34(4), 1312 e1–8. 61. Kwon, M. J., Baek, W., Ki, C. S., Kim, H. Y., Koh, S. H., Kim, J. W., et al. (2012). Screening of the SOD1, FUS, TARDBP, ANG, and OPTN mutations in Korean patients with familial and sporadic ALS. Neurobiol Aging, 33(5), 1017 e17–23. 62. DeJesus-Hernandez, M., Kocerha, J., Finch, N., Crook, R., Baker, M., Desaro, P., et al. (2010). De novo truncating FUS gene mutation as a cause of sporadic amyotrophic lateral sclerosis. Hum Mutat, 31(5), E1377–1389. 63. Chio, A., Calvo, A., Moglia, C., Ossola, I., Brunetti, M., Sbaiz, L., et  al. (2011). A de novo missense mutation of the FUS gene in a “true” sporadic ALS case. Neurobiol Aging, 32(3), 553, e23–26. 64. Baumer, D., Hilton, D., Paine, S. M., Turner, M. R., Lowe, J., Talbot, K., et al. (2010). Juvenile ALS with basophilic inclusions is a FUS proteinopathy with FUS mutations. Neurology, 75(7), 611–618. 65. Huey, E. D., Ferrari, R., Moreno, J. H., Jensen, C., Morris, C. M., Potocnik, F., et  al. (2012). FUS and TDP43 genetic variability in FTD and CBS. Neurobiol Aging, 33(5), 1016 e9–17. 66. Dormann, D., Rodde, R., Edbauer, D., Bentmann, E., Fischer, I., Hruscha, A., et al. (2010). ALS-associated fused in sarcoma (FUS) mutations disrupt Transportin-mediated nuclear import. Embo J, 29(16), 2841–2857. 67. Sama, R. R., Ward, C. L., & Bosco, D. A. (2014). Functions of FUS/TLS from DNA repair to stress response:  Implications for ALS. ASN Neuro, 6(4), pii. 68. Couthouis, J., Hart, M. P., Shorter, J., Dejesus-Hernandez, M., Erion, R., Oristano, R., et al. (2011). A yeast functional screen predicts new candidate ALS disease genes. Proc Natl Acad Sci U S A, 108(52), 20881–20890. 69. Couthouis, J., Hart, M. P., Erion, R., King, O. D., Diaz, Z., Nakaya, T, et al. (2012). Evaluating the role of the FUS/TLS-related gene EWSR1 in amyotrophic lateral sclerosis. Hum Mol Genet, 21(13), 2899–2911. 70. Kim, H. J., Kim, N. C., Wang, Y. D., Scarborough, E. A., Moore, J., Diaz, Z., et  al. (2013). Mutations in prion-like domains in hnRNPA2B1 and hnRNPA1 cause multisystem proteinopathy and ALS. Nature, 495(7442), 467–473. 71. Deng, H. X., Chen, W., Hong, S. T., Boycott, K. M., Gorrie, G. H., Siddique, N., et al. (2011). Mutations in UBQLN2 cause dominant X-linked juvenile and adult-onset ALS and ALS/dementia. Nature, 477(7363), 211–215. 72. Gellera, C., Tiloca, C., Del Bo, R., Corrado, L., Pensato, V., Agostini, J., et al. (2013). Ubiquilin 2 mutations in Italian patients with amyotrophic lateral sclerosis and frontotemporal dementia. J Neurol Neurosurg Psychiatry, 84(2), 183–187. 73. Daoud, H., Suhail, H., Szuto, A., Camu, W., Salachas, F., Meininger, V., et al. (2012). UBQLN2 mutations are rare in French and French-Canadian amyotrophic lateral sclerosis. Neurobiol Aging, 33(9), 2230 e1–e5. 74. Millecamps, S., Corcia, P., Cazeneuve, C., Boillee, S., Seilhean, D., DanelBrunaud, V., et al. (2012). Mutations in UBQLN2 are rare in French amyotrophic lateral sclerosis. Neurobiol Aging, 33(4), 839, e1–3. 75. van Doormaal, P.  T., van Rheenen, W., van Blitterswijk, M., Schellevis, R.  D., Schelhaas, H.  J., de Visser, M., et  al. (2012). UBQLN2 in familial amyotrophic lateral sclerosis in The Netherlands. Neurobiol Aging, 33(9), 2233, e7–e8.





30. Mizielinska, S., Gronke, S., Niccoli, T., Ridler, C.  E., Clayton, E.  L., Devoy, A., et  al. (2014). C9orf72 repeat expansions cause neurodegeneration in Drosophila through arginine-rich proteins. Science, 345(6201), 1192–1194. 31. Rosen, D. R., Siddique, T., Patterson, D., Figlewicz, D. A., Sapp, P., Hentati, A., et al. (1993). Mutations in Cu/Zn superoxide dismutase gene are associated with familial amyotrophic lateral sclerosis. Nature, 362(6415), 59–62. 32. Chio, A., Traynor, B. J., Lombardo, F., Fimognari, M., Calvo, A., Ghiglione, P., et al. (2008). Prevalence of SOD1 mutations in the Italian ALS population. Neurology, 70(7), 533–537. 33. Battistini, S., Giannini, F., Greco, G., Bibbo, G., Ferrera, L., Marini, V., et al. (2005). SOD1 mutations in amyotrophic lateral sclerosis. Results from a multicenter Italian study. J Neurol, 252(7), 782–788. 34. Wicks, P., Abrahams, S., Papps, B., Al-Chalabi, A., Shaw, C. E., Leigh, P. N., et al. (2009). SOD1 and cognitive dysfunction in familial amyotrophic lateral sclerosis. J Neurol, 256(2), 234–241. 35. Cudkowicz, M. E., McKenna-Yasek, D., Chen, C., Hedley-Whyte, E. T., & Brown, R. H., Jr. (1998). Limited corticospinal tract involvement in amyotrophic lateral sclerosis subjects with the A4V mutation in the copper/zinc superoxide dismutase gene. Ann Neurol, 43(6), 703–710. 36. Cudkowicz, M. E., McKenna-Yasek, D., Sapp, P. E., Chin, W., Geller, B., Hayden, D. L., et al. (1997). Epidemiology of mutations in superoxide dismutase in amyotrophic lateral sclerosis. Ann Neurol, 41(2), 210–221. 37. Del Grande, A., Conte, A., Lattante, S., Luigetti, M., Marangi, G., Zollino, M., et  al. (2011). D11Y SOD1 mutation and benign ALS:  A  consistent genotype-phenotype correlation. J Neurol Sci, 309(1-2), 31–33. 38. Andersen, P.  M., Forsgren, L., Binzer, M., Nilsson, P., Ala-Hurula, V., Keranen, M.  L., et  al. (1996). 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97. Lahut, S., Omur, O., Uyan, O., Agim, Z. S., Ozoguz, A., Parman, Y., et al. (2012). ATXN2 and its neighbouring gene SH2B3 are associated with increased ALS risk in the Turkish population. PLoS ONE, 7(8), e42956. 98. Farg, M. A., Soo, K. Y., Warraich, S. T., Sundaramoorthy, V., Blair, I. P., & Atkin, J. D. (2013). Ataxin-2 interacts with FUS and intermediate-length polyglutamine expansions enhance FUS-related pathology in amyotrophic lateral sclerosis. Hum Mol Genet, 22(4), 717–728. 99. Hart, M. P., & Gitler, A. D. (2012). ALS-associated ataxin 2 polyQ expansions enhance stress-induced caspase 3 activation and increase TDP-43 pathological modifications. J Neurosci, 32(27), 9133–9142. 100. Rayaprolu, S., Mullen, B., Baker, M., Lynch, T., Finger, E., Seeley, W. W., et al. (2013). TREM2 in neurodegeneration: evidence for association of the p.R47H variant with frontotemporal dementia and Parkinson’s disease. Mol Neurodegener, 8, 19. 101. Jonsson, T., Stefansson, H., Steinberg, S., Jonsdottir, I., Jonsson, P.  V., Snaedal, J., et al. (2013). Variant of TREM2 associated with the risk of Alzheimer’s disease. N Engl J Med, 368(2), 107–116. 102. Guerreiro, R., Wojtas, A., Bras, J., Carrasquillo, M., Rogaeva, E., Majounie, E., et  al. (2013). TREM2 variants in Alzheimer’s disease. N Engl J Med, 368(2), 117–127. 103. Benitez, B. A., & Cruchaga, C; United States–Spain Parkinson’s Disease Research Group. (2013). TREM2 and neurodegenerative disease. N Engl J Med, 369(16), 15671568. 104. Cady, J., Koval, E.  D., Benitez, B.  A., Zaidman, C., Jockel-Balsarotti, J., Allred, P., et al. (2014). TREM2 variant p.R47H as a risk factor for sporadic amyotrophic lateral sclerosis. JAMA Neurol, 71(4), 449–453. 105. Fratta, P., Charnock, J., Collins, T., Devoy, A., Howard, R., Malaspina, A., et al. (2014). Profilin1 E117G is a moderate risk factor for amyotrophic lateral sclerosis. J Neurol Neurosurg Psychiatry, 85(5), 506–508. 106. Van Hoecke, A., Schoonaert, L., Lemmens, R., Timmers, M., Staats, K. A., Laird, A. S., et al. (2012). EPHA4 is a disease modifier of amyotrophic lateral sclerosis in animal models and in humans. Nat Med, 18(9), 1418–1422. 107. Saeed, M., Siddique, N., Hung, W. Y., Usacheva, E., Liu, E., Sufit, R. L., et  al. (2006). Paraoxonase cluster polymorphisms are associated with sporadic ALS. Neurology, 67(5), 771–776. 108. Slowik, A., Tomik, B., Wolkow, P.  P., Partyka, D., Turaj, W., Malecki, M. T., et al. (2006). Paraoxonase gene polymorphisms and sporadic ALS. Neurology, 67(5), 766–770. 109. Cronin, S., Greenway, M.  J., Prehn, J.  H., & Hardiman, O. (2007). Paraoxonase promoter and intronic variants modify risk of sporadic amyotrophic lateral sclerosis. J Neurol Neurosurg Psychiatry, 78(9), 984–986. 110. Valdmanis, P. N., Kabashi, E., Dyck, A., Hince, P., Lee, J., Dion, P., et al. (2008). Association of paraoxonase gene cluster polymorphisms with ALS in France, Quebec, and Sweden. Neurology, 71(7), 514–520. 111. Wills, A. M., Cronin, S., Slowik, A., Kasperaviciute, D., Van Es, M. A., Morahan, J.  M., et  al. (2009). A large-scale international meta-analysis of paraoxonase gene polymorphisms in sporadic ALS. Neurology, 73(1), 16–24. 112. van Blitterswijk, M., Blokhuis, A., van Es, M.  A., van Vught, P.  W., Rowicka, P. A., Schelhaas, H. J., et al. (2012). Rare and common paraoxonase gene variants in amyotrophic lateral sclerosis patients. Neurobiol Aging, 33(8), 1845 e1–3. 113. Schymick, J. C., Scholz, S. W., Fung, H. C., Britton, A., Arepalli, S., Gibbs, J. R., et al. (2007). Genome-wide genotyping in amyotrophic lateral sclerosis and neurologically normal controls: First stage analysis and public release of data. Lancet Neurol, 6(4), 322–328. 114. Laaksovirta, H., Peuralinna, T., Schymick, J. C., Scholz, S. W., Lai, S. L., Myllykangas, L., et al. (2010). Chromosome 9p21 in amyotrophic lateral sclerosis in Finland:  a genome-wide association study. Lancet Neurol, 9(10), 978–985. 115. Shatunov, A., Mok, K., Newhouse, S., Weale, M. E., Smith, B., Vance, C., et al. (2010). Chromosome 9p21 in sporadic amyotrophic lateral sclerosis in the UK and seven other countries: A genome-wide association study. Lancet Neurol, 9(10), 986–994. 116. van Es, M. A., van Vught, P. W., Blauw, H. M., Franke, L., Saris, C. G., Van den Bosch, L., et al. (2008). Genetic variation in DPP6 is associated with susceptibility to amyotrophic lateral sclerosis. Nat Genet, 40(1), 29–31. 117. Cronin, S., Berger, S., Ding, J., Schymick, J. C., Washecka, N., Hernandez, D. G., et al. (2008). A genome-wide association study of sporadic ALS in a homogenous Irish population. Hum Mol Genet, 17(5), 768–774. 118. van Es, M. A., Van Vught, P. W., Blauw, H. M., Franke, L., Saris, C. G., Andersen, P. M., et al. (2007). ITPR2 as a susceptibility gene in sporadic amyotrophic lateral sclerosis: A genome-wide association study. Lancet Neurol, 6(10), 869–877.





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76. Brettschneider, J., Van Deerlin, V.  M., Robinson, J.  L., Kwong, L., Lee, E. B., Ali, Y. O., et al. (2012). Pattern of ubiquilin pathology in ALS and FTLD indicates presence of C9ORF72 hexanucleotide expansion. Acta Neuropathol, 123(6), 825–839. 77. Johnson, J.  O., Mandrioli, J., Benatar, M., Abramzon, Y., Van Deerlin, V.  M., Trojanowski, J.  Q., et  al. (2010). Exome sequencing reveals VCP mutations as a cause of familial ALS. Neuron, 68(5), 857–864. 78. Wu, C. H., Fallini, C., Ticozzi, N., Keagle, P. J., Sapp, P. C., Piotrowska, K., et al. (2012). Mutations in the profilin 1 gene cause familial amyotrophic lateral sclerosis. Nature, 488(7412), 499–503. 79. Ingre, C., Landers, J. E., Rizik, N., Volk, A. E., Akimoto, C., Birve, A., et al. (2012). A novel phosphorylation site mutation in profilin 1 revealed in a large screen of US, Nordic, and German amyotrophic lateral sclerosis/ frontotemporal dementia cohorts. Neurobiol Aging, 34(6), 1708. 80. Johnson, J.  O., Glynn, S.  M., Gibbs, J.  R., Nalls, M.  A., Sabatelli, M., Restagno, G., et al. (2014). Mutations in the CHCHD10 gene are a common cause of familial amyotrophic lateral sclerosis. Brain, 137(Pt 12), e311. 81. Ajroud-Driss, S., Fecto, F., Ajroud, K., Lalani, I., Calvo, S.  E., Mootha, V. K., et al. (2014). Mutation in the novel nuclear-encoded mitochondrial protein CHCHD10 in a family with autosomal dominant mitochondrial myopathy. Neurogenetics, 16(1), 1–9. 82. Chaussenot, A., Le Ber, I., Ait-El-Mkadem, S., Camuzat, A., de Septenville, A., Bannwarth, S., et  al. (2014). Screening of CHCHD10 in a French cohort confirms the involvement of this gene in frontotemporal dementia with amyotrophic lateral sclerosis patients. Neurobiol Aging, 35(12), 2884, e1-4. 83. Muller, K., Andersen, P.  M., Hubers, A., Marroquin, N., Volk, A.  E., Danzer, K.  M., et  al. (2014). Two novel mutations in conserved codons indicate that CHCHD10 is a gene associated with motor neuron disease. Brain, 137(Pt 12), e309. 84. Bannwarth, S., Ait-El-Mkadem, S., Chaussenot, A., Genin, E. C., LacasGervais, S., Fragaki, K., et al. (2014). A mitochondrial origin for frontotemporal dementia and amyotrophic lateral sclerosis through CHCHD10 involvement. Brain, 137(Pt 8), 2329–2345. 85. Takahashi, Y., Fukuda, Y., Yoshimura, J., Toyoda, A., Kurppa, K., Moritoyo, H., et  al. (2013). ERBB4 mutations that disrupt the neuregulin-ErbB4 pathway cause amyotrophic lateral sclerosis type 19. Am J Hum Genet, 93(5), 900–905. 86. van Blitterswijk, M., van Es, M.  A., Hennekam, E.  A., Dooijes, D., van Rheenen, W., Medic, J., et al. (2012). Evidence for an oligogenic basis of amyotrophic lateral sclerosis. Hum Mol Genet, 21(17), 3776–3784. 87. Fogh, I., Ratti, A., Gellera, C., Lin, K., Tiloca, C., Moskvina, V., et  al. (2014). A genome-wide association meta-analysis identifies a novel locus at 17q11.2 associated with sporadic amyotrophic lateral sclerosis. Hum Mol Genet, 23(8), 2220–2231. 88. Keller, M. F., Ferrucci, L., Singleton, A. B., Tienari, P. J., Laaksovirta, H., Restagno, G., et  al. (2014). Genome-wide analysis of the heritability of amyotrophic lateral sclerosis. JAMA Neurol, 71(9), 1123–1134. 89. Elden, A. C., Kim, H. J., Hart, M. P., Chen-Plotkin, A. S., Johnson, B. S., Fang, X.  D., et  al. (2010). Ataxin-2 intermediate-length polyglutamine expansions are associated with increased risk for ALS. Nature, 466(7310), 1069-1075. 90. Lee, T., Li, Y. R., Ingre, C., Weber, M., Grehl, T., Gredal, O., et al. (2011). Ataxin-2 intermediate-length polyglutamine expansions in European ALS patients. Hum Mol Genet, 20(9), 1697–1700. 91. Van Dammem,P., Veldink, J. H., van Blitterswijk, M., Corveleyn, A., van Vught, P. W., Thijs, V., et al. (2011). Expanded ATXN2 CAG repeat size in ALS identifies genetic overlap between ALS and SCA2. Neurology, 76(24), 2066–2072. 92. Ross, O. A., Rutherford, N. J., Baker, M., Soto-Ortolaza, A. I., Carrasquillo, M. M., DeJesus-Hernandez, M., et al. (2011). Ataxin-2 repeat-length variation and neurodegeneration. Hum Mol Genet, 20(16), 3207–3212. 93. Soraru, G., Clementi, M., Forzan, M., Orsetti, V., D’Ascenzo, C., Querin, G., et al. (2011). ALS risk but not phenotype is affected by ataxin-2 intermediate length polyglutamine expansion. Neurology, 76(23), 2030–2031. 94. Daoud, H., Belzil, V., Martins, S., Sabbagh, M., Provencher, P., Lacomblez, L., et  al. (2011). Association of long ATXN2 CAG repeat sizes with increased risk of amyotrophic lateral sclerosis. Arch Neurol, 68(6), 739–742. 95. Gispert, S., Kurz, A., Waibel, S., Bauer, P., Liepelt, I., Geisen, C., et  al. (2012). The modulation of amyotrophic lateral sclerosis risk by ataxin-2 intermediate polyglutamine expansions is a specific effect. Neurobiol Dis, 45(1), 356–361. 96. Gellera, C., Ticozzi, N., Pensato, V., Nanetti, L., Castucci, A., Castellotti, B., et al. (2012). ATAXIN2 CAG-repeat length in Italian patients with amyotrophic lateral sclerosis: risk factor or variant phenotype? Implication for genetic testing and counseling. Neurobiol Aging, 33(8), 1847, e15–21.

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132. Urushitani, M., Ezzi, S.  A., & Julien, J.  P. (2007). Therapeutic effects of immunization with mutant superoxide dismutase in mice models of amyotrophic lateral sclerosis. Proc Natl Acad Sci U S A, 104(7), 2495–2500. 133. Foust, K.  D., Salazar, D.  L., Likhite, S., Ferraiuolo, L., Ditsworth, D., Ilieva, H., et  al. (2013). Therapeutic AAV9-mediated suppression of mutant SOD1 slows disease progression and extends survival in models of inherited ALS. Mol Ther, 21(12), 2148–2159. 134. Miller, T.  M., Kaspar, B.  K., Kops, G.  J., Yamanaka, K., Christian, L. J., Gage, F. H., et al. (2005). Virus-delivered small RNA silencing sustains strength in amyotrophic lateral sclerosis. Ann Neurol, 57(5), 773–776. 135. Ralph, G.  S., Radcliffe, P.  A., Day, D.  M., Carthy, J.  M., Leroux, M.  A., Lee, D.  C., et  al. (2005). Silencing mutant SOD1 using RNAi protects against neurodegeneration and extends survival in an ALS model. Nat Med, 11(4), 429–433. 136. Raoul, C., Abbas-Terki, T., Bensadoun, J. C., Guillot, S., Haase, G., Szulc, J., et  al. (2005). Lentiviral-mediated silencing of SOD1 through RNA interference retards disease onset and progression in a mouse model of ALS. Nat Med, 11(4), 423–428. 137. Wang, H., Yang, B., Qiu, L., Yang, C., Kramer, J., Su, Q., et  al. (2014). Widespread spinal cord transduction by intrathecal injection of rAAV delivers efficacious RNAi therapy for amyotrophic lateral sclerosis. Hum Mol Genet, 23(3), 668–681. 138. Smith, R.  A., Miller, T.  M., Yamanaka, K., Monia, B.  P., Condon, T.  P., Hung, G., et al. (2006). Antisense oligonucleotide therapy for neurodegenerative disease. J Clin Invest, 116(8), 2290–2296. 139. Miller, T.  M., Pestronk, A., David, W., Rothstein, J., Simpson, E., Appel, S. H., et al. (2013). An antisense oligonucleotide against SOD1 delivered intrathecally for patients with SOD1 familial amyotrophic lateral sclerosis:  a phase 1, randomised, first-in-man study. Lancet Neurol, 12(5), 435–442. 140. Lagier-Tourenne, C., Baughn, M., Rigo, F., Sun, S., Liu, P., Li, H. R., et al. (2013). Targeted degradation of sense and antisense C9orf72 RNA foci as therapy for ALS and frontotemporal degeneration. Proc Natl Acad Sci U S A, 110(47), E4530–4539. 141. Sareen, D., O’Rourke, J.  G., Meera, P., Muhammad, A.  K., Grant, S., Simpkinson, M., et al. (2013). Targeting RNA foci in iPSC-derived motor neurons from ALS patients with a C9ORF72 repeat expansion. Sci Transl Med, 5(208), 208ra149. 142. Butovsky, O., Siddiqui, S., Gabriely, G., Lanser, A. J., Dake, B., Murugaiyan, G., et  al. (2012). Modulating inflammatory monocytes with a unique microRNA gene signature ameliorates murine ALS. J Clin Invest, 122(9), 3063–3087. 143. Koval, E. D., Shaner, C., Zhang, P., du Maine, X., Fischer, K., Tay, J., et al. (2013). Method for widespread microRNA-155 inhibition prolongs survival in ALS-model mice. Hum Mol Genet, 22(20), 4127–4135.





119. Dunckley, T., Huentelman, M. J., Craig, D. W., Pearson, J. V., Szelinger, S., Joshipura, K., et al. (2007). Whole-genome analysis of sporadic amyotrophic lateral sclerosis. N Engl J Med, 357(8), 775–788. 120. Landers, J. E., Melki, J., Meininger, V., Glass, J. D., van den Berg, L. H., van Es, M.  A., et  al. (2009). Reduced expression of the Kinesin-Associated Protein 3 (KIFAP3) gene increases survival in sporadic amyotrophic lateral sclerosis. Proc Natl Acad Sci U S A, 106(22), 9004–9009. 121. Simpson, C.  L., Lemmens, R., Miskiewicz, K., Broom, W.  J., Hansen, V. K., van Vught, P. W., et al. (2009). Variants of the elongator protein 3 (ELP3) gene are associated with motor neuron degeneration. Hum Mol Genet, 18(3), 472–481. 122. van Es, M. A., Veldink, J. H., Saris, C. G., Blauw, H. M., van Vught, P. W., Birve, A., et al. (2009). Genome-wide association study identifies 19p13.3 (UNC13A) and 9p21.2 as susceptibility loci for sporadic amyotrophic lateral sclerosis. Nat Genet, 41(10), 1083–1087. 123. Diekstra, F.  P., van Vught, P.  W., van Rheenen, W., Koppers, M., Pasterkamp, R.  J., van Es, M.  A., et  al. (2012). UNC13A is a modifier of survival in amyotrophic lateral sclerosis. Neurobiol Aging, 33(3), 630, e3–8. 124. Chio, A., Schymick, J. C., Restagno, G., Scholz, S. W., Lombardo, F., Lai, S. L., et al. (2009). A two-stage genome-wide association study of sporadic amyotrophic lateral sclerosis. Hum Mol Genet, 18(8), 1524–1532. 125. van Doormaal, P. T., Ticozzi, N., Gellera, C., Ratti, A., Taroni, F., Chio, A., et  al. (2014). Analysis of the KIFAP3 gene in amyotrophic lateral sclerosis:  A  multicenter survival study. Neurobiol Aging, 35(10), 2420, e13–14. 126. Al-Chalabi, A., & Hardiman, O. The epidemiology of ALS: A conspiracy of genes, environment and time. Nat Rev Neurol, 9(11), 617–628. 127. Borghero, G., Pugliatti, M., Marrosu, F., Marrosu, M. G., Murru, M. R., Floris, G., et al. (2014). Genetic architecture of ALS in Sardinia. Neurobiol Aging, 35(12), 2882. 128. Al-Chalabi, A., Calvo, A., Chio, A., Colville, S., Ellis, C. M., Hardiman, O., et al. (2014). Analysis of amyotrophic lateral sclerosis as a multistep process:  a population-based modelling study. Lancet Neurol, 13(11), 1108–1113. 129. Miller, T.M., Smith, R.  A., Kordasiewicz, H., & Kaspar, B.  K. (2008). Gene-targeted therapies for the central nervous system. Arch Neurol, 65(4), 447–451. 130. Lange, D. J., Andersen, P. M., Remanan, R., Marklund, S., & Benjamin, D. (2013). Pyrimethamine decreases levels of SOD1 in leukocytes and cerebrospinal fluid of ALS patients: A phase I pilot study. Amyotroph Lateral Scler Frontotemporal Degener, 14(3), 199–204. 131. Nowak, R. J., Cuny, G. D., Choi, S., Lansbury, P. T., & Ray, S. S. (2010). Improving binding specificity of pharmacological chaperones that target mutant superoxide dismutase-1 linked to familial amyotrophic lateral sclerosis using computational methods. J Med Chem, 53(7), 2709–2718.

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28 |  AMYOTROPHIC LATERAL SCLEROSIS: IN VITRO AND IN VIVO DISEASE MODELS

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The role of RNA-binding proteins in ALS rose to the forefront in 2006 with the recognition that the 43-kDa TAR DNA-binding protein (TDP-43) forms a major component of the ubiquitin-positive ​

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The modern era of ALS research began in 1993 with the identification of the superoxide dismutase 1 (SOD1) gene1 and the subsequent development of transgenic mice overexpressing mutant human SOD1 that exhibited a phenotype strongly resembling ALS.2 This mouse has been the workhorse of ALS research, and treatment benefit using the SOD1 mouse model has been the foundation upon which dozens of ALS clinical trials have been based. SOD1 catalyzes the detoxification of free radicals and is ubiquitously expressed. Aggregates of misfolded cytoplasmic SOD1 are found in both the mouse model and in human familial ALS resulting from SOD1 mutation.3 More than 160 distinct SOD1 mutations have now been identified. Almost all are dominant, although the D90A mutation is recessive in specific Scandinavian populations, for reasons that are not completely clear.4 The SOD1 mouse model has been critical for identifying molecular pathways that contribute to neurodegeneration in ALS, including downstream defects in mitochondrial metabolism, axonal transport, endoplasmic reticulum stress, proteasome dysfunction, and excitotoxicity.5 That successes in treating the SOD1 mouse model have not translated to improvements in treating humans with ALS unfortunately does not provide answers to the ultimate accuracy of the model and leaves a list of potential explanations for the discrepancy. First, the SOD1 mouse model may accurately reflect human SOD1 but not

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Amyotrophic lateral sclerosis (ALS), first described by Charcot in 1869 and known colloquially as Lou Gehrig’s Disease, is a devastating, progressive and rapidly fatal degenerative disease of the motor nervous system. About 10% of ALS cases are familial, and the remainder are sporadic. ALS is heterogenous on clinical, genetic, and pathological levels, and this diversity has become increasingly clear over the past decade. Thus, properties of specific subpopulations may not generalize to ALS as a broader clinical syndrome. These are key issues to consider in evaluating not only ALS clinical research but also in the development, use, and interpretation of ALS disease models. The need for disease models arises in part from the limits of mechanistic studies in primary human tissue. Pathological brain or spinal cord specimens, which reflect the end stage of the disease, have few surviving motor neurons and may reveal little about pathogenesis, particularly early key steps in disease onset and progression. In contrast, patient blood or even cerebrospinal fluid samples may not be proximal enough to the active disease site to yield substantial information about the disease process. However, we keep in mind that the utility of a disease model ultimately depends upon the underlying assumption that the model is sufficiently similar to human ALS in order to reveal valuable information about the human disease.

sporadic ALS, and drugs that yielded benefit in SOD1 mouse models may have been successful if evaluated specifically in SOD1 ALS. Thus, elucidating the role of SOD1 in sporadic ALS is critical, as this will help determine the relevance of advances in the SOD1 mouse to sporadic ALS. Although aggregates of misfolded SOD1 have not been observed in the vast majority of sporadic ALS cases, some studies have demonstrated misfolded SOD1 in sporadic ALS.6 Similarly, in vitro studies have also suggested that wild-type SOD1 in ALS patients may be toxic to motor neurons.7 Second, nonphysiological overexpression of mutant SOD1 may have yielded a condition in the mouse model that is even more refractory to treatment than ALS in humans, and, consequently, drugs that may indeed benefit humans with ALS may have been forgone because of an inability to improve survival in the mouse model. Along these lines, use of outcomes in mouse studies more directly related to motor function than survival may identify drugs that could still have potential clinical value in human ALS. Third, differences in drug dose, route of administration, and pharmacokinetic properties between rodents and humans may underlie discrepancies between benefit in rodent models and lack of benefit in human ALS. Fourth, design and analysis flaws in mouse trials may have led to false conclusions that drugs were efficacious in SOD1 mice.8 These concerns relate primarily to unappreciated intricacies of the mouse model, such as sex-based differences in lifespan and instability of the mutant human transgene from generation to generation, as well as insufficient sample group size and improper blinding and statistical analysis. A fifth consideration involves differences in the timing of treatment in mouse and human studies. Mouse model treatment trials often begin while animals are presymptomatic and less commonly after the onset of the disease phenotype. However, except in cases of fully penetrant familial dominant mutations identified prior to disease onset, human treatment studies can begin only after the establishment of a diagnosis. This process frequently takes a year or more after disease symptom onset,9 and thus the condition of humans at the time of treatment initiation may be comparatively poorer than in the mouse studies. Relatedly, in general, greater success has been achieved delaying disease onset in the mouse model than in slowing disease progression. Despite its limits, the SOD1 mouse model has laid the foundation for a molecular understanding of ALS and set the stage for subsequent genetic and molecular developments.

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these RNA foci.26 Mutant C9orf72 protein or RNA could be toxic directly or indirectly, for example, by sequestering RNA binding proteins that then consequently are not able to serve their normal physiological role.22 The mislocalization of the ribonucleoprotein nucleolin in response to C9orf72 repeat expansion transcripts provides a specific mechanism by which this may occur.27 Similar to that described in spinocerebellar ataxia type 8,28 RAN translation of the C9orf72 GGGGCC hexanucleotide repeat yields repeats of two amino acids that form aggregates in neurons.29,30 Indeed, this translation occurs in three reading frames from both the sense and nonsense strands, yielding (after redundancy) five unique dipeptide repeat sequences, and specific antibodies have confirmed the presence of these different repeats. To what extent the RNA repeats themselves, the RNA foci, or the RAN products are responsible for the toxicity remains to be determined. Antisense oligonucleotides improved an in vitro motor neuron toxicity phenotype, despite the continued presence of RAN products.26 In an elegant contrasting experiment, RAN translation products, particularly those containing basic residues, specifically contributed to neurodegeneration in drosophila, as RNA expansions that were interrupted by stop codons and thus were unable to make protein repeats exhibited much less toxicity.31

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The intracellular aggregation of TDP-43 and FUS in ALS raises comparisons with SOD1 ALS, as well as other neurodegenerative disease in which protein deposits are a primary pathological feature. Mutation in other genes associated with protein homeostasis and protein clearing can also cause ALS and include ubiquilin 2,32 vasolincontaining protein,33 vesicle-associated membrane protein-associated protein B,34 optineurin,35 and charged multivesicular body protein 2B or chromatin modifying protein 2b (CHMP2B).36 Exactly how TDP43 and FUS connect the protein homeostatic regulation remains to be determined, although reduction of TDP-43 alters the expression of many genes associated with neurodegenerative disease including FTD and ALS.37 Impaired protein homeostasis may also be involved in the progressive disease extension, which bears semblance to the spread that occurs in prion diseases.6 Consistent with this hypothesis, TDP-43 and FUS contain prion-like domains, and a combination of in vitro and in vivo studies suggest that mutant TDP-43 as well as SOD1 may seed the spread of pathological findings from initial foci into surrounding regions. The connections between increased endoplasmic reticulum stress observed in SOD1 ALS and RNA stress granule formation in TDP-43 and FUS ALS need additional clarification. Nonetheless, the identification of TDP-43 mRNA in granules in the distal axon and the interference of this process by ALS-causing mutations38 also provides a link to evidence for axonal pathology in ALS, in particular that pathological changes involve the axon before either the ventral roots or the motor neuron cell bodies in the ventral horn. Genetic evidence also supports a role for impaired axonal biology, and particularly axonal transport in ALS, as the profilin-1 gene, which contributes to actin polymerization, and the dynactin gene, which mediates transport via microtubules, are both identified causes of familial ALS cases.39,40 Delayed motor neuron and survival phenotypes are found in mice models of dynactin mutation.41,42 Furthermore, the finding that EPHA4 modulates ALS disease course implicates ephrin signaling, which is involved in synapse formation and regulation.43

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Interest in RNA-processing mechanisms in both ALS and FTD spiked when a large intronic hexanucleotide expansion in the C9orf72 gene was found to be responsible for as much as 50% of familial ALS and about 5% of sporadic ALS.21,22 Consistent with a spectrum that encompasses both ALS and FTD, similar repeat expansions were also associated in up to 25% of familial FTD and 5% of sporadic FTD. Although the normal functioning of the C9orf72 gene is unknown, comparisons to other repeat expansion diseases suggest a number of potential mechanisms. Loss of function, or haploinsufficiency, effects refer to disease contributions resulting from the deficiency of the normal functioning gene. Initial studies suggesting reduction in RNA levels in the disease are consistent with this hypothesis22,23 and this mechanism is supported by motor deficits in zebrafish C9orf72 knockdown; however, case reports of humans with homozygous repeat expansions without an exacerbation of clinical phenotype as well as the absence of disease mutations within coding regions of the gene may argue against a loss of function.24,25 Alternatively, gain-of-function effects may result from effects of the RNA repeats themselves or the unusual phenomenon of abnormal protein translation of RNA repeats that does not require the standard ATG for translation initiation, known as “repeat associated non-ATG (RAN)” translation products. C9orf72 repeat expansions cause neuronal cytoplasmic inclusions in many areas of the brain, including the neocortex, hippocampus, spinal cord lower motor neurons, and cerebellar granule cells.22 Stem cell derived motor neurons from C9orf72 repeat-expansion ALS patients produce RNA foci, consistent with postmortem human samples, and antisense against C9orf72 reduces

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inclusions present in sporadic and most familial ALS.10,11 Soon after, mutations in TDP-43 and the related fused in sarcoma/translocated in liposarcoma (FUS/TLS) were each identified in about 4% of familial ALS cases.12–15 The findings that these same two proteins are the principle components of pathological inclusions in more than 95% of ALS as well about 45% of frontotemporal dementia (FTD) have prompted rapid investigation to determine how RNA binding and inclusions may contribute to disease. Furthermore, this overlap in pathology as well as the approximately 15% of ALS patients who have FTD-like symptoms have cemented the connections between the two diseases, which are now viewed as a spectrum, in particular with regard to RNA-binding protein defects. TDP-43 and FUS are both highly conserved, widely expressed, and primarily nuclear proteins that bind single-stranded DNA and RNA. However, both proteins also translocate to the cytoplasm, and cytoplasmic sequestration of both TDP-43 and FUS are observed in disease. Ubiquinated, TDP-43-containing inclusions are present in all sporadic ALS and the vast majority of non-SOD1 familial ALS, and they are similar in patients with and without TDP-43 mutation.16 The presence or absence of FUS inclusions in sporadic ALS and familial ALS not resulting from FUS mutations is controversial.17 Nonetheless, most ALS-causing mutations in FUS fall within the C-terminal nuclear localization signal, and are consistent with cytoplasmic aggregates in disease.13,14 Studies with yeast, worms, and flies have shown both loss and gain of function effects of mutant TDP-43,6 and rodent models of TDP-43 have not captured the full spectrum of the clinical disease.18 Efforts to examine the intersection of TDP-43 and FUS function have identified that both play a role in the RNA processing of a group of genes with unusually long introns.19 The recent identification that Matrin 3, an RNA and DNA-binding protein able to interact with TDP-43, also can cause ALS may reveal additional clues as to how these different RNA-binding proteins cause ALS.20

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Animal and cellular models of ALS have revealed tremendous insight into the molecular processes that lead to ALS. Challenges relate not only to the accuracy of a specific model in capturing the key features of a particular ALS variant but also to the heterogeneity of ALS itself:  to what extent therapies must be tailored to multiple specific molecular mechanisms or whether an approach that addresses the convergent pathology of motor neuron death may be broadly effective. Relatedly, models of ALS and other neurodegenerative diseases have led to emergent molecular themes that span several diseases. In this vein, future models must account for neuronal subtype specificity of different neurodegenerative diseases, particularly between tightly related diseases such as FTD and ALS: Why do some cases of C9orf72 repeat expansion cause FTD, others ALS, and others both. Aggressive development of new in vitro and in vivo disease models will begin to elucidate these questions in the near future. Finally, human iPSCderived motor neurons offer promise both with regard to the use of human cells and in particular the ability to model sporadic disease, which is critically important given the overwhelming abundance of sporadic disease in ALS and other neurodegenerative diseases.

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1. Rosen, D. R., Siddique, T., Patterson, D., Figlewicz, D. A., Sapp, P., Hentati, A., Donaldson, D., Goto, J., O’Regan, J. P., Deng, H. X., and et al. (1993). Mutations in Cu/Zn superoxide dismutase gene are associated with familial amyotrophic lateral sclerosis. Nature, 362(6415), 59–62. 2. Gurney, M. E., Pu, H., A. Y. Chiu, A. Y., Dal Canto, M. C., Polchow, C. Y., Alexander, D. D., Caliendo, J., Hentati, A., Kwon, Y. W., Deng, H. X., et al. (1994). Motor neuron degeneration in mice that express a human Cu,Zn superoxide dismutase mutation. Science, 264(5166), 1772–1775. 3. Bruijn, L.  I., Miller, T.  M., & Cleveland, D.  W. (2004). Unraveling the mechanisms involved in motor neuron degeneration in ALS. Annu Rev Neurosci, 27, 723–749. 4. Pasinelli, P., & Brown, R.  H. (2006). Molecular biology of amyotrophic lateral sclerosis: insights from genetics. Nat Rev Neurosci, 7(9), 710–723. 5. Sreedharan, J., & Brown, R.  H., Jr. (2013). Amyotrophic lateral sclerosis: Problems and prospects. Ann Neurol, 74(3), 309–316. 6. Ling, S.  C., Polymenidou, M., & Cleveland, D.  W. (2013). Converging mechanisms in ALS and FTD: Disrupted RNA and protein homeostasis. Neuron, 79(3), 416–438. 7. Haidet-Phillips, A. M., Hester, M. E., Miranda, C. J., Meyer, K., Braun, L., Frakes, A., Song, S., Likhite, S., Murtha, M. J., Foust, K. D., Rao, M., Eagle, A., Kammesheidt, A., Christensen, A., Mendell, J. R., Burghes, A. H., & Kaspar, B. K. (2011). Astrocytes from familial and sporadic ALS patients are toxic to motor neurons. Nat Biotechnol, 29(9), 824–828. 8. Scott, S., Kranz, J. E., Cole, J., Lincecum, J. M., Thompson, K., Kelly, N., Bostrom, A., Theodoss, J., Al-Nakhala, B. M., Vieira, F. G., Ramasubbu, J., & Heywood, J. A. (2008). Design, power, and interpretation of studies in the standard murine model of ALS. Amyotroph Lateral Scler, 9(1), 4–15. 9. Aggarwal, S., & Cudkowicz, M. (2008). ALS drug development:  reflections from the past and a way forward. Neurotherapeutics, 5(4), 516–527. 10. Neumann, M., Sampathu, D.  M., Kwong, L.  K., Truax, A.  C., Micsenyi, M.  C., Chou, T.  T., Bruce, J., Schuck, T., Grossman, M., Clark, C.  M., McCluskey, L. F., Miller, B. L., Masliah, E., Mackenzie, I. R., Feldman, H., Feiden, W., Kretzschmar, H. A., Trojanowski, J. Q., & Lee, V. M. (2006). Ubiquitinated TDP-43 in frontotemporal lobar degeneration and amyotrophic lateral sclerosis. Science, 314(5796), 130–133. 11. Arai, T., Hasegawa, M., Akiyama, H., Ikeda, K., Nonaka, T., Mori, H., Mann, D., Tsuchiya, K., Yoshida, M., Hashizume, Y., & Oda, T. (2006). TDP-43 is a component of ubiquitin-positive tau-negative inclusions in frontotemporal lobar degeneration and amyotrophic lateral sclerosis. Biochem Biophys Res Commun, 351(3), 602–611.

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Mouse genetic and transplant techniques to restrict mutant SOD1 expression to specific cells as well as co-culture of motor neurons with other cell types in vitro have allowed detailed investigation of how the cellular environment of a motor neuron may contribute to ALS. Thus, motor neuron, or cell-autonomous, effects can be differentiated from those induced by surrounding nonneuronal cells, so called “non-cell autonomous effects.” A number of studies have evaluated how changing the expression pattern of mutant SOD1 affects the survival of ALS rodent models. Reduction of mutant SOD1 in microglia yields a large increase in mouse lifetime, predominantly by slowing the late phase of disease progression.49 Transplantation of astrocyte precursors expressing wild-type SOD1 into mutant SOD1 rodents also reduced the disease phenotype.50 Similarly, astrocyte precursors from SOD1mutant animals induced motor neuron death and symptoms of motor neuron disease after transplantation into wild-type rats.51 However, selective expression of mutant SOD1 in astrocytes was not sufficient to cause motor neuron death.52 Another set of experiments has explored non-cell autonomous effects by co-culturing motor neurons with other cell types. Astrocytes or whole brain glia from mice overexpressing mutant SOD1 produced a motor neuron-specific toxicity that was reproduced by the application of conditioned media.53,54 Whereas these experiments were performed using mouse neurons, subsequent studies confirmed the toxicity of mutant SOD1-overexpressing astrocytes and whole brain glia in human stem cell-derived human motor neurons.55,56 An additional paper showed that astrocytes derived from postmortem neural progenitor cells from both sporadic and familial ALS patients were toxic to motor neurons in vitro.7 Interestingly, knockdown of SOD1 using short hairpin RNAs in the astrocytes made from both familial as well as sporadic ALS subjects reduced the toxicity, providing evidence for a pathological role of SOD1 in sporadic ALS. Together, these in vivo and in vitro studies have established a firm role for non-cell autonomous toxicity in motor neuron death, primarily in SOD1 ALS. Further investigation will continue to probe whether these effects are as prominent in other familial variants and sporadic ALS. Some but not all initial studies suggest that non-cell

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The ability to derive motor neurons from stem cells, first in mice and then ultimately via induced pluripotent stem cells (iPSCs) from ALS patients, offers a new powerful approach to studying motor neuron disease.44,45 One of the main benefits of this approach is the potential to study motor neurons in sporadic ALS, which accounts for the vast majority of ALS patients and for which animal models cannot be developed. Nonetheless, most iPSC-derived motor neuron work up to this point has focused on familial ALS. A number of studies using stem cell-derived motor neurons have verified some but not all pathological features observed in both SOD1 mouse models and human post-mortem specimens.46,47 Work using motor neurons derived from patients with C9orf72 repeat expansions successfully modeled the RNA foci found in pathological samples.26,48 The stem cell-based approach has undergone tremendous advancement within the past several years, powered by novel tools that include the gene-targeted correction of specific disease causing mutations, so that observed morphological, molecular, or physiological effects could confidently be attributed to the disease and not variation among individual cell lines.

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autonomous toxicity may be important more broadly, as mutant TDP-43 in rat astrocytes and sporadic ALS stem cell-derived astrocytes both appear toxic to motor neurons.57–59 ​

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Nature, 507(7491), 195–200. Zu, T., Gibbens, B., Doty, N.  S., Gomes-Pereira, M., Huguet, A., Stone, M. D., Margolis, J., Peterson, M., Markowski, T. W., Ingram, M. A., Nan, Z., Forster, C., Low, W. C., Schoser, B., Somia, N. V., Clark, H. B., Schmechel, S., Bitterman, P.  B., Gourdon, G., Swanson, M.  S., Moseley, M., & Ranum, L. P. (2011). Non-ATG-initiated translation directed by microsatellite expansions. Proc Natl Acad Sci U S A, 108(1), 260–265. Ash, P. E., Bieniek, K. F., Gendron, T. F., Caulfield, T., Lin, W. L., DejesusHernandez M., van Blitterswijk M.  M., Jansen-West, K., Paul, J.W., 3rd, Rademakers, R., Boylan K.  B., Dickson, D.  W., & Petrucelli, L. (2013). Unconventional translation of C9ORF72 GGGGCC expansion generates insoluble polypeptides specific to c9FTD/ALS. Neuron, 77(4), 639–646. Mori, K., Weng, S. M., Arzberger, T., May, S., Rentzsch, K., Kremmer, E., Schmid, B., Kretzschmar, H. A., Cruts, M., Van Broeckhoven, C., Haass, C., & Edbauer, D. (2013). The C9orf72 GGGGCC repeat is translated into aggregating dipeptide-repeat proteins in FTLD/ALS. Science, 339(6125), 1335–1338. Mizielinska, S., Gronke S., Niccoli, T., Ridler C. E., Clayton, E. L., Devoy, A., Moens, T., Norona, F. E., Woollacott, I. O., Pietrzyk, J., Cleverley, K., Nicoll, A. J., Pickering-Brown, S., Dols, J., Cabecinha, M., Hendrich, O., Fratta, P., Fisher, E.M., Partridge, L., & Isaacs, A. M. (2014). C9orf72 repeat expansions cause neurodegeneration in Drosophila through arginine-rich proteins. Science, 345(6201), 1192–1194. Deng, H. X., Chen, W., Hong, S. T., Boycott, K. M., Gorrie, G. H., Siddique, N., Yang, Y., Fecto, F., Shi, Y., Zhai, H., Jiang, H., Hirano, M., Rampersaud, E., Jansen G. H., Donkervoort, S., Bigio, E. H., Brooks, B. R., Ajroud, K., Sufit, R. L., Haines, J. L., Mugnaini, E., Pericak-Vance, M. A., & Siddique, T. (2011). Mutations in UBQLN2 cause dominant X-linked juvenile and adult-onset ALS and ALS/dementia. Nature, 477(7363), 211–215. 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12. Sreedharan, J., Blair, I.  P., Tripathi V.  B., Hu, X., Vance, C., Rogelj, B., Ackerley, S., Durnall, J.  C., Williams, K.  L., Buratti, E., Baralle, F., de Belleroche, J., Mitchell, J.  D., Leigh, P.  N., Al-Chalabi, A., Miller, C.  C., Nicholson, G., & Shaw, C.  E. (2008). TDP-43 mutations in familial and sporadic amyotrophic lateral sclerosis. Science, 319(5870), 1668–1672. 13. Vance, C., Rogelj, B., Hortobagyi, T., De Vos, K.  J., Nishimura, A.  L., Sreedharan, J., Hu, X., Smith, B., Ruddy, D., Wright, P., Ganesalingam, J., Williams, K. L., Tripathi, V., Al-Saraj, S., Al-Chalabi, A., Leigh, P. N., Blair, I. P., Nicholson, G., de Belleroche, J., Gallo, J. M., Miller, C. C., & Shaw, C. E. (2009). Mutations in FUS, an RNA processing protein, cause familial amyotrophic lateral sclerosis type 6. Science, 323(5918), 1208–1211. 14. Kwiatkowski, T.  J., Jr., Bosco, D.  A., Leclerc, A.  L., Tamrazian E., Vanderburg, C. R., Russ, C., Davis, A., Gilchrist, J., Kasarskis, E. J., Munsat, T., Valdmanis, P., Rouleau, G. A., Hosler, B. A., Cortelli, P., de Jong, P. J., Yoshinaga, Y., Haines, J.  L., Pericak-Vance, M.  A., Yan, J., Ticozzi, N., Siddique, T., McKenna-Yasek, D., Sapp, P. C., Horvitz, H. R., Landers, J. E., & Brown, R.  H., Jr. (2009). Mutations in the FUS/TLS gene on chromosome 16 cause familial amyotrophic lateral sclerosis. Science, 323(5918), 1205–1208. 15. Kabashi, E., Valdmanis, P. N., Dion, P., Spiegelman, D., McConkey, B. J., Vande Velde, C., Bouchard, J. P., Lacomblez, L., Pochigaeva, K., Salachas, F., Pradat, P.  F. Camu, W., Meininger, V., Dupre N., & Rouleau, G.  A. (2008). TARDBP mutations in individuals with sporadic and familial amyotrophic lateral sclerosis. Nat Genet, 40(5), 572–574. 16. Pamphlett, R., Luquin, N., McLean, C., Jew, S.  K., & Adams, L. (2009). 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36. Parkinson, N., Ince, P.  G., Smith, M.  O., Highley, R., Skibinski, G., Andersen, P.  M., Morrison, K.  E., Pall, H.  S., Hardiman, O., Collinge, J., Shaw, P.  J., Fisher, E.  M; MRC.Proteomics in ALS Study; & FReJA Consortium. (2006). ALS phenotypes with mutations in CHMP2B (charged multivesicular body protein 2B). Neurology, 67(6), 1074–1077. 37. Polymenidou, M., Lagier-Tourenne, C., Hutt, K. R., Huelga, S. C., Moran, J., Liang, T. Y., Ling, S. C., Sun, E., Wancewicz, E., Mazur, C., Kordasiewicz, H., Sedaghat, Y., Donohue, J.  P., Shiue, L., Bennett, C.  F., Yeo, G.  W., & Cleveland, D. W. (2011). Long pre-mRNA depletion and RNA missplicing contribute to neuronal vulnerability from loss of TDP-43. Nat Neurosci, 14(4), 459–468. 38. Alami, N.  H., Smith, R.  B., Carrasco, M.A., Williams, L.  A., Winborn, C. S., Han, S. S., Kiskinis, E., Winborn, B., Freibaum, B. D., Kanagaraj, A., Clare, A. J., Badders, N. M., Bilican, B., Chaum, E., Chandran, S., Shaw, C. E., Eggan, K. C., Maniatis, T., & Taylor, J. P. (2014). Axonal transport of TDP-43 mRNA granules is impaired by ALS-causing mutations. Neuron, 81(3), 536–543. 39. Puls, I., Jonnakuty, C., LaMonte, B. H., Holzbaur, E. L., Tokito, M., Mann, E., Floeter, M. K., Bidus, K., Drayna, D., Oh, S. J., Brown, R. H., Jr., Ludlow, C. L., and Fischbeck, K. H. (2003). Mutant dynactin in motor neuron disease. Nat Genet, 33(4), 455–456. 40. Wu, C.  H., Fallini C., Ticozzi, N., Keagle, P.  J., Sapp, P.  C., Piotrowska, K., Lowe, P., Koppers, M., McKenna-Yasek, D., Baron, D. M., Kost, J. E., Gonzalez-Perez, P., Fox, A.  D., Adams, J., Taroni, F., Tiloca, C., Leclerc, A. L., Chafe, S. C., Mangroo, D., Moore, M. J., Zitzewitz, J. A., Xu, Z. S., van den Berg, L. H., Glass, J. D., Siciliano, G., Cirulli, E.T., Goldstein, D. B., Salachas, F., Meininger, V., Rossoll, W., Ratti, A., Gellera, C., Bosco, D. A., Bassell, G.  J., Silani, V., Drory, V.  E., Brown, R.  H., Jr., & Landers, J.  E. (2012). Mutations in the profilin 1 gene cause familial amyotrophic lateral sclerosis. Nature, 488(7412), 499–503. 41. Laird, F. M., Farah, M. H., Ackerley, S., Hoke, A., Maragakis, N., Rothstein, J. D., Griffin, J., Price, D. L., Martin, L. J., & Wong, P. C. (2008). Motor neuron disease occurring in a mutant dynactin mouse model is characterized by defects in vesicular trafficking. J Neurosci, 28(9), 1997–2005. 42. Lai, C., Lin, X., Chandran, J., Shim, H., Yang, W. J., & Cai, H. (2007). The G59S mutation in p150(glued) causes dysfunction of dynactin in mice. J Neurosci, 27(51), 13982–13990. 43. Van Hoecke, A., Schoonaert, L., Lemmens, R., Timmers, M., Staats, K. A., Laird, A.  S., et  al. (2012). EPHA4 is a disease modifier of amyotrophic lateral sclerosis in animal models and in humans. Nature Medicine, 18(9), 1418–1422. http://doi.org/10.1038/nm.2901 44. Wichterle, H., Lieberam, I., Porter, J. A., & Jessell, T. M. (2002). Directed differentiation of embryonic stem cells into motor neurons. Cell, 110(3), 385–397. 45. Dimos, J. T., Rodolfa, K. T., Niakan, K. K., Weisenthal, L. M., Mitsumoto, H., Chung, W., Croft, G. F., Saphier, G., Leibel, R., Goland, R., Wichterle, H., Henderson, C. E., & Eggan, K. (2008). Induced pluripotent stem cells generated from patients with ALS can be differentiated into motor neurons. Science, 321(5893), 1218–1221. 46. Chen, H., Qian, K., Du, Z., Cao, J., Petersen, A., Liu, H., Blackbourn, L. W., IV, Huang, C. L., Errigo, A., Yin, Y., Lu, J., Ayala, M., & Zhang, S.C. (2014) Modeling ALS with iPSCs reveals that mutant SOD1 misregulates neurofilament balance in motor neurons. Cell Stem Cell, 14(6), 796–809. 47. Kiskinis, E., Sandoe, J., Williams, L.  A., Boulting, G.  L., Moccia, R., Wainger, B.  J., Han, S., Peng, T., Thams, S., Mikkilineni, S., Mellin, C., Merkle, F.  T., Davis-Dusenbery, B.  N., Ziller, M., Oakley, D., Ichida, J., Di Costanzo, S., Atwater, N., Maeder, M. L., Goodwin, M. J., Nemesh, J.,

29 |  A MYOTROPHIC LATERAL SCLEROSIS: NEUROPATHOLOGY 

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after three nosological concepts developed and were distinguished as: progressive muscular atrophy (PMA)—a disease primarily affecting lower motor neurons (LMN), primary lateral sclerosis (PLS)—a disease affecting primarily upper motor neurons (UMN), and ALS (Charcot’s disease)—affecting both UMN and LMN. Raymond is credited with recognizing the constellation of symptoms as coming from UMN and LMN degeneration. Today, we understand from extensive clinical and laboratory investigation that ALS is more than exclusively LMN/UMN degeneration with muscle wasting. ALS exists within a spectrum of neurodegenerative diseases that can include variable degree of cognitive impairment showing significant clinical and pathological overlap with some frontotemporal lobar degeneration (FTLD) diseases as well as exclusive LMN or UMN diseases PMA and PLS, respectively. Both familial and sporadic forms with multiple different genetic backgrounds and possible environmental exposures lead to a highly variable clinical and pathological expression of the disease from individual to individual. Published population-based studies for “classic ALS” involving progressive UMN and LMN symptoms suggest that there is a 9 to 12 month delay from first symptoms to diagnosis and a median survival of 2 to 3 years from symptom onset. Individuals with more rapid progression have factors that include bulbar site onset, elderly age, early associated cognitive impairment, and some genotypes. Adults with disease predominantly restricted to UMN (PLS) or LMN (PMA) generally have a better prognosis and can live many years with the disease. ​

Amyotrophic Lateral Sclerosis (ALS) is pathologically defined as a human neurodegenerative disease that results in atrophy and other specific skeletal muscle changes (“amyotrophic”). It is largely due to lower motor neuron degeneration in combination with upper motor neuron degeneration that results in loss of corticospinal neuronal soma in the primary motor cerebral cortex and loss of corresponding axons within the lateral corticospinal tracts of the spinal cord. Surrounding changes in the brain and spinal cord (“lateral sclerosis”) as well as specific protein aggregations within glial and neuronal cells are also histopathological hallmarks of the disease. Sporadic forms of the disease predominate over the familial forms and have no clearly defined genetic and/or environmental factors as yet established in their pathogenesis. Familial forms of the disease and genetically defined cases with over 15 genes implicated to date are providing some clues about the molecular pathogeneses for both familial and sporadic ALS. How the aberrantly formed/expressed molecules alter normal biochemical/physiological processes and lead to the neurodegenerative ALS disease(s) is unknown. Synonyms: Motor Neuron Disease and Lou Gehrig’s Disease

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ALS was first described in the medical literature in the 19th century, and it is unclear if it was recognized or what the prevalence of the disease was prior to that. Some give credit to Charles Bell for reporting a case in 1824. He was interested in pure motor deficit patients. He distinguished the relation between motor function and anterior spinal nerves from sensory function and posterior spinal nerves. In 1850 Aran used the term “progressive spinal muscular atrophy” for some similar cases. Cruveilhier is credited to be the first to describe the pathology of this disease in 1853. His report discussed atrophy of anterior nerve roots and suspected anterior horn cell dysfunction. In the later 1800s Jean-Martin Charcot greatly extended investigation into the relation between pathology and clinical aspects and proposed the naming of this disease as “amyotrophic lateral sclerosis.” In 1869 Charcot and Joffrey reported two cases of individuals having lesions in the gray matter, anterolateral fascicles of the spinal cord, hypoglossal nerve roots, and anterior roots of spinal nerves. Clinically, the three main criteria selected by Charcot to characterize ALS were: 1) motor weakness of rapid onset, without clear relation to atrophy, 2)  a permanent “contracture,” and 3)  spontaneous muscular pain triggered by pressure or traction. In 1874 he gave the name “amyotrophic lateral sclerosis” to this disease and linked the autopsy pathology findings of lateral spinal column sclerosis together with lower motor neuron degeneration and clinical muscle wasting (amyotrophic). Many would go on to call this “Charcot’s disease.” Soon

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Autopsy continues to be the gold standard for accurate diagnosis of neurodegenerative diseases, including ALS spectrum diseases. Genetic evaluation of individuals with neurodegenerative diseases either premortem or postmortem can also provide important information to assist with the diagnosis, establish familial patterns, and investigate pathogenic/pathophysiologic molecular pathways possibly involved in the disease. However, in many countries around the world the autopsy rate is drastically decreasing due to a combination of financial, logistical, premortem diagnostic, and social issues. This is especially true for individuals with neurodegenerative diseases who often do not die at academic medical centers where autopsy facilities/ personnel are available. Efforts to follow longitudinally individuals with clinical evaluations, imaging studies, and fluid collections for biomarker investigation combined with neuropathological evaluation at autopsy and tissue collection for research is primarily only being done in the United States for Alzheimer’s disease through NIHfunded Alzheimer’s disease research and clinical centers. Modest

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from the anterior horn region of the spinal cord (Figure  29.1C, D). Accompanying this loss is a generalized gliosis with prominent astroand microgliosis (Figure 29.1B, D, Figure 29.2A, C,). Other areas of the frontal cortex can show loss of neurons and gliosis, and this is especially true when significant dementia is involved. Cranial nerve motor nuclei such as the oculomotor and spinal nuclei such as Onuf ’s nucleus were once thought to be spared from the neurodegenerative process. However, they are now recognized through careful autopsy studies to show aggregates and degeneration, albeit at a slower pace than within the UMNs and LMNs. Also, as some individuals are remaining on a respirator for more prolonged periods with the disease, the degree of frontal neuronal loss and gliosis seems to become more apparent (personal observations; no large cases studies have been published). Additional areas of the central nervous system are affected, especially in longer term survivors. Careful cognitive testing and analysis of prefrontal brain areas at autopsy also reveals cytoplasmic aggregates and neurodegeneration, especially in the dorsolateral regions. Under standard pathological staining with hematoxylin and eosin (H&E) these changes are readily apparent if the correct areas of the brain and cord are examined. Like the UMN loss, the spinal cord shows patchy loss of LMNs corresponding to clinically affected regions, and by the end-stages of disease there is severe loss of most LMNs (Figure 29.1C, D). Also, like the cerebral motor cortex, there is regional neuroinflammatory activation in the anterior horns as well as in the corticospinal tracts (both lateral and anterior medial). The resulting “lateral sclerosis” shows loss of corticospinal myelinated axons and reactive gliosis, which can be highlighted well with myelin stains such as Luxol Fast Blue stain (Figure 29.3). Careful microscopic examination by H&E also discloses characteristic cytoplasmic inclusions such as Bunina bodies or hyaline, eosinophilic inclusions within motor neuron soma, though immunohistochemistry to better identify cellular inclusions is now part of the standard diagnostic workup. ​

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numbers of ALS autopsies and tissue collections have been performed at scattered academic medical centers around the country for more than 20  years. However, several multi-institutional concerted and targeted collection projects for ALS tissues have recently begun with funding from ALS foundations, with the goal of obtaining and distributing to the research community clinical information, tissues, and genetic information from the generous individuals/families who have made these important donations. Establishing a diagnosis of ALS at autopsy requires knowledge of the clinical and family history of the individual combined with sufficient observation and sampling of tissues for gross and microscopic examination by an experienced neuropathologist. Patients at autopsy with long-standing disease are often very thin and cachectic appearing, with widespread muscle atrophy. In many cases there are relatively few gross pathological changes noted in the brain and spinal cord. Often the only change observed grossly at autopsy is the relative thinned appearance of motor nerve roots when viewed in comparison with the sensory roots. Focal atrophy in the motor cortex can occasionally be observed in ALS. More pronounced atrophy of frontal and temporal lobes can sometimes be seen in frontotemporal lobar dementia-motor neuron disease and bilateral motor cortices specifically in PLS. Although imaging studies have shown loss of white matter in ALS patients, diminished weight of the brain or gross changes to the centrum semiovale or internal capsule are not generally observed. ALS characteristic microscopic changes may be widespread throughout the motor pathway system or can show only patchy involvement of upper motor cortex and spinal cord; the degree of tissue involvement often correlates with the severity, duration, and extent of clinically evident disease. In the primary motor cortex there is a loss of upper motor neurons (also known at Betz cells) from cortical layer 5 (Figure 29.1A, B), loss of cranial nerve motor neurons of the medulla (especially CN XI, V, VII), and loss of lower motor neurons

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Figure 29.1 Cerebral motor cortices showing abundant large upper motor neuron soma (Betz cells) from an unaffected individual (A) and region with complete loss and marked gliosis from an ALS individual (B). The anterior horn shows more abundant and normal lower motor neuron soma in the spinal cord of an unaffected individual (C) compared with an ALS individual (D). (Hematoxylin & Eosin stain).

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Figure 29.2 The motor cortex shows increased microglial activation (A) indicated by brown coloration from CD68 immunohistochemistry in an ALS individual

 

compared with the same individual’s adjacent sensory cortex (B). Reactive astrocytosis evidenced by increased GFAP immunoreactivity is similarly observed in motor (C) compared with sensory (D) cortices.

possible similar mechanisms of pathology. Not only does TDP43 immunohistochemistry highlight aberrant loss of the normal nuclear staining pattern and increased aggregate staining in motor neuron cytoplasm and nuclei, it also shows similar findings in glial cells within affected areas of brain and spinal cord (Figure 29.4B). These pathological protein localization/aggregation patterns further implicate both neurons and glia participating in the pathogenesis/ pathophysiology of these diseases. Another new discovery in ALS/ FTLD genetics is the abnormal expansion of a GGGGCC hexanucleotide repeat in the noncoding region of the chromosome 9 open reading frame 72 (C9ORF72) which is now recognized as the most common genetic abnormality in familial and some sporadic FTLD and ALS cases. Many of these cases have an interesting immunohistochemical staining pattern that shows increased ubiquitin and p62

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With the explosion of new immunohistochemical markers of disease in the last 20  years, new ideas have emerged regarding pathogenesis and nomenclature for ALS spectrum diseases. Glial fibrillary acidic protein (GFAP) immunohistochemistry highlights the reactive astrocytes in affected areas (Figure 29.2C). CD68 or other macrophage/microglial markers similarly show increased numbers of activated microglia/macrophages (Figure 29.2A). Ubiquitin immunohistochemistry was the first marker to assist with distinguishing cytoplasmic inclusions in motor neurons for both familial and sporadic cases. Ubiquitin highlights both hyaline inclusions as well as more threadlike skeins within the cytoplasm (Figure 29.4A). More recently, TDP43 (discussed elsewhere in this and other chapters) has become an important marker of FTLD and ALS spectrum diseases and has linked these diseases as having

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Figure 29.3 Lower motor neurons with cytoplasmic aggregates (arrows). Ubiquitin aggregates in center motor neuron (A). Multiple TDP43 aggregates in several

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motor neurons (B). Note the loss of normal TDP43 nuclear immunoreactivity in upper left motor neuron.

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Figure 29.4 Spinal cord in ALS patient showing lateral sclerosis and loss of anterior horn motor neurons. A Luxol Fast Blue stain to highlight myelin shows loss of staining in the later corticospinal tract (arrow) on left and loss of large motor neurons in the anterior horns. Motor nerve routes at the bottom of (A) are also diminished in size.

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I  and II myocytes), the muscle converts from the normal “checkerboard” appearance of interspersed type I  and type II myocytes to groupings of type I and II fibers. Atrophied fibers will also stain darkly for the enzyme stains of NADH and esterase. Mitochondria tend to move toward the periphery of affected myocytes, and histochemical stains of mitochondria (NADH and cyclooxygenase/ succinic dehydrogenase) show central clearing (“target” fibers) or irregular staining pattern (“moth-eaten” fibers). In summary the pathological findings at autopsy or on muscle biopsy when taken in context with the clinical history are fairly characteristic for ALS. However, individuals with familial forms of the disease and those with overlapping FTLD may have more variable pathological and clinical findings. The molecular pathways leading to these diseases are being dissected by neuroscientists at a rapid pace, with hopes of defining and classifying the spectrum of these diseases, discovering the etiology of these diseases, and identifying new therapeutic targets.

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Figure 29.5 Muscle atrophy in ALS. H&E stained section shows variable size fibers with areas of grouped atrophy and no inflammation.

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Al-Chalabi, A., Jones, A., Troakes, C., King, A., Al-Sarraj, S., van den Berg, L. H. (2012). The genetics and neuropathology of amyotrophic lateral sclerosis. Acta Neuropathol, 124(3), 339–352. Al-Sarraj, S., King, A., Troakes, C., Smith, B., Maekawa, S., Bodi, I., Rogelj, B., Al-Chalabi, A., Hortobágyi, T., & Shaw, C. E. (2011). p62 positive, TDP-43 negative, neuronal cytoplasmic and intranuclear inclusions in the cerebellum and hippocampus define the pathology of C9orf72-linked FTLD and MND/ALS. Acta Neuropathol, 122(6), 691–702. Boillée, S., Vande Velde, C., & Cleveland, D.  W. (2006). ALS:  A  disease of motor neurons and their nonneuronal neighbors. Neuron, 52(1), 39–59. Cruts, M., Gijselinck, I., Van Langenhove, T., van der Zee, J., Van Broeckhoven, C. (2013). Current insights into the C9orf72 repeat expansion diseases of the FTLD/ALS spectrum. Trends Neurosci, 36, 450–459. Goetz, C. G. (2000). Amyotrophic lateral sclerosis: early contributions of JeanMartin Charcot. Muscle Nerve, 23(3), 336–343. Ling, S. C., Polymenidou, M., & Cleveland, D.W. (2013). Converging mechanisms in ALS and FTD: disrupted RNA and protein homeostasis. Neuron, 79, 416–438. Machenzie, I. R., Frick, P., & Neumann, M. (2014). The neuropathology associated with repeat expansions in the C9ORF72 gene. Acta Neuropathol, 127(3), 347–357. Murray, M.  E., DeJesus-Hernandez, M., & Rutherford, N.  J., et  al. (2011). Clinical and neuropathologic heterogeneity of c9FTD/ALS associated with hexanucleotide repeat expansion in C9ORF72. Acta Neuropathol, 122(6), 673–690. Ravits, J., Appel, S., & Baloh, R.  H., et  al. (2013). Deciphering amyotrophic lateral sclerosis: What phenotype, neuropathology and genetics are telling us about pathogenesis. Amyotroph Lateral Scler Frontotemporal Degener, 14(1), 5–18. ​

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cytoplasmic inclusions in many areas of the CNS, including some not typically associated with ALS such as the hippocampus and cerebellum. TDP43 aggregate staining is not seen associated with these particular inclusions. These and other new molecular markers of disease show remarkably different patterns of staining from individual to individual and are challenging how we classify FTLD and ALS spectrum diseases. Skeletal muscle should be sampled at autopsy and is occasionally biopsied in surgical neuropathology when a differential clinical diagnosis includes chronic inflammatory myopathies such as inclusion body myositis, adult onset dystrophies, and neurodegenerative diseases like ALS. The muscle changes observed in biopsies are not unique to ALS and can be seen when there is damage to motor neurons from other causes, as well, such as: prior traumatic injury, chronic radiculopathy, or chronic inflammatory demyelinating polyradiculoneuropathy or vasculitis where there can be loss motor neuron fibers. This change and the diagnosis conferred on all of these biopsies is a nonspecific neurogenic myopathy. The histochemical/ histopathological findings are dependent on the timing of loss of innervation to the muscle and degree of re-innervation. Myocytes atrophy when not innervated properly, and often this atrophy produces groupings of smaller, acutely-angulated myofibers (Figure 29.5). Remaining motor neurons that have not degenerated yet are signaled to send out sprouts to reinnervate the atrophied fibers. When immunostained for fast or slow myosin or histochemically stained for the enzyme ATPase (both methods to distinguish type

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www.cdc.gov/als www.ninds.nih.gov/disorders/amyotrophiclateralsclerosis/detail_ALS.htm http://www.alsconsortium.org ​

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Valori, C., Brambilla, L., Martorana, F., & Rossi, D. (2013). The multifaceted role of glial cells in amyotrophic lateral sclerosis. Cell Mol Life Sci, 71, 287–297. Vonsattel, J. P., Amaya Mdel, P., & Keller, C. E. (2008). Twenty-first century brain banking. Processing brains for research:  the Columbia University methods. Acta Neuropathol, 115(5), 509–532.

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30 |  AMYOTROPHIC LATERAL SCLEROSIS CLINICAL TRIALS: PAST REFLECTIONS INFORMING NEW DIRECTIONS

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Previous ALS trials have developed robust outcome measures that continue to be enormously helpful in quantifying disease progression, particularly in such a variable disease. New tools are being developed to supplement and improve upon the existing measures (Table 30.2). EFFICACY MEASURES C U R R E N T LY   I N   U S E

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The SOD1 gene discovery was followed in short order by the development of the SOD1G93A transgenic mouse model of ALS,9 which gave rise to a better understanding of disease pathophysiology and compelling new drug targets. This robust model has since become the standard for preclinical work and has led to critical discoveries in ALS. Yet from the perspective of ALS clinical trialists, its success is more difficult to evaluate, as translation to human trials has been imperfect. In some cases, the mouse model has predicted benefit when none was seen in humans10–13; in other cases (i.e., Minocycline), the mouse

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Commonly employed efficacy outcome measures in the ALS trials of the past quarter decade have included:  survival (i.e., generally tracheostomy-free survival), impairment (e.g., hand-held dynamometry, vital capacity), and functional limitations (e.g., ALSFRSR).22 These outcome measures appear to accurately capture the natural history of ALS, but are inherently variable and require a large sample size and long duration of follow-up to demonstrate efficacy. One strength of the ALSFRS-R is its ability to capture a broad picture of overall function to reflect progression of the disparate deficits of ALS patients (e.g., bulbar and limb dysfunction) in the same scale. But this breadth may also lead it to be less sensitive to specific changes, and changes in subdomains may not be equivalent.23 As a result, these outcome measures are best suited to late-phase ​

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Several clinical trials demonstrating the effect of riluzole in ALS patients have had outsized impact on our current research approach in ALS. Two separate trials demonstrated improved tracheostomyfree survival at 12 or 18 months of treatment with riluzole1,2 leading to FDA-approval for the treatment of ALS. The trials did not reveal a functional benefit, but whether there was truly no effect on function or whether the Norris ALS Scale3 was insensitive to change in function in ALS is debated. This debate has driven the development of subsequent scales of function in ALS, including the Appel Scale,4 the ALS Functional Rating Scale (ALSFRS),5 and the revised ALSFRS (ALSFRS-R).6 The ALSFRS-R remains the most commonly employed functional outcome in ALS trials today. A follow-up trial of riluzole in elderly patients with advanced ALS failed to show the benefits seen in the original trials, suggesting early treatment is important for riluzole to exert its benefit.7 Nearly all ALS trials now enroll patients early in the disease course. The achievements of the riluzole trials have been followed by a series of early phase ALS trials with mixed results, only to result in large late-phase clinical trials that did not reveal benefit (Table 30.1). However, these efforts have led to the development and validation of numerous clinical end points, insights into disease natural history, and improvements in trial design and methodology.8 At the same time, the lack of successful new therapies developed in the last two decades highlights the challenges of ALS therapy development. The pathogenesis of ALS is not well understood. The disease is progressive and debilitating, limiting the number of trials in which any one patient can reasonably expect to participate. The site of onset and rate and pattern of progression are widely variable, leading to statistical challenges in detecting treatment effect. There are no sensitive or specific biomarkers of diagnosis, prognosis, disease progression, disease subtype, or staging system. But, with new methods, information, and tools, we have the opportunity to address many of these challenges.

model suggested a benefit but humans experienced a detrimental effect.14,15 Theorized reasons for poor translation include overexpression of mutant SOD1 protein, key differences in pathology between SOD1-mediated disease and other forms of ALS,16,17 and growing evidence that ALS may be a spectrum of pathophysiologically distinct, yet overlapping clinical syndromes. Different disease subtypes might benefit from unique therapies. Newer transgenic animal models such as the TDP-43 mouse model18 and early C9ORF72 mouse models (Author’s personal communication), when used in combination or to explore specific genetic therapies, may improve translation into successful human ALS trials. The discovery of biomarkers linking human disease to mouse models may help subcategorize patients and increase the chances of successfully using mouse models to identify effective therapies for subsets of ALS patients. Human embryonic and induced pluripotent stem cell (iPS)derived motor neurons have also emerged as promising preclinical disease models and therapy screening.19,20 A  recent study demonstrated hyperexcitability in iPS-derived motor neurons from ALS patients relative to controls, that normalized with application of retigabine, a potassium channel activator.21 iPS-derived motor neurons can be made from people with ALS, providing the opportunity to investigate human disease in vitro. This may provide a platform for individualized medicine or at least a means to screen candidate therapies and subset patients into likely responders for trial enrollment.

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Death

Higher mortality in drug group

L-Threonine2

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Norris scale

No benefit

Prednisolone/Azathioprine3

Immunomodulant

Survival

No benefit

Riluzole4– 6

Antiglutamatergic

Survival and functional status score (includes Norris scale)

Improved survival at 12 and 18 months. Slower muscle deterioration in 1994 study*

Acetylcysteine7

Antioxidant

Survival

No benefit*

Brain derived neurotrophic factor (BDNF, oral)8

Neurotrophic factor

Survival and isometric muscle No benefit. Initial decrease in strength strength early in drug group.

Ciliary neurotrophic factor (CNTF)9

Neurotrophic factor

Isometric muscle strength (dynamometry)

No benefit

Gluthathione10

Antioxidant

Disease progression (muscle strength, Norris scale, bulbar scale, and FVC)

No benefit*

Methylcobalamin11

Antiglutamatergic

CMAP amplitude

No benefit at low dose. Increased amplitude with 25mg/day IM dose at 4 weeks

Nimodipine12

Antiglutamatergic

WALS group modified TQNE

No benefit

Selegiline13

Antioxidant

Appel ALS total score

No benefit

Gabapentin14,15

Antiglutamatergic

Isometric arm muscle strength

No benefit.* More rapid FVC decline in drug group (combined phase II &III data)

Creatine16–18

Mitochondrial dysfunction

Upper extremity MVIC or survival.

No benefit*

Lamotrigine19

Antiglutamatergic

Norris scale, Plaitakis bulbar and spinal scales

No benefit

Recombinant β-1a interferon20

Immunomodulant

Non–self-supporting status

No benefit

Riluzole21,22

Antiglutamatergic

Safety and efficacy in advanced stage ALS/ age >75

Safe and tolerated in advanced stage ALS/age >75 but no survival benefit

Survival

Confirmed survival benefits in early stage ALS

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No benefit. Faster MVIC decline in high-dose group

Xaliproden24

Neurotrophic

Time to death and time to FVC C in exon 7 of SMN2 results in an approximate 20% increase in full-length SMN protein and a mild SMA phenotype.36–38 Interestingly, this variant does not occur in type 1 patients, is found in one copy in type 2 patients, and in two copies in milder type 3b patients.36–38 First, because mini genes with this variant produce approximately 20% more full-length SMN, and second, that two copies of this allele results in a type 3b patient, it is predicted that a 20% increase in full-length SMN (in a 2 copy SMN2 individual) will result in type 3b SMA. Furthermore, a 25% increase in full-length SMN

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Figure 34.2 The survival motor neuron genes SMN1 and SMN2 essentially differ by a single nucleotide change in exon 7 (C or T, as indicated). This change affects the splicing so that most of the SMN transcripts from SMN2 lack exon 7. However, SMN2 does produce some full-length SMN and can be viewed as a gene with reduced function. The loss of the amino acids that are encoded by exon 7 results in the production of an SMN protein with severely decreased oligomerization efficiency and stability, and the SMN monomers are rapidly degraded. The SMN oligomer is represented as an octomer.

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copy number of SMN2 was not determined it is thus assumed to be severe and the patient have multiple SMN2 copies based on SMN G279V. B. Diagram of mild SMA causing missense mutations and their mode of action. Homomeric complexes of missense mutations do not rescue Smn-/- mice or perform snRNP assembly. In the presence of SMN2 small amounts of full-length SMN are produced and heteromeric complexes with SMN protein containing the missense mutation are formed. These heteromeric complexes perform snRNP assembly and rescue Smn-/- mice.

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Many animal models of SMA have been created and are widely used. The animal models are discussed in chapter 35. There are certain features that are important to realize when discussing these models for ­

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with the SMN missense mutation protein making a functional SMN complex. Thus heteromeric SMN complexes are functional and homomeric complexes are not49 (see Figure 34.3). The amount of full-length SMN and the amount of missense SMN expressed then becomes critical in determining phenotype, as it appears likely that only one monomer of wild-type full-length SMN per complex is required for function. Although this was first found for SMNA2G and SMNA111G it applies to the mutations SMND44V, SMNT274I, and SMNQ282A as well. Thus it appears to be a general phenomenon to all mild missense alleles (unpublished observation). Indeed, although missense alleles are rare, no consanguineous cases with the absence of SMN2 have been reported. One current conundrum is the behavior of equivalent missense mutations in non-mammalian species. In C. elegans the equivalent of SMND44V (SmnD27N) has been examined. Animals with this mutation can survive and offspring can be obtained in the absence of wild type SMN.50 Homozygous mutants show various phenotypes including a motility defect. However this invertrabrate finding is different than the observation in mammals wherein SMND44V does not rescue Smn-/- mice in the absence of full-length SMN from SMN2. At least some of the mild SMN alleles have been analyzed in Drosophila and appear to complement the maternal SMN present in these mutants.51 Although some severe alleles behave in the expected manner others such as SmnG210V (equivalent to SMNG279V, a severe allele in humans) do not. The exact reasons for these differences among species remain unclear.

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SMN1 loss accounts for 95% of SMA cases. In the remaining 5% of cases the SMN1 gene contains a small mutation. Most of the mutations disrupt the SMN reading frame or disrupt a splice site in the gene and are thus similar to the loss of SMN1. However, many missense mutations that disrupt SMN function have been reported. These mutations are diagramed Figure 34.3 along with the domains they disrupt and the severity of each mutation.17,45 Insights can be gained by studying how these missense mutations function upon disruption of SMN domains. At least some of the severe missense mutations disrupt the ability of SMN to efficiently oligomerize and thus act much like SMN lacking the sequence encoded by exon 7. This form of SMN is rapidly degraded and thus in essence results in minimal amounts of SMN protein.17,33 An example of a mutation like this is SMNY272C, which results in a severe phenotype in the presence of 2 copies of SMN2. Patient lymphoblasts containing the SMNY272C mutation have the same amount of SMN protein as severe SMA patients with two copies of SMN2.34 This indicates that minimal amounts of SMN are produced by the SMNY272C allele. Other severe mutations result in unfolding of protein domains including the Tudor domain. Perhaps one of the most interesting severe missense mutations is SMNE134K, which appears to disrupt the binding of SmD1,D3/HuD proteins.46,47 This mutation could be used to dissect the contributions of different SMN assembly48 reactions to the phenotype. We then come to the mild SMN missense mutations. These mutations occur in similar domains (see Figure 34.3) yet produce a mild SMA phenotype. Thus, is a homomeric complex just composed of mutant SMNs functional or is the small amount of full-length SMN protein produced by SMN2 required to complement the missense mutations? We have found that the mutations SMNA2G and SMNA111G, both mild mutations, can rescue the survival of Smn-/ mice only in the presence of full-length SMN and therefore do not have function on their own. Furthermore, these two amino terminal mutations also do not complement each other in the absence of fulllength SMN.49 The full-length SMN protein from SMN2 oligomerizes

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The identification of SMN1 and SMN2 and their roles in SMA led directly to the development of therapeutics in SMA. SMN2 is always present in SMA patients and produces at least some full-length SMN. Furthermore, increased copy number of SMN2 results in a milder SMA phenotype.56 At least some SMN is always present, thus immune reactions to SMN replacement in gene therapy strategies is not an issue. To date three major therapeutic approaches have been developed. All have been shown to be highly effective in mouse models of SMA and are quickly moving into clinical trials.56 SMN2 possess both negative and positive elements that control the inclusion of SMN exon7. Thus enhancing the positive or blocking the negative elements can make SMN2 behave like SMN1 and produce a large amount of full-length SMN.56 Indeed, this has been accomplished in mice with antisense oligonucleotides that block the negative regulatory ISS-N1 sequence. In particular, two chemistries of ASO have been successfully used:  the 2′-O-(2-methoxyethyl) (MOE) and the morpholino.57,58 The morpholinos can be administered at high concentrations without side effects and have shown marked impact when given in the CNS in mice. More recently it has also become possible to obtain widespread distribution in the CNS of adult mice.59 The MOE against ISS-N1, known as ISIS-SMN Rx, is currently in clinical trials and has been safely administered with multiple injections (NCT02193074, https://clinicaltrials.gov). The degree of efficacy at different stages of disease progression is determined by the response of biomarkers, electrophysiological measures, and muscle strength in the patient. The second strategy has been to identify compounds that can make SMN2 produce more full-length SMN protein. A number of screens have resulted in small molecules that activated the SMN promoter or stabilized SMN mRNA and/or protein. Some compounds were identified in these screens that somewhat increased SMN, but in general not to the level required for therapy.60 Of note is the fact that a number of these screens should have detected molecules that altered the incorporation of exon 7 by SMN2 but did not. This is likely due to the fact that the libraries of small molecules screened did not cover the required chemical space for molecules that could or would alter the SMN2 splicing or that very weak hits where not followed up and optimized chemically. As such, the NIH based libraries in particular appear to be missing critical molecules that can alter splicing. In the future the publically accessible libraries will need to be improved. PTC/Roche and Novartis have performed screens and identified compounds that alter the splicing of SMN2. Indeed these compounds have a major impact on SMA mice and are in the first stage of clinical testing in healthy volunteers.61,62 Interestingly, the compounds developed by Roche/PTC appear to affect the splicing of a limited set of genes, thus giving hope that there will not be significant off-target effects of these drug compounds.61 Thus when looking for molecules that alter splicing in SMA or other disorders, the nature of the chemical library should be considered. Last, gene therapy using scAAV9-SMN has shown remarkable improvement of SMA mice when delivered into the vascular system or delivered into the CNS via the CSF.63–66 The scAAV9-SMN gene therapy is currently in Phase 1 clinical trials for type 1 patients (NCT02122952). Until recently, a large animal model of SMA to assess therapy has not been available. The mouse can give information on the activation of SMN2; however, the drawbacks of the mice need to be considered.

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invoke all changes detected as having a role in SMA but to garner specific genetic information that shows that a particular biochemical pathway is involved.

use in genetic screens to identify critical pathways in SMA. First, in species such as Drosophila there is a very large contribution of maternal SMN and a short life span. Drosophila can survive to late larval stages based on the maternal SMN loaded into the embryo when a particular Drosophila gene is zygotically deleted or mutated. This is also true in Zebrafish, with a large maternal contribution of RNA from the yolk. This situation of course is very different in mammals, wherein embryo development times are generally longer with a limited contribution of maternal RNA. Thus in the mouse loss of the single functional Smn gene results in death of cells at an extremely early stage before any organs or tissues have developed.52 Any animal model is further complicated by the presence of SMN2 in humans. In humans the loss of SMN1 is compensated by the production of SMN from SMN2 throughout the patient’s life. Thus SMA in humans is a condition of low levels of continuously produced SMN protein. In order to more closely model SMA in both lower species or under specific circumstances, either siRNA or shRNA can be used. Invertebrates and nonmammalian vertebrates should be used to carry out experiments that cannot be done efficiently in mammals. We would advocate exploiting the strengths of each species. Genetic screens in C. elegans and Drosophila can be used to quickly identify suppressors and genetic interactors that can then be confirmed in both Zebrafish and SMA mice.17 In Drosophila a genetic screen was performed using RNAi lines to knock down SMN expression under a universal driver. This study resulted in the identification of 302 modifiers of SMN deficiency in which survival of the organism was slightly altered.53 None of the suppressors identified could be classified as a strong suppressor of the phenotype. Further homologue searches resulted in the identification of 322 human genes. The potential human genetic modifiers were then overlapped with the human interactome. Interestingly, one of the modifiers found in this screen was SmD1 as well as modifiers in other RNA pathways. Certainly these data can be used to generate candidate genes. which can then be further investigated in mammalian systems. Indeed, it is important to test both these candidates as well as the proposed biochemical pathways in vertebrates for confirmation. Even if survival of an organism is not corrected, the measurement of critical physiological parameters can indicate how a particular pathway contributes to SMA. The absence of an effect might well indicate that this is not critical in mammals. It is important to realize, however, that SMN functions in snRNP biogenesis. With altered snRNP production, splicing is known to be affected; however, intron structure is not well conserved across species. Thus intron structure and sensitivity to SMN reduction can vary. As such, determining altered splicing patterns across species can be particularly informative in SMA. Currently there is limited information on these changes and their affects. Although some splicing targets of SMN deficiency have been described, the list is far from comprehensive and in some cases the changes appear variable between SMA samples.54,55 The question that remains is which changes contribute significantly to the SMA phenotype? Some propose that multiple small changes all contribute collectively to the SMA phenotype. However, this appears unlikely because the SMA phenotype is relatively specific to the motor system, at least in humans. It should be possible to link the physiological changes in the motor system to specific SMN functions. Last, others have identified a role of SMM in mRNA translation and transport.17 If these SMN functions are critical in SMA, then specific rescue of these functions, apart from snRNP assembly, should have an impact on the SMA phenotype. It is also possible that more than one function contributes to different aspects of the SMA phenotype. Again, rescue using specific mutations that suppress a particular function can be informative about its role in SMA. As a large number of expression and splicing changes in SMA tissues are likely not primary but secondary to SMN deficiency in animals, it is very important to not just

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Implications for disease process and clinical phenotype. Am J Hum Genet, 61(1), 40–50. McAndrew, P. E., Parsons, D. W., Simard, L. R., et al. (1997). Identification of proximal spinal muscular atrophy carriers and patients by analysis of SMNT and SMNC gene copy number. Am J Hum Genet, 60(6), 1411–1422. Burghes, A. H., & Beattie, C. E. (2009). Spinal muscular atrophy: Why do low levels of survival motor neuron protein make motor neurons sick? Nat Rev Neurosci, 10(8), 597–609. Melki, J., Lefebvre, S., Burglen, L., et  al. (1994). De novo and inherited deletions of the 5q13 region in spinal muscular atrophies. Science, 264(5164), 1474–1477. Gilliam, T.  C., Brzustowicz, L.  M., Castilla, L.  H., et  al. (1900). Genetic homogeneity between acute and chronic forms of spinal muscular atrophy. Nature, 345(6278), 823–825. Melki, J., Abdelhak, S., Sheth, P., et al. (1990). Gene for chronic proximal spinal muscular atrophies maps to chromosome 5q. Nature, 344(6268), 767–768. Burghes, A. H., Ingraham, S. E., McLean, M., et al. (1994). A multicopy dinucleotide marker that maps close to the spinal muscular atrophy gene. Genomics, 21(2), 394–402. DiDonato, C.  J., Morgan, K., Carpten, J.  D., et  al. (1994). Association between Ag1-CA alleles and severity of autosomal recessive proximal spinal muscular atrophy. Am J Hum Genet, 55(6), 1218–1229. Carpten, J. D., DiDonato, C. J., Ingraham, S. E., et al. (1994). A YAC contig of the region containing the spinal muscular atrophy gene (SMA, identification of an unstable region. Genomics, 24(2), 351–356. Kleyn, P. W., Wang, C. H., Lien, L. L., et al. (1993). Construction of a yeast artificial chromosome contig spanning the spinal muscular atrophy disease gene region. Proc Natl Acad Sci U S A, 90(14), 6801–6805. Roy, N., McLean, M. D., Besner-Johnston, A., et al. (1995). Refined physical map of the spinal muscular atrophy gene (SMA) region at 5q13 based on YAC and cosmid contiguous arrays. Genomics, 26(3), 451–460. Wirth, B., Schmidt, T., Hahnen, E., et al. (1997). De novo rearrangements found in 2% of index patients with spinal muscular atrophy: Mutational mechanisms, parental origin, mutation rate, and implications for genetic counseling. Am J Hum Genet, 61(5), 1102–1111. Monani, U. R., Lorson, C. L., Parsons, D. W., et al. (1999). A single nucleotide difference that alters splicing patterns distinguishes the SMA gene SMN1 from the copy gene SMN2. Hum Mol Genet, 8(7), 1177–1183. Lorson, C. L., Hahnen, E., Androphy, E. J., & Wirth, B. (1999). A single nucleotide in the SMN gene regulates splicing and is responsible for spinal muscular atrophy. Proc Natl Acad Sci U S A, 96(11), 6307–6311. Cartegni, L., Krainer, A. R. (2002). Disruption of an SF2/ASF-dependent exonic splicing enhancer in SMN2 causes spinal muscular atrophy in the absence of SMN1. Nat Genet, 30(4), 377–384. Gennarelli, M., Lucarelli, M., Capon, F., et  al. (1995). Survival motor neuron gene transcript analysis in muscles from spinal muscular atrophy patients. Biochem Biophys Res Commun, 213(1), 342–348. Lorson, C. L., Strasswimmer, J., Yao, J. M., et al. (1998). SMN oligomerization defect correlates with spinal muscular atrophy severity. Nat Genet, 19(1), 63–66. Lorson, C. L., & Androphy, E. J. (2000). An exonic enhancer is required for inclusion of an essential exon in the SMA-determining gene SMN. Hum Mol Genet, 9(2), 259–265. Burnett, B.  G., Munoz, E., Tandon, A., Kwon, D.  Y., Sumner, C.  J., & Fischbeck, K.  H. (2009). Regulation of SMN protein stability. Mol Cell Biol, 29(5), 1107–1115. Lefebvre, S., Burlet, P., Liu, Q., et al. (1997). Correlation between severity and SMN protein level in spinal muscular atrophy. Nat Genet, 16(3), 265–269. Coovert, D.  D., Le, T.  T., McAndrew, P.  E., et  al. (1997). The survival motor neuron protein in spinal muscular atrophy. Hum Mol Genet, 6(8), 1205–1214. Prior, T.  W., Krainer, A.  R., Hua, Y., et  al. (2009). A positive modifier of spinal muscular atrophy in the SMN2 gene. Am J Hum Genet, 85(3), 408–413. Vezain, M., Saugier-Veber, P., Goina, E., et al. (2010). A rare SMN2 variant in a previously unrecognized composite splicing regulatory element induces exon 7 inclusion and reduces the clinical severity of spinal muscular atrophy. Hum Mutat, 31(1), E1110–1125. Bernal, S., Alias, L., Barcelo, M. J., et al. (2010). The c.859G>C variant in the SMN2 gene is associated with types II and III SMA and originates from a common ancestor. J Med Genet, 47(9), 640–642. Burghes, A.  H., Ingraham, S.  E., Kote-Jarai, Z., et  al. (1994). Linkage mapping of the spinal muscular atrophy gene. Hum Genet, 93(3), 305–312. Cobben, J. M., van der Steege, G., Grootscholten, P., de Visser, M., Scheffer, H., & Buys, C. H. (1995). Deletions of the survival motor neuron gene in ​



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First, unlike humans, the blood brain-barrier is relatively open in the early developmental stages of the mouse. Second, the SMA mouse model has heart abnormalities and necrosis, neither of which is typically present in human SMA. Third, the introns in mouse can have a different sensitivity to SMN depletion. Finally, there have been reports of a peripheral requirement of SMN in the mouse, whereas there is little indication even in older SMA patients of abnormalities in peripheral organs. Thus investigation of SMN restoration to the motor neuron at different stages in SMA disease progression in a large animal is critical to effective therapeutic development. We have shown that reduction of SMN in motor neurons of the pig results in SMA with fibrillations on EMG, reduction of CMAP, reduction of MUNE, and pathological loss of motor neuron roots and motor neuron cell bodies.67 Administration of scAAV9-SMN early in disease progression results in correction of the motor neuron, showing the SMN dependence of these changes. Symptomatic correction resulted in stabilization of the phenotype, increased CMAP, and partial correction of MUNE and motor neuron loss. Although the phenotype did improve, the results indicate that early introduction of SMN will be necessary to produce the greatest rescue of motor neurons, regardless of the particular therapeutic used. One promising feature of SMN inducing therapies is that they function through different modalities and can therefore be combined if necessary to give further increases in SMN. It will be interesting over the next few years to see how these targeted therapies behave in clinical trials, and to expand research into improving motor neuron function in SMA.

unaffected siblings of patients with spinal muscular atrophy. Am J Hum Genet, 57(4), 805–808. Hahnen, E., Forkert, R., Marke, C., et al. (1995). Molecular analysis of candidate genes on chromosome 5q13 in autosomal recessive spinal muscular atrophy:  Evidence of homozygous deletions of the SMN gene in unaffected individuals. Hum Mol Genet, 4(10), 1927–1933. Wirth, B., el-Agwany, A., Baasner, A., et  al. (1995). Mapping of the spinal muscular atrophy (SMA) gene to a 750-kb interval flanked by two new microsatellites. European journal of human genetics:  EJHG, 3(1), 56–60. Oprea, G. E., Krober, S., McWhorter, M. L., et al. (2008). Plastin 3 is a protective modifier of autosomal recessive spinal muscular atrophy. Science, 320(5875), 524–527. Bernal, S., Also-Rallo, E., Martinez-Hernandez, R., et al. (2011). Plastin 3 expression in discordant spinal muscular atrophy (SMA) siblings. Neuromuscul Disord, 21(6), 413–419. Jedrzejowska, M., Gos, M., Zimowski, J.  G., Kostera-Pruszczyk, A., Ryniewicz, B., & Hausmanowa-Petrusewicz, I. (2014). Novel point mutations in survival motor neuron 1 gene expand the spectrum of phenotypes observed in spinal muscular atrophy patients. Neuromuscul Disord, 24(7), 617–623. Tripsianes, K., Madl, T., Machyna, M., et  al. (2011). Structural basis for dimethylarginine recognition by the Tudor domains of human SMN and SPF30 proteins. Nat Struct Mol Biol, 18(12), 1414–1420. Hubers, L., Valderrama-Carvajal, H., Laframboise, J., Timbers, J., Sanchez, G., & Cote, J. (2011). HuD interacts with survival motor neuron protein and can rescue spinal muscular atrophy-like neuronal defects. Hum Mol Genet, 20(3), 553–579. Li, D. K., Tisdale, S., Lotti, F., & Pellizzoni, L. (2014). SMN control of RNP assembly: From post-transcriptional gene regulation to motor neuron disease. Semin Cell Dev Biol, 32, 22–29. Workman, E., Saieva, L., Carrel, T. L., et al. (2009). A SMN missense mutation complements SMN2 restoring snRNPs and rescuing SMA mice. Hum Mol Genet, 18(12), 2215–2229. Sleigh, J. N., Buckingham, S. D., Esmaeili, B., et al. (2011). A novel Caenor habditis elegans allele, smn-1(cb131), mimicking a mild form of spinal muscular atrophy, provides a convenient drug screening platform highlighting new and pre-approved compounds. Hum Mol Genet, 20(2), 245–260. Praveen, K., Wen, Y., Gray, K.  M., et  al. (2014). SMA-causing missense mutations in survival motor neuron (Smn) display a wide range of phenotypes when modeled in drosophila. PLoS Genet, 10(8), e1004489. Schrank, B., Gotz, R., Gunnersen, J. M., et al. (1997). Inactivation of the survival motor neuron gene, a candidate gene for human spinal muscular atrophy, leads to massive cell death in early mouse embryos. Proc Natl Acad Sci U S A, 94(18), 9920–9925. Sen, A., Dimlich, D. N., Guruharsha, K. G., et al. (2013). Genetic circuitry of Survival motor neuron, the gene underlying spinal muscular atrophy. Proc Natl Acad Sci U S A, 110(26), E2371–2380.

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54. Lotti, F., Imlach, W.  L., Saieva, L., et  al. (2012). An SMN-dependent U12 splicing event essential for motor circuit function. Cell, 151(2), 440–454. 55. Zhang, Z., Pinto, A. M., Wan, L., et al. (2013). Dysregulation of synaptogenesis genes antecedes motor neuron pathology in spinal muscular atrophy. Proc Natl Acad Sci U S A, 110(48), 19348–19353. 56. Arnold, W. D., & Burghes, A. H. (2013). Spinal muscular atrophy: development and implementation of potential treatments. Ann Neurol, 74(3), 348–362. 57. Hua, Y., Sahashi, K., Rigo, F., et al. (2011). Peripheral SMN restoration is essential for long-term rescue of a severe spinal muscular atrophy mouse model. Nature, 478(7367), 123–126. 58. Porensky, P.  N., Mitrpant, C., McGovern, V.  L., et  al. (2012). A single administration of morpholino antisense oligomer rescues spinal muscular atrophy in mouse. Hum Mol Genet, 21(7), 1625–1638. 59. Porensky, P. N., & Burghes, A. H. (2013). Antisense oligonucleotides for the treatment of spinal muscular atrophy. Hum Gene Ther, 24(5), 489–498. 60. Cherry, J. J., Kobayashi, D. T., Lynes, M. M., et al. (2014). Assays for the identification and prioritization of drug candidates for spinal muscular atrophy. Assay Drug Dev Technol, 12(6), 315–341. 61. Naryshkin, N. A., Weetall, M., Dakka, A., et al. (2014). Motor neuron disease. SMN2 splicing modifiers improve motor function and longevity in mice with spinal muscular atrophy. Science, 345(6197), 688–693. 62. Palacino, J., Swalley, S.  E., Song C., et  al. (2015). SMN2 splice modulators enhance U1-pre-mRNA association and rescue SMA mice. Nat Chem Biol, 11(7), 511–517. 63. Foust, K. D., Wang, X., McGovern, V. L., et al. (2010). Rescue of the spinal muscular atrophy phenotype in a mouse model by early postnatal delivery of SMN. Nat Biotechnol, 28(3), 271–274. 64. Dominguez, E., Marais, T., Chatauret, N., et  al. (2011). Intravenous scAAV9 delivery of a codon-optimized SMN1 sequence rescues SMA mice. Hum Mol Genet, 20(4), 681–693. 65. Valori, C.  F., Ning, K., Wyles, M., et  al. (2010). Systemic delivery of scAAV9 expressing SMN prolongs survival in a model of spinal muscular atrophy. Sci Transl Med, 2(35), 35ra42. 66. Passini, M. A., Bu, J., Richards, A. M., et al. (2014). Translational fidelity of intrathecal delivery of self-complementary AAV9-survival motor neuron 1 for spinal muscular atrophy. Hum Gene Ther, 25(7), 619–630. 67. Duque, S., Arnold, W. D., Odermatt, P., et al. (2015). A large animal model of Spinal Muscular Atrophy and correction of phenotype. Ann Neurol, 77(3), 399–414.

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Lymphoblast and fibroblasts have been derived from SMA patients of various SMA types.15,16 Essentially, patient-derived fibroblasts and lymphoblasts grow normally and have no marked phenotype. However, SMA type 1 patient-derived cell lines do show reduced SMN levels and reduced snRNP assembly.17 Reduced SMN levels in SMA fibroblasts result in reduced gem numbers in the nucleus.15 Both the reduced levels of SMN/gems and reduced snRNP levels can be used in high-throughput screens to identify drug compounds that alter these properties. In most cases high-throughput assays to detect molecules that either alter the amount of SMN (through promoter activity for example) or the incorporation of SMN exon 7 have been screened using a reporter system.18 Then the compounds are subsequently tested in secondary screens using fibroblasts from SMA type 1 patients to show activity on the endogenous SMN2 gene. This has proved to be very useful, but the increase of SMN or gems in these cells should not be interpreted as a functional improvement, as the cells have no overt phenotype.15,19 Muscle cells in culture have also been developed from SMA patients. Type 1 and some type 2-derived muscle cultures show different properties when co-cultured with rat primary motor neurons.20 In this case, when normal rat nerve is included to innervate the muscle, the type 1 cultures and some of the type 2 cultures undergo degeneration. Whether SMN restoration is able to rescue this phenotype is unknown, and this system has not been used in therapeutic screens. Yet these findings have raised the possibility that muscle may be a target tissue. The satellite cell has been studied from SMA mice of various severities. Satellite cells are found at normal numbers at early stages in SMA mice. Yet when cultured, satellite cells show defects in forming fully mature myotubes suggesting a cell autonomous defect.21,22 There are a series of concerns with the current interpretation of these studies. First is the issue of whether there is reversibility with expression of SMN and whether selective expression in muscle or satellite cells results in normal fusion of myoblast derived from these mice. This is important to determine, as chronic denervation ​

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Spinal muscular atrophy (SMA) is an autosomal recessive motor neuron disorder that represents a major cause of infant mortality. In 1995 the cause of SMA was determined to be homozygous deletion or mutation of the SMN1 gene.1 Importantly, humans have two nearly identical SMN genes, SMN1 and SMN2, on chromosome 5.  SMN1 predominantly produces full-length SMN protein, whereas SMN2 produces limited amounts of full-length SMN and the majority is a shortened form that is unstable and rapidly degraded.2–5 Some fulllength SMN is produced from SMN2 that is sufficient for most cell types, but for as yet to be determined reasons is insufficient for normal motor neuron function.6 Much of our understanding of SMA is the direct result of the development and investigation of the numerous model systems. Within 5 years of the discovery of the causative gene, the first viable animal models were created.7,8 The presence of two forms of the SMN gene occurs only in humans9; all other organisms contain only the SMN1 gene. The only exception occurs in the chimpanzee, which carries a duplication of the SMN1 gene,9 Null mutations result in embryonic lethality in every organism that has been studied, and no human has ever been identified lacking both SMN1 and SMN2.6 The critical issue for any SMA model is that SMA is not caused by complete loss of SMN protein, instead SMA results from the reduced amount of SMN produced from the SMN2 gene.6 This situation has been recreated in both cell lines and animals using various methods (Figure 35.1). The SMN2 transgene has been introduced in both mice and zebrafish.7,10,11 In these systems it is important to consider the SMN level and expression in various tissues and the nature of SMN requirement in different species. In particular, species with a large yolk including the nematode, Drosophila and zebrafish, all have considerable contribution of maternal SMN in early development stages that at some point becomes depleted. There are models in which the Smn allele completely disrupts production of functional SMN, yet mutants survive through various developmental stages due to the presence of maternal SMN. However, this situation is not the same as reduced SMN levels throughout life, and this requires the creation of maternal zygotic mutants so that the contribution of maternal SMN is minimized.12 Knockdown of SMN using antisense morpholinos, shRNA, and RNAi have been reported both in culture and model organisms. Again it is important to consider the level of knockdown. If SMN protein is eliminated in any cell type, that cell will die. Regardless of how reduced SMN levels are created, SMN clearly functions in the assembly of snRNPs and altered snRNP levels have been observed in SMA tissues.13 Reduced snRNP function can result in the alteration of gene splicing. However, it is clear that the majority of genes do splice correctly when SMN is deficient14 (and unpublished data). One critical question concerns which intron structures are sensitive to SMN depletion and whether these changes are conserved across

species. Thus it is possible that critical targets of SMN deficiency are not present in model organisms, thus resulting in a different phenotype. Alternatively, these models could require lower levels of SMN to obtain a phenotype such that other genes then become affected. This depends on whether splicing is a critical target in the cause of SMA or whether other functions of SMN are critical to the development of SMA, and this has been discussed previously.6 The objective of this chapter is to provide an overview of the models that have been developed in the field of SMA and the insight that these models have provided to our understanding of the disease.

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Figure 35.1 Various strategies utilized to recapitulate low SMN levels in models of SMA and the associated reduction in mRNA or protein levels.

proteins such as HuD have been reported to rescue axonal defects either in culture or zebrafish or both.33 This is used as evidence of the genetic suppression of phenotype. However in SMA mice there is no defect in axonal growth or pathfinding,34 and this is also very unlikely in humans because presymptomatic type 1 patients show normal electrophysiological measures including motor unit number estimation (MUNE) and compound muscle action potential (CMAP) size, indicating normal innervation of muscle.35,36 The identification of axonal defects in zebrafish has led to a number of studies in which knockdown and rescue of the axonal defects is performed, and the interpretation of rescue is used to support that the identified molecule is critical in SMA. Yet, whether these suppress the phenotype of SMA in a mammalian model of the disease or SMA itself remains an important question. In other words, does the neuromuscular junction (NMJ) develop differently in zebrafish and mammals or is there any electrophysiological improvement in the motor neuron in the zebrafish? Furthermore we have shown other contradictory findings with SMN alleles that do not rescue axonal MN zebrafish defects but do rescue SMA mice (unpublished data). An important experiment that has not been reported is the overexpression of HuD. For instance, overexpression of HuD could be tested using scAAV9 and determined whether motor neuron function is improved in SMA mice models. In the end, relevancy of findings in model systems to human SMA is crucial and “the Holy Grail.” It can be argued that one model is more relevant than the other, but what findings replicate in SMA in humans ultimately resolves the issue. Both embryonic stem cells (human ES) and human iPS cells can be used to produce motor neurons from SMA patients.37,38 (listed in NIH Approved stem cells). Mouse SMA ES cells have also been utilized to generate motor neurons.39 iPS-derived motor neuronal cells show some interesting phenotypes including reduced axonal outgrowth and enhanced death, though the cell death phenotype is not pronounced.38 ShRNA knockdown of SMN has also been performed in ES-derived mouse motor neurons, and similarly there is an enhanced cell death.38 Both iPS cells and ES cells can be used in both primary and secondary screens for compounds that alter SMN levels.18 One feature that is important to consider is whether SMN expression is altered over time in culture. In particular, does selection for cells with higher SMN expression occur? Moving to the future, the use of iPS cells from SMA patients can confirm that a drug molecule will work in the motor neuron of humans.

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or loss of a functioning motor neuron can alter growth in an indirect manner.23 How the lack of nerve innervation will affect the ability of myoblasts to fuse or the exact condition of satellite cells in denervated muscle is hard to determine. Second, Nicole and colleagues showed that SMN+/D7 heterozygotes satellite cells showed decreased ability to repopulate muscle and fuse with degenerating muscle.24 In essence this a carrier of SMA as opposed to an SMA sample. It would be interesting to compare Smn+/− myoblast to the SMA myoblasts used in the studies of Hayhurst and coleagues and Boyer and coleagues, as Smn+/ − mice have no marked muscle phenotype in vivo.21,22 Last, it is often reported that these defects occur before loss of innervation. However, trophic factors to the muscle and functional synaptic integrity may be altered prior to appearance of obvious morphological disruption. We have performed studies that reduce SMN to SMA levels in muscle while maintaining levels in other tissues in the body in mice. In our studies we have found that reduction of SMN to SMA levels had no marked impact on muscle function.25 Thus whether cultured muscle is suitable for examination of function of reduced SMN to SMA levels remains controversial. SMN has also been knocked down in a series of different cell types, including cells that are likely not relevant to the SMA phenotype, but these cells can inform on SMN function or be used in screens. SMN knockdown to 15% in HeLa cells, which showed no effects on growth, revealed the first effects on snRNP levels. When SMN is reduced to 5% in HeLa cells, severe effects on growth of cells are seen.26 In a similar manner, knockdown of SMN to 5% in NIH3T3 cells results in growth defects, and this system can be used in screens of compounds that increase SMN or to analyze SMN mutants.27 However, the severe reduction of SMN below levels seen in spinal cord of SMA patients makes it difficult to determine the importance of splicing changes detected in this system.16,28 The most common knockdown of SMN is in the cell line NSC34, which, like MN1 cells, are created by fusion of motor neuron cells with neuroblastoma cells and can be called motor neuron-like because they retain expression of a series of motor neuron markers.29,30 The first knockdown of SMN in NSC34 cells was performed by the Sendtner group and revealed reduced levels of β-actin at the growth cones of axons and reduced axonal length.31 In addition, similar phenotypes were reported from primary motor neurons cultured from SMA mice.31 This phenotype is consistent with studies in zebrafish with morpholino knockdown of SMN.32 A number of molecules/

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Progressive loss of mobility, and increased uncoordinated movements. NMJ synaptic recordings show reduced EPSC amplitudes. Enlarged NMJ boutons in mutants. Homozygous lethal in late larval stages. Survival is due to large maternal contribution of wild type SMN activity to yolk sac. Correction of phenotype with SMN expression in muscle and neuronal tissues.

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The nematode, C. elegans, is a very effective model organism due to its rapid generation time of 3 days and short lifespan of about 3 weeks, allowing inexpensive and efficient culture in the laboratory and rapid screening capability.40 Additionally, the cell lineage of C. elegans has been fully reconstructed including its 302 neurons and the synaptic network.41 The C. elegans SMN ortholog, smn-1, is 36% identical to human SMN1.42 Various strategies have been utilized to model SMA in C.  elegans (see Table 35.1). The first models of SMN deficiency employed knockdown of SMN using RNAi to knock down the maternal SMN, resulting in embryonic lethality. The level of knockdown was less in neurons and can vary between animals, with the knockdown always

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Invertebrate organisms offer an efficient and economical platform for therapeutic screening due to short lifespans and rapid generation periods. In particular, models in Drosophila and C.elegans allow genetic screens to be performed relatively easily, although potential limitations of each model such as splicing differences due to intron structure should be kept in mind. Several models of SMA have been generated using both Caenorhabditis elegans and Drosophila melanogaster (Table 35.1).

TAB L E   35. 1

affecting fertility. The smn-1 mutant allele (smn-1(ok355)) is a null allele with a deletion of all but 87 bp of the 3′ end of the gene. This mutant survives to larvae stages, as maternal SMN results in survival through the embryonic stages.43 This null mutant displays normal early development over the first 2 days following hatching and subsequent development of defects in growth, pharyngeal pumping, and swimming (thrashing).43 These defects are partially corrected with pan-neuronal, but not muscular, expression of SMN.43 Another C. elegans smn-1 allele (cb131) that contains a point mutation (D27N) is analogous to a point mutation (D44V) in a patient with mild SMA (type 3b). This allele is associated with mild phenotypic changes of motility defect associated with abnormal neurotransmission but with retained fertility.44 However, this mutant is clearly not viable without the presence of wild-type SMN from SMN2 in mice (unpublished data). The SMN D44V allele in mice cannot rescue a null allele but can rescue an SMA mouse containing SMN2. These differences raise concern of how the SMN alleles behave between species and whether critical downstream targets, particularly those in splicing, have different sensitivities in lower species. One advantage of both C. elegans and Drosophila is that genetic screens for enhancers and suppressors of phenotype can be performed to identify pathways that are disrupted in the SMN deficient state and thus increase understanding of the disease. In this regard, RNAi screens have been performed in C.elegans (smn-1(ok355)) to identify enhancers and suppressors of Smn deficiency and a number have been reported.44,45 None of the ​

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neurons restored certain phenotypes and not others.53 Muscle size and NMJ excitatory postsynaptic potential amplitudes were rescued, but unlike SMN expression decreased locomotion and altered rhythmic motor activity were not rescued.53 In mouse motor neurons, Stasimon shows a splicing change at PND6 but not at PND1, perhaps indicating that this is a late change.14,53 It remains to be determined what the consequences of Stasimon are in regards to the physiology of the NMJ or the survival of SMA mice. This information is critical to determine any significance to the SMA phenotype, as we have discussed previously.54

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In contrast to the human neuromuscular system, the motor neurons of Drosophila are localized in the cortex of the central nervous system and project axons to muscle to form boutons that are opposed by glutamanergic receptors (in contrast to cholinergic).46 Nevertheless, Drosophila is well suited as a model system, with homologs for over 70% of human disease genes.47 The genome of Drosophila has a single SMN gene homolog (Smn) that contains a single exon encoding for a 226 amino acid protein, is located on chromosome 3, and is 41% identical to the human gene.48 Several mutants with loss of function point mutations and transposon insertions have been generated to model SMA (see Table 35.1). The first models characterized included two point mutations in a region that leads to reduced self-oligomerization of Smn (similar region as seen in human mutations also implicated in reduced self-oligomerization).49 These mutants as well as another deletion such as SmnX7, which removes just Smn,50 survive on the maternal Smn from the yolk sac. This does lead to low Smn levels, but at the late larvae stage when death occurs the level of Smn is 6%, which appears to be lower than that found in human SMA spinal cord.51 The mutants are reliant on maternal Smn to survive and die as larvae. The larvae show a phenotype of motor weakness associated with disorganized motor neuron boutons, loss of receptors at the neuromuscular junction, and reduced excitatory postsynaptic currents.49 A Drosophila model has been reported with a hypomorphic SmnE33 allele, which was generated by imprecise excision of a transposon element in the regulatory region of the Smn gene.52 The mutant, however, produces low Smn in the thorax region of an adult fly. It is unclear whether this means absence from specific cell types. Furthermore this is not a low level of SMN throughout the organism or in all motor neurons. So although this is a hypomorphic allele, it is somewhat different from the situation in humans due to the temporally and regionally limited reduction of Smn. Last there are Drosophila lines in which RNAi has been used to reduce Smn. RNAi lines of different strengths were developed, but the results remain confusing. Longer survival is obtained with the milder lines, but how they modify specific phenotypes used in suppressor screens is unclear. In addition the Smnf 05960 allele did not produce bouton (NMJ) alteration whereas the milder allele Smnf 01109 did, but why this is the case is unclear.50 A genetic screen to identify suppressors or enhancers of lethality in Drosophila has been performed. Theoretically this is a very powerful way to identify genetic pathways that are critical. Although interesting candidates that affect various pathways have been reported,45,50 none are strong suppressors. It remains unclear whether any act in mammals to suppress or enhance the SMA phenotype. If SMN reduction works through splicing, then targets can be absent in fly or at least the intron sensitivities can be different. In Drosophila the motor neuron is not cholinergic. However expression of SMN in cholinergic neurons of SMN deficient flies results in correction of the neuromuscular defects including neuromuscular transmission defects.51 One gene called Stasimon that contains a U12 intron shows a splicing alteration in SMN deficient Drosophila.53 Expression of Stasimon in cholinergic

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The well-understood and characterized motor neuron circuits and simplistic neuromuscular system of the zebrafish lend themselves to an excellent model platform for the study of motor neuron diseases including SMA (Table 35.2). Morpholino antisense oligonucleotides that reduce SMN levels from both the maternal contributed SMN as well as that produced by the zygote have been used to model SMA in the fish. The antisense oligonucleotide knockdown leads to the fish having truncated motor axons as well as defective branching of the motor axon.32 This assay has become widely used for assaying of molecules or genes that can suppress this phenotype. Thus various genes have been tested for suppression in this model and found to correct the axonal defects. It is less clear how this translates into mammals or human SMA. ENU mutagenesis has been used in the fish and mutant alleles (Smn L265stop, Y262 stop, and G264D) equivalent to human mutations have been found. These mutations result in very low or no Smn when homozygous, but zebrafish do survive with stop mutation surviving 12.5 days and the missense mutations 17 days.55 However, these fish show no axonal defects, as the maternal SMN provides sufficient SMN for normal development. They do show lower levels of SV2 protein in the motor neuron terminals. One method to overcome the maternal contribution is the use of maternal:zygotic SMN-deficient mutants. In this system the Hsp70 promoter, which is only slightly leaky when not heat shocked, provides the low levels of SMN consistent with SMA. Thus one can heat shock animals to activate high expression of SMN from the Hsp70 promoter and obtain adult Smn-/- animals that are capable of breeding. When crossed, offspring that are not heat shocked have SMN only at a low level from the leaky Hsp70 promoter. This is the case thoughout development of the motor neuron similar to the situation in transgenic mammalian models.56 In this case, similar to the situation in the antisense morpholinos, motor axons are abnormal showing truncation and branching. This indicates there is a requirement for SMN at a certain level during motor neuron development in the fish. However, in SMA mice no abnormal growth or patterning of motor neuron axons is observed,34 and it appears that NMJs form in the normal pattern. Also, in man the available evidence indicates normal innervation followed by decay. The muscle of fish is polyneuronally innervated, which is similar to neonatal mice up to day 14 when pruning occurs. Why these differences occur is unclear. However, the fact that the phenotype of SMA mice can be corrected with SMN restoration after the developmental period of motor axons suggests that at least some major problems are not due to development. A zebrafish model containing SMN2 has been developed, but the human SMN2 promoter does not appear to be robust in zebrafish. The SMN2 transgene on a null Smn zebrafish background resulted in only a mild increase in SMN protein levels and a modest increase in survival.11 It might be interesting to combine the maternal zygotic SMN with the SMN2 line to determine the resulting phenotype. Zebrafish with reduced SMN levels have been made and used to determine

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suppressors reported appear to be particularly strong. However some do have intriguing roles, for instance, endocytosis which could alter neurotransmitter release. The current difficulty is assessing which of these pathways is critical in mammalian SMA. For instance, if splicing of a particular gene is altered and significant, will this pathway be represented in C.elegans? Alternatively, can the pathways found in C.elegans be found to be significantly altered in mammalian models of SMA or in patients? This currently remains unresolved, and it is hard to know the significance of the currently identified pathways.

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Dose dependent Morpholino knockdown Translation blocking morpholino Maternal:zygotic smn Presynaptic NMJ defect Survival ~12–17 days post fertilization (dpf) reduction of 7%–8% of body length at death Correction of NMJ defects and partial extension of survival with motor neuron-specific human SMN correction

[55]

smnY262stop-/- Plus human SMN2 transgene

Human SMN2 corrects presynaptic NMJ defect Survival of ~15 dpf (compared with 12 without SMN2)

[11]

Smn−/− (Smn knockout)

Homozygous Smn knockout

Embryonic lethal

[57]

Smn−/−;SMN2 (2Hung)+/+) (Taiwanese)

Homozygous Smn knockout, Bac SMN2

Variable dependent on copy number of SMN2

[10]

Smn−/−; SMN2 (89Ahmb)+/+

Homozygous Smn knockout, two copies of SMN2 transgene

Severe weakness Survival ~5 days

Smn−/−; SMN2 (89Ahmb)+/+

Eight copies of SMN2

Normal phenotype

Smn−/−;SMN2 (89Ahmb)+/+; SMN∆7+/+) (SMN∆7)

SMN2 transgene on background of line89 with SMN2 transgene

Motor neuron loss by 9 days Survival ~2 weeks

[58]

Smn2B/(2B)

Mutation of exonic enhancer in exon 7 of Smn

Motor neuron loss, muscle weakness and atrophy at 21 days Survival ~28 days

[71]

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whether molecules correct axonal defects. Although these are straightforward to score, it would also be helpful to know if other features of the NMJ are also rescued. The correction of axonal phenotype is taken as evidence that the molecule is a suppressor of what could be called a relatively severe model of SMA. One would expect correction of either survival or electrophysiology of the neuromuscular system in the severe mouse. Currently this has not been shown or determined for any molecule to any significant extent. Indeed we have found that the mutant SMN282A, which does not correct axon defects in zebrafish, completely corrects SMA mice containing SMN2 by complementation. In our view, it is important to test the molecules found in invertebrates and lower vertebrates, in mice, to determine which phenotypes show parallels to the pathways most relevant to SMA. That is not to say the mouse is completely representative of the human situation, but this will allow at least some prioritization of the myriad of pathways being put forward. It seems unlikely that all are correct, but rather that a limited number will give insight into the disease.

Mouse models are the most extensively used animal models for the study of SMA. The highly conserved nervous system between mouse and human affords an excellent model system. There are numerous 268 | M o t o r n e u r o n D i s e a s e s

mouse models with variable severities of phenotype available. The main factor contributing to variability of clinical severity of patients with SMA is copy number of the SMN2 gene.54 Unlike humans, mice have a single homolog of the SMN1 gene. Homozygous loss of the Smn gene results in embryonic lethality and massive cell death, but mice that are heterozygous for null alleles of Smn are phenotypically normal.1,57 Therefore strategies have been utilized to incorporate a human SMN2 transgene onto a null Smn background to model SMA (Table 35.3).7,10 In general, severe SMA mice have 2 copies of SMN2 on a Smn null background whereas 1 copy SMN2 mice generally die in embryonic stages.7,34 When either a transgene expressing SMN∆7 is added, or two copies of SMN2 are placed on an allele capable of making mouse SMN∆7, the mice are slightly milder with mean life span of 14 days or 10 days.10,58 Animals with three copies of SMN2 on a C57BL/6 background have been developed that have a mean survival of 15 days or 22 days depending on the exact breeding scheme used. They show similar phenotypes to the SMN∆7 mice and have reduced CMAP size.59 One major difference with this line compared with SMN∆7 is the fact that there are escapers that appear to develop into adulthood normally. The latter animals show no marked phenotype except for tail necrosis similar to other SMN2 mice lines. Other mild SMA mice have also been generated, but in all cases these are on the milder end of the expected phenotype. The four copy number SMN2 mice, often said to be a model of mild SMA, show ​

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Embryonic lethal Incompatible with cellular function[68]

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Type 0: Weakness before or shortly after birth

Still born or die in utero[7,34]

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6–8 day survival[7, 10]

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The clinical presentation of SMA is remarkably restricted to loss of the lower motor neuron and associated features of chronic motor axonal loss. Phenotypically, patients may present with a range of clinical severity from onset prior to birth to mild weakness in adulthood. SMA is classically divided into three subtypes (type 1–3), with type 1 SMA being the most common with onset prior to 6 months of age and features of weakness preventing the ability to sit independently. There are sparse reports of non–motor-related features in patients with SMA and some similar features have been noted in mouse models (Table 35.4).77–93 Yet, there are a number of important points to consider. First, these non-motor pathological changes have not been reported in typical type 1 SMA with 2 copies of SMN2, but these rare reports are restricted to very severe, fetal-onset SMA. Though the designation of type 1 is often used in these very severe cases, we favor designating these very severe forms of SMA as type 0 or type 1a. Second, different mice lines show various peripheral organ

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There are a number of lines used in SMA research that we have not covered previously, as they are not strictly a model of SMA but are very useful in addressing questions in SMA. There are mouse lines with doxycycline inducible SMN expression in an SMA background as well as reversible allele based on expression of Cre.65,72,73 These can be used to determine when SMN can be reintroduced to have a therapeutic effect as well where high levels of SMN are required utilizing the Cre lines. Floxed alleles can also be used to selective delete or reduce SMN levels.74,75 In addition, we have placed the SMN missense mutations into a SMA background.61,76 This work demonstrated that mild missense alleles are not functional on their own but are capable of complementing the SMN produced by SMN2 (unpublished) (see chapter 34).

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tail necrosis but no overt weakness.10 These mice show electrophysiological findings of preserved CMAP and mildly reduced MUNE (personal observation, unpublished data), and thus can be considered a model of extremely mild SMA (type 4). The C/C mice have a chimeric gene composed of mouse exon 1-6 and the SMN2 exon 7 and 8 and an intact SMN2 gene integrated into the mouse Smn locus. This mouse has a very mild phenotype with no loss of motor neurons but a reduced CMAP.60 The SMNA2G mice with SMN2 are smaller and show weakness in grip strength but again are very mild.61 There are also milder mouse models of SMA that lack SMN2 but have reduced SMN levels. Smn+/- mice show normal muscle strength and CMAP amplitude but reduced motor neuron number and increased single motor unit action potential, indicating expansion of the motor neuron territory. Histological studies revealed extensive motor neuron sprouting, which compensates for the motor neuron loss, and thus these mice do not have an overt phenotype.62 The findings of very extensive ability of mouse motor neurons to sprout and compensate for lost motor neurons is one reason why it is difficult to model the mild alleles in SMA. An allele that disrupts the splicing of the mouse Smn gene has been developed with the SMN2 C to T change, and this mouse has no SMA phenotype.63 Whereas a double mutation combined with a null Smn allele gives 2B/- mice, which have SMN levels of 15% compared with wild-type mice and a milder phenotype than SMN∆7 mice.64–66 The 2B/- mice have an average survival of 28  days, have reduced CMAP size, and at 10  days show abnormal neuromuscular junctions.66,67 This model has been used in testing therapeutics and has shown a very enhanced response to therapeutics, in some case even without correction of CMAP size (an indirect measure of motor neuron function in vivo).67 This model currently appears to be the model most closely resembling a mild SMA phenotype. Unfortunately this mouse model is not deposited in any of the major repositories such as The Jackson Laboratory, and therefore is not easily available to maximize its utilization. Although this model does not have SMN2, the SMN2 inducers can be relatively easily tested in the current severe SMN∆7 SMA mice, and the 2B/- mice can be used to study the effect of SMN restoration at different time points in mild SMA as well as the pathobiology of milder SMA. ​

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Four copies of SMN2 results in features of necrosis starting in the tail at ~3 weeks but no overt weakness[10]

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TA B L E   35. 3 SMN2 Modification of  M

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lectrophysiological, and xtra-Motor Phenotypic Features of the M ∆7 Mouse Compared with  pinal Muscular

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TAB L E   35. 4 Motor,

Motor Phenotype

[58,103]

SMA type 0: prenatal SMA type 1: 0–6 months SMA type 2: 18 months SMA type 3 b: >3years SMA type 4: >21 years

[105]

Spinal cord

Normal motor neuron counts at PND 4; reduced ~20% at PND 9

[58]

Fetal increase in MN apoptosis

[106–108]

Nerve

Accumulation of NF in axons

[34]

Intramuscular nerve twigs demonstrate accumulation of NF

[109]

Muscle

Reduced muscle fiber cross-sectional size. Uniform small muscle fibers similar to type 0 patients.

[58,110]

Fiber Type grouping and grouped atrophy Uniform small muscle fibers in type 0 SMA

Neuromuscular Junction (NMJ)

Normal synapse formation and subsequent failure of maintenance and denervation (variable severity in different muscles) Reduced postsynaptic size and NF accumulation

[111–113]

Fetal disassembly of postsynaptic receptors

[114]

ex vivo patch clamp recordings at NMJ

Reduced endplate potential amplitude; Corrected with SMN

[102,104, 110, 111,115]

Unknown; decrement with slow frequency repetitive nerve stimulation in type 2&3 (in vivo)

[116]

Spinal cord recordings

Reduced sensory-motor (proprioceptive) [100,102] input loss

Unknown, peripheral sensory neuropathy in some severe cases

[92,117–119]

Compound Muscle Action Potential

Reduced; corrected with SMN

[98]

Reduced, normal in at least some patients prior to onset, may be normal in less severe cases

[35,36, 94-96, 120]

Motor Unit Number Estimates

Reduced; corrected with SMN

[98]

Reduced in proportion to severity

[35, 95, 96]

Electromyography

Fibrillations at 2 weeks

[98]

Fibrillation potentials, reduced recruitment, and variable enlargement of motor unit action potentials

[121, 122]

Cardiac

Decreased cardiac function at 7 days; bradycardia and diminished contractility

[83]

Septal defects, secondary bradycardia (rare and mainly very severe cases)

[89]

Vascular, GI/GI, and autonomic

Distal extremity necrosis*, bowel [104, impaction*, urinary retention*, priapism* 123, 124]

Rarely reported distal limb necrosis; Reduced sympathetic skin responses and cold-induced vasodilatation, rarely reported decreased intestinal peristalsis and dilatation; Frequently reported constipation

[77–81, 88]

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Progressive weakness starting at PND 2–5 and subsequent atrophy

Onset

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GI/GU: Gastrointestinal/genitourinary. Δ

*Only noted in aged rescued SMN 7 animals.

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Extra-motor features

evident in the hind limbs when weakness develops and is noted subsequently in the front legs prior to euthanasia.125 The pigs show both reduced CMAP and MUNE, mimicking the clinical presentation that occurs in humans. Rescue of the pigs was also performed at different stages. Presymptomatic treatment with scAAV9-SMN was introduced the day after injection of scAAV9-shRNA, and this, in essence, completely rescued the pig with all parameters corrected. This demonstrates that the observed phenotypes are dependent on SMN. Substantial, though not complete, correction of the phenotype was also achieved with delivery of the scAAV9-SMN at postsymptomatic stages when hind limb weakness was evident. There was variation in the degree of correction when the pig had more advanced symptoms. In the animals treated after symptomatic onset, CMAP was preserved but MUNE and motor neuron counts were not. This confirms that scAAV9-SMN halted progression of motor neuron loss, and thus stabilized the animal.125 These studies indicate that early symptomatic treatment can have a major impact. As expected the MUNE and motor neuron loss was not completely rescued when animals were treated symptomatically. Once the motor neuron is lost it cannot be replaced, but importantly, it is likely that SMA can be stabilized and some sprouting of the motor neurons will occur if treated during early symptomatic stages. Yet the longer the condition has been present and the greater the motor neuron loss, the less the response is going to be. The development of the pig has allowed question on the timing of treatment to be addressed in a large animal model. In addition, the knockdown of SMN in motor neurons does give a marked phenotype and the comparison of the splicing changes that occur in pig and mouse can be used to look at intron sensitivity to SMN depletion and how similar these changes are in two mammalian models of SMA. ​

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developmental defects that are most likely due to different full-length SMN expression from the SMN2 transgene. One other tissue worth mentioning is the thalamus, which clearly shows pathology in human cases with type I SMA (with 2 copies of SMN2), but this organ has not been studied in the mouse.90–93

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Electromyographic features noted in patients with SMA include features of chronic motor neuron loss. These features were historically utilized for clinical diagnosis prior to availability of molecular diagnostic testing. Techniques of CMAP, MUNE, and electromyography (EMG) demonstrate features of axonal loss and correlate with severity of disease and functional level (see Table 35.4).35,36,94–97 Similar studies of CMAP, MUNE, and EMG can be applied in mouse models of SMA, but only occasionally have these techniques been utilized.61,62,67,98 Nevertheless, these studies demonstrate similar findings of motor neuron/axonal loss that are corrected with SMN restoring therapies.98 Other electrophysiological techniques ex vivo have been frequently utilized to characterize disease phenotype in mouse models. Neuromuscular junction electrophysiological techniques demonstrate defects of reduced endplate current amplitude and quantal content at the NMJ and sensory and motor synaptic defects.99–102 The findings of ex vivo NMJ recordings provide important insight into the pathogenesis of SMA, but these measures have not been utilized in the investigation of human disease.

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Recently a pig model of SMA has been created125 using scAAV9. Previous studies have shown that motor neurons can be efficiently transduced when scAAV9 is delivered via intrathecal injection.125–128 The SMA pig was made by developing a shRNA that selectively knocked down pig SMN to level found in SMA spinal cord samples. The pigs have a phenotype of clear weakness. This is particularly

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In a matter of two decades since the discovery of the pathogenic gene mutation, the utilization of in vitro and in vivo models has allowed development of promising preclinical therapeutics in the form of antisense oligonucleotides, gene therapy, and small drug molecules that are now being tested in the clinic. Using findings from preclinical work, these therapies are predicted to have significant impact. Despite early implementation of these therapeutics in clinical trials, a clear understanding of how SMN protein reduction leads to selective loss of spinal motor neurons has yet to be unraveled. In this regard there are some important considerations as we move forward. In invertebrates, do the suppressors identified show a similar suppression in vivo in mammals? Can we find a truly strong suppressor in invertebrates that gives confidence that we are looking at the correct pathway? What role does alteration of splicing play in SMA, and if splicing plays a major role, how do the intron sensitivities in different species affect the phenotype? We cannot assume the sensitivities are the same in human, mouse and Drosophila. Alternatively, other functions of SMN have been implicated in SMA. What are these functions and how can they be assayed? One critical experiment in this regards is to attempt to restore, for instance, just Sm assembly onto snRNA and ask whether that does not correct, partially corrects, or completely corrects SMA in mice. If complete or partial correction occurs, then splicing can be regarded as having a key role. Other functions can also be studied in this manner to confirm or disprove their importance. Care should be taken in certain aspects, as correction can occur due to modifications further downstream than expected. For instance, correction of secretion by overexpression of Golgi component might correct because increased secretion occurs, but the primary alteration could be splicing of that secreted

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Various mouse models have been used in a wide range of studies to understand the pathophysiology of SMA. This discussion is covered in detail in other chapters, and here we wish to outline the models available and some of their key characteristics. SMA mice, particularly those containing SMN2, have been used in the testing of therapeutics for SMA. It is now clear that SMN2 inducers can be effectively tested in these mice despite their severe phenotype. Indeed in some ways this is an advantage, as truly large extension of life span can be obtained when the molecules are effective.54 A number of SMN2inducing molecules are now in clinical trials, including antisense oligonucleotides that increase SMN production from SMN2 (Ionis) and small molecules (Roche). Furthermore scAAV9-SMN is in phase 1 clinical trials (AveXis Nationwide Children’s/OSU), and all three of these strategies were tested in the available SMA models. For testing molecules that do not act upon SMN2, testing endpoints that assess pertinent motor neuron function, such as electrophysiological measures, or muscle force in the case of muscle enhancers, such as physiological testing of strength, should be employed. We have previously extensively discussed therapeutic and the molecules that have been tested.54

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1. Lefebvre, S., et al. (1995). Identification and characterization of a spinal muscular atrophy-determining gene. Cell, 80(1), 155–165. 2. Gennarelli, M., et al. (1995). Survival motor neuron gene transcript analysis in muscles from spinal muscular atrophy patients. Biochem Biophys Res Commun, 213(1), 342–348. 3. Lorson, C.  L., et  al. (1998). SMN oligomerization defect correlates with spinal muscular atrophy severity. Nat Genet, 19(1), 63–66. 4. Lorson, C. L., & Androphy, E. J. (2000). An exonic enhancer is required for inclusion of an essential exon in the SMA-determining gene SMN. Hum Mol Genet, 9(2), 259–265. 5. Burnett, B. G., et al. (2009). Regulation of SMN protein stability. Mol Cell Biol, 29(5), 1107–1115. 6. Burghes, A. H., & Beattie, C. E. (2009). Spinal muscular atrophy: Why do low levels of survival motor neuron protein make motor neurons sick?. Nat Rev Neurosci, 10(8), 597–609. 7. Monani, U. R., et al. (2000). The human centromeric survival motor neuron gene (SMN2) rescues embryonic lethality in Smn–/– mice and results in a mouse with spinal muscular atrophy. Hum Mol Genet, 9(3), 333–339. 8. Hsieh-Li, H. M., et al. (2000). A mouse model for spinal muscular atrophy. Nat Genet, 24(1), 66–70. 9. Rochette, C. F., Gilbert, N., & Simard, L. R. (2001). SMN gene duplication and the emergence of the SMN2 gene occurred in distinct hominids: SMN2 is unique to Homo sapiens. Hum Genet, 108(3), 255–266. 10. Hsieh-Li, H. M., et al. (2000). A mouse model for spinal muscular atrophy. Nat Genet, 24(1), 66–70. 11. Hao le, T., Burghes, A. H., & Beattie, C. E. (2011). Generation and characterization of a genetic zebrafish model of SMA carrying the human SMN2 gene. Mol Neurodegener, 6(1), 24. 12. Hao, L. T., et al. (2015). Motoneuron development influences dorsal root ganglia survival and Schwann cell development in a vertebrate model of spinal muscular atrophy. Hum Mol Genet, 24(2), 346–360. 13. Gabanella, F., et al. (2007). Ribonucleoprotein assembly defects correlate with spinal muscular atrophy severity and preferentially affect a subset of spliceosomal snRNPs. PLoS One, 2(9), e921. 14. Zhang, Z., et al. (2013). Dysregulation of synaptogenesis genes antecedes motor neuron pathology in spinal muscular atrophy. Proc Natl Acad Sci U S A, 110(48), 19348–19353. 15. Coovert, D. D., et al. (1997). The survival motor neuron protein in spinal muscular atrophy. Hum Mol Genet, 6(8), 1205–1214. 16. Lefebvre, S., et al. (1997). Correlation between severity and SMN protein level in spinal muscular atrophy. Nat Genet, 16(3), 265–269. 17. Wan, L., et al. (2005). The survival of motor neurons protein determines the capacity for snRNP assembly: Biochemical deficiency in spinal muscular atrophy. Mol Cell Biol, 25(13), 5543–5551. 18. Cherry, J. J., et al. (2014). Assays for the identification and prioritization of drug candidates for spinal muscular atrophy. Assay Drug Dev Technol, 12(6), 315–341. 19. Naryshkin, N.  A., et  al. (2014). Motor neuron disease. SMN2 splicing modifiers improve motor function and longevity in mice with spinal muscular atrophy. Science, 345(6197), 688–693. 20. Braun, S., et al. (1995). Constitutive muscular abnormalities in culture in spinal muscular atrophy. Lancet, 345(8951), 694–695. 21. Hayhurst, M., et al. (2012). A cell-autonomous defect in skeletal muscle satellite cells expressing low levels of survival of motor neuron protein. Dev Biol, 368(2), 323–334. 22. Boyer, J. G., et al. (2014). Myogenic program dysregulation is contributory to disease pathogenesis in spinal muscular atrophy. Hum Mol Genet, 23(16), 4249–4259. 23. Lapalombella, R., et al. (2008). Persistence of regenerative myogenesis in spite of down-regulation of activity-dependent genes in long-term denervated rat muscle. Neurol Res, 30(2), 197–206. 24. Nicole, S., et  al. (2003). Intact satellite cells lead to remarkable protection against Smn gene defect in differentiated skeletal muscle. J Cell Biol, 161(3), 571–582. 25. Iyer CC, McGovern VL, Murray JD, et al. Low levels of Survival Motor Neuron protein are sufficient for normal muscle function in the SMN∆7 mouse model of SMA. Hum Mol Genet. 2015;24(21):6160–6173.



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26. Zhang, Z., et al. (2008). SMN deficiency causes tissue-specific perturbations in the repertoire of snRNAs and widespread defects in splicing. Cell, 133(4), 585–600. 27. Li, D. K., et al. (2013). A cell system for phenotypic screening of modifiers of SMN2 gene expression and function. PLoS One, 8(8), e71965. 28. Tisdale, S., et al. (2013). SMN is essential for the biogenesis of U7 small nuclear ribonucleoprotein and 3’-end formation of histone mRNAs. Cell Rep, 5(5), 1187–1195. 29. Cashman, N.R., et  al. (1992). Neuroblastoma x spinal cord (NSC) hybrid cell lines resemble developing motor neurons. Dev Dyn, 194(3), 209–221. 30. Salazar-Grueso, E. F., Kim, S., & Kim, H. (1991). Embryonic mouse spinal cord motor neuron hybrid cells. Neuroreport, 2(9), 505–508. 31. Rossoll, W., et al. (2003). Smn, the spinal muscular atrophy-determining gene product, modulates axon growth and localization of beta-actin mRNA in growth cones of motoneurons. J Cell Biol, 163(4), 801–812. 32. McWhorter, M. L., et al. (2003). Knockdown of the survival motor neuron (Smn) protein in zebrafish causes defects in motor axon outgrowth and pathfinding. J Cell Biol, 162(5), 919–931. 33. Hubers, L., et al. (2011). HuD interacts with survival motor neuron protein and can rescue spinal muscular atrophy-like neuronal defects. Hum Mol Genet, 20(3), 553–579. 34. McGovern, V. L., et al. (2008). Embryonic motor axon development in the severe SMA mouse. Hum Mol Genet, 17(18), 2900–2909. 35. Swoboda, K.  J., et  al. (2005). Natural history of denervation in SMA:  Relation to age, SMN2 copy number, and function. Ann Neurol, 57(5), 704–712. 36. Finkel, R. S. (2013). Electrophysiological and motor function scale association in a pre-symptomatic infant with spinal muscular atrophy type I. Neuromuscul Disord, 23(2), 112–115. 37. Wang, Z. B., Zhang, X., & Li, X. J. (2013). Recapitulation of spinal motor neuron-specific disease phenotypes in a human cell model of spinal muscular atrophy. Cell Res, 23(3), 378–393. 38. Ebert, A.  D., et  al. (2009). Induced pluripotent stem cells from a spinal muscular atrophy patient. Nature, 457(7227), 277–280. 39. Makhortova, N.  R., et  al. (2011). A screen for regulators of survival of motor neuron protein levels. Nat Chem Biol, 7(8), 544–552. 40. Corsi, A. K. (2005). A biochemist’s guide to Caenorhabditis elegans. Anal Biochem, 359(1), 1–17. 41. Hobert, O. (2013). The neuronal genome of Caenorhabditis elegans. WormBook, Aug 13, 1–106. 42. Miguel-Aliaga, I., et  al. (1999). The Caenorhabditis elegans orthologue of the human gene responsible for spinal muscular atrophy is a maternal product critical for germline maturation and embryonic viability. Hum Mol Genet, 8(12), 2133–2143. 43. Briese, M., et  al. (2009). Deletion of smn-1, the Caenorhabditis elegans ortholog of the spinal muscular atrophy gene, results in locomotor dysfunction and reduced lifespan. Hum Mol Genet, 18(1), 97–104. 44. Sleigh, J.  N., et  al. (2011). A novel Caenorhabditis elegans allele, smn1(cb131), mimicking a mild form of spinal muscular atrophy, provides a convenient drug screening platform highlighting new and pre-approved compounds. Hum Mol Genet, 20(2), 245–260. 45. Dimitriadi, M., et al. (2010). Conserved genes act as modifiers of invertebrate SMN loss of function defects. PLoS Genet, 6(10), e1001172. 46. Johansen, J., et al. (1989). Stereotypic morphology of glutamatergic synapses on identified muscle cells of Drosophila larvae. J Neurosci, 9(2), 710–725. 47. Reiter, L.  T., et  al. (2001). A systematic analysis of human diseaseassociated gene sequences in Drosophila melanogaster. Genome Res, 11(6), 1114–1125. 48. Miguel-Aliaga, I., et  al. (2000). Disruption of SMN function by ectopic expression of the human SMN gene in Drosophila. FEBS Lett, 486(2), 99–102. 49. Chan, Y. B., et al. (2003). Neuromuscular defects in a Drosophila survival motor neuron gene mutant. Hum Mol Genet, 12(12), 1367–1376. 50. Chang, H.  C., et  al. (2008). Modeling spinal muscular atrophy in Drosophila. PLoS One, 3(9), e3209. 51. Imlach, Wendy L., et al. (2012). SMN is required for sensory-motor circuit function in Drosophila. Cell, 151(2), 427–439. 52. Rajendra, T. K., et al. (2007). A Drosophila melanogaster model of spinal muscular atrophy reveals a function for SMN in striated muscle. J Cell Biol, 176(6), 831–841. 53. Lotti, F., et al. (2012). An SMN-dependent U12 splicing event essential for motor circuit function. Cell, 151(2), 440–454. 54. Arnold, W.  D., & Burghes, A.  H. (2013). Spinal muscular atrophy:  The development and implementation of potential treatments. Ann Neurol, 74(3), 348–362.

component. In SMA, rather than creating a plethora of biochemical alterations and implicating them all, we should try to design rigorous genetic experiments that confirm the importance of a particular mechanism.

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80. Ionasescu, V., Christensen, J., & Hart, M. (1994). Intestinal pseudoobstruction in adult spinal muscular atrophy. Muscle Nerve, 17(8), 946–948. 81. Messina, S., et al. (2008). Feeding problems and malnutrition in spinal muscular atrophy type II. Neuromuscul Disord, 18(5), 389–393. 82. Crawford, T. O., et al. (1999). Abnormal fatty acid metabolism in childhood spinal muscular atrophy. Ann Neurol, 45(3), 337–343. 83. Bevan, A. K., et al. (2010). Early heart failure in the SMNDelta7 model of spinal muscular atrophy and correction by postnatal scAAV9-SMN delivery. Hum Mol Genet, 19(20), 3895–3905. 84. Porensky, P. N., et al. (2012). A single administration of morpholino antisense oligomer rescues spinal muscular atrophy in the mouse. Hum Mol Genet, 21(7), 1625–1638. 85. Rudnik-Schöneborn, S., et al. (2003). Classical infantile spinal muscular atrophy with SMN deficiency causes sensory neuronopathy. Neurology, 60(6), 983–987. 86. Bowerman, M., et al. (2014). Defects in pancreatic development and glucose metabolism in SMN-depleted mice independent of canonical Spinal Muscular Atrophy neuromuscular pathology. Hum Mol Genet, 23(13), 3432–3444. 87. Bowerman, M., et al. (2012). Glucose metabolism and pancreatic defects in spinal muscular atrophy. Ann Neurol, 72(2), 256–268. 88. Rudnik-Schoneborn, S., et al. (2010). Digital necroses and vascular thrombosis in severe spinal muscular atrophy. Muscle Nerve, 42(1), 144–147. 89. Rudnik-Schoneborn, S., et al. (2008). Congenital heart disease is a feature of severe infantile spinal muscular atrophy. J Med Genet, 45(10), 635–638. 90. Harding, B. N., et al. (2015). Spectrum of neuropathophysiology in spinal muscular atrophy type I. J Neuropathol Exp Neurol, 74(1), 15–24. 91. Shishikura, K., et  al. (1983). A neuropathologic study of WerdnigHoffmann disease with special reference to the thalamus and posterior roots. Acta Neuropathol, 60(1-2), 99–106. 92. Araki, S., et  al. (2003). Neuropathological analysis in spinal muscular atrophy type II. Acta Neuropathol, 106(5), 441–448. 93. Ito, Y., et al. (2004). Thalamic lesions in a long-surviving child with spinal muscular atrophy type I: MRI and EEG findings. Brain Dev, 26(1), 53–56. 94. Montes, J., et al. (2009). Clinical outcome measures in spinal muscular atrophy. J Child Neurol, 24(8), 968–978. 95. Kaufmann, P., et al. (2012). Prospective cohort study of spinal muscular atrophy types 2 and 3. Neurology, 79(18), 1889–1897. 96. Kang, P. B., et al. (2014). The motor neuron response to SMN1 deficiency in spinal muscular atrophy. Muscle Nerve, 49(5), 636–644. 97. Finkel, R. S., et al. (2014). Observational study of spinal muscular atrophy type I and implications for clinical trials. Neurology, 83(9), 810–817. 98. Arnold, W.  D., et  al. (2014). Electrophysiological biomarkers in spinal muscular atrophy: Preclinical proof of concept. Ann Clin Transl Neurol, 1(1), 34–44. 99. Kong, L., et al. (2009). Impaired synaptic vesicle release and immaturity of neuromuscular junctions in spinal muscular atrophy mice. J Neurosci, 29(3), 842–851. 100. Mentis, G.  Z., et  al. (2011). Early functional impairment of sensorymotor connectivity in a mouse model of spinal muscular atrophy. Neuron, 69(3), 453–467. 101. Martinez, T.  L., et  al. (2012). Survival motor neuron protein in motor neurons determines synaptic integrity in spinal muscular atrophy. J Neurosci, 32(25), 8703–8715. 102. Ling, K. K., et al. (2010). Synaptic defects in the spinal and neuromuscular circuitry in a mouse model of spinal muscular atrophy. PLoS One, 5(11), e15457. 103. Butchbach, M.  E. R., Edwards, J.  D. & Burghes, A.  H. M. (2007). Abnormal motor phenotype in the SMNΔ7 mouse model of spinal muscular atrophy. Neurobiol Dis, 27(2), 207–219. 104. Foust, K. D., et al. (2010). Rescue of the spinal muscular atrophy phenotype in a mouse model by early postnatal delivery of SMN. Nat Biotech, 28(3), 271–274. 105. Kolb, S.  J., & Kissel, J.  T. (2011). Spinal muscular atrophy:  A  timely review. Arch Neurol, 68(8), 979–984. 106. Soler-Botija, C., et  al. (2002). Neuronal death is enhanced and begins during foetal development in type I spinal muscular atrophy spinal cord. Brain, 125(Pt 7), 1624–1634. 107. Fidzianska, A., & Rafalowska, J. (2002). Motoneuron death in normal and spinal muscular atrophy-affected human fetuses. Acta Neuropathol, 104(4), 363–368. 108. Soler-Botija, C., et al. (2003). Downregulation of Bcl-2 proteins in type I  spinal muscular atrophy motor neurons during fetal development. J Neuropathol Exp Neurol, 62(4), 420–426. 109. Coers, C., & Woolf, A.  L. (1959). The innervation of muscle. Oxford: Blackwell.





55. Boon, K. L., et al. (2009). Zebrafish survival motor neuron mutants exhibit presynaptic neuromuscular junction defects. Hum Mol Genet, 18(19), 3615–3625. 56. Hao le, T., et al. (2013). Temporal requirement for SMN in motoneuron development. Hum Mol Genet, 22(13), 2612–2625. 57. Schrank, B., et al. (1997). Inactivation of the survival motor neuron gene, a candidate gene for human spinal muscular atrophy, leads to massive cell death in early mouse embryos. Proc Natl Acad Sci, 94(18), 9920–9925. 58. Le, T. T., et al. (2005). SMNDelta7, the major product of the centromeric survival motor neuron (SMN2) gene, extends survival in mice with spinal muscular atrophy and associates with full-length SMN. Hum Mol Genet, 14(6), 845–857. 59. Michaud, M., et al. (2010). Neuromuscular defects and breathing disorders in a new mouse model of spinal muscular atrophy. Neurobiol Dis, 38(1), 125–135. 60. Li, J., Geisbush, T.  R., Arnold, W.  D., Rosen, G.  D., Zaworski, P.  G., & Rutkove, S. B. (2014). A comparison of three electrophysiological methods for the assessment of disease status in a mild spinal muscular atrophy mouse model. PLoS One, 9(10), e111428. 61. Monani, U. R., et al. (2003). A transgene carrying an A2G missense mutation in the SMN gene modulates phenotypic severity in mice with severe (type I) spinal muscular atrophy. J Cell Biol, 160(1), 41–52. 62. Simon, C. M., et al. (2010). Ciliary neurotrophic factor-induced sprouting preserves motor function in a mouse model of mild spinal muscular atrophy. Hum Mol Genet, 19(6), 973–986. 63. Gladman, J. T., et al. (2010). A humanized Smn gene containing the SMN2 nucleotide alteration in exon 7 mimics SMN2 splicing and the SMA disease phenotype. Hum Mol Genet, 19(21), 4239–4252. 64. DiDonato, C. J., et al. (2001). Regulation of murine survival motor neuron (Smn) protein levels by modifying Smn exon 7 splicing. Hum Mol Genet, 10(23), 2727–2736. 65. Hammond, S. M., et al. (2010). Mouse survival motor neuron alleles that mimic SMN2 splicing and are inducible rescue embryonic lethality early in development but not late. PLoS One, 5(12), e15887. 66. Bowerman, M., et  al. (2012). A critical smn threshold in mice dictates onset of an intermediate spinal muscular atrophy phenotype associated with a distinct neuromuscular junction pathology. Neuromuscul Disord, 22(3), 263–276. 67. Gogliotti, R. G., et al. (2013). The DcpS inhibitor RG3039 improves survival, function and motor unit pathologies in two SMA mouse models. Hum Mol Genet, 22(20), 4084–4101. 68. Schrank, B., et al. (1997). Inactivation of the survival motor neuron gene, a candidate gene for human spinal muscular atrophy, leads to massive cell death in early mouse embryos. Proc Natl Acad Sci U S A, 94(18), 9920–9925. 69. Wirth, B., et  al. (2006). Mildly affected patients with spinal muscular atrophy are partially protected by an increased SMN2 copy number. Hum Genet, 119(4), 422–428. 70. Prior, T.  W., et  al. (2004). Homozygous SMN1 deletions in unaffected family members and modification of the phenotype by SMN2. Am J Med Genet, 130A(3), 307–310. 71. Bowerman, M., et  al. (2009). SMN, profilin IIa and plastin 3:  a link between the deregulation of actin dynamics and SMA pathogenesis. Mol Cell Neurosci,42(1), 66–74. 72. Le, T. T., et al. (2011). Temporal requirement for high SMN expression in SMA mice. Hum Mol Genet, 20(18), 3578–3591. 73. Lutz, C. M., et al. (2011). Postsymptomatic restoration of SMN rescues the disease phenotype in a mouse model of severe spinal muscular atrophy. J Clin Invest, 121(8), 3029–3041. 74. Cifuentes-Diaz, C., et al. (2001). Deletion of murine SMN exon 7 directed to skeletal muscle leads to severe muscular dystrophy. J Cell Biol, 152(5), 1107–1114. 75. Park, G. H., et al. (2010). Reduced survival of motor neuron (SMN) protein in motor neuronal progenitors functions cell autonomously to cause spinal muscular atrophy in model mice expressing the human centromeric (SMN2) gene. J Neurosci, 30(36), 12005–12019. 76. Workman, E., et  al. (2009). A SMN missense mutation complements SMN2 restoring snRNPs and rescuing SMA mice. Hum Mol Genet, 18(12), 2215–2229. 77. Araujo, A., Araujo, M., & Swoboda, K. J. (2009). Vascular perfusion abnormalities in infants with spinal muscular atrophy. J Pediatr, 155(2), 292–294. 78. Arai, H., et  al. (2005). Finger cold-induced vasodilatation, sympathetic skin response, and R-R interval variation in patients with progressive spinal muscular atrophy. J Child Neurol, 20(11), 871–875. 79. Karasick, D., Karasick, S., & Mapp, E. (1982). Gastrointestinal radiologic manifestations of proximal spinal muscular atrophy (Kugelberg-Welander syndrome). J Natl Med Assoc, 74(5), 475–478.

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120. Lewelt, A., et al. (2010). Compound muscle action potential and motor function in children with spinal muscular atrophy. Muscle Nerve, 42(5):703–708. 121. Buchthal, F., & Olsen, P. Z. (1970). Electromyography and muscle biopsy in infantile spinal muscular atrophy. Brain, 93(1), 15–30. 122. Hausmanowa-Petrusewicz, I., Karwańska, A. (1986). Electromyographic findings in different forms of infantile and juvenile proximal spinal muscular atrophy. Muscle Nerve, 9(1), 37–46. 123. Porensky, P. N., & Burghes, A. H. (2013). Antisense oligonucleotides for the treatment of spinal muscular atrophy. Hum Gene Ther, 24(5):489–498. 124. Valori, C. F., et al. (2010). Systemic delivery of scAAV9 expressing SMN prolongs survival in a model of spinal muscular atrophy. Sci Transl Med, 2(35), 35ra42. 125. Duque, S. I., et al. (2015). A large animal model of spinal muscular atrophy and correction of phenotype. Ann Neurol, 77(3), 399–414. 126. Federici, T., et al. (2012). Robust spinal motor neuron transduction following intrathecal delivery of AAV9 in pigs. Gene Ther, 19(8), 852–859. 127. Bevan, A. K., et al. (2011). Systemic gene delivery in large species for targeting spinal cord, brain, and peripheral tissues for pediatric disorders. Mol Ther, 19(11), 1971–1980. 128. Passini, M. A., et al. (2014). Translational fidelity of intrathecal delivery of self-complementary AAV9-survival motor neuron 1 for spinal muscular atrophy. Hum Gene Ther, 25(7), 619–630. 129. Gogliotti, R.  G., et  al. (2011). Characterization of a commonly used mouse model of SMA reveals increased seizure susceptibility and heightened fear response in FVB/N mice. Neurobiol Dis, 43(1), 142–151. 130. Ruggiu, M., et al. (2012). A role for SMN exon 7 splicing in the selective vulnerability of motor neurons in spinal muscular atrophy. Mol Cell Biol, 32(1), 126–138.

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110. Kong, L.  L., et  al. (2009). Impaired synaptic vesicle release and immaturity of neuromuscular junctions in spinal muscular atrophy mice. J Neurosci, 29(3), 842–851. 111. Murray, L. M., et al. (2008). Selective vulnerability of motor neurons and dissociation of pre- and post-synaptic pathology at the neuromuscular junction in mouse models of spinal muscular atrophy. Hum Mol Genet, 17(7):949–962. 112. Dale, J.  M., et  al. (2011). The spinal muscular atrophy mouse model, SMADelta7, displays altered axonal transport without global neurofilament alterations. Acta Neuropathol, 122(3), 331–341. 113. Ling, K. K., et al. (2012). Severe neuromuscular denervation of clinically relevant muscles in a mouse model of spinal muscular atrophy. Hum Mol Genet, 21(1), 185–195. 114. Martinez-Hernandez, R., et al. (2013). Synaptic defects in type I spinal muscular atrophy in human development. J Pathol, 229(1), 49–61. 115. Ruiz, R., et al. (2010). Altered intracellular Ca2+ homeostasis in nerve terminals of severe spinal muscular atrophy mice. J Neurosci, 30(3), 849–857. 116. Wadman, R. I., et al. (2012). Dysfunction of the neuromuscular junction in spinal muscular atrophy types 2 and 3. Neurology, 79(20):2050–2055. 117. Korinthenberg, R., et  al. (1997). Congenital axonal neuropathy caused by deletions in the spinal muscular atrophy region. Ann Neurol, 42(3), 364–368. 118. Omran, H., et al. (1998). Axonal neuropathy and predominance of type ii myofibers in infantile spinal muscular atrophy. J Child Neurol, 13(7), 327–331. 119. Anagnostou, E., et al. (2005). Type I spinal muscular atrophy can mimic sensory-motor axonal neuropathy. J Child Neurol, 20(2), 147–150.



SE CT I ON IV |  PAROXYSM AL DI SO R DER SSOLOMON L . M O SH E, EIN STEIN C O L L EG E O F M ED I C I N E

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36 |  BIOLOGICAL BASIS OF PRIMARY GENERALIZED EPILEPSIES— GENETICS  CARL A M A R IN I A N D R E N Z O GU ERRIN I

are considered to be exclusion criteria. Absences are very frequent, occurring up to 100 times per day. The age of onset of CAE is between 4 and 10 years with a peak at 5 to 7 years, and girls are more frequently affected than boys.4,5 There are no clear-cut boundaries in age of onset, and cases beginning before 3 years or after 10 years have been described.4,8 Most children with CAE exhibit normal developmental skills and normal cognitive functions. About 10% to 15% of patients experience febrile convulsions prior to the onset of absences.5,9 Up to 40% of children with CAE develop rare generalized tonic-clonic seizures (TCS),4 whereas myoclonic seizures can occur in about 8% of cases and mainly in teenagers with persisting CAE.10,11 The EEG pattern consists of generalized, bilaterally synchronous and symmetrical spike–wave (GSW) discharges, the frequency is around 3.0 to 3.5 Hz at onset and slows to 2.5 to 3.0 Hz toward the end of the discharge. Discharges arise suddenly from a normal background and the ending is less abrupt than onset. Hyperventilation is the most effective activator of the GSW pattern. Transient focal epileptiform activity such as centrotemporal spikes may occur.12 The general view is that CAE has an excellent prognosis13; absences disappear before adulthood in up to 90% of cases.4 Early and late onset (before 4 and after 9 years), initial drug resistance, and photosensitivity have a less favorable prognosis.13,14 JAE typically begins during puberty, between the ages of 10 and 17 years.4,16 Absence seizures are clinically similar to those seen in CAE; however, loss of awareness appears to be less pronounced and attacks have a much lower frequency, usually occurring a few times per day. TCS occur in 80% of cases, beginning at the same time or even prior to the onset of absences.15 About 16% of patients will also have myoclonic seizures, especially early in the morning.4,15 On EEG recording, absences may have a faster rhythm of GSW at 4 to 5 Hz, especially at the onset of the attack. About 60% of patients have a long-term remission.15

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The primary generalized epilepsies, known as idiopathic generalized epilepsies (IGEs)1 and more recently defined as genetic generalized epilepsies (GGEs)2 represent 20% to 30% of all epilepsies.3 IGEs/GGE include a group of syndromes characterized by the occurrence of absence, myoclonic, and generalized tonic-clonic seizures in a child or adolescent with normal developmental skills and no structural brain lesions. Based on age of onset and predominant seizure type, four main subsyndromes are recognized, including1:



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Childhood absence epilepsy (CAE) Juvenile absence epilepsy (JAE) Juvenile myoclonic epilepsy (JME) Epilepsy with generalized tonic-clonic seizures alone.

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ABSENCE EPILEPSIES

EPILEPSIES WITH ABSENCES A S S O C I AT E D W I T H   AT O N I C OR MYOCLONIC COMPONENT

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Epilepsy with myoclonic absences (EMA) is a childhood onset epilepsy— mean age at onset is 7 years—with daily myoclonic absences and with other infrequent seizure types such as TCS, drop attacks, and atypical absences.16 Myoclonic absences manifest with rhythmic myoclonic jerks of the head, shoulders, and arms, often associated with a tonic muscle contraction. They usually last from 10 to 60 seconds and can be easily precipitated by hyperventilation or tend to cluster upon awakening. There is a male preponderance, and cognitive impairment is present in 45% of patients before the onset of epilepsy. Myoclonic absences are associated with 3-Hz GSW similar to those observed in CAE. Epilepsy with myoclonic-atonic seizures (EMAS) epitomizes a spectrum of IGEs with prominent myoclonic seizures, appearing in

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Absence epilepsies are the prototype of IGEs. Childhood (CAE) and juvenile (JAE) forms are recognized in which, by definition, all patients manifest absence seizures associated with an EEG pattern of 3-Hz generalized spike–wave (GSW) discharges.1,4 Children with CAE manifest daily absences with sudden and brief (5–15 s) periods of loss of awareness, with interruption of ongoing activities, followed by immediate and complete recovery. Although absences were initially described as staring spells, only a minority of patients has “simple absences.”5 The great majority of children exhibit “complex absences,” with additional clinical phenomena such as automatisms or a tonic, atonic, or autonomic component.5,6 A mild myoclonic component of the eyelids or mild jerking of the perioral region have traditionally been considered compatible with the diagnosis of CAE. However, Loiseau and Panayiotopoulos7 suggested new diagnostic criteria in which eyelid and perioral myoclonias

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Other generalized syndromes typical of childhood such as epilepsy with myoclonic-astatic seizures (EMAS) and epilepsy with myoclonic absences (EMA) were considered at the time to be cryptogenic or symptomatic, due to their less favorable outcome and to the presence of cognitive impairment in some patients. Concepts have evolved and at present both EMAS and EMA are recognized as IGE phenotypes at least in some patients, whereas benign neonatal convulsions and benign familial infantile convulsions are no longer considered to be generalized syndromes.2 SYNONYMS: Idiopathic generalized epilepsy: IGE; primary generalized epilepsy: GGE

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In 1960 Lennox formulated the important concept that the division between idiopathic and symptomatic epilepsy does not have a clearcut boundary. In every patient there is a unique combination of genetic and environmental factors interacting to produce the clinical phenotype.27 The semantic distinction of IGE in several sub syndromes based upon age of onset and predominant seizure types offers a nosologic framework within which patients can be placed to facilitate their clinical management. However, patients do not always fit into the widely recognized IGE sub syndromes. Clinical similarities are seen between subsyndromes and there may be no clear-cut boundaries. This clinical overlap, observed within single individuals and families, led some authors to suggest that generalized epilepsies are different expressions of a continuum.28 Under this alternative view, IGEs might also be regarded as a spectrum with age-dependent expression of particular seizure types and similar etiology (Figure 36.1). ​

The characteristic clinical feature of JME is myoclonic jerks, single or repetitive, usually affecting shoulders and arms bilaterally, but not always symmetrically, usually appearing upon awakening in the morning.18 Jerks can sometimes involve muscles in the face or the legs and very rarely may cause a sudden fall. The age at seizure onset varies between 8 and 26 years, but most patients exhibit the first manifestations between 12 and 18 years. Males and females are equally affected.18 The EEG during myoclonic jerks shows GPSW complexes or GSW at 3.5 to 6 Hz. Photosensitivity is found in about 30% of males and 40% of females.18,19 Tonic-clonic seizures occur in 90% to 95% of patients, more frequently in the morning and often preceded by a crescendo of myoclonic jerks.18 Absences are reported in 10% to 33% of cases, and are infrequent, relatively short, and often unnoticed by the patient.19 JME is described as the prototype of pharmacodependant epilepsies; assuming that treatment will be lifelong,20 although about 10% appear to have permanent remission in adolescence.11

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JUVENILE MYOCLONIC EPILEPSY

clinic have adult onset IGE with predominant TCS.25 Adults with TCS and occasional absence status may have unrecognized “phantom” absences beginning in childhood or adolescence.26 Absences in these adult patients may escape recognition, as they are imperceptible to the observer. Thus, the diagnosis of phantom absences is possible with appropriate video-EEG recordings. A family history of epilepsy is also a common feature in adultonset cases, suggesting that seizures appear in subjects with a genetic predisposition.25 Adult-onset IGE is still a poorly recognized syndrome, yet a real phenomenon that may be encountered in clinical practice, and these patients are often misdiagnosed as having partial epilepsies.

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previously healthy children.14 Onset is between 2 and 6 years of age. Myoclonic seizures and atonic falls are often repeated many times daily and may be associated with episodes of nonconvulsive status epilepticus and TCS. Outcome is unpredictable. Remission within a few months or years with normal cognition is possible even after a severe course. About 30% of children experience an epileptic encephalopathy with long-lasting intractability and cognitive impairment.14 Absences with a mild clonic component, often manifesting as flickering of the eyelids, are well recognized in CAE and JAE. However, no clear-cut boundaries exist in severity, frequency, and distribution of the jerking component, with the consequence that a confusing nomenclature and several subtypes of absence seizures and epilepsies have been proposed, including eyelid myoclonia with absences and perioral myoclonia with absences.7,17 Whether or not all various syndromes that have been proposed represent distinct clinical and genetic entities is still debated.

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Idiopathic generalized epilepsy with generalized tonic-clonic seizures only (IGE–TCS), previously referred to as “grand mal epilepsy,” is a broad and nonspecific category including all patients with TCS and an interictal EEG pattern of GSW discharges. The initial defining feature of IGE–TCS was the occurrence of TCS predominantly on awakening or in the evening period of relaxation.1 However, subsequent clinical studies have shown that in almost half of the patients seizures do not occur in relation to awakening or relaxation.21 Others have instead proposed the recognition of two separate entities depending upon whether TCSs occur on awakening or not.22 Age of onset ranges from childhood to early adulthood but without clear boundaries; seizures are often infrequent, and provoked by sleep deprivation and excessive alcohol intake. Some studies have described patients with TCS immediately preceded by 3-Hz GSW or by an absence seizure.23 The EEG shows normal background and interictal discharges of GSW or GPSW.

The IGEs have a predominant genetic etiology, and current data are in favor of complex inheritance with several genes interacting to determine the phenotype. IGEs have long been considered to be particularly suitable for genetic studies because they are common, have a relatively well-defined phenotype, and often occur in familial clusters. Close relatives of IGE probands have a 4% to 10% risk of developing epilepsy.29,30 Higher risk is seen in siblings and offspring, and lower risk in second-degree relatives. As expected with polygenic inheritance, ​

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I D I O PAT H I C G E N E R A L I Z E D E P I L E P S Y WITH TONIC-CLONIC SEIZURES

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Figure 36.1 IGEs spectrum with age-dependent expression of seizure types and

etiology.

 

Age of onset is one of the main criteria to define the various IGE sub syndromes (1,2,24) Most patients have indeed a characteristic childhood or adolescence onset, whereas onset in adulthood is generally considered to be rare. About 28% of patients seen at a first seizure

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Primary generalized epilepsies should be differentiated from nonepileptic phenomena, including diseases presenting with nonepileptic myoclonia and convulsive syncope. Often ictal EEG recordings might be the only way to solve the diagnostic issue. Among the various epilepsies and syndromes the most challenging yet important differential diagnosis includes the progressive myoclonic epilepsies such as Lafora disease, the ceroid lipofuscinoses, and Unverricht-Lundborg disease. Progressive myoclonic epilepsies at onset may present with tonic-clonic or myoclonic seizures and mimic an IGE, especially of adolescent onset. Repeated neurophysiological studies including sleep EEG recordings, and visual and somatosensory

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ummarizing the Genetics of Primary Generalized pilepsies

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An impairment of GABAergic synaptic inhibition represents a key pathway of epileptogenesis. Indeed, in addition to the aforementioned mutations in genes coding for subunits of the GABAA,36,37,42 exonic microdeletions were identified in the gephyrin gene (GPHN).46 GPHN is a postsynaptic scaffolding protein, essential for the clustering of glycine and γ-aminobutyric acid type-A receptors at inhibitory synapses. Patients with IGEs, with or without intellectual disability, have also been studied with the arrayCGH technique. About 3% of patients are shown to carry copy number variations, especially microdeletions, in chromosomes 15q13.3, 15q11.2, and 16p13.11 that might be considered as disease risk or predisposing factors.47,48 SLC2A1 mutations causing GLUT1 transporter defects are also listed as a rare cause of classic IGE.8,49 Screening should be considered in IGE featuring absence epilepsies with onset from early childhood to adult life, because this diagnosis may have important implications for treatment and genetic counseling.

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there is a rapid decrease of the risk in relatives as the distance from the affected individual(s) increases.31,32 The risk is comparable for the subsyndromes of CAE, JAE, and JME.29 Again, higher risk is seen in siblings and offspring and is lower in second-degree relatives.29,30 Analysis of epilepsy phenotypes in families with several affected family members shows that, usually, relatives also have an IGE, with about 30% phenotypic concordance (affected relatives have the same IGE subsyndrome as the proband), both for absence epilepsies and JME.29 In contrast, very few affected relatives of probands with absence epilepsies have JME and vice versa, suggesting that absence epilepsies and JME tend to segregate separately. These findings suggest that, within a polygenic model of inheritance, absence epilepsies are closely related and genetically distinct from JME. Febrile seizures (FS) and TCS are equally distributed in affected individuals of all IGEs. Twin studies have shown higher concordance for IGE in monozygotic than in dizygotic twins (0.76 vs. 0.33), which is also consistent with polygenic inheritance.33 Linkage studies and genome-wide association analysis on a large number of families with IGE have identified several susceptibility loci:  1q43; 2p16.1; 2q22.3; 3q; 14q, 17q21.32, and 18q,34,35 yet these loci have not been replicated. In rare families pathogenic mutations in single genes have been reported including: GABRG2 gene identified in families with FS and CAE,36 GABRA1 gene in families with dominantly inherited JME,37 and CLCN2 in families with heterogeneous IGE phenotypes, including CAE (Table 36.1).38 Rare variants in CACNA1H, coding for a T-type voltage-gated calcium channel have been identified in CAE and other IGEs (see Table 36.1).39,40 In a spontaneous rat model of absences, it has been shown that the Cacna1h variant R1584P is a susceptibility factor.41 Finally, the study of variants has provided some evidence that GABRD,42 ME2,43 BRD2,44 and NEDD4L45 are susceptibility genes for IGE (see Table 36.1).

 

 

 

 

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ME2

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BRD2

6p21.32

TCS, Ab, My

NEDD4

15q21.3

TCS, Ab, My

SLC2A1

1p34

TCS, Ab, My

GPHN

14q23.3

TCS, Ab, My

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no

1q43; 2p16.1; 2q22.3; 3q; 14q, 17q21.32, 18q

TCS, Ab, My

 

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no

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Legend: Ab: absences; AD: autosomal dominant CAE: childhood absence epilepsy; FS: febrile seizures; IGE-TCS: idiopathic generalized epilepsy with tonic-clonic seizures; JAE: juvenile absence epilepsy, JME: juvenile myoclonic epilepsy; My: myoclonic.

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synaptic connectivity, due to genetic or acquired intrauterine factors, that underlie diffuse cortical hyperexcitability.

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Despite the interest in the genetics of IGEs in the last 50-year period, the extent of the genetic overlap between the IGE subsyndromes is still controversial, the mode of inheritance remains uncertain, and common genes for IGEs have not yet been identified. Rare families with mutations in genes encoding subunits of voltage- or ligand-gated ion channels have been described.56 Future directions should therefore point to uncovering the genetic background of primary generalized epilepsies. How researchers will do this is still uncertain. The new tools of next generation sequencing of selected ion channel genes or of the entire exome/genome are being applied to sporadic as well as familial cases, yet with disappointing results.57,58 Large consortia of laboratories working in synchrony might allow an increase in number of patients being studied and lead to more rewarding results. ​

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Subtle developmental abnormalities of brain architecture (microdysgenesis) have been described in patients with IGE.53 There were no macroscopic abnormalities, and neurons and glial cells were normal morphologically. However these results were not replicated in a more recent study of five brains of IGE patients.54 Syndrome heterogeneity with different seizure types, the number of convulsive seizures suffered, the small sample sizes, and technical factors could contribute to this discrepancy. In patients with various IGE syndromes, quantitative magnetic resonance imaging studies have shown volume and structural abnormalities reflecting possible underlying structural abnormalities, supporting the idea that brains of patients with IGE may be morphologically abnormal.55 The presence of subtle abnormalities of brain architecture remains an open question yet very interesting as it might represent the morphologic correlate of abnormal



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1. ILAE Commission on Classification and Terminology. (1989). Proposal for revised classification of epilepsies and epileptic syndromes. Epilepsia, 30, 389–399. 2. Berg, A. T., Berkovic, S. F., Brodie, M. J., Buchhalter, J., Cross, J. H., van Emde Boas, W., et al. (2010). Revised terminology and concepts for organization of seizures and epilepsies:  Report of the ILAE Commission on Classification and Terminology, 2005-2009. Epilepsia, 51, 676–685. 3. Hauser, W. A., Annegers, J. F., & Kurland, L. T. (1993). Incidence of epilepsy and unprovoked seizures in Rochester, Minnesota:  1935–1984. Epilepsia, 34, 453–468. 4. Berkovic S.  F. (1996). Childhood absence epilepsy and juvenile absence epilepsy. In E. Wyllie (Ed.), The treatment of epilepsy: Principles and practice (pp. 461–466). Baltimore, MD: Williams and Wilkins. 5. Penry J. K., Porter R. J., & Dreifuss F.E. (1975). Simultaneous recording of absence seizures with video tape and electroencephalography: A study of 374 seizures in 48 patients. Brain, 98, 427–440. 6. Holmes, G. L., McKeever, M., & Adamson, M. (1987). Absence seizures in children: Clinical and electroencephalographic features. Ann Neurol, 21, 268–273. 7. Loiseau, P., & Panayiotopoulos, C. P. (2005). Childhood absence epilepsy. Available online at www.ilae-epilepsy.org/Visitors/Centre/ctf. 8. Suls, A., Mullen, S. A., Weber, Y. G., Verhaert, K., Ceulemans, B., Guerrini, R., et al. (2009). Early-onset absence epilepsy caused by mutations in the glucose transporter GLUT1. Ann Neurol, 66(3), 415–419. 9. Rocca, W.  A., Sharbrough, F.  W., Hauser, W.  A., Annegers, J.  F., & Schoenberg, B.  S. (1987). Risk factors for generalized tonic-clonic seizures:  A  population-based case-control study in Rochester, Minnesota. Neurology, 37, 1315–1322 10. Janz, D. (1985). Epilepsy with impulsive petit mal (juvenile myoclonic epilepsy). Acta Neurol Scand, 72, 449–459. 11. Camfield, C., & Camfield, P. (2005). Management guidelines for children with idiopathic generalized epilepsy. Epilepsia, 46(Suppl 9), 112–116. 12. Hedstrom, A., & Olsson, I. (1991. Epidemiology of absence epilepsy: EEG findings and their predictive value. Pediatr Neurol, 7, 100–104. 13. Trinka, E., Baumgartner, S., Unterberger, I., Luef, G., Haberlandt, E., & Bauer, G. (2004), Long-term prognosis for childhood and juvenile absence epilepsy. J Neurol, 251, 1235–1241. 14. Guerrini, R. (2006). Epilepsy in children. Lancet, 367, 499–524. 15. Obeid, T. (1994). Clinical and genetic aspects of juvenile absence epilepsy. J Neurol, 241, 487–491. 16. Bureau, M., Tassinari, C. A. (2005). The syndrome of myoclonic absences. In J. Roger, M. Bureau, C. Dravet, P. Genton, C. A. Tassinari, & P. Wolf (Eds.), Epileptic syndromes in infancy, childhood and adolescence (4th ed., pp. 337–344). Montrouge, France: John Libbey Eurotext. 17. Appleton R. E., Panayiotopoulos, C. P., Acomb, B. A., & Beirne, M. (1993). Eyelid myoclonia with typical absences: An epilepsy syndrome. J Neurol Neurosurg Psychiatry, 56, 1312–1316.

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Most IGEs are classified among the pharmacosensitive epilepsies in which appropriate drug treatment leads to seizure control, followed, after a few years, by spontaneous remission.14 However, several studies that have assessed the prognosis of IGEs, especially in the last 20 years, converge in indicating that seizures may persist into adulthood and promptly relapse after drug withdrawal (as typically seen in JME) or even be resistant throughout. This group of “refractory IGEs” includes patients who have more or less typical absences in childhood or adolescence, which continue into adulthood and may be accompanied by other seizure types such as myoclonus, atonic, tonic, or TCSs. Some IGE patients have a fluctuating course; benign forms can manifest transient periods of worsening, whereas some difficult-to-treat patients may later experience spontaneous improvement. Ethosuximide and valproic acid are the most appropriate drugs and suppress absences in 80% of CAE patients and 60% of JAE.14 Factors predicting unfavorable prognosis are: TCS in the active stage of absences, myoclonic jerks, eyelid myoclonias or perioral myoclonias, failure of the first appropriate antiepileptic drug, and atypical EEG features (photoparoxysmal response, irregular ictal 3- to 4-Hz spike–wave complexes, excessive slow background activity during the waking record).7 Juvenile myoclonic epilepsy is regarded as a benign but chronic disorder that may require lifelong treatment. About 80% to 90% of JME patients are controlled on valproate monotherapy.18 Lamotrigine, either in combination with valproate or in monotherapy, can also be effective in a lower number of cases.50 Valproic acid has also been reported as effective in patients with IGE–TCS. However, there is also a significant subgroup of JME patients who pose difficult treatment problems; about 15.5% of JME are resistant to adequate drugs.18 Aggravation of IGEs by inappropriate antiepileptic drugs is also increasingly recognized as a serious and common problem.51 New-generation antiepileptic drugs such as levetiracetam, topiramate, and zonisamide have been proven to be useful in the treatment of pharmacoresistant IGEs.52

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evoked potentials help distinguishing these disorders and lead the clinicians to obtain the appropriate and diagnostic genetic testing. IGEs especially with adult onset are often misdiagnosed as focal epilepsy. Occasionally, metabolic diseases such as phenylketonuria, lysosomal storage disorders, metabolic encephalopathies, and hypothalamic hamartomas have also been associated with GSW and with absence attacks

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39. Chen, Y., Lu, J., Pan, H., Zhang, Y., Wu, H., Xu, K., et al. (2003). Association between genetic variation of CACNA1H and childhood absence epilepsy. Ann Neurol, 54(2), 239–243. 40. Heron, S.  E., Phillips, H.  A., Mulley, J.  C., Mazarib, A., Neufeld, M.  Y., Berkovic, S. F., et al. (2004). Genetic variation of CACNA1H in idiopathic generalized epilepsy. Ann Neurol, 55(4), 595–596. 41. Powell, K. L., Cain, S. M., Ng, C., Sirdesai, S., David, L. S., Kyi, M. et al. (2009). A Cav3.2 T-type calcium channel point mutation has splicevariant-specific effects on function and segregates with seizure expression in a polygenic rat model of absence epilepsy. J Neurosci, 29(2), 371–380. 42. Dibbens, L. M., Feng, H. J., Richards, M. C., Harkin, L. A., Hodgson, B. L., Scott, D., et  al. (2004). GABRD encoding a protein for extra- or perisynaptic GABAA receptors is a susceptibility locus for generalized epilepsies. Hum Mol Genet, 13(13), 1315–1319. 43. Greenberg D.A., Cayanis E., Strug L., Marathe S., Durner M., Pal D.K., et al. (2005). Malic enzyme 2 may underlie susceptibility to adolescentonset idiopathic generalized epilepsy. Am J Hum Genet, 76, 139–146. 44. Pal, D.  K., Evgrafov, O.  V., Tabares, P., Zhang, F., Durner, M., & Greenberg, D. A. (2003). BRD2 (RING3) is a probable major susceptibility gene for common juvenile myoclonic epilepsy. Am J Hum Genet, 73, 261–270. 45. Dibbens, L. M., Ekberg, J., Taylor, I., Hodgson, B. L., Conroy, S. J., Lensink, I. L., et al. (2007). NEDD4-2 as a potential candidate susceptibility gene for epileptic photosensitivity. Genes Brain Behav, 6, 750–755 46. Dejanovic, B., Lal, D., Catarino, C. B., Arjune, S., Belaidi, A. A., Trucks, H. et  al. (2014). Exonic microdeletions of the gephyrin gene impair GABAergic synaptic inhibition in patients with idiopathic generalized epilepsy. Neurobiol Dis, 67, 88–96. 47. de Kovel, C. G., Trucks, H., Helbig, I., Mefford, H. C., Baker, C., Leu, C., et al. (2010). Recurrent microdeletions at 15q11.2 and 16p13.11 predispose to idiopathic generalized epilepsies. Brain, 133, 23–32. 48. Helbig, I., Mefford, H. C., Sharp, A. J., Guipponi, M., Fichera, M., Franke, A., et al. (2009). 15q13.3 microdeletions increase risk of idiopathic generalized epilepsy. Nat Genet, 41, 160–162. 49. Striano, P., Weber, Y.  G., Toliat, M.  R., Schubert, J., Leu, C., Chaimana, R., et al. (2012). GLUT1 mutations are a rare cause of familial idiopathic generalized epilepsy. Neurology, 78, 557–562. 50. Wallace, S.  J (1998). Myoclonus and epilepsy in childhood:  a review of treatment with valproate, ethosuximide, lamotrigine and zonisamide. Epilepsy Res, 29, 147–154. 51. Marini, C., Parmeggiani, L., Masi, G., D’Arcangelo, G., & Guerrini, R. (2005). Nonconvulsive status epilepticus precipitated by carbamazepine presenting as dissociative and affective disorders in adolescents. J Child Neurol, 20, 693–696. 52. Verrotti, A., Greco, R., Giannuzzi, R., Chiarelli, F., & Latini, G. (2007). Old and new antiepileptic drugs for the treatment of idiopathic generalized epilepsies. Curr Clin Pharmacol, 2, 249–259. 53. Meencke, H. J., & Janz, D. (1984). Neuropathological findings in primary generalized epilepsy: a study of eight cases. Epilepsia, 25, 8–21. 54. Opeskin, K., Kalnins, R. M., Halliday, G., Cartwright, H., & Berkovic, S. F. (2000). Idiopathic generalised epilepsy: Lack of significant microdysgenesis. Neurology, 55, 1101–1106. 55. Woermann, F.  G., Sisodiya, S.  M., Free, S.  L., & Duncan, J.  S. (1998). Quantitative MRI in patients with idiopathic generalized epilepsy:  Evidence of widespread cerebral structural changes. Brain, 121, 1661–1667. 56. Helbig, I., Scheffer, I. E., Mulley, J. C., & Berkovic, S. F. (2008). Navigating the channels and beyond: unravelling the genetics of the epilepsies. Lancet Neurol, 7, 231–245. 57. Klassen, T., Davis, C., Goldman, A., Burgess, D., Chen, T., Wheeler, D., et  al (2011). Exome sequencing of ion channel genes reveals complex profiles confounding personal risk assessment in epilepsy. Cell, 145(7), 1036–1048 58. Depondt, C., Cavalleri, G. L., Ruzzo, E. K., Walley, N. M., Need, A. C., Ge, D., et  al. (2012). Exome sequencing followed by large-scale genotyping fails to identify single rare variants of large effect in idiopathic generalized epilepsy. Am J Hum Genet, 91(2), 293–302).

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18. Delgado-Escueta, A.  V., Serratosa, J.  M., & Medina, M.  T. (1996). Juvenile myoclonic epilepsy. In E. Wyllie (Ed.), The treatment of epilepsy:  principles and practice (pp. 484–501). Baltimore, MD:  Williams and Wilkins. 19. Asconape, J., & Penry, J.  K. (1984). Some clinical and EEG aspects of benign juvenile myoclonic epilepsy. Epilepsia, 25, 108–114. 20. Baruzzi, A., Procaccianti, G., & Tinuper, P. (1988). Antiepileptic drug withdrawal in childhood epilepsies: Preliminary results of a prospective study. In C. Faienza, & G. L.  Prati (Eds.), Diagnostic and therapeutic problems in pediatric epileptology (pp. 117–123). Amsterdam: Elsevier Science. 21. Reutens, D.  C., Berkovic, S.  F. (1995). Idiopathic generalized epilepsy of adolescence:  Are the syndromes clinically distinct? Neurology, 45, 1469–1476. 22. Unterberger, I., Trinka, E., Luef, G., Bauer, G. (2001). Idiopathic generalised epilepsy with pure grand mal:  clinical and genetics data. Epilepsy Res, 44, 19–25. 23. Mayville, C., Fakhoury, T., & Abou-Khalil, B. (2000). Absence seizures with evolution into generalised tonic–clonic activity:  Clinical and EEG features. Epilepsia, 41, 391–394. 24. Engel, J., Jr. (2001). A proposed diagnostic scheme for people with epileptic seizures and with epilepsy: Report of the ILAE Task Force on classification and terminology. Epilepsia, 42, 796–803. 25. Marini, C., King, M.  A., Archer, J.  S., Newton, M.  R., & Berkovic, S.  F. (2003) Idiopathic generalised epilepsy of adult onset: Clinical syndromes and genetics. J Neurol Neurosurg Psychiatry, 74, 192–196. 26. Panayiotopoulos, C.  P., Koutroumanidis, M., Giannakodimos, S., & Agathonikou, A. (1997). Idiopathic generalised epilepsy in adults manifested by phantom absences, generalised tonic-clonic seizures, and frequent absence status. J Neurol Neurosurg Psychiatry, 63(5), 622–627. 27. Lennox, W.  G. (1960.) Epilepsy and related disorders. Boston, MA: Little, Brown. 28. Berkovic, S. F., Reutens, D. C., Andermann, E., & Andermann, F. (1994). The epilepsies:  specific syndromes or a neurobiological continuum? In P. Wolf (Ed.), Epileptic seizures and syndromes (pp. 25–37). Montrouge, France: John Libbey Eurotext. 29. Marini, C., Scheffer, I. E., Crossland, K. M., Grinton, B. E., Phillips, F. L, McMahon, J. M., et al. (2004). Genetic architecture of idiopathic generalized epilepsy: clinical genetic analysis of 55 multiplex families. Epilepsia, 45, 467–478. 30. Annegers, J. F., Hauser, W. A., Anderson, V. E., & Kurland, L. T. (1982). The risks of seizure disorders among relatives of patients with childhood onset epilepsy. Neurology, 32(2), 174–179. 31. Risch, N. (1990). Linkage strategies for genetically complex traits. I. Multilocus models. Am J Hum Genet, 46(2), 222–228. 32. Tsuboi, T. (1989). Genetic risk in offspring of epileptic patients. In G. Beck-Mannagetta, V. E. Anderson, H. Doose, & D. Janz (Eds.), Genetics of epilepsies (pp. 111–118). Berlin: Springer- Verlag. 33. Berkovic, S. F., Howell, R. A., Hay, D. A., & Hopper,J. L. (1998). Epilepsies in twins:  genetics of the major epilepsy syndromes. Ann Neurol, 43(4), 435–445. 34. Durner, M., Keddache, M. A., Tomasini, L., Shinnar, S., Resor, S. R., Cohen, J. et al. (2001). Genome scan of idiopathic generalized epilepsy: Evidence for major susceptibility gene and modifying genes influencing the seizure type. Ann Neurol, 49(3), 328–335. 35. EPICURE Consortium; EMINet Consortium; Steffens, M., Leu, C., Ruppert, A.  K., & Zara, F. (2012). Genome-wide association analysis of genetic generalized epilepsies implicates susceptibility loci at 1q43, 2p16.1, 2q22.3 and 17q21.32. Hum Mol Genet, 21(24), 5359–5372 36. Wallace R.H., Marini C., Petrou S., Harkin L.A., Bowser D.N., Panchal R.G. et al. (2001). Mutant GABA(A) receptor gamma2-subunit in childhood absence epilepsy and febrile seizures. Nat Genet, 28(1), 49–52. 37. Cossette, P., Liu, L., Brisebois, K., Dong, H., Lortie, A., Vanasse, M., et al. (2002). Mutation of GABRA1 in an autosomal dominant form of juvenile myoclonic epilepsy. Nat Genet, 31(2), 184–189. 38. D’Agostino, D., Bertelli, M., Gallo, S., Cecchin, S., Albiero, E., Garofalo, P. G., et al. (2004). Mutations and polymorphisms of the CLCN2 gene in idiopathic epilepsy. Neurology, 63(8), 1500–1502.

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37 |  BIOLOGICAL BASIS OF PRIMARY GENERALIZED EPILEPSIES— PATHOPHYSIOLOGY 

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The primary generalized epilepsies (PGEs) are a set of idiopathic disorders that comprise approximately 15% to 20% of all epilepsies.3 Patients typically present with no obvious anatomical defects or intellectual impairment, and may show no abnormalities on interictal electroencephalogram (EEG) or neurological exam.4 Recent work, however, has demonstrated that deficits in attention, and executive and psychosocial function are common during nonseizure periods.5–8 In addition, neuroimaging studies of patients with childhood absence epilepsy have shown increased levels of interhemispheric resting ers

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An expansive network of intricate neuronal connections and precise receptor expression levels is necessary for the advanced functional capabilities of the human brain. Although this extraordinary degree of interconnectedness allows for sophisticated levels of reasoning and cognition, it can also cause dramatic neurological dysfunction in the presence of hyperexcitable discharges. The brain is intrinsically poised on the edge of instability, and any imbalance between excitatory and inhibitory signals can quickly escalate into widespread abnormal synchrony across broad sets of neuronal circuits. Such is the case in patients with primary generalized epilepsy, who experience profound disruptions in normal neurological function that is marked by widespread hypersynchronous cortical discharges involving both hemispheres. These disorders are by definition idiopathic, and most patients show no signs of neurological distress during interictal periods. The abrupt switch from normal function into an epileptic state provides an intriguing window into the structure and function of neurological circuitry, particularly networks responsible for relay of sensory and other subcortical information through the thalamus and into cortical association areas. The primary generalized epilepsies include a heterogeneous group of seizures that are not strictly localized on EEG and not secondary to another disorder.1 The seizures are often associated with a loss of consciousness and may present with motor manifestations, including violent convulsions and arrest of respiration.2 Although patient presentation may vary, generalized spike-and-wave discharges on electroencephalogram are a uniting feature. This pattern of activity is a direct manifestation of the underlying mechanism of these disorders. This chapter examines the biological basis of primary generalized epilepsy, focusing on absence, myoclonic, and generalized tonicclonic seizures. A  review of important underlying circuitry will set the stage to discuss the pathological and genetic basis of these disorders. The chapter concludes with a review of current and potential therapeutics.

functional connectivity,9 which is consistent with animal models of this disease,10 as well as other interictal functional and structural abnormalities.7,11–13 These disorders encompass a heterogeneous collection of seizure types, ranging from brief staring spells (absence seizures), to involuntary jerking (myoclonic seizures) or dramatic episodes of tonic fixation and clonic muscle contractions (generalized tonic-clonic seizures). In a given patient, the primary seizure type, age of onset, and other clinical characteristics can be used to diagnose one of several generalized epilepsy syndromes, such as childhood absence epilepsy, juvenile myoclonic epilepsy, and generalize tonic-clonic seizures on awakening. Although most patients will present with a single seizure type, multiple types may coexist in an individual.14 The remainder of this section discusses important features of each of the principle seizure types seen in PGE. Tonic-clonic (or grand-mal) seizures are a dramatic form of generalized paroxysmal activity that present with loss of consciousness and vivid motor manifestations. These events often involve a period of tonic muscle extension lasting between 10 and 20 seconds, followed by repetitive, violent clonic jerking for several minutes. A  period of postictal somnolence or confusion may occur, and is often demonstrated by an abrupt quiescence or slow wave activity on EEG. Amnesia is frequently reported during these periods. Patients may suffer secondary injury due to a sudden loss of consciousness and motor control. The primary generalized form of tonic-clonic seizures should be carefully distinguished from cases of focal epilepsy with secondary generalization, which show differences in treatment and prognosis.15 Absence (or petit-mal) seizures often present at an earlier age than other forms of PGE, and are frequently associated with a diagnosis of childhood absence epilepsy. These seizures are characterized by sudden, brief periods of impaired consciousness that may occur hundreds of times in a single day.16 Convulsions are seen in less than 30% of cases of typical childhood absence epilepsy, and seizures stop in 70% to 80% of patients during adolescence. However, the disruptions in attention can have significant social and educational consequences for school-age children, and previous studies have established long-term adverse effects on employment, behavior, and other psycosocial outcomes.17 Children with absence epilepsy also show higher rates of anxiety and depression than matched controls.18 Although most children will show spontaneous remission before adulthood, the coexistence of other seizure types is associated with poor prognosis.19 Myoclonic seizures are characterized by sudden, involuntary jerking (more often in the upper extremities), that typically lasts only a few seconds or less. On EEG, a generalized polyspike wave burst is characteristic, with a slighter higher frequency compared with childhood absence epilepsy. Myoclonic seizures are most commonly associated with a syndrome called “juvenile myoclonic epilepsy,” which presents in adolescents and frequently has tonic-clonic seizures as a ​

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The duration of thalamic inhibition is determined by the kinetics of different GABA receptors found within the thalamus. GABAA receptors are ligand-gated ion channels that produce inhibitory postsynaptic potentials through an increase in chloride current. By contrast, GABAB receptors are metabotropic, and therefore exhibit slower kinetics with longer refractory periods. Both receptor classes are expressed in thalamic nuclei, and their relative levels of activation in response to nRT afferents determine the frequency of oscillation in spike-wave discharge. Previous work in ferret thalamic slices has demonstrated that low intensity firing in nRT more often results in exclusive GABAA receptor activation, whereas prolonged burst firing increases the relative proportion of GABAB receptor activation.25 This principle explains why physiological levels of cortical activity can result in higher frequency spike-wave patterns on EEG (such as nonpathological sleep spindles occurring at >10 Hz) compared with the low-frequency firing observed during seizures (typically less than 1800 malignant peripheral nerve sheath tumor patients with and without neurofibromatosis type 1. Neuro Oncol, 15(2), 135–147. doi: 10.1093/neuonc/nos287 25. Packer, R. J., Ater, J., Allen, J., Phillips, P., Geyer, R., Nicholson, H. S., . . . Boyett, J. M. (1997). Carboplatin and vincristine chemotherapy for children with newly diagnosed progressive low-grade gliomas. J Neurosurg, 86(5), 747–754. doi: 10.3171/jns.1997.86.5.0747 26. Rodriguez, F. J., Folpe, A. L., Giannini, C., & Perry, A. (2012). Pathology of peripheral nerve sheath tumors:  Diagnostic overview and update on selected diagnostic problems. Acta Neuropathol, 123(3), 295–319. doi: 10.1007/s00401-012-0954-z 27. Huttner, A. J., Kieran, M. W., Yao, X., Cruz, L., Ladner, J., Quayle, K., . . . Ullrich, N. J. (2010). Clinicopathologic study of glioblastoma in children with neurofibromatosis type 1. Pediatr Blood Cancer, 54(7), 890–896. doi: 10.1002/pbc.22462 28. Plotkin, S. R., Albers, A. C., Babovic-Vuksanovic, D., Blakeley, J. O., Breakefield, X. O., Dunn, C. M., .  .  . Lloyd, A. C. (2014). Update from the 2013 international neurofibromatosis conference. Am J Med Genet A, 164(12), 2969–2978. doi: 10.1002/ajmg.a.36754



52 |  NEUROBIOLOGY OF AUTISM AND INTELLECTUAL DISABILITY: FRAGILE X SYNDROME

FMRP) are overactive glutamatergic signaling, increased dendritic protein synthesis, and increased density of dendritic spines (“neuronal connections”).1,14,20–24 Because FMRP is an important regulator of both basal and activity-dependent local neuronal protein synthesis25–28 and synaptic function,29 FMR1 gene mutations can alter the course of brain development, cognition, and behavior throughout life.

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The average age of diagnosis of FXS is 35 to 37 months.30 Typically, physicians may not consider it without a family history of intellectual disability (ID) or other dysmorphic features. However, these features are not present in approximately one third of individuals with FXS. Moreover, in contrast to some other genetic disorders (i.e., Down syndrome), FXS has no apparent physical features at birth. Therefore, it must be “detected” after atypical behaviors and delays in skill acquisition begin to emerge.31,32 The continued emphasis on early diagnosis and management, in conjunction with the identification of family members at risk for or affected by FMR1 mutations, has led to intense discussion about the appropriate timing for early identification of FMR1 mutations.33 Nevertheless, one survey revealed that almost 38% of parents of children eventually diagnosed with FXS underwent more than 10 symptom-related visits to their health care professional before the FMR1 diagnostic test was ordered.34 Guidance statements from professional organizations emphasize the need for fragile X testing. The Fragile X Clinical & Research Consortium has specific guidelines that begin with care by a physician-led team with expertise in FXD. However, general clinical practice and available literature reveal that only one third35 of individuals with autism spectrum disorder (ASD) are tested for FMR1 mutations. Effectiveness of health care in this population has been hampered by the delay in diagnosis of ASD (average age ~6) and delay in time from recognition to expert evaluation. Clinically, FXS presents a complex but rather consistent behavioral phenotype. The mutation in FMR1 is the most common known monogenetic cause of ASD8 and ID.3,36 As FMRP is ubiquitously expressed in the brain and other tissues, FXS is associated with a wide array of physical and neurobehavioral problems.2,8,37

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Fragile X syndrome (FXS) is caused by silencing of the FMR1 gene, leading to a loss of production of its encoded protein, fragile X mental retardation protein (FMRP). More than 99% of the time, FXS results from an expansion of the CGG triplet repeat in the first exon of the (5’UTR) regulatory region of the FMR1 gene on the X chromosome (Figure 52.1). When the normal number (4-45) of CGG repeats increases to greater than 200 (full mutation), the FMR1 gene becomes hypermethylated and transcriptionally silenced,1 and lack of, or reduced, expression of FMRP results in the symptoms of FXS.2–4 Intermediate level expansions (55–200 CGG repeats), which are termed “premutations,” are not associated with FXS2 but with a “carrier” status. The clinical significance of the latter can range from minimal to moderate clinical phenotypes (e.g., mild cognitive/behavioral problems) to severe such as fragile X-associated primary ovarian insufficiency syndrome [FX-POI], and fragile X tremor ataxia syndrome [FX-TAS]) in some adults.5,6 Although all these disorders (i.e., FXS, FX-POI, FX-TAS) fall under the umbrella of fragile X-associated disorders (FXS),7 they differ in their mechanisms of pathogenesis and age of onset (neurodegenerative, adults in FX-POI and FX-TAS) in contrast to FXS which is neurodevelopmental and essentially present at birth.

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Remarkable progress has been made in elucidating the molecular pathogenesis and neurobehavioral features of FXS since the discovery of the FMR1 gene in 1991. FXS affects 1:4,000 males and 1:6,000 females across all racial and ethnic groups.3 Moreover, it is estimated that over one million are fragile X carriers. The most frequent clinically relevant situation involves a mother with premutation and her son with full mutation.8 FXS is a global neuropsychiatric disorder with abnormalities in signaling pathways coupled to multiple neurotransmitter receptors. FMRP belongs to the family of RNA binding proteins, whose four RNA binding domains can bind messenger RNAs as well as noncoding RNAs.9 Specifically, FMRP forms a complex with the Cytoplasmic FMRP Interacting Protein 1 (CYFIP1)10 and the capbinding scaffolding protein eIF4E,11 prevents the formation of active translational initiation complexes, and represses (acts as a “brake”) protein synthesis.12–14 As a result, the loss of FMRP in FXS leads to “runaway” translation of important synaptic proteins and subsequently disrupts many neuronal signaling pathways. For example, upregulated are mGluR5 and mTOR signaling15,16 and down-regulated are GABA and dopaminergic systems.17,18 Since FMRP and mGluR5 work in functional opposition,15,19 hallmark effects of FMR1 silencing (no

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P H Y S I C A L F E AT U R E S Physical features of FXS were described as early as 1943, long before the genetic basis of the disorder was understood (Martin & Bell, 1943).38 These include dysmorphic features (i.e., long and narrow face with prominent ears), connective tissue abnormalities (e.g., lax joints, flat feet), and other non-CNS phenotypic anomalies (e.g., macroorchidism after puberty). The facial abnormalities are most prominent in postpubertal males, whereas young boys may only have large heads | 375

SOCIAL INTERACTION DISORDERS IN FXS Social interaction disorders in FXS are ASD and social anxiety. They are the most prevalent, severe, and highly debilitating phenotypes from both phenomenological48 and therapeutic perspectives of FXS.8,49

set of complex disorders of brain development that are behaviorallydefined according to the Diagnostic and Statistical Manual of Mental Disorders (DSM). The recent fifth edition of DSM (DSM-5)52 has generated a single “umbrella” diagnosis of ASD and also consolidated diagnostic criteria. For example, the three major symptom domains in DSM-IV have been reduced to two domains in the DSM-5 criteria; namely, with social and communication impairments being merged into a single domain, and restricted, repetitive behaviors remaining a distinct domain.53,54 Because of an overlap in the behavioral features of FXS and those of ASD (e.g., gaze avoidance, hand flapping),37 the vast majority of males with FXS have some autistic features. Moreover, despite early controversy,55,56 it is now accepted that approximately 46% to 67% of males and 20% of females with FXS meet DSM-IV criteria for a nonregressive type of ASD.37,42,43,57–62 Of these, 18% to 36% of males meet the criteria for autism as defined by DSM-IV. We42,43 and others63,64 have demonstrated that it is possible to identify a group of boys with FXS who exhibit a core social interaction impairment in accordance with the DSM-IV definition of ASD. Intriguingly, impairments in basic nonverbal social behaviors (e.g., diminished eye contact or social smile) and the presence of certain stereotypes (e.g., hand flapping) are not contributors to the DSM-IV diagnosis of ASD in FXS, emphasizing its core deficit in complex social interactions. Overall, ASD in FXS shows striking similarities to ASD in the general population, particularly with groups that have language delays.61,63 Indeed, these individuals also show a neurobehavioral profile similar to those with idiopathic ASD65,66 such as 1) severe social indifference,43 2) a spectrum of social interaction deficits42,67,68 that is relatively independent of cognitive function,42,64 3)  greater receptive than expressive language delay, 43,64,69 4)  persistence of gaze avoidance during continuous social challenge,69 and 5) a fairly stable diagnosis over time.43,64,70,71 Further emphasizing the core social disturbance in males with FXS and ASD, we have shown that deficit in adaptive socialization is the only significant predictor of ASD.42 Extending the abovementioned findings, we also found that delay in adaptive socialization skills and degree of social withdrawal (SW) are the two primary determinants of the severity of ASD diagnosis in boys with FXS.43,72 It is important to note that among boys with FXS, the most severe ASD phenotype is linked to both impaired adaptive socialization and prominent SW.43,72 Finally, the previously reported decline in the rate of acquisition of cognitive skills throughout childhood in FXS73,74 was observed only in boys without ASD. Though lower, overall cognitive function remained relatively stable in boys with FXS and ASD.71 In short, ASD in FXS is characterized by deficit in complex social interaction and adaptive socialization, with severe social withdrawal but no regression.72 In light of ongoing debates about similarities and differences between ASD in FXS and idiopathic ASD, studies further contrasting these two populations are needed as detailed in the ASD in FXS Experts Consensus Document by Budimirovic and colleagues [(2014) http://www.fragilex.org/2014/ support-and-resources/ fragile-x-syndrome- and-autism-spectrumdisorder-similarities-and-differences/.] Wolff and colleagues68 found that the behavioral phenotype of ASD in FXS and idiopathic ASD are most similar with respect to lower-order (motoric) restricted, repetitive behaviors and social approach, but differ in more complex forms of restricted, repetitive behaviors and some social response behaviors. Regardless, FXS is a genetically-defined condition that can be diagnosed by a DNA blood test, unlike ASD that is a behaviorally-defined diagnosis.

utism pectrum isorder Of all genetic disorders associated with ASD, FXS is the best characterized, 8,36,50,51 accounting for about 5% of all cases of ASD. Whereas FXS is a genetic diagnosis, ASD and autism are both broad terms for a

ocial nxiety Based on the National Parent Survey, anxiety is the second most common behavioral abnormality (after ADHD) in FXS individuals older than 6 years, with a frequency of 70% in males and 56% in females

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or no dysmorphia at all.39 These individuals frequently need medical attention from different specialties during early childhood (i.e., gastroesophageal reflux, recurrent ear infections, strabismus, or musculoskeletal ailments).37,40 Females with FXS are much less likely to present with abnormal physical features, but some have characteristically prominent ears. Other neurologic features of the FXS phenotype include poor suck and hypotonia at birth, nystagmus, and in particular seizures.41

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N E U R O B E H AV I O R A L F E AT U R E S Neurobehavioral features of FXS consist of variable cognitive and language impairments as well as associated neurobehavioral problems (i.e., attentional difficulties, hyperactivity, anxiety, and autistic features). Together, they constitute the major medical and educational concerns for patients with FXS,2,37 especially typically more affected males. Moreover, ASD is almost exclusively a clinical problem in the latter group. Cognitively, boys diagnosed with FXS without cooccurring ASD are generally in the mild ID range (FSIQ 55–70), whereas those with ASD are in the moderate range (FSIQ 40–54).42,43 Expressive language is typically more affected than receptive language in individuals with uncomplicated FXS (i.e., no ASD). Because FXS is an X-linked condition, males are typically more frequently and severely affected, whereas females show substantial phenotypic variability because of variable X inactivation (i.e., some cells are able to produce FMRP). For example, only 25% of females with FXS meet the criteria for ID; most have learning disabilities (i.e., math)44 and milder behavioral problems.8,45,46 Impaired executive function is particularly noticeable in females due to their better overall cognitive function.47

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Courtesy of Gary Latham, Ph.D., Asuragen Inc.

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Figure 52.1 FMR1: One gene, many markers. An expansion in the number of CGG nucleotide repeats in the FMR1 gene leads to the microscopic appearance of a break, or weakness, on the long arm of the X chromosome (red oval). This region is responsible for FXS and other FXD due to effects of the CGG repeats, AGG interruptions, and hypermethylation. (FXS and other FXD occur due to abnormal CGG repeats, AGG interruptions, and methylation in this region).

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Molecular diagnostic testing of the FMR1 mutation has historically been conducted by both Southern blot analysis and polymerase chain reaction (PCR) using genomic DNA. Prior to and shortly after the identification of the causative FMR1 gene, cytogenetic testing was used to establish the diagnosis of FXS. This older diagnostic technique is less sensitive than current DNA-based methods, which can directly assess mutations of the FMR1 gene. Thus, it can be assumed that early diagnostic approaches failed to detect many cases of mosaic FXS (see below). Molecular testing for fragile X has been improved in recent years “beyond Southern Blot”85 with the development of a PCR-based method that uses a CGG repeat primer to detect expanded alleles throughout the permutation and full-mutation ranges in both genders. This approach has been since validated by several other groups (Figure 52.4).86,87 Furthermore, it is critical to assess the spectrum of methylation characteristics in patients with FMR1 expansions,88 including X-activation (females), expanded allele methylation (males and females), and methylation mosaicism (males and females). Clinical implications of the methylation status are that disease-specific methylation patterns have been suggested to be a potential mediator of treatment response in a subset of FXS individuals with ASD.89 Yet, the preliminary finding that could be one of potential treatment-sensitive biomarkers in FXS needs to be replicated.90,91 ​

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(Bailey et al., 2008).75 Nevertheless, characteristics, severity, and diagnostic threshold of anxiety in FXS have not been well established. Anxiety in FXS is characterized by impairment in nonverbal communication, as these individuals typically have an eye gaze aversion during initial greeting with a stranger (Figure 52.2). Furthermore, evidence exists that anxiety spectrum disorder, in particular social anxiety, is also related to specific aspects of autistic behavior in individuals with the milder form of ASD.43,76–78 The debilitating nature of SA raises the importance of its identification and characterization in idiopathic ASD79 and FXS.80 Because FXS is a homogeneous and well-established genetic disorder (i.e., ~ 99.5% is related to the mutation of the FMR1 gene), it is an ideal model for examining the relationship between ASD and SA, and their potential co-occurrence. Our study43 was the first to directly demonstrate the interaction between ASD and SW behaviors in boys with FXS. Specifically, in-depth analyses of standardized measures of SW revealed that SW behaviors, including both avoidance and indifference, are distributed in a continuum of severity among boys with FXS.43,72 We also demonstrated that the severity of both types of behaviors influences the diagnosis and severity of ASD in boys with FXS in an age-dependent fashion, with avoidance behaviors being a strong correlate of ASD in FXS after age 5.43,71 Furthermore, by applying clinically relevant cutoffs for the SW scales and confirmatory factor analyses, we have identified two groups of boys with FXS and severe SW.72 Boys with intermediate severe social withdrawal (SSW-I) display predominantly avoidance items whereas boys in the high severe social withdrawal (SSW-H) group show high scores on both avoidance and diverse and severe indifferent behavior profile. Consequently, the SSW-H and SSW-I groups are selectively associated with either ASD or SA, respectively.72 Thus, these SW classifications provide a unified view of the relationship between ASD and SA in FXS and their underlying behavioral manifestations (Figure 52.3). These clinical observations also suggest that SA and ASD have a common behavioral root in FXS, namely SW, and that the interactions between SW, impaired adaptive socialization, and cognitive

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dysfunctions (e.g., deficit in verbal reasoning)43 will ultimately determine the overall ASD phenotype (see Figure 52.3). We have also reproduced our finding of severe SW in most boys with FXS and ASD, particularly severe social avoidance behavior in late childhood.43,71 In summary, a central feature of ASD in FXS is a core social interaction impairment, which is also known to be the key aspect of idiopathic ASD. At the neurobiological level, the behavioral profiles suggest an obligatory cortical component (i.e., adaptive socialization), probably involving prefrontal and temporal regions,81 which when combined with limbic dysfunction leads to a severe ASD phenotype.82 Other cognitive deficits (e.g., severe nonverbal delay/parietal lobe dysfunction) would constitute variable components of ASD in FXS. The study of ASD in FXS could provide important clues about the core elements of impaired reciprocal social interaction, as well as the limbic (i.e., amygdalar) components of the social cognition system that are disrupted in idiopathic ASD.83,84 As categorical diagnosis of ASD in FXS may mask important differences within ASD in FXS and between the syndromic ASD and idiopathic ASD, dimensional measures ought to be applied as well.

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impairment, social anxiety, and autism spectrum disorder (ASD) in Fragile X Syndrome (FXS). Note that either severe social withdrawal (SSW) per se, or mild social withdrawal (MSW) in conjunction with lower nonverbal skills would lead to social anxiety (SA). A more complex combination of deficits, specifically the addition of lower socialization or verbal skills, is required for ASD alone or co-morbid with SA. SSW = Severe social withdrawal; SW-I = social withdrawalintermediate; SW-S = social withdrawal-severe; MSW = mild social withdrawal; SA = social anxiety (see fig. 4.2, p. 88, in ref. 72).

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Figure 52.4 Workflow for amplification and detection of FMR1 amplicons using AmplideX® three-primer FMR1 PCR. Input gDNA is amplified by two gene-specific primers (forward [Fwd] and reverse [Rev]) and a CGG repeat primer in a single tube. After amplification, the products, which include the full-length amplicon that completely encompasses the triplet repeat region and a multiplicity of CGG repeat primed products, are resolved by CE. The resulting electropherogram supports quantification of the number of CGG repeats, determination of the allele zygosity, and the sequence context of any AGG spacer elements. Courtesy of Gary Latham, Ph.D., Asuragen Inc.

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1. The first level of analysis has included measurements of FMR1 mRNA and protein levels in peripheral leukocyte samples, as well as the number of CGG repeats. In contrast to premutation, in FXS the size of the CGG repeat expansion is irrelevant once the CGG repeat threshold reaches the 200 cut off when the gene gets hypermethylated (“shut down”). On the other hand, the severity of the FXS physical phenotype and intellectual impairment is correlated with the magnitude of the FMRP deficit.2,67,04,95 Largescale studies have shown a modest relationship between FMRP deficit and severity of autistic behavior.96–97 Although it is clear that FMRP is a key regulator of molecular events triggered by synaptic activity,98 how exactly the loss of FMRP leads to specific features of the FXS phenotype is mostly unknown. Nonetheless, precise genetic origins such as single-gene mutations (i.e., FMR1 gene) have been found to be shared among disorders that are held to be clinically distinct. Studies continue to emerge that assess whether the specific neural pathways affected in FXS are implicated in idiopathic ASD as well. Indeed, a replicated link between FXS and at least a subset of ASD has been increasingly reported99,100 wherein FMRP is the critical unifying factor for FXS.101 At the molecular level, FMRP shuttles between nucleus and cytoplasm and in granules containing translationally silent preinitiation complexes that repress protein synthesis

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at synapses.19 FMRP interacts with several cytoplasmic and nuclear proteins and has been found to bind about 4% of total brain RNA;2,4,19,97,99 thus, a key to understanding FMRP function is to identify its RNA targets.101 Among the best characterized FMRP targets are α -CaMKII, Arc, Map1b, Sapap4, and PSD-95 mRNAs.14 Therefore, specific neurobehavioral features of FXS are likely to depend on dysregulation of specific FMRP targets and neuronal circuits that are not reflected in general measures of FMRP such as mTOR,16,102,103 CYFIP,10,104 eIF4E,105 and GABA,106,107 which may also interact with multiple dysregulated genes in idiopathic ASD.108,109 Both CYFIP1 and eIF4E, key components for the FMRP-regulated protein synthesis, have been correlated and implicated with ASD in FXS.98 Moreover, CYFIP family proteins appear to link ASD and ID aspects of FXS favoring “the cross talk” between actin polymerization and translational control.110 CYFIP1 gene is located on a hot spot chromosomal region for ASD, the 15q11-13 chromosome. CYFIP1 interacts with FMRP and Rac1, the WAVE (WAS protein family member) complex linking two processes which underlie synaptic remodeling—cytoskeletal reorganization and protein translation.10,111,112 FXS children with Prader-Willi phenotype have a significant reduction in CYFIP1 mRNA levels compared with FXS individuals without PWS-like phenotype or unaffected individuals.104 Furthermore, studies on X-linked intellectual disability have revealed the association of ASD with mutations in at least 8 of the 102 genes most frequently disrupted in FXS (reviewed in ref. 113). Mutations in genes involved in synapse remodeling (NLGN4 and NLGN3),4,114,115 RPL10, RAB39B, PTCHD1,116 DLG3, the synapse scaffolding

analyses of biological samples from affected subjects, 2) investigations of animal models of FXS, and 3)  neuroimaging studies of affected subjects.

Interestingly, most of these abnormalities have been described in children with FXS younger than 3 years132 and are specific to the disorder.132,135 Alterations in volume of caudate nucleus131 and posterior vermis have been correlated with higher severity scores on several subscales of the Aberrant Behavior Checklist, including stereotypy and body object use.136 Boys with FXS who met DSMIV criteria for autism (as opposed to milder forms of ASD) have relatively larger posterior-superior cerebellar vermii than their counterparts without autism, although they are smaller than in normal individuals.137 This result is intriguing because this region (i.e., vermian lobules VI–VII) has also consistently been shown to be relatively smaller in individuals with idiopathic ASD,138 a finding confirmed in a study by Kaufmann and colleagues.137 Furthermore, there are several lines of evidence that anxious and autism-like traits in the disorder are associated with HPA axis dysfunction. Cortisol reactivity (i.e., variability in cortisol levels) to a social challenge is decreased in children with FXS and prominent autism features (i.e., persistent eye gaze avoidance);139 The opposite seems to be true for boys with FXS with prominent social avoidance, who demonstrate a markedly slow return to baseline cortisol levels after a cognitive/ social challenge.140–142 In short, studies of FXS and ASD have found anomalies in the cerebellar vermis and the limbic system. ​

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In conclusion, our knowledge of the neurobiology of SA and ASD and other neurobehavioral features of FMR1-related disorders is limited but grows continuously. Nevertheless, some theses are emerging: 1) The limbic system is particularly susceptible to FMRP deficit, and its complex cerebral circuits implicated in emotional regulation in FXS may lead to either SA or ASD, or both. 2) Secondary genetic events (e.g., modifier gene polymorphisms) may be responsible for the considerable phenotypic variability in this monogenic disorder. 3)  FXS shares molecular and neural circuitry features with other genetic etiologies of ASD and, perhaps, SA. The emerging knowledge from neuroimaging of ASD in FXS emphasizes the involvement of brain areas already implicated in idiopathic ASD, in particular the cerebellum and limbic regions. These MRI morphometric approaches may eventually identify additional neural circuits involved in both FXS and idiopathic ASD. 4) Knowledge of the neurobiology of FXS shows emerging evidence that might lead to specific “core targeted” therapies such as mGluR5 receptor antagonists,89 GABA-B agonists,43,144 CRH 1 receptor antagonists,8 CYFIP1,98,110 eIF4E98, and other emerging compounds. Yet they all need to be found effective in clinical trials in humans with FXS, and ASD, especially when combined with relevant learning paradigm(s). ​

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A wide range of maladaptive behaviors and social deficits is common in FXS. It causes enormous impairments in normal day-to-day function that goes beyond pure intellectual deficits. Thus, psychotropic medications are often used to target different symptom clusters.8 Non-FXS specific pharmacological treatments are frequently recommended in combination with therapeutic services (i.e., speech-language, behavioral, educational). These treatments are aimed at decreasing the problem behaviors while facilitating the individual’s ability to attain optimal life skills, and to allow for better integration into educational and social environments.145–146 The most common target symptoms are anxiety, attentional difficulties and hyperactivity, and aggression, which may be treated by a variety of non-FXS medications (i.e., psychostimulants, atypical or newer generation antipsychotics).145 Despite their high rates of use in clinical practice, there is no systematic data to date describing the efficacy or safety of these agents in individuals with FXS. Participants with

3. Virtually all relevant FXS neuroimaging data are derived from structural neuroimaging that has demonstrated volumetric abnormalities in regions implicated in social cognition. Indeed, these studies indicate widespread abnormalities in the brain regions involved in the processing and response to emotional and social stimuli,127 which might underlie the characteristic SA and SW phenotypes observed in FXS.72 These affected brain areas include the fusiform gyrus, superior temporal sulcus, amygdala,128,129 and frontal cortex.130 The aforementioned volumetric abnormalities demonstrated 1) larger overall cerebral volumes, 2) increased caudate volume,131–134 which correlates with FMRP levels, 3) decreased volume of the superior temporal gyrus, amygdala,131,132,135 and 4) medial prefrontal cortex.132 White matter volumetric abnormalities have also been reported.133,135

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2. The mouse model of FXS (FMR1 knock-out mouse) has reproduced hallmark features of FMR1 silencing, including abnormal dendritic spine morphology (long, tortuous, immature appearance)23 and impaired synaptic plasticity and learning. Studies in FMR1 KO mice have demonstrated enhanced activity of class I metabotropic glutamate receptors and increased hippocampal long-term depression due to excessive protein translation in the absence of FMRP.122 These findings have implicated mGluRs as potential therapeutic targets in FXS. The FMR1 KO mice display features compatible with social anxiety (i.e., high levels of grooming) and ASD (i.e., blunted negative reaction to a more aggressive “nonpreferred” unfamiliar mouse).123,124 However, comparisons of different the FMR1 KO mouse strains suggest that genetic background can critically affect the behavioral manifestations. Behavioral phenotypes in the FVB/129 mouse strain resemble those of mice with disruption in the serotonin transporter gene.125 In support of a secondary gene modulation of the neurobehavioral phenotype of FXS, including ASD in FXS, Hessl and colleagues126 reported that polymorphisms in the serotonin transporter gene, but not in the monoamine oxidase A gene, influenced aberrant behavior in males with FXS. In line with these data, neuroimaging and neuroendocrine studies suggest a preferential involvement of the limbic system and HPA axis in subjects with FXS.

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(CASK), and MED12 are becoming increasingly informative as well. Importantly, NLGN3,4 DLG3 (http://goo.gl/eMJRBg) and CASK (http://goo.gl/yKYQ0) have several FMRP RNA-binding sites. Therefore, a current focus in the field is to identify protein targets of FMRP and to understand how dysregulation of these proteins leads to FXS phenotypes.101 Because many of these genes are involved in synapse remodeling and maintenance of synaptic structure, these abnormalities in FXS and ASD represent “disorders of synapse.” Although all these genes affect a wide range of functions, they are likely to have a synergistic effect on synaptic pathology and behavioral phenotypes. Furthermore, research using models of FXS that further defines FMRP- and CYFIP1-related proteins98,110 to elucidate converging molecular pathways underlying autistic behaviors might identify novel therapeutic targets for ASD. The up-regulation of mGluR5 and down regulation of the GABAergic pathways have both been used in an animal model system to study autistic behaviors.117 The increasing evidence for altered expression of mGluR5, FMRP, and GABA receptors in individuals with autism118–120 holds promise that therapies targeting these two pathways may be useful in ASD. Finally, although treatment modifications for FXS and related ASD have long been thought to be effective only during a narrow window early in development, nevertheless new animal studies begin to provide evidence to the contrary.121

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and further refinement and validation of existing outcome measures will be much needed as well.160

FXS have also been uniformly excluded from systematic research on atypical antipsychotics in ASD. Thus, no controlled studies of antipsychotics, either typical or atypical, have been conducted in individuals with FXS. Because serotonergic deficits have long been hypothesized in FXS, selective serotonin reuptake inhibitors (SSRIs) have been widely used to treat anxiety (i.e., SA) and affective symptoms, as is the case in ASD in general. However, there have been no clinical trials of any size, open or controlled, of SSRIs, other antidepressants, or anticonvulsants for the treatment of affective symptoms in FXS. Sympatholytics (alpha2-agonists) are used for hyperarousal, hyperactivity, and sleep difficulties. Although disturbed sleep patterns are a frequent problem in children with FXS, these symptoms are rarely associated with affective abnormalities. Mood stabilizers and anticonvulsants are used for mood instability and seizures, respectively. In summary, non-FXS specific psychotropic medications can be helpful to target different symptom clusters. Nevertheless, to date, there have been no adequately controlled studies of any of the pharmacological treatments commonly prescribed for FXS. In current clinical use, no curative treatment exists directed specifically at the underlying neuronal defect due to the absence of FMRP or ASD core symptoms. The major problem with the target symptom-based approach to treatment is that FXS individuals typically present with a wide range of symptoms, and treatment for one cluster of symptoms (i.e., SSRIs for anxiety) may aggravate another (i.e., hyperactivity). FXS specific disease-modifying treatment could address a clear unmet need for medications with improved precision and efficacy not only for the secondary symptoms, but more importantly the new targeted treatments may be able to ameliorate core impairments in cognition, language, and social function.147 mGluR5 is expressed in areas of the brain involved in emotion, motivation, and motor control.148,149 Fragile X molecular targeted therapeutics show potential to correct defects in protein synthesis and modify social behaviors in human with FXS and ASD. Compelling evidence started to emerge that activation of a particular neuronal receptor using GABA-B receptor agonist STX209 can improve symptoms in both mice150 and humans.144 Results of studies with mGluR5 antagonists, including mavoglurant (AFQ056), also showed they could rescue several synaptic phenotypes in animal models,115,151–155 and the potential to treat the underlying pathophysiology of FXS (i.e., restores social behavior,156 rescues dendritic spine phenotype157). Furthermore, clinical trials in FXS of the aforementioned potentially disease-modifying treatments show promise. For example, in a phase II human study that investigated AFQ056, as noted earlier, the methylation status of the FMR1 gene was predictive of response to therapy.89 The effects of STX209 in a phase II and III controlled trial showed significant beneficial improvements on outcome measures such as global, behavioral (i.e., Aberrant Behavior Checklist—Social Avoidance scale43,158), and adaptive socialization.43,144 In addition, a phase II trial of minocycline in children and adolescents with FXS reported a significant overall improvement on a global outcome measure.159 Yet in light of challenges with outcome measures that were encountered during these clinical trials, future studies are required to demonstrate significant meaningful clinical effects in humans. These results also warrant further studies to include relevant learning paradigms, and an investigation into the specific molecular features of the FMR1 gene that impact ASD. Indeed, this targeted approach that may help restore the balance between excitatory and inhibitory neurotransmission, has promise for improving social function in FXS and potentially ASD linked to dysregulation of the FMR1 gene. Nevertheless, even when these novel targeted treatments are available for general use in treating FXS, it is likely that psychiatric comorbidity will still require administration of the conventional psychotropic medications in many cases. In the absence of biomarkers or cognitive measures that can detect effects of these investigational drugs during relatively brief clinical trials, clinical researchers must rely almost entirely on these targeted symptoms. Thus, development of biomarkers

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1. Oberle, I., Rousseau, F., Heitz, D., & Kretz, C. (1991). Instability of a 550base pair DNA segment and abnormal methylation in fragile X syndrome. Science, 252(5009), 1097–1102. 2. Kaufmann, W. E., & Reiss, A. L. (1999). Molecular and cellular genetics of fragile X syndrome. Am J Med Genet, 88(1), 11–24. ​





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The first goal in the field of ASD associated with FXS is to acquire more data on the aforementioned areas. Yet, it is also necessary to introduce new approaches. In terms of behavioral studies, experimental paradigms should complement findings derived from clinical measures.161 Further studies are needed to refine our understanding of the molecular and cellular overlap between mechanisms of FXS and ASD, clarify the predictive value of FMRP levels in ASD, and elucidate the role of interacting genetic defects and environmental factors in modulation of ASD phenotypes in individuals with FXS. Most likely, the study of gene expression profiles in lymphoid and postmortem samples from affected individuals will continue to provide promising clues. The challenge here is to integrate molecular and neurobiological data; the comprehensive evaluation of CYFIP family proteins and its targets in ASD associated with FXS,110 and chromosome 15 duplication by Nishimura and colleagues109 illustrates that such work is feasible. Treatment studies with clinical trials of both standard psychopharmacologic agents and new treatments targeted to neural mechanisms are needed to explore treatment overlap and differences between FXS and ASD. Indeed, these trials of novel FXS therapies have highlighted several challenges such as the populations heterogeneity with subpopulations based on differential therapeutic responses, the lack of specific and sensitive outcome measures capturing the full range of improvements of patients with FXS, and a lack of reliable biomarkers that can track whether a specific mechanism is responsive to a new drug and whether the response correlates with clinical improvement.91 Identifying endophenotypic subgroups within FXS through different patients (i.e., imaging-behavioral, molecular-behavioral, etc.) stratification may offer insights to further delineate the biological basis of neuropsychiatric pathology (e.g., the RDoC approach articulated by NIMH:  http://www.nimh.nih.gov/research-priorities/rdoc/index. shtml). Evidence for existence of neurobehavioral subgroups in FXS based on whether individuals met criteria for ASD54,68 need to be integrated with subgroups based on severity of SW set of behaviors as a unifying factor of ASD and anxiety.43,72,80 There has been very little work suggesting the existence of separable neurobiological phenotypes within FXS. Only two studies suggest that FXS may lack homogeneity at the neurobiological level despite arising from the single gene mutation. 89,162 The heterogeneity in the FXS population and the varying treatment responses observed in recent trials now require new paradigms to design and implement future clinical trials for FXS.90 Finally, studies of educational, behavioral and therapeutic interventions are needed to generate evidence on which to base recommendations about supportive interventions and the similarities and differences between those recommendations for patients with FXS and ASD. The integration of all these pieces of data is a major challenge, to be better addressed when additional data become available.

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150. Henderson, C., Wijetunge, L., Kinoshita, M. N., Shumway, M., Hammond, R. S., Postma, F. R., et al. (2012). Reversal of disease-related pathologies in the fragile X mouse model by selective activation of GABAB receptors with arbaclofen. Sci Transl Med, 4(152), 152ra128. 151. Choi, C. H., McBride, S. M., Schoenfeld, B. P., Liebelt, D. A., Ferreiro, D., Ferrick, N. J., Hinchey, P., Kollaros, M., Rudominer, R. L., Terlizzi, A. M., Koenigsberg, E., Wang, Y., Sumida, A., Nguyen, H. T., Bell, A. J., McDonald, T. V., & Jongens, T. A. (2010). Age-dependent cognitive impairment in a Drosophila fragile X model and its pharmacological rescue. Biogerontology, 11(3), 347–362. 152. de Vrij, F., Levenga, J., Van der Linde, H. C., Koekkoek, S. K., De Zeeuw, C. I., Nelson, D. L., Oostra, B.A., & Willemsen, R. (2008). Rescue of behavioral phenotype and neuronal protrusion morphology in Fmr1 KO mice. Neurobiol Dis, 31(1), 127–132. 153. Levenga, J., Hayashi, S., de Vrij, F., Koekkoek, S. K., van der Linde, H. C., Nieuwenhuizen, I., Song, C., Buijsen, R. A.  M., Pop, A. S., GomezMancilla, B., Nelson, D. L., Willemsen, R., Gasparini, F., & Oostra, B. A. (2011). AFQ056, a new mGluR5 antagonist for treatment of fragile X syndrome. Neurobiol Dis, 42(3), 311–317. 154. McBride, S. M., Choi, C. H., Wang, Y., Liebelt, D., Braunstein, E., Ferreiro, D., Sehgal, A., Siwicki, K. K., Dockendorff, T. C., Nguyen, H. T., McDonald, T. V., & Jongens, T. A. (2005). Pharmacological rescue of synaptic plasticity, courtship behavior, and mushroom body defects in a Drosophila model of fragile X syndrome. Neuron, 45(5), 753–764. 155. Tucker, B., Richards, R. I., & Lardelli, M. (2006). Contribution of mGluR and Fmr1 functional pathways to neurite morphogenesis, craniofacial development and fragile X syndrome. Hum Mol Genet, 15(23), 3446–3458. 156. Gantois, I., Pop, A. S., Esch, R. A., Pooters, T., Gomez-Mancilla, B., Gasparini, F., Oostra, B. A., D’Hooge, R., & Willemsen, R. (2013). Chronic administration of AFQ056/Mavoglurant restores social behavior in Fmr1 KO mice. Behav Brain Res, 239, 72–79. 157. Pop, A. S., Levenga, J., de Esch, C. E., Buijsen, R. A., Nieuwenhuizen, I. M., Li, T., Isaacs, A., Gasparini, F., Oostra, B. A., & Willemsen, R. (2012). Rescue of dendritic spine phenotype in Fmr1 KO mice with the mGluR5 antagonist AFQ056/Mavoglurant. Psychopharmacology, 231(6), 1227–1235. 158. Sansone, S. M., Widaman, K. F., Hall, S. S., Reiss, A. L., Lightbody, A., Kaufmann, W. E., Berry-Kravis, E., Lachiewicz, A., Brown, E. C., & Hessl, D. (2012). Psychometric study of the aberrant behavior checklist in Fragile X syndrome and implications for targeted treatment. J Autism Dev Disord, 42(7), 1377–1392. 159. Leigh, M. J.  S., Nguyen, D. V., Mu, Y., Winarni, T. I., Schneider, A., Chechi, T., Polussa, J., Doucet, P., Tassone, F., Rivera, S., Hessl, D., & Hagerman, R. J. (2013). A randomized double-blind, placebo-controlled trial of minocycline in children and adolescents with fragile X syndrome. J Dev Behav Pediatr, 34(3), 147–155. 160. Tranfaglia, M. R. (2012). Fragile X syndrome:  A  psychiatric perspective. In R. B. Denman (Ed.), Modeling fragile X syndrome (pp. 281–295). Berlin: Springer. 161. Roberts, J. E., Weisenfeld, L. A. H., Hatton, D. D., Heath, M., & Kaufmann, W. E. (2007). Social approach and autistic behavior in children with fragile X syndrome. J Autism Dev Disord, 37(9), 1748–1760. 162. Romano, D., Nicolau, M., Quintin, E.M., Mazaika, P.K., Lightbody, A.A., Cody Hazlett, H., Piven, J., Carlsson, G., Reiss, A.L. (2014). Topological methods reveal high and low functioning neurophenotypes within fragile X syndrome. Hum Brain Mapp, 35(9), 4904–4915.

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in Fragile X syndrome visualized using tensor-based morphometry. Neuroimage, 34(3), 924–938. Reiss, A. L., Freund, L. S., Baumgardner, T. L., Abrams, M. T., & Denckla, M. B. (1995). Contribution of the FMR1 gene mutation to human intellectual dysfunction. Nat Genet, 11(3), 331–334. Kates, W. R., Folley, B. S., Lanham, D. C., Capone, G. T., & Kaufmann, W. E. (2002). Cerebral growth in Fragile X syndrome: review and comparison with Down syndrome. Microsc Res Tech, 57(3), 159–167. Krug, D. A., Arick, J., & Almond, P. (1980). Behavior checklist for identifying severely handicapped individuals with high levels of autistic behavior. J Child Psychol Psychiatry, 21(3), 221–229. Kaufmann, W. E., Cooper, K. L., Mostofsky, S. H., Capone, G. T., Kates, W. R., Newschaffer, C. J., Bukelis, I., Stump, M. H., Jann, A. E., & Lanham, D. C. (2003). Specificity of cerebellar vermian abnormalities in autism: A quantitative magnetic resonance imaging study. J Child Neurol, 18(7), 463–470. Stanfield, A. C., McIntosh, A. M., Spencer, M. D., Philip, R., Gaur, S., & Lawrie, S. M. (2008). Towards a neuroanatomy of autism: A systematic review and meta-analysis of structural magnetic resonance imaging studies. Eur Psychiatry, 23(4), 289–299. Hessl, D., Glaser, B., Dyer-Friedman, J., & Reiss, A. L. (2006). Social behavior and cortisol reactivity in children with fragile X syndrome. J Child Psychol Psychiatry, 47(6), 602–610. Hessl, D., Glaser, B., Dyer-Friedman, J., Blasey, C., Hastie, T., Gunnar, M., & Reiss, A. L. (2002). Cortisol and behavior in fragile X syndrome. Psychoneuroendocrinology, 27(7), 855–872. Roberts, J. E., Boccia, M. L., Hatton, D. D., Skinner, M. L., & Sideris, J. (2006). Temperament and vagal tone in boys with fragile X syndrome. J Dev Behav Pediatr, 27(3), 193–201. Hall, S. S., Lightbody, A. A., Huffman, L. C., Lazzeroni, L. C., & Reiss, A. L. (2009). Physiological correlates of social avoidance behavior in children and adolescents with fragile X syndrome. J Am Acad Child Adolesc Psychiatry, 48(3), 320–329. Berry-Kravis, E., Hessl, D., Coffey, S., Hervey, C., Schneider, A., Yuhas, J., Hutchison, J., Snape, M., Tranfaglia, M., Nguyen, D. V., & Hagerman, R. (2009). A pilot open label, single dose trial of fenobam in adults with fragile X syndrome. J Med Genet, 46(4), 266–271. Berry-Kravis, E. M., Hessl, D., Rathmell, B., Zarevics, P., Cherubini, M., Walton-Bowen, K., Mu, Y., Nguyen, D. V., Gonzalez-Haydrich, J., Wang, P. P., Carpenter, R. L., Bear, M. F., & Hagerman, R. J. (2012). Effects of STX209 (arbaclofen) on neurobehavioral function in children and adults with fragile X syndrome:  A  randomized, controlled, phase 2 trial. Sci Transl Med, 4(152), 152ra127–152ra127. Berry-Kravis, E., & Potanos, K. (2004). Psychopharmacology in fragile X syndrome—present and future. Ment Retard Dev Disabil Res Rev, 10(1), 42–48. Bailey Jr, D. B., Raspa, M., Bishop, E., Olmsted, M., Mallya, U. G., & Berry-Kravis, E. (2012). Medication utilization for targeted symptoms in children and adults with fragile X syndrome: US Survey. J Dev Behav Pediatr, 33(1), 62–69. Dlen, G., & Bear, M. F. (2009). Fragile x syndrome and autism: From disease model to therapeutic targets. J Neurodev Disord, 1(2), 133–140. Spooren, W., & Gasparini, F. (2004). mGlu5 receptor antagonists: A novel class of anxiolytics. Drug News Perspect, 17(4), 251–257. Swanson, C. J., Bures, M., Johnson, M. P., Linden, A. M., Monn, J. A., & Schoepp, D. D. (2005). Metabotropic glutamate receptors as novel targets for anxiety and stress disorders. Nat Rev Drug Discov, 4(2), 131–144.



53 |  AUTISM AND INTELLECTUAL DISABILITIES: PTEN GENE MUTATION

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Bannayan-Riley-Ruvalcaba syndrome (BRRS) is an autosomal dominant congenital disorder marked by macrocephaly, lipomatosis, hemangiomamatosis, and speckled penis.33 In about 60% of BRRS patients germline PTEN mutations have been found,26 and the mutations are noted at the 3 encoded C2 domain within exons 6 and 9. Developmental delay and macrocephaly were the hallmarks of BRRS.33 Macrocephaly is believed to be secondary to megalencephaly/overgrowth of brain tissues as opposed to hydrocephalus34,34a, and it is hypothesized to be due to increased cellular proliferation related to the up regulation of the AKT pathway. Hemangiomas are also an associated feature,33 as are hamartomas, which consist of a mixture of adipocyte and or myxoid fibrous tissue with distinct vascular component and on rare occasions lymphoid, bone, and nerve tissue.35 The most common locations for these lesions are the brain and limbs,36 and they can be treated with embolization or resection. However a

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Cowden syndrome is a multisystem disorder that is characterized by an increased risk of malignancy of the breast and thyroid; benign hamartomas of the skin, breast, thyroid, and GI tract; and also macrocephaly. Skin lesions and hamartomas are usually present by 20 years of age. The incidence is believed to be one in 200,000.23,24 In 2008 the National Comprehensive Cancer Network revised the Cowden syndrome diagnostic criteria, proposing the use of major and minor criteria (Box 53.1). Many of the cases of Cowden syndrome (CS) appear to be sporadic. However 40% to 65% of CS cases appear to be familial (Marsh et al 1998, 1999).25,26 About 90% of the individuals with CS manifest features by 20  years of age.4,27 The commonly reported features are mucocutaneous lesions, thyroid issues, fibrocystic disease and carcinoma of the breast, multiple early onset uterine leiomyomas, and macrocephaly.4,27–31 Breast and thyroid epithelial cancers are most commonly reported, and women with CS have an increased risk for breast cancer at 25% to 50% as compared with 11% in the general population,28,31 and breast cancers are usually adenocarcinomas affecting both lobules and ductal systems. The lifetime risk for thyroid epithelial cancers is as high as 10% in males and females with CS. In familial cases of CS, susceptibility locus was mapped to the 10q22q23 region and noted to be germline mutations, particulary affecting exons 5, 7, and 8 in 61% of familial cases with 38% occurring in exon 5 alone.4 Germline mutation appear to be highly correlated to breast cancer25 and mutations in the phosphatase core motif appear to be associated with involvement of five or more organs.25 Twenty percent of CS cases were found to be mutation negative and 10% had germline promoter mutations that resulted in loss of function.32

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PTEN (phosphatase and tensin homolog deleted on chromosome 10) was identified in 19971,2 as a tumor suppressor gene that was mutated in prostate, breast, and brain tumors including glioblastoma multiforme. Loss of heterozygosity on 10q23.3, the region that contained the PTEN gene, was also subsequently found to be associated with sporadic tumors.3 Germline mutations on PTEN were then found to be associated with a group of inherited disorders that were collectively called the PTEN hamartoma syndromes and included the Cowden syndrome, Bannayan-Riley-Ruvalcalaba syndrome(BRRS), and Proteus syndrome.4 Inherited mutations of PTEN are associated with varying phenotypes and include hamartomas in multiple tissues and with a high risk for breast, thyroid, and endometrial cancers as well as a varying neurological presentation.5 Cowden syndrome is a familial cancer syndrome characterized by multiple hamartomas of the skin and with a high risk for breast, thyroid, and endometrial cancers. BRRS is characterized by macrocephaly, developmental delays, lipomatosis, and pigmented macules of the penis. Proteus syndrome is marked by asymmetrical limb overgrowth, macrocephaly, lipomatosis, and connective tissue naevi.6 The common features of these inherited disorders include a predisposition to hamartomas, and thus they have been collectively called the PTEN hamartoma syndrome7 (Figure 53.1). PTEN functions as a phosphatase for the lipid signaling intermediate phosphatidylinositol 3,4,5-triphosphate (PIP3) by removing the phosphate from the three-position of the inositol ring8 to create the phosphatidylinositol-4,5-biphosphate(PIP2) which directly antagonizes signaling in the phosphatidylinositol-2-kinase (PI3K) pathway.5 Thus PTEN is an important negative regulator of the PI3K/AKT signaling pathway9 This is a highly conserved pathway that regulates cell growth, proliferation, survival, apoptosis, metabolism, and cell migration as well as developmental processes within the central nervous system. Autism spectrum disorders (ASD) is a neurodevelopmental disorder characterized by abnormal social interaction, deficits in verbal and nonverbal communication, and restricted/repetitive behaviors and interests (DSM5). Although causes of most ASD cases are currently unknown, scientific and research studies demonstrate strong heritability and a genetic predisposition in about 10% of children with ASD.10 So far hundreds of genes and multiple chromosome regions have been associated with autism.11 Reported ASD susceptibility genes function in various intracellular signaling pathways that control multiple aspects of cell function like neuronal growth, migration, and synaptic function. Several reports have identified PTEN mutations in children with ASD, intellectual disability, and macrocephaly.6,12–16 Recent studies have further shown that germline PTEN mutations are present in 1% to 5% of the ASD population.17–22 Hence screening for PTEN mutations in autism patients with macrocephaly is strongly recommended.6 53

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predilection for recurrence as well as exuberant keloid formation has been reported.37

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PROTEUS AND PROTEUS-LIKE SYNDROME

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Proteus syndrome (PS) is characterized by segmental overgrowth of brain, bone, skin, and other tissues.38 A  familial case of Proteus syndrome was attributed to somatic mutation of the PTEN gene and reports of PTEN mutation have been reported to be linked to Proteus and Proteus-like syndrome.39,40,40a,40b It is thought that an activating mutation in AKT1 in somatic tissues is causative in PS and Proteuslike syndrome. Proteus syndrome can affect any body part but commonly affects bone and skin. Overgrowth of a bone can cause orthopedic problems, whereas skin lesions can cause cosmetic problems. Rarely, individuals with Proteus syndrome require monitoring of lung problems due to predisposition to bullae. Most children and adults with PS have a normal life span and normal intelligence. However, they are at a greater risk for deep-vein thrombosis and pulmonary embolism.

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Adult Lhermitte-Duclos disease Mucucutaneous lesions (trichelemmomas, facial acral keratosis, papillomatous lesions) Major Criteria Breast cancer Thyroid cancer (papillary and follicular) Macrocephaly (HC >97%) Endometrial cancer Minor criteria Other structural thyroid lesions (adenoma, multinodular goiter) Mental retardation (IQ 5 mV. C. Burst suppression: periods of low voltage (inactivity) intermixed with bursts of higher amplitude. D. Continuous background pattern of very low voltage (around or