Autosomal Dominant Hereditary Ataxia

Resumen

Summary

The hereditary ataxias are a group of neurological disorders (ataxias) of varying degrees of rarity that are inherited, in contrast to a related group of neurological disorders that are acquired through accidents, injuries, or other external agents. The hereditary ataxias are characterized by degenerative changes in the brain and spinal cord that lead to an awkward, uncoordinated walk (gait) accompanied often by poor eye-hand coordination and abnormal speech (dysarthria). Hereditary ataxia in one or another of its forms may present at almost any time between infancy and adulthood.

The classification of hereditary ataxias is complex with several schools of thought vying for recognition. This report follows the classification presented by Dr. Thomas D. Bird and the University of Washington’s GeneReviews.

This classification is based on the pattern of inheritance or mode of genetic transmission of the disorder: i.e., autosomal dominant, autosomal recessive and X-linked. The autosomal dominant ataxias, also called the spinocerebellar ataxias, are usually identified as SCA1 through SCA37. Also included are several “episodic ataxias”, as well as a very rare disorder known as DRPLA (dentato-rubro-pallido-luysian atrophy). This report deals with the autosomal dominant hereditary ataxias. There are fewer autosomal recessive hereditary ataxias than autosomal dominant hereditary ataxias, and X-linked forms of ataxia are very rare.

Introduction

At one time, all autosomal dominant ataxias were called Marie’s ataxia and all autosomal recessive ataxias were called Friedreich’s ataxia. This is no longer appropriate because there is now much more accurate information about these diseases.

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Sinónimos

• episodic ataxia
• spinocerebellar ataxia

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Signos y Síntomas

Ataxia is most often associated with degeneration of the region of the brain known as the cerebellum where movement, posture, and balance are coordinated. Thus, many of the symptoms and signs are those expected from cerebellar dysfunction. Ataxia may also be associated with damage (lesions) to the spinal cord. Symptoms and signs often include a characteristic wide-based and unsteady way of walking (gait) that may be accompanied by awkward eye-hand coordination and slow, weak, or imprecise speech.

Other symptoms and signs may include involuntary eye movement (nystagmus) or double vision (diplopia), sensory loss, and cognitive impairment.
Some types of ataxia may be complicated by vision disorders including optic atrophy, retinitis pigmentosa, and eye movement paralysis (ophthalmoplegia).

Other types of hereditary ataxia may be associated with heart disease, breathing problems, bone abnormalities and diabetes.

Some clinical features that may be associated with specific forms of autosomal dominant hereditary ataxia are listed below. In this list, SCA refers to spinocerebellar ataxia; DRPLA refers to dentato-rubro-pallido-luysian atrophy; EA refers to episodic ataxia; and SAX refers to spastic ataxia.

SCA1: Tremors of the hands (Parkinson-like), numbness in fingers and toes (peripheral neuropathy)

SCA2: Involuntary, irregular eye movements that occur when changing focus from one point to another (saccade), numbness of fingers and toes (peripheral neuropathy), loss of deep tendon reflexes such as at the kneecap, sometimes dementia

SCA3 (Machado Joseph Disease): Hand tremors, some rigidity, slowness of movement (extrapyramidal signs), involuntary eye movement (nystagmus), drawn back eyelids (lid retraction), numbness (sensory loss), eye jerking (saccade), muscle weakness and wasting (amyotrophy) with muscle twitches, most common dominant genetic ataxia

SCA4: Progressive painless clumsiness, muscle weakness and atrophy

SCA5: Early onset and slow progression

SCA6: Very slow course, usually adult onset

SCA7: Damage to the retina (retinopathy) with vision loss

SCA8: Decreased sense of vibrations

SCA10: Occasional seizures

SCA11: Mild signs, able to walk about

SCA12: Early tremor, late dementia

SCA13: Mild intellectual disability, short stature

SCA14: Slow progression of disease

SCA15: Very slow worsening of the walk or gait

SCA16: Head tremor

SCA17: Mental function declines

SCA18: Ataxia with early sensory/motor neuropathy, nystagmus, dysarthria, decreased tendon reflexes

SCA19/22: Mild ataxia, spasms (myoclonus), mental deterioration and tremor, slow worsening of the walk or gait

SCA20: Early dysarthria, spasmodic dysphonia, hyperreflexia, bradykinesia

SCA21: Mild mental deterioration

SCA23: Dysarthria, abnormal eye movements, reduced vibration and position sense

SCA25: Associated sensory neuropathy

SCA26: Dysarthria, irregular visual pursuits

SCA27: Early onset tremor, cognitive deficits

SCA28: Nystagmus, ptosis

SCA29: childhood learning deficits

SCA30: Hyper reflexia, adult onset

SCA31: Normal sensation, adult onset

SCA32: Males infertile

SCA34: Skin lesions

SCA35: Hyperreflexia, babinski responses

SCA36: Tongue atrophy, adult onset

SCA37: Abnormal vertical eye movements

SCA38: Adult onset, axonal neuropathy

SCA40: Adult onset, brisk reflexes, spasticity

SCA42: Mild pyramidal signs, saccadic pursuit

ADCADN: Deafness, sensory loss, narcolepsy

Hypomyelinating leukoencephalopathy: Hypomyelination, basal ganglia atrophy, rigidity, dystonia, chorea

GRID2-related spinocerebellar ataxia: Cognitive delay, abnormal eye movements, hearing loss

Pure cerebellar ataxia: Other family members may have frontotemporal dementia or motor neuron disease

Cerebellar atrophy with epileptic encephalopathy: Infantile seizures, intellectual deficits, microcephaly

Rapid-onset ataxia: Cerebellar atrophy

DRPLA: Rapid, sudden involuntary movements (chorea), seizures, dementia, shocklike spasms (myoclonus), more common in Japan

EA1: Involuntary, rippling, muscular motion (myokymia), startle- or exercise-induced,

EA2: Involuntary rapid eye movements (nystagmus), dizziness (vertigo)

EA3: Vertigo, spasticity, involuntary eye movements (vestibulo-ocular reflex), ringing in the ears (tinnitus), double vision (diplopia)

EA4: Vertigo, rippling of muscles (myokymia), ringing in ears (tinnitus), double vision, and blurred vision

EA5: Childhood to adolescent onset

EA6: Seizures, migraine, childhood onset

EA7: Vertigo, weakness, ? seizures, childhood to adolescent onset

CAPOS: Cerebellar ataxia, areflexia, Pes cavus, optic atrophy, sensorineural hearing loss, also alternating hemiplegia

Episodic ataxia with neonatal epilepsy: neonatal epilepsy, later-onset episodic ataxia, autism, hypotonia, dystonia

SAX1: Progressive leg spasticity, gait ataxia

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Causas y Herencia

As noted above, some forms of the hereditary ataxias are transmitted in a dominant mode, others are transmitted through a recessive mode, and still others are transmitted in an X-linked fashion. This report deals with the disorders transmitted in an autosomal dominant fashion.

For many of the ataxias, the chromosomal site of the faulty gene is known or the actual gene involved has been identified. These are listed below for autosomal dominant hereditary ataxias. Little p indicated the short arm of the chromosome, little q represents the long arm of the chromosome.

SCA1: 6p23; ATXN1
SCA2: 12q24; ATXN2
SCA3: 14q24.3-q31; ATXN3
SCA4: 16q22.1
SCA5: 11p11-q11; SPTBN2
SCA6: 19p13; CACNA1A
SCA7: 3p21.1-p12; ATXN7
SCA8: 13q21; ATXN8 / ATXN80S
SCA10: 22q13; ATXN10
SCA11: 15q14-q21.3; TTBK2
SCA12: 5q31-q33; PPP2R2B
SCA13: 19q13.3-q13.4; KCNC3
SCA14: 19q13.4-qter; PRKCG
SCA15: ITPR1
SCA16: 8q22.1-q24.1; SCA16
SCA17: 6q27; TBP
SCA18: IFRD1
SCA19/22: KCND3
SCA20: 11q12.2-11q12.3
SCA21: 7p21-p15; TMEM240
SCA22: 1p21-q23; KND3
SCA23: PDYN
SCA25: 2p15-21; SCA25
SCA26: 19p13.3; EEF2
SCA27: FGF14
SCA28: AFG3L2
SCA29: 3p26; ITPR1
SCA30: 4q34.3-q35.1
SCA31: BEAN1
SCA32: 7q32
SCA34: 6p12.3-q16.2; ELOVL4
SCA35: TGM6
SCA36: NOP56
SCA37:1p32
SCA38: ELOVL5
SCA40: CCDC88C
SCA42: CACNA1G
DRPLA: 12p13.31; ATN1
ADCADN: DNMT1
Hypomyelinating leukoencephalopathy: TUBB4A
GRID2-related spinocerebellar ataxia: GRID2
Pure Cerebellar Ataxia: C9orf72
Cerebellar atrophy with epileptic encephalopathy: FGF12
Rapid-onset ataxia: ATP1A3
EA1: 12p13; KCNA1
EA2: 19p13; CACNA1A
2q22-q23; CACNB4
EA3: 1q42
EA5: CACNB4
EA6: SLC1A3
EA7: 1q13
Episodic ataxia with neonatal epilepsy: SCN2A
CAPOS: ATP1A3
SAX1: 12p13; VAMP1

Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome, and females have two X chromosomes. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered. For example, “chromosome 11p11-q11” refers to a region between band 11 on the short arm of chromosome 11 and band 11 on the long arm of chromosome 11. The numbered bands specify the location of the thousands of genes that are present on each chromosome.

Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother.
Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy regardless of the gender of the resulting child.

Autosomal dominant hereditary ataxias have been further classified as trinucleotide repeat disorders. A trinucleotide repeat is a segment of DNA that is repeated. An abnormally large number of repeated segments of DNA can interfere with normal protein function. Trinucleotide repeats are unstable and can change in length when a gene containing them is passed to the next generation. An increased number of repeats often leads to an earlier age of onset and more severe disease.

Some forms of ataxia are not hereditary and can occur as a result of severe infections or side effects of drugs or alcohol. In many cases, ataxia is a symptom of another neurological disorder rather than a distinct and separate illness.

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Frecuencia

Hereditary ataxias affect males and females in equal numbers. It is estimated that 150,000 people in the United States are affected by, or at risk for, hereditary ataxia. There is variation among the specific forms of hereditary ataxia as to when they typically first appear. Some ataxias are more common in certain ethnic groups. For example, SCA3 is more common in the Portuguese population, SCA10 is more common in the Mexican population, and DRPLA is more common in Japan.

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Enfermedades con síntomas similares

Symptoms of the following disorders can be similar to these conditions. Comparisons may be useful for a differential diagnosis:

Olivopontocerebellar atrophy (OPCA) refers to a group of ataxias characterized by progressive neurological degeneration affecting the cerebellum, the pons and the inferior olives. OPCA may be classified based on clinical, genetic, or neuropathological findings; thus, there are many classifications of the disorder. Many of these cases now fall into the SCA category and the term OPCA is relatively unused nowadays. Among the different classifications, there is wide variation in severity and age of onset. The symptoms of OPCA differ from person to person. Most patients experience difficulty with balance and coordination of the legs and arms (ataxia) and slurred speech (dysarthria). Other symptoms may include muscle spasms or weakness and stiffness of the muscles; numbness or tingling of the hands or feet; shaking (tremor) of the hand or arm; reduction or slowness of movements; loss of thinking and/or memory skills; difficulty controlling the bladder or bowels; and feeling faint when standing up. Some patients also have fatigue and/or trouble with sleep. Generally, symptoms of OPCA begin in mid-adult life and progress slowly over the course of many years. (For more information on this disorder, choose “Olivopontocerebellar Atrophy, Hereditary” as your search term in the Rare Disease Database.)

Multiple system atrophy (MSA) refers to three slowly progressive related disorders that affect the central and autonomic nervous systems. The disorders are an ataxic form which primarily affects balance, coordination, and speech; a parkinsonian form, which can resemble Parkinson’s disease because of slow movement and stiff muscles; and a form sometimes called Shy-Drager disease that primarily includes low blood pressure on standing (Orthostatic Hypotension). In all three forms of MSA, the patient can have a drop in blood pressure when the patient stands up, which causes dizziness or momentary blackouts. Other symptoms may include stiffness and rigidity, loss of balance and coordination, impaired speech, breathing and swallowing difficulties, blurred vision, male impotence, constipation and urinary difficulties. Most patients develop dementia late in the course of the disease, which is usually diagnosed in persons over age 50. MSA is twice as common in men as in women. (For more information on this disorder, choose “Multiple System Atrophy” as your seach term in the Rare Disease Database.)

Charcot-Marie-Tooth disease is usually inherited as a dominant trait. However, in some families it can occur as a recessive trait or even as an X-linked trait. This hereditary form of peripheral nerve disease is characterized by weakness and atrophy, primarily in the legs. Disappearance of the fatty shield surrounding the nerves (segmental demyelination of peripheral nerves) and associated degeneration of part of the nerve cells (axons) characterize this disorder. When it is passed to offspring as an X-linked trait, it affects males more severely than females. (For more information on this disorder, choose “Charcot-Marie-Tooth disease” as your search term in the Rare Disease Database).

Friedreich’s ataxia is an autosomal recessive type of hereditary neuromuscular syndrome characterized by slow degenerative changes of the spinal cord, peripheral nerves and the brain. Dysfunction of the central nervous system affects coordination of the muscles in the limbs. Speech can be affected and numbness or weakness of the arms and legs develop. Heart disease (cardiomyopathy) often occurs later in the disease and there is an increased frequency of diabetes. This syndrome appears to be the most common of the many forms of hereditary ataxia. It usually begins during childhood or the teen years. (For more information on this disorder, choose “Ataxia, Friedreich” as your search term in the Rare Disease Database).

Ataxia telangiectasia, also known as Louis-Bar syndrome, is inherited as an autosomal recessive trait. It is a progressive cerebellar ataxia that usually begins during infancy. It involves progressive loss of coordination in the limbs, head and eyes with a below-normal immune response to infections. In later stages, dilated blood vessels (telangiectasias) appear in the eyes and skin. Individuals with this form of ataxia are more susceptible to sinus and lung infections, and are at higher risk for developing certain tumors (neoplasms). Ataxia telangiectasia may be misdiagnosed as Friedreich ataxia until dilated blood vessels appear in the skin (telangiectasias). (For more information on this disorder, choose “Ataxia Telangiectasia” as your search term in the Rare Disease Database).

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Diagnóstico

For a diagnosis of hereditary ataxia, there must be a neurological examination that shows poorly coordinated gait, often combined with uncoordinated finger/hand movements. Difficulty with speech (dysarthria) and uncontrolled eye movements (nystagmus) may also be present. In addition, non-genetic causes of ataxia must be excluded. The hereditary nature of the disorder may be established by a positive family history of ataxia or identifying an ataxia-causing gene mutation.

Molecular genetic testing is currently available for many hereditary ataxias. To find out whether that is the case for a specific type, speak to your physician or a certified genetic counselor or access the GeneTests website (www.genetests.org).

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Tratamiento

Treatment
Treatment of ataxia is symptomatic and supportive. Continuous medical supervision to avoid potential complications involving the heart, lungs spine, bones and muscles is recommended. Mental functions usually remain unaffected in most forms of hereditary ataxia but emotional strain can affect patients and their families. In such cases, psychological counseling may be helpful.

Physical therapy may be recommended by a physician. In addition, various aids may assist muscular movement. Some drugs may be useful in treating some symptoms of ataxia. Propanalol may be effective against static tremors, for instance. Dantrolene, Baclofen, or Tizanidine may help some patients with muscle spasms of the legs. Genetic counseling will be of benefit for patients and families affected by the hereditary ataxias.

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Investigaciones

Clinical trials involving the hereditary ataxias are currently in progress, sponsored by the National Institute of Neurological Disorders and Stroke (NINDS) of the National Institutes of Health (NIH).

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov . All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.
For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222
TTY: (866) 411-1010
Email: [email protected]

Some current clinical trials also are posted on the following page on the NORD website:
https://rarediseases.org/living-with-a-rare-disease/find-clinical-trials/

For information about clinical trials sponsored by private sources, contact:
www.centerwatch.com

For information about clinical trials conducted in Europe, contact:
https://www.clinicaltrialsregister.eu/

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Referencias

TEXTBOOKS
Adams RD, Victor M, Ropper AA, eds. Principles of Neurology. 10th ed. McGraw-Hill Companies. New York, NY, 2015.

Rosenberg RN, DiMauro S, Paulson HL, et al, eds. The Molecular and Genetic Basis of Neurologic and Psychiatric Disease. 5th ed. Lippincott Williams & Wilkins. Philadelphia, PA. 2014.

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Lynch DR, ed. Neurogenetics: Scientific and Clinical Advances. Taylor & Francis, New York, NY, 2006.

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Burns RS. Episodic Ataxia Type II. NORD Guide to Rare Disorders. Lippincott Williams & Wilkins. Philadelphia, PA. 2003:601-02.

REVIEW ARTICLES
Rossi M, Perez-Lloret S, Doldan L, et al. Autosomal dominant cerebellar ataxias: a systematic review of clinical features. Eur J Neurol 2014; 21:607-615.

Ruano L, Melo C, Silva MC, Coutinho P. The Global Epidemiology of Hereditary Ataxiaand Spastic Paraplegia: A systematic review of prevalence studies. Neuroepidemiology 2014; 24:174-183.

Ashizawa T, Figueroa KP, Perlman SL, et al. Clinical characteristics of patients with spinocerebellar ataxias 1, 2, 3, and 6 in the US; a prospective observational study. Orph J Rare Dis 2013;8:177-84.

Jayadev S, Bird TD. Hereditary ataxias: overview. Genet Med. 2013 Sep;15(9):673-83.

Shakkottai VG, Fogel BL. Clinical Neurogenetics: Autosomal Dominant Spinocerebellar Ataxia. Neurol Clin 2013;31:987-1007.

Durr A. Autosomal dominant cerebellar ataxias: polyglutamine expansions and beyond. Lancet Neurol 2010; 9:885-894.

Gasser T, Finsterer J, Baets J et al. EFNS Guidelines on the molecular diagnosis of ataxias and spastic paraplegias. Eur J NEurol 2010;17:179-188.

Finsterer J. Ataxias with autosomal, X-choromosal or Maternal Inheritance. Can J Neurol Sci 2009; 36:409-428.

Embirucu EK, Martyn ML, Schlesinger D, Kok F. Autosomal Recessive Ataxia: 20 types and counting. Arq Neuropsiquiatr 2009;67(4):1143-1156.

INTERNET
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Gatti R. Ataxia-Telangiectasia. 1999 Mar 19 [Updated 2016 Oct 27]. In: Pagon RA, Adam MP, Ardinger HH, et al., editors. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2017. Available from: https://www.ncbi.nlm.nih.gov/books/NBK26468/ February 9, 2017.

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Bidichandani SI, Delatycki MB. Friedreich Ataxia. 1998 Dec 18 [Updated 2014 Jul 24]. In: Pagon RA, Adam MP, Ardinger HH, et al., editors. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2017. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1281/ Accessed February 9, 2017.

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Houlden H. Spinocerebellar Ataxia Type 11. 2008 Jul 22 [Updated 2013 Mar 7]. In: Pagon RA, Adam MP, Ardinger HH, et al., editors. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2017. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1757/ Accessed February 9, 2017.

Gomez CM. Spinocerebellar Ataxia Type 6. 1998 Oct 23 [Updated 2013 Jul 18]. In: Pagon RA, Adam MP, Ardinger HH, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2017. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1140/ Accessed February 13, 2017.

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Paulson H. Spinocerebellar Ataxia Type 3. 1998 Oct 10 [Updated 2015 Sep 24]. In: Pagon RA, Adam MP, Ardinger HH, et al., editors. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2017. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1196/ Accessed February 9, 2017.

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Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Spinocerebellar Ataxia 14; SCA14. Entry No: 605361. Last Edited 08/30/2016. Available at: https://omim.org/entry/605361 Accessed February 13, 2017.

Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Spinocerebellar Ataxia 15; SCA15. Entry No: 606658. Last Update 06/24/2016. Available at: https://omim.org/entry/606658 Accessed February 13, 2017.

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Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Spinocerebellar Ataxia 10; SCA10. Entry No: 603516. Last Update 05/26/2016. Available at: https://omim.org/entry/603516 Accessed February 13, 2017.

Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Spinocerebellar Ataxia 19; SCA19. Entry No: 607346. Last Edited 10/08/2013. Available at: https://omim.org/entry/607346 Accessed February 13, 2017.

Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Spinocerebellar Ataxia 7; SCA7. Entry No: 164500. Last Update 05/23/2016. Available at: https://omim.org/entry/164500 Accessed February 13, 2017.

Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Spinocerebellar Ataxia 20; SCA20. Entry No: 608687. Last Edited 05/31/2011. Available at: https://omim.org/entry/608687 Accessed February 13, 2017.

Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Spinocerebellar Ataxia 2; SCA2. Entry No.: 183090. Last Update 10/12/2016. Available at: https://omim.org/entry/183090 Accessed February 13, 2017.

Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Episodic Ataxia, Type 1; EA1. Entry No: 160120. Last Update 10/16/2014. Available at: https://omim.org/entry/160120 Accessed February 13, 2017.

Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Spinocerebellar Ataxia 6; SCA6. Entry No: 183086. Last Edited 06/02/2016. Available at: https://omim.org/entry/183086 Accessed February 13, 2017.

Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Spinocerebellar Ataxia 12; SCA12. Entry No: 604326. Last Update 08/17/2016 . Available at: https://omim.org/entry/604326 Accessed February 13, 2017.

Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Spinocerebellar Ataxia 5; SCA5. Entry No: 600224. Last Update 07/20/2016. Available at: https://omim.org/entry/600224 Accessed February 13, 2017.

Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Spinocerebellar Ataxia 1; SCA1. Entry No: 164400. Last Update 08/22/2016. Available at: https://omim.org/entry/164400 Accessed February 13, 2017.

Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Episodic Ataxia, Type 2: EA2. Entry No: 108500. Last Update 09/15/2016. Available at: https://omim.org/entry/108500 Accessed February 13, 2017.

Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Spinocerebellar Ataxia 18; SCA18. Entry No: 607458. Last Edited 09/22/2011. Available at: https://omim.org/entry/607458 Accessed February 13, 2017.

Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Episodic Ataxia, Type 5: EA5. Entry No: 613855. Last Update 12/02/2016. Available at: https://omim.org/entry/613855 Accessed February 13, 2017.

Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Episodic Ataxia, Type 6: EA6. Entry No: 612656. Last Update 09/15/2016. Available at: https://omim.org/entry/612656 Accessed February 13, 2017.

Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Spinocerebellar Ataxia 11; SCA11. Entry No: 604432. Last Edited 05/30/2012. Available at: https://omim.org/entry/604432 Accessed February 13, 2017.

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