Autosomal Dominant Hereditary Ataxia

National Organization for Rare Disorders, Inc.

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Important

It is possible that the main title of the report Autosomal Dominant Hereditary Ataxia is not the name you expected.

Disorder Subdivisions

  • None

General Discussion

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.



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.

Symptoms

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 spine. 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 mental retardation, short stature



SCA14: Slow progression of disease



SCA15: Very slow worsening of the walk or gait



SCA16: Head tremor



SCA17: Mental function declines



SCA19: Mild ataxia, spasms (myoclonus), mental deterioration and tremor



SCA21: Mild mental deterioration



SCA22: Slow worsening of the walk or gait



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



SCA36: Tongue atrophy, adult onset



SCA37: Abnormal vertical eye movements



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



SAX1: Progressive leg spasticity

Causes

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 site of the faulty gene is known or the actual involved gene has been identified. These are listed below for autosomal dominant hereditary ataxias.



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: KCND3



SCA20: 11q12.2-11q12.3



SCA21: 7p21-p15; SCA21



SCA22: 1p21-q23; KND3



SCA23: PDYN



SCA25: 2p15-21; SCA25



SCA26: 19p13.3; EEF2



SCA27: FGF14



SCA28: AFG3L2



SCA29: 3p26



SCA30: 4q34.3-q35.1



SCA31: BEAN1



SCA32: 7q32



SCA34: 6p12.3-q16.2



SCA35: TGM6



SCA36: NOP56



SCA37:1p32



DRPLA: 12p13.31; ATN1



EA1: 12p13; KCNA1



EA2: 19p13; CACNA1A



2q22-q23; CACNB4



EA3: 1q42



EA5: CACNB4



EA6: SLC1A3



SAX1: 12p13



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.

Affected Populations

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.

Diagnosis

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 specific ones, speak to your physician or a certified genetic counselor or access the GeneTests website (www.genetests.org).

Standard Therapies

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.

Investigational Therapies

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: prpl@cc.nih.gov



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/

References

TEXTBOOKS



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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



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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.



Paulson HL. The Spinocerebellar Ataxias. J Neuro-Ophthalmol 2009;29:277-237.



Bird TD. The Physician's Guide to Hereditary Ataxia. NORD. 2003:1-10.



La Spada AR, Taylor JP. Polyglutamines placed in context. Neuron.



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INTERNET



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Supporting Organizations

Genetic and Rare Diseases (GARD) Information Center

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Tel: (301)496-5751
Fax: (301)402-2186
Tel: (800)352-9424
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National Ataxia Foundation

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Minneapolis, MN 55447
USA
Tel: (763)553-0020
Fax: (763)553-0167
Email: naf@ataxia.org
Website: //www.ataxia.org

For a Complete Report

This is an abstract of a report from the National Organization for Rare Disorders, Inc.® (NORD). Cigna members can access the complete report by logging into myCigna.com. For non-Cigna members, a copy of the complete report can be obtained for a small fee by visiting the NORD website. The complete report contains additional information including symptoms, causes, affected population, related disorders, standard and investigational treatments (if available), and references from medical literature. For a full-text version of this topic, see http://www.rarediseases.org/search/rdblist.html.