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Spinocerebellar Ataxia Type 1.

Authors

Opal P1, Ashizawa T2.

Source

GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2018.
1998 Oct 1 [updated 2017 Jun 22].

Author information

1
Director, Ataxia Clinic, Department of Neurology, Northwestern Feinberg School of Medicine, Chicago, Illinois
2
Director, Neuroscience Research Program, Houston Methodist Research Institute, Houston, Texas

Excerpt

CLINICAL CHARACTERISTICS:

Spinocerebellar ataxia type 1 (SCA1) is characterized by progressive cerebellar ataxia, dysarthria, and eventual deterioration of bulbar functions. Early in the disease, affected individuals may have gait disturbance, slurred speech, difficulty with balance, brisk deep tendon reflexes, hypermetric saccades, nystagmus, and mild dysphagia. Later signs include slowing of saccadic velocity, development of up-gaze palsy, dysmetria, dysdiadochokinesia, and hypotonia. In advanced stages, muscle atrophy, decreased deep tendon reflexes, loss of proprioception, cognitive impairment (e.g., frontal executive dysfunction, impaired verbal memory), chorea, dystonia, and bulbar dysfunction are seen. Onset is typically in the third or fourth decade, although childhood onset and late-adult onset have been reported. Those with onset after age 60 years may manifest a pure cerebellar phenotype. Interval from onset to death varies from ten to 30 years; individuals with juvenile onset show more rapid progression and more severe disease. Anticipation is observed. An axonal sensory neuropathy detected by electrophysiologic testing is common; brain imaging typically shows cerebellar and brain stem atrophy.

DIAGNOSIS/TESTING:

The diagnosis of SCA1 rests on the result of molecular genetic testing to detect an abnormal CAG trinucleotide expansion in ATXN1. Affected individuals have alleles with 39 or more CAG trinucleotide repeats. Such testing detects 100% of cases.

MANAGEMENT:

Treatment of manifestations: Canes and walkers to help prevent falls; modifexomiication of the home with grab bars, raised toilet seats, and ramps for motorized chairs; speech therapy and communication devices for dysarthria; weighted eating utensils and dressing hooks to help maintain independence. Intensive rehabilitation (coordinative physiotherapy) may be beneficial. Weight control is important because obesity can exacerbate difficulties with ambulation and mobility. Video esophagram can help to identify the consistency of food least likely to trigger aspiration and feeding devices may be indicated when dysphagia becomes troublesome. Prevention of secondary complications: Medications may help symptomatic secondary problems such as spasticity, bladder urgency, depression, and pain; vitamin supplements are recommended if caloric intake is reduced. Surveillance: Neurologic evaluation every three to six months. Agents/circumstances to avoid: Alcohol, medications known to cause nerve damage (e.g., isoniazid). Circumstances that could lead to physical harm, such as operating machinery or climbing to great heights, should be avoided.

GENETIC COUNSELING:

SCA1 is inherited in an autosomal dominant manner. Offspring of an affected individual have a 50% chance of inheriting the expanded allele. Prenatal diagnosis for at-risk pregnancies is possible if the diagnosis has been confirmed by molecular genetic testing in an affected relative; however, requests for prenatal testing of typically adult-onset diseases are not common.

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