Spinocerebellar ataxias (SCA1, 2, 3, 6, 7)
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A 35-year-old man with progressive gait ataxia and dysarthria has a father and two paternal aunts who developed similar symptoms at age 45. Genetic testing reveals a CAG repeat expansion in the ATXN2 gene.
AD; CAG (polyglutamine) repeat expansions
- SCA1: ATXN1, 39-82 repeats (normal <35)
- SCA2: ATXN2, 35-64 repeats (normal <32) - slow saccades
- SCA3 (Machado-Joseph): ATXN3, most common worldwide, 55-84 repeats - "bulging eyes"
- SCA6: CACNA1A, 21-33 repeats (normal <19) - pure cerebellar, later onset
- SCA7: ATXN7, 37-460 repeats - retinal degeneration (pigmentary)
Key Concept: Anticipation (earlier onset, more severe in successive generations) - especially paternal
- Slowly progressive ataxia (loss of balance and coordination). These are similar symptoms to being under the influence of alcohol.
- May include dysarthria, dysphagia
- Trinucleotide repeat testing.
- Brain MRI in SCA show atrophy of the cerebellum.
- Referral to physical and occupational therapy (for working on balance, as well as home accommodations to reduce the risk of falls)
Spino-cerebellar ataxia refers to degeneration of the spine and cerebellum that leads to ataxia. The cerebellum controls balance and coordination, and patients' movements may appear as if they are under the influence of alcohol.