Spinocerebellar Ataxia (SCA): Genetic Causes and Subtypes
SCAs are hereditary neurodegenerative disorders caused by specific gene mutations, most commonly CAG repeat expansions (polyglutamine diseases).
Major Subtypes
| Type | Gene | Mutation | Key Features |
|---|---|---|---|
| SCA1 | ATXN1 | CAG repeat | Ataxia, dysarthria, neuropathy |
| SCA2 | ATXN2 | CAG repeat | Slow saccades, neuropathy |
| SCA3 (MJD) | ATXN3 | CAG repeat | Ophthalmoplegia, spasticity, dystonia |
| SCA6 | CACNA1A | CAG repeat | Pure cerebellar ataxia, late onset |
| SCA7 | ATXN7 | CAG repeat | Macular degeneration + ataxia |
| SCA8 | ATXN8OS | CTG repeat | Variable, often milder |
Inheritance
Most are autosomal dominant; some (e.g., SCA2 recessive variants) are recessive. Genetic testing confirms diagnosis, enables counseling, and guides prognosis.
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