Spinocerebellar ataxia type 1 (SCA1) is a subtype of type I autosomal dominant cerebellar ataxia (ADCA type I; see this term) characterized by dysarthria, writing difficulties, limb ataxia, and commonly nystagmus and saccadic abnormalities.
Prevalence is estimated to be 1-2 in 100,000 with significant geographical and ethnic variations.
The disease typically presents in the 4th decade (age range = 4-74 years). Ataxia gradually progresses and additional features may emerge including proprioceptive loss, hypoactive reflexes, ophthalmoparesis, and mild optic neuropathy. Initial presentation with blepharospasm, oromandibular dystonia, and retrocollis preceding ataxia has been reported. Cognition is relatively spared early on; however, executive dysfunction and impaired verbal memory may develop in later stages.
SCA1 is caused by CAG repeat expansions in the ATXN1 gene region on chromosome 6p23.
Prognosis is poor. In the late stages of the disease, usually 10 to 15 years following onset, bulbar dysfunction secondary to affection of lower medullary nuclei results in aspiration which is life-threatening.