A Case of Spinocerebellar Ataxia Type 6

ABSTRACT

Spinocerebellar ataxia (SCA) type 6 was recently identified as a form of autosomal dominant cerebellar ataxia associated with the small expansion of CAG repeats. The number of CAG repeats varies from 4 to 18 on normal alleles and 21 to 30 on the SCA type 6 chromosome. SCA type 6 is characterized by cerebellar ataxia and dysarthria associated with cerebellar atrophy. Many patients with SCA type 6 have horizontal gaze-evoked nystagmus, and some have a limitation of eye movements on the upward and lateral gaze. A 59-year-old woman without any noticeable family history presented with slowly progressive cerebellar ataxia, dysarthria, and oscillopsia. She had vertical nystagmus and horizontal gaze-evoked nystagmus. Brain MRI revealed a moderate cerebellar atrophy, most prominent in the vermis, with relative sparing of the brain stem. A genomic polymerase chain reaction (PCR) analysis showed 24 CAG repeats at the SCA6 locus compatible with the sporadic SCA type 6.