This disorder is caused by an expanded CAG repeat in the ataxin-1 gene (ATXN1) at 6p23. It is an autosomal dominant disorder. Alleles with 39-44 or more CAG repeats are likely to be associated with symptoms.
A male bias and the phenomenon of anticipation have been demonstrated in this disorder as in spinocerebellar ataxia 7 (SCA7) (164500), in which affected offspring of males with SCA develop disease earlier and symptoms progress more rapidly than in offspring of females. This is often explained by the fact that males generally transmit a larger number of CAG repeats.
SCA7 (164500), also inherited in an autosomal dominant pattern and caused by expanded CAG repeats on chromosome 3, has many similar ocular and neurologic features.