Spinocerebellar ataxia type 1 (SCA1, MIM 164,400) and type 2 (SCA2, OMIM 183090) are autosomal dominant inherited diseases caused by an expansion of a highly polymorphic CAG repeat sequence within the coding region of the ATXN1 and ATXN2 gene, respectively. Here, ATXN1 is linked to spinocerebellar ataxia type 1.