The spinocerebellar ataxias (SCAs) are a clinically and genetically heterogeneous group of late onset neurodegenerative disorders. To date, seven different genes causing autosomal dominant SCA have been mapped: SCA1, SCA2, Machado-Joseph disease (MJD)/SCA3, SCA4, SCA5, SCA7 and dentatorubropallidoluysian atrophy (DRPLA). Expansions of an unstable trinucleotide CAG repeat cause three of these disorders: SCA1, MJ...