The mechanism of pathology is different in polyglutamine ataxias. Humans with spinocerebellar Ataxia 1 (SCA1), spinocerebellar ataxia 2 (SCA2), and spinocerebellar ataxia 3 (SCA3), and their corresponding mouse models, have large numbers of unstable polyglutamine (polyQ, CAG) repeats in the Ataxin-1 [23,24], Ataxin-2 [25], and Ataxin-3 [26-28] proteins, respectively. The gene discussed is ATXN2; the disease is spinocerebellar ataxia type 2.