The homozygous (Hb-SS) and the heterozygotous forms (Hb-SS and HbSA or SCT, respectively) of SCA affect 1 in 400 to 600 and 1 in 12 to 14 Afro-American and Caribbean people, respectively [21]. This evidence concerns the gene GSTM1 and autosomal dominant cerebellar ataxia.