CACNA1A and autosomal dominant cerebellar ataxia: A total of 33 subjects formed the MGH psychometric cohort representing SCA genotypes SCA1, SCA2, SCA3, SCA6, SCA6/8, and SCA8, with the most common ataxias being SCA3 (54.5%), SCA2 (15.2%), and SCA6 (15.2%) (Table 1).