CACNA1A and Huntington disease: 1 ~ 3/100 000 Europeans have autosomal dominant cerebellar ataxias (ADCAs) [7], such as SCA1, SCA2, SCA3/MJD, SCA6, SCA7 and SCA17, while 1.6/100 000 individuals have SBMA [8] and 5 ~ 7/100 000 white people suffered HD [9].