In 1993, a group of investigators led by Huda Zoghbi and Harry Orr identified a heterozygous expansion of CAG repeat that encodes a polyglutamine (polyQ) tract in a novel gene, ATXN1, in a family with an autosomal-dominant cerebellar ataxia, now known as spinocerebellar ataxia type 1 (SCA1) (4). This evidence concerns the gene ATXN1 and autosomal dominant cerebellar ataxia.