Genes involved in polyQ SCAs are ataxin 1 (ATXN1; SCA1), ataxin 2 (ATXN2; SCA2), ataxin 3 (ATXN3; MJD/SCA3), calcium voltage-gated channel subunit α1A (CACNA1A; SCA6), ataxin 7 (ATXN7; SCA7), TATA-box binding protein (TBP; SCA17) and atrophin 1 (ATN1; DRPLA) (Table 1). The gene discussed is ATXN3; the disease is Machado-Joseph disease.