ATXN3 and Machado-Joseph disease: The CAG repeat length of the expanded ATXN3 is the major AAO factor of SCA3/MJD, but other polyQ-related genes (CACNA1A, TBP, KCN3, RAI1, HTT, ATN 1, ATXN1, 2, and 7) and gene interactions also have modifying effects on the AAO (Andresen et al., 2007; Tezenas Du Montcel et al., 2014; Chen et al., 2016a).