ATXN1 and Machado-Joseph disease: The most frequent SCA worldwide are those caused by CAG repeat expansions, as SCA1 (in ATXN1), DRPLA (ATN1), SCA2 (ATXN2), Machado-Joseph disease (MJD)/ SCA3 (ATXN3), SCA6 (CACNA1A), SCA7 (ATXN7), and SCA17 (TBP), usually designated polyglutamine (polyQ) ataxias [7, 8].