Six of these mutations [specifically SCA1, SCA2, SCA3/Machado-Joseph disease (SCA3/MJD), SCA6, SCA7, and SCA17], result from pathogenic CAG trinucleotide repeat amplifications within coding sequences that produce extended polyglutamine tracts in the respective disease-associated proteins. The gene discussed is ATXN1; the disease is Machado-Joseph disease.