ATXN3 and Machado-Joseph disease: Dominant inheritance of mutant Ataxin-3 (ATX3) leads to neurodegenerative disorder Machado-Joseph disease (MJD1, also known as spinocerebellar ataxia type 3/SCA3), with abnormal expansion of its C terminal polyglutamine (polyQ) repeats up to 55–87 in comparison to 10–51 in healthy individuals.