ATXN3 and Machado-Joseph disease: Machado-Joseph Disease (MJD) or spinocerebellar ataxia type 3 (SCA3) is a neurodegenerative disease caused by Cytosine-Adenine-Guanine (CAG) triplet repeat expansions which result in an expanded polyglutamine tract in the ataxin-3 (ATX3) protein [51].