ATXN3 and cerebellar ataxia: Machado-Joseph disease (MJD), or spinocerebellar ataxia type 3, is the most common dominantly inherited ataxia worldwide and it is caused by a polyglutamine (polyQ) expansion in ataxin-3 (Atx3), a polyubiquitin-binding protein [1] with ubiquitin protease activity [2].