ATXN2 and Parkinson disease: Ataxin-2 (Atx2), the disease protein of SCA2, which has been also linked to ALS and PD, regulates RNA metabolism and mRNA translation, whereas MJD protein ataxin-3 (Atx3) is a deubiquitinase, which trims ubiquitin chains on various target proteins, thereby influencing their stability and function.