The mutated form of the ATXN3 gene, usually present in heterozygous MJD patients, exhibits an expanded CAG tract surpassing 60 CAG repeats (reviewed in [5]), which translates into an abnormally elongated polyglutamine protein that gains a neurotoxic function, is prone to aggregation, and interferes with cellular homeostasis, initiating a cascade of pathogenic events, including disturbance of important cellular systems, such as transcription, autophagy, and mitochondrial function [16]. Here, ATXN3 is linked to Spinocerebellar ataxia type 3.