MJD is caused by a mutation in the exon 10 of the MJD1/ATXN3 gene, located at the chromosome 14, which leads to an extension of the trinucleotide cytosine-adenine-guanine (CAG), coding for the glutamine aminoacid, resulting in a polyglutamine tract expansion in the ataxin-3 protein3–5. This evidence concerns the gene ATXN3 and Spinocerebellar ataxia type 3.