In normal individuals, the length of the CAG repeat varies between 12 and 37 trinucleotides whereas in SCA3/MJD patients it varies between 49 to 86 repeat units which located near the carboxy-terminus of SCA3 gene (MJD1) on chromosome 14q32.1 [5], leading to the toxic translational product of polyQ-expanded ataxin-3. Here, ATXN3 is linked to Machado-Joseph disease.