These results show that the length of the GGGGCC repeats in the C9orf72 gene influence the SCA3/MJD phenotypes, i.e., larger repeats may cause earlier onset, which indicates that the expansion of the GGGGCC repeats exerts a modifying effect on SCA3/MJD disease diversity. The gene discussed is C9orf72; the disease is Machado-Joseph disease.