Therefore, it is getting clearer that the number of D4Z4 repeats at 4q35 or the DUX4 misexpression do not per se fully characterize FSHD, and increasing efforts should be implemented to elucidate additional molecular or clinical features which could help patient stratification and promote the understanding of disease pathogenesis. Here, DUX4 is linked to facioscapulohumeral muscular dystrophy.