DUX4 and Facioscapulohumeral dystrophy: The remaining 5% of FSHD patients (named FSHD2, OMIM #158901) do not show the D4Z4 contraction but carry a mutation in the epigenetic modifier genes SMCHD1 or DNMT3B [144,145], also leading to the hypomethylation of the D4Z4 array and to the aberrant expression of the DUX4 protein in the context of a permissive chromosome 4.