This DUX4 expression is also observed in the remaining 5% of FSHD patients (termed FSHD2) who, unlike FSHD1 patients, present a demethylation of the D4Z4 array of both alleles of chromosomes 4 and 10 [15,16] due to mutations in epigenetic repressors including the structural maintenance chromosome flexible hinge domain containing 1 (SMCHD1) [17] or the DNA methyltrasferase 3B (DNMT3B) genes [18]. This evidence concerns the gene SMCHD1 and facioscapulohumeral muscular dystrophy.