In all forms of FSHD, expression of the pathogenic DUX4 mRNA full-length isoform (DUX4-fl) is induced upon epigenetic de-repression of the 4q35 D4Z4 locus brought about by genetic mutations (de Greef et al., 2009; Jones et al., 2015; Snider et al., 2010; van Overveld et al., 2003). This evidence concerns the gene DUX4 and facioscapulohumeral muscular dystrophy.