DUX4 and facioscapulohumeral muscular dystrophy: All forms of FSHD are caused by the loss of local epigenetic repression resulting in aberrantly increased expression of the DUX4 (double homeobox 4) retrogene from the chromosome 4q35 D4Z4 array (Himeda and Jones, 2019; Lemmers et al., 2010; Snider et al., 2010).