DUX4 and facioscapulohumeral muscular dystrophy: Thus, in FSHD, the D4Z4 array exhibits a less repressed epigenetic state, and the DUX4 gene can be stochastically activated in rare myoblasts or myonuclei by ‘available’ regulatory elements (e.g. DUX4 myogenic enhancer 1 and 2) [81] and transcription factors such as Sp1, p53, WDR5 and SIX family members [24, 82–84].