DUX4 and Facioscapulohumeral dystrophy: Recently, we and others showed that facioscapulohumeral dystrophy (FSHD), a muscular dystrophy predominantly affecting facial and upper extremity muscles [7], is caused by D4Z4 repeat contraction-dependent (FSHD1) or –independent (FSHD2) chromatin relaxation in somatic tissues and low levels of DUX4 mRNA expression in skeletal muscle [5], [8]–[10].