Contrary to DMD, resulting from the loss of dystrophin, Facioscapulohumeral muscular dystrophy (FSHD)43 is a gain of function disease caused by the inappropriate expression in skeletal muscle of DUX4, a gene normally only expressed in germline and early embryogenesis44–55. The gene discussed is DUX4; the disease is facioscapulohumeral muscular dystrophy.