DUX4 and facioscapulohumeral muscular dystrophy: Two types of FSHD exist (called FSHD1 and FSHD2); both are caused by genetic and epigenetic changes, converging in the misexpression of DUX4 in skeletal muscles.5 A copy of DUX4 is situated in every unit of the D4Z4 macrosatellite repeat array on chromosome 4q35.6-8 Normally, the D4Z4 repeat array consists of 8–100 units.