DUX4 is expressed early in development and in very limited healthy adult tissues, leading to the hypothesis that FSHD may be caused, at least in part, by an autoimmune response to the aberrant skeletal muscle expression of DUX4 and its downstream targets [7] or impaired nonsense-mediated decay [35]. Here, DUX4 is linked to facioscapulohumeral muscular dystrophy.