DUX4 and facioscapulohumeral muscular dystrophy: Although the DUX4 DMEs are known to be active in human and murine myogenic cells (Himeda et al., 2014), we did not see a strong X-gal signal in whole skeletal muscle mounts, which is consistent with rare expression of DUX4 in FSHD skeletal muscle (Jones et al., 2012; Tassin et al., 2013).