Because tMALDUX4–VP16 but not tMALDUX4–ERD reduced Myod levels, it is likely that DUX4 activates genes involved in Myod repression rather than by directly repressing Myod transcription itself, providing insight into MYOD-dependent pathway suppression in FSHD (Celegato et al., 2006; Winokur et al., 2003b). Here, MYOD1 is linked to facioscapulohumeral muscular dystrophy.