DUX4 and facioscapulohumeral muscular dystrophy: Given that DUX4 has evolved independently in primates,6,21 generation of non-primate animal models that fully recapitulate the disease remains challenging, although the mouse DUX4 homologue, Dux, does seem to have largely overlapping functions.22,23 Transgenic mouse models overexpressing DUX4 exhibit some aspects of FSHD muscle pathophysiology; nevertheless, species differences exist.24 Cellular models using primary25,26 or immortalized myoblasts27,28 and embryonic stem cell-derived skeletal muscle cells29 have contributed to our understanding of DUX4 regulation in muscle tissue.