DUX4 and facioscapulohumeral muscular dystrophy: Our observations are consistent with those made in primary FSHD myoblasts, where both DUX4 and its transcriptional activity can be detected in proliferating and differentiating human myoblasts (Dixit et al., 2007; Jones et al., 2012; Kowaljow et al., 2007; Rickard et al., 2015; Snider et al., 2010).