DUX4 and facioscapulohumeral muscular dystrophy: Late-onset and progressive muscle pathology in FSHD patients is thought to be initiated by chronic, low, sporadic expression of DUX4 throughout one's lifetime (Haynes et al., 2018; Jones et al., 2012; Kowaljow et al., 2007; Rickard et al., 2015; Snider et al., 2010; Tassin et al., 2013).