DUX4 and facioscapulohumeral muscular dystrophy: In myotubes formed from FSHD patient-derived myoblasts or iPS cells, DUX4-FL expressed from its endogenous promoter is detectable by immunocytochemistry in only a small percentage of nuclei (Haynes et al., 2018; Himeda et al., 2014; Homma et al., 2015; Jones et al., 2012; Snider et al., 2010).