DUX4 and facioscapulohumeral muscular dystrophy: In cultures of myogenic cells or iPS cells from FSHD patients, DUX4-FL expression from its endogenous promoter is detectable by immunocytochemistry in only a small percentage of nuclei in differentiated myotubes (Haynes et al., 2017; Himeda et al., 2014; Homma et al., 2015; Jones et al., 2012; Snider et al., 2010).