DUX4 and facioscapulohumeral muscular dystrophy: DUX4 target gene expression is detected in inflamed FSHD muscle biopsies but less robustly in non-inflamed muscle, implying that a systemic component may also activate DUX4 expression in vivo (Banerji and Zammit, 2021; Banerji, 2020; Banerji et al., 2020b).