DUX4 mRNA is typically detected in a small proportion (0.5–3.8%) of FSHD myoblasts in vitro (Jiang et al., 2020; van den Heuvel et al., 2019; Banerji and Zammit, 2019), and protein expression is similarly rare (0.1%) (Snider et al., 2010). The gene discussed is DUX4; the disease is facioscapulohumeral muscular dystrophy.