Another challenge to consider is that DUX4 expression is very rare in skeletal muscle, only detected in 1/1000 or 1/200 nuclei in FSHD myoblasts and myotubes, respectively (Snider et al., 2010; Tassin et al., 2013). The gene discussed is DUX4; the disease is facioscapulohumeral muscular dystrophy.