DUX4 and facioscapulohumeral muscular dystrophy: Linking to genotype in FSHD, DUX4 is functional in primary satellite cell‐derived myoblasts from FSHD patients (Rickard et al, 2015) and detectable in myogenic cells during muscle regeneration in the D4Z4‐2.5 mouse, transgenic for a 2.5 D4Z4 unit region from an FSHD patient (Krom et al, 2013; Knopp et al, 2016).