DUX4 and facioscapulohumeral muscular dystrophy: DUX4 expression and each of the three DUX4 target gene expression signatures derived from ectopic DUX4 expression in myogenic cells were perfect classifiers of FSHD status in LCLs (FSHD vs control: Wilcoxon P < 3.9 × 10−4, AUC = 1, n = 18 (9 FSHD, 9 controls), Fig. 2A–D).