DUX4 and facioscapulohumeral muscular dystrophy: Fat fraction was also associated with DUX4 signature expression, with DUX4 signature levels being increased in FatPOS FSHD biopsies and being significantly more often detected in FatPOS [9/10 (90%)] compared to FatNEG FSHD biopsies [11/29 (40%)] (Fig. 4b).