The remaining 20/39 (51.3%) FSHD biopsies showed a DUX4 signature level similar to the controls (average cumulative normalized read count of 5.4, range 0–15.4 reads) and were labeled DUX4-negative (DUX4NEG) (Fig. 2a and Supplementary Fig. S2). Here, DUX4 is linked to Facioscapulohumeral dystrophy.