Strikingly, increased DUX4 activity was also shown in DPED patient-derived fibroblasts transdifferentiated into the myogenic lineage (Lemmers et al., 2021), further strengthening the hypothesis that DUX4c buffers DUX4 function in FSHD. Here, DUX4L9 is linked to facioscapulohumeral muscular dystrophy.