The nature of the muscle damage seen in the AAV model is quite distinct from that seen in FSHD, and DUX4 expression is in fact quite difficult to detect in biopsies of FSHD muscle, to the point where the most reliable readout of its expression in biopsies is its target-gene fingerprint (Yao et al., 2014). Here, DUX4 is linked to facioscapulohumeral muscular dystrophy.