DUX4 expression in FSHD patient-derived, multi-nucleated myotubes also displays a gradient across myonuclei, suggesting that DUX4 may ‘diffuse’ either actively or passively from an origin nucleus to neighboring nuclei, bypassing their need to wait for the rare DUX4 burst (Rickard et al., 2015; Tassin et al., 2013). Here, DUX4 is linked to facioscapulohumeral muscular dystrophy.