The search for successful FSHD therapeutics has been challenging due to the sporadic and variable nature of disease pathogenesis in individuals and the difficulties of detecting low levels of DUX4 RNA and protein, as DUX4 is expressed sporadically in ~ 0.1%–1% of cells in patient myoblast samples [5, 10, 65]. Here, DUX4 is linked to Facioscapulohumeral dystrophy.