DUX4 and facioscapulohumeral muscular dystrophy: Overall, these dose-dependent DUX4-fl FSHD-like phenotypic mouse models strongly support the DUX4 misexpression model for levels of DUX4 expression mediating levels of FSHD pathology [17, 20] and provide a useful and highly flexible tool for performing FSHD preclinical testing of therapeutic approaches targeting DUX4-fl mRNA and protein.