To address this issue, we generated and characterized a highly reproducible series of phenotypic FSHD-like transgenic mouse models varying in severity and pathogenic progression based on differing levels of mosaic expression of the pathogenic DUX4-fl mRNA isoform of human DUX4 in adult murine skeletal muscle. The gene discussed is DUX4; the disease is facioscapulohumeral muscular dystrophy.