The recognition that DUX4 is expressed in a variegated pattern in cultured FSHD muscle cells might explain some of the difficulty identifying a clear gene expression signature when testing either cultures of FSHD cells or biopsies from FSHD muscle where DUX4 might be expressed in only a minority of the nuclei. This evidence concerns the gene DUX4 and Facioscapulohumeral dystrophy.