DUX4 and facioscapulohumeral muscular dystrophy: We show that FSHD myoblasts lack expression of both DUX4 itself and early DUX4 target genes, but exhibit clear up-regulation of late DUX4 target genes: indicating a historic, transient expression of DUX4. A transient DUX4 expression profile in satellite cell-derived myoblasts could explain the robust repression of PAX7 target genes seen in FSHD muscle biopsies (32,33).