DUX4 and facioscapulohumeral muscular dystrophy: Instead, all PACS PMOs were effective in down-regulating mRNA levels of DUX4 and three examined genes, which have been identified to be predominantly up-regulated in FSHD cells and muscle biopsies (34,35), by 80–90% for DUX4, 65–85% for PRAMEF2, 53–68% for TRIM43 and 57–81% for ZSCAN4 (Fig. 1A–D).