HEY1 (hairy/enhancer-of-split related with YRPW motif 1) inhibits myogenesis by repressing myogenin and Mef2C [40], and its ∼13-fold activation by DUX4 in muscle cells could inhibit muscle differentiation in FSHD. This evidence concerns the gene MEF2C and facioscapulohumeral muscular dystrophy.