Recently, mutations in human SMCHD1 have been shown to underlie type 1 and type 2 facioscapulohumeral muscular dystrophy (FSHD) (8, –, 10), with both types of the disease being dependent on the epigenetic silencing function of SMCHD1 at the D4Z4 repeat sequence. Here, SMCHD1 is linked to facioscapulohumeral muscular dystrophy.