DUX4 and facioscapulohumeral muscular dystrophy: The deletion of a large region of the D4Z4 repeat array to 1–10 units [3], prevalent in the majority of FSHD patients (classified as FSHD1), induces chromatin relaxation and extensive hypomethylation, leading to transcription of DUX4 from the most distal D4Z4 repeat [3].