Therefore, we hypothesized that epigenetic changes, including DNA methylation at the 4q35 D4Z4 array and stability of epigenetic repression of the DUX4-fl mRNA, between individuals could account, at least in part, for the wide variability in clinical presentation of FSHD and similarly for the large number of asymptomatic individuals that fit the genetic criteria for FSHD1 [1,12,15,17,60,75,77]. The gene discussed is DUX4; the disease is facioscapulohumeral muscular dystrophy.