In addition to the DUX4 ORF within each unit of the tandem array, there is a DUX4-like sequence (named DUX4c) near FRG2. Preliminary data suggest that DUX4c may be expressed in FSHD samples [14], and it has been shown that its ectopic overexpression interferes with myogenic regulators and abolishes myoblast differentiation [15]. Here, DUX4L9 is linked to facioscapulohumeral muscular dystrophy.