The D4Z4-2.5 mouse contains four copies of an FSHD patient-derived sequence, each containing 2.5 repeats of the D4Z4 array, as well as the endogenous DUX4 polyadenylation signal on a permissive 4qA haplotype. This evidence concerns the gene DUX4 and facioscapulohumeral muscular dystrophy.