DUX4 and facioscapulohumeral muscular dystrophy: Our strategy for developing FSHD mouse models involved creating AAV vectors expressing only the DUX4 ORF (exon 1) [8], or the DUX4 ORF containing the natural DUX4 3’ UTR (exons 2 and 3 with the DUX4 poly A signal) and intervening introns (an FSHD-permissive locus).