DUX4 and Facioscapulohumeral dystrophy: In fact, in FSHD muscle, DUX4 mRNA is expressed in 0.8 ÷ 1 out of 1000 nuclei [28], and the protein in 1 out of 1000 ÷ 2000 nuclei [29], thus associating the disease with sporadic expression of DUX4.