MBD3L5 and facioscapulohumeral muscular dystrophy: Compared to healthy control-engrafted mice, FSHD muscle biopsy-engrafted hosts displayed DUX4-fl expression associated with an upregulation of DUX4-target genes such as MBD3L5, TRIM43, and ZSCAN4. Using affected muscle biopsies from FSHD patients grafted into hindlimbs of NOD-Rag immunodeficient mice, a morpholino designed to target the polyadenylation signal of DUX4 mRNA efficiently reduced levels of the toxic DUX4-fl and its downstream genes MBD3L5 and ZSCAN4 [47].