Our group proved the “MBNL loss of function” hypothesis by creating knockout (KO) mouse lines of three MBNL family members (Mbnl1, Mbnl2 and Mbnl3): While Mbnl1 KO mice (Mbnl1ΔE3/ΔE3) recapitulate myotonia and typical DM muscle pathology (Kanadia et al., 2003), Mbnl2 constitutive KO mice (Mbnl2 KO, Mbnl2ΔE2/ΔE2) exhibit REM sleep misregulation and cognitive dysfunction (Charizanis et al., 2012). The gene discussed is MBNL1; the disease is Myotonia.