During postnatal brain development, MBNL-mediated binding promotes inclusion of exon-9 encoding γ2L (Weyn-Vanhentenryck et al., 2018); however, loss of MBNL results in exclusion of exon 9, possibly increasing expression of γ2S protein in adult brain of Mbnl2 KO mice and human DM1 (Charizanis et al., 2012; Otero et al., 2021; Degener et al., 2022). The gene discussed is MBNL2; the disease is myotonic dystrophy type 1.