In summary, while the ratio of DMPK/MBNL1 and the levels of CNBP reflect muscle susceptibility to some degree in DM1 and DM2, our evidence of MBNL loss alone differentially affecting mouse muscles suggests that it is more complicated than this and highlights a possible role for yet-to-be-identified modifier genes. The gene discussed is CNBP; the disease is myotonic dystrophy type 1.