Using combined in situ hybridization and immunohistochemistry, we observed that the majority of RNA foci co-localized with MBNL1 and MBNL2 in heart, muscle and brain from human DM1 fetal samples and from DMSXL embryonic and postnatal samples (Fig 4 and data not shown). Here, MBNL1 is linked to myotonic dystrophy type 1.