MBNL1 and myotonic dystrophy type 1: In contrast, deletion of MBNL1-exon 3 (Del-Linker) or deletion of MBNL1-exon 6 (Del-C′) dramatically reduced the efficiency of MBNL1 in rescuing splicing defects in both DM1 myoblasts and the HEK293T cells (Fig. 6A–B).