MBNL1 and myotonic dystrophy type 1: The primary cause of DM1 is the gain‐of‐function of toxic transcripts carrying expanded noncoding CUG repeats that aggregate into foci in nuclei, sequestering RNA‐binding protein Muscleblind‐like 1 (MBNL1) (Fardaei et al, 2001, 2002).