DM1 is caused by an abnormal and unstable CTG nucleotide repeat in the 3′‐untranslated region of the dystrophia myotonica protein kinase (DMPK) gene, resulting in mutant mRNA foci composed of auto‐complementary hairpin structures, which bind and sequester RNA‐binding proteins from the muscleblind‐like (MBNL) family and abnormally stabilize the CUGBP Elav‐like family member 1 (CELF1) [3]. The gene discussed is DMPK; the disease is myotonic dystrophy type 1.