DMPK and myotonic dystrophy type 1: DM1 is a multisystemic repeat expansion disorder with pathogenic effects brought about by an expanded (CTG⋅CAG)n repeat in the DMPK/DM1-AS gene pair.15, 16, 17 Because this repeat tends to show somatic and intergenerational instability, DM1 is one of the most variable genetic diseases.18, 19 An increase in repeat length, from 50 up to a few thousand triplets, correlates with more severe symptoms and an earlier age of onset.