DMPK and myotonic dystrophy type 1: In DM1 patient-derived cells and in a DM1 mouse model, the hairpin-like structures of the repeats can induce chromatin changes, such as CpG methylation, resulting in haploinsufficiency of DMPK and neighboring genes, or cause replication-fork stalling during DNA duplication, leading to cell stress [12,13,14].