Several studies have shown that abnormal CTG repeat expansion promotes DNA hypermethylation and heterochromatin formation at the DM1 locus, making this locus less accessible to transcription factors and eventually causing downregulation of DMPK and its neighboring genes, SIX 5 and DMWD [47,49,50,51,52,53,90,91,92]. Here, DMPK is linked to myotonic dystrophy type 1.