Although decreased gene expression at the DM1 locus is not sufficient to explain the complex DM1 phenotype, downregulation of DMPK, SIX5 and DMWD genes by epigenic changes in DM1 could participate in some clinical features such as DM1 cataracts, muscle defects or cardiac conduction defects. The gene discussed is DMPK; the disease is myotonic dystrophy type 1.