HNPCC is caused by genomic mutations in DNA mismatch repair genes (MMR), namely MLH1, MSH2, MSH6, PMS2, and EPCAM. A non-hereditary, acquired process of hypermethylation of the MLH1 promoter can also lead to silencing of MLH1 protein expression. This evidence concerns the gene MRC1 and hereditary nonpolyposis colon cancer.