Lynch syndrome, or hereditary nonpolyposis CRC, is caused by an inherited alteration in one of the MMR genes (MLH1 (OMIM,120436), MSH2 (OMIM, 609309), MSH6 (OMIM, 600678), PMS2 (OMIM, 600259) and EPCAM (OMIM, 185535)). The gene discussed is MLH1; the disease is Lynch syndrome.