MRC1 and hereditary nonpolyposis colon cancer: Lynch syndrome, formerly known as hereditary non-polyposis colorectal cancer, is an autosomal dominant disorder caused by germline mutations in one of the DNA mismatch repair (MMR) genes MLH1, MSH2, MSH6, and PMS2, or EPCAM. MMR gene mutation carriers are at increased risk of developing cancers of the colorectum and endometrium, as well as cancers of the ovary, kidney, pancreas, stomach, and urinary bladder.