The MMR genes MLH1, MSH2, MSH6, and PMS2 that were originally implicated in Lynch syndrome or hereditary nonpolyposis colorectal cancer (HNPCC), also play a role in breast and ovarian cancer since haploinsufficiency of MLH1, MSH2, and PMS2 appears to increase the risk for ovarian cancer and to a minor extent breast cancer 90, 91. Here, MRC1 is linked to hereditary nonpolyposis colon cancer.