In humans, heterozygous pathogenic germline variants in four MMR genes (MLH1, MSH2, MSH6, and PMS2) or heterozygous germline deletions of the EPCAM gene are causative for Lynch syndrome (LS; also known as hereditary non-polyposis colorectal cancer, HNPCC). This evidence concerns the gene MLH1 and hereditary nonpolyposis colon cancer.