MLH1 and hereditary nonpolyposis colon cancer: Lynch syndrome (LS), previously known as hereditary nonpolyposis colorectal cancer (HNPCC), is an autosomal dominant disorder caused by pathogenic germline variants in one of the DNA mismatch repair (MMR) genes, MLH1, MSH2, MSH6, or PMS2, or by deletions in the EPCAM gene (1–3).