MLH1 and hereditary nonpolyposis colon cancer: The two most common syndromes are familial adenomatous polyposis (FAP) and hereditary non-polyposis colon cancer (HNPCC) that arise due to mutations in the APC (Adenomatous polyposis coli) gene and mismatch repair genes (MSH2, MLH1, MSH6 and PMS2), respectively.