MLH1 and Lynch syndrome: Lynch syndrome is caused by germline mutations in one of several mismatch repair genes, MLH1, MSH2, and MSH6, and more rarely, PMS2. In addition to an up to 85% lifetime risk of colorectal cancer, Lynch syndrome confers a 40% lifetime risk of endometrial cancer, and 10% ovarian cancer as well as elevated risks of gastric and hepatobiliary cancers.