Lynch Syndrome/Hereditary Non-polyposis Colorectal Cancer (HNPCC).

Lynch Syndrome (LS), also known as Hereditary Non-polyposis Colorectal Cancer (HNPCC), is the most common hereditary colorectal cancer syndrome and is estimated to account for 3-5% of CRC cases. LS is caused by mutations in DNA mismatch repair (MMR) genes which are inherited in an autosomal dominant pattern and are associated with accelerated development of cancers. Families affected with Lynch Syndrome typically contain multiple individuals affected with CRC and/or endometrial cancer, with many of the cases diagnosed at younger ages. Lifetime risk for colorectal and endometrial cancers approaches 70-80% and 40-60% respectively, in the absence of medical intervention. Individuals with Lynch Syndrome also have an increased risk for developing other cancers and variations in clinical presentation can make diagnosis difficult. Clinical genetic testing has identified mutations in the MMR genes MLH1, MSH2, MSH6, and PMS2 in many families with Lynch Syndrome. Colonoscopy at frequent intervals has been shown to be effective in reducing morbidity and mortality from Lynch-associated colorectal cancer.