MLH1 and Leigh syndrome: Also known as hereditary nonpolyposis colorectal cancer (HNPCC), LS is associated with germline mutations in one (or more) genes (MLH1, MSH2, MSH6, and PMS2) associated with mismatch repair (MMR), as well as with deletions in the EpCAM gene that lead to the loss of MSH2 expression (2, 3).