MSH6 and Leigh syndrome: The diagnosis of LS is based on the identification of germline mutations in the DNA mismatch repair (MMR) genes MutL homolog 1 (MLH1), MutS homolog 2 (MSH2), MutS homolog 6 (MSH6), PMS1 homolog 2 (PMS2), and/or epithelial cell adhesion molecule (EPCAM).