PMS2 and Leigh syndrome: Lynch syndrome (LS) is an autosomal dominant predisposition toward neoplasia caused predominantly by germline mutations in one of four DNA mismatch repair (MMR) genes, including MLH1, MSH2, MSH6 and PMS2 [1], and rarely by EpCAM (epithelial cell adhesion molecule) deletions, which cause MSH2 promoter methylation and ultimately inactivation [2].