MRC1 and Leigh syndrome: The main cause of LS is a germline mutation in one of the four mismatch repair (MMR) genes (MLH1, MSH2, MSH6, and PMS2), and a large fragment deletion of the epithelial cell adhesion molecule (EPCAM) gene which leads to methylation of the promoter of MSH2 and results in gene silencing of MSH2 can also cause LS (3).