MLH1 and Leigh syndrome: LS is characterized by heterozygous pathogenic mutation(s) in one or more (very rarely) of the DNA MMR genes with clinical relevance to CRC, chiefly MLH1, MSH2, MSH6 and PMS2, or large deletion in the 3′ terminus of the EPCAM (epithelial cell adhesion molecule) gene that silences MSH2 expression (17).