Pathogenic variants in MLH1, MSH2, MSH6 and PMS2 Mismatch Repair (MMR) genes (OMIM: 120436, 609309, 600678 and 600259) are causative of Lynch Syndrome (LS), an autosomal dominant condition that confers elevated risk of developing colorectal cancer (CRC), endometrial cancer (EC) and several other types of cancer. The gene discussed is MSH2; the disease is Leigh syndrome.