MSH2 and Leigh syndrome: Lynch syndrome (LS) is an autosomal-dominant cancer syndrome caused by germline variants in 1 of 4 DNA mismatch repair (MMR) genes: mutL homologue 1 (MLH1), mutS homologue 2 (MSH2), mutS homologue 6 (MSH6), and much less frequently PMS1 homologue 2 (PMS2) [1,2].