Lynch syndrome (LS) is an autosomal dominant inherited disorder characterized by a germline pathogenic variant in mismatch repair (MMR) genes, including MLH1, MSH2, MSH6, PMS2, constitutional MLH1 hypermethylation, and a 3′ end truncating EPCAM deletion, with a population prevalence estimated at 1:279 [1]. The gene discussed is MLH1; the disease is Leigh syndrome.