Since the initial reports on disease-predisposing mutations in the mismatch-repair (MMR) genes MLH1 [MIM:120436], MSH2 [MIM:609309] and MSH6 [MIM:600678] in the early 1990’ies, a large number of studies have contributed to the establishment of the molecular map of Lynch syndrome with over 3,072 unique genetic MMR gene variants identified. This evidence concerns the gene MLH1 and Lynch syndrome.