In addition to the more common genetic mutation events described above, mutations in mismatch repair (MMR) genes such as MLH1, MSH2, MSH6 and PMS2 form an important basis for the diagnosis of Lynch syndrome, Around 50% of cases of Lynch syndrome are diagnosed at the onset of EC and OC (78, 79), mainly endometrioid and clear cell carcinoma (80–82). The gene discussed is MLH1; the disease is Lynch syndrome.