MLH1 and Lynch syndrome: Lynch syndrome is caused by mutations in DNA mismatch repair (MMR) genes, including MutS homolog 2 (MSH2; 38% of cases), MutL protein homolog 1 (MLH1; 59% of cases), and, to a lesser extent, MSH6 and PMS1 homolog 2, mismatch repair system component (PMS2) [29].