MSH6 and neoplasm: Conversely, dMMR, which involves loss of function in DNA mismatch repair (MMR) genes such as MLH1, MSH2, MSH6, or PMS2, leads to high microsatellite instability (MSI-H) and increased tumor mutational burden Conversely, dMMR involves the loss of function in DNA mismatch repair genes, including MLH1, MSH2, MSH6, or PMS2, which in turn leads to increased microsatellite instability (MSI-H) and a rise in tumor mutational burden (15, 16).