MLH1 and neoplasm: LS is an autosomal dominant disorder caused by a pathogenic variant in one of the mismatch repair (MMR) genes, which include MLH1, MSH2 (EPCAM), MSH6 and PMS2. Loss of MMR function leads to the molecular phenotype of microsatellite instability (MSI) in tumours, which in turn drives carcinogenesis [4].