MLH1 and cancer: CGI hypermethylation at gene promoter regions can result in transcriptional gene silencing (“epimutations”), and examples of cancer driver genes inactivated by epimutation include MLH1 [mutL homolog 1] which can cause microsatellite instability [MSI] and CDKN2A [cyclin-dependent kinase inhibitor 2A] resulting in defective cell cycle regulation [1–3].