Abstract
BACKGROUND: Lynch syndrome is an autosomal dominant cancer predisposition syndrome classically caused by germline mutations of the mismatch repair genes MLH1, MSH2, MSH6 and PMS2. Epimutation (also called germline hypermethylation) of the MLH1 gene promoter explains rare Lynch syndrome cases. To date, there is no recommendation regarding the techniques to be used to detect this epimutation, nor any clinical criteria for when it should be investigated. We present a retrospective study involving 73 patients whose Lynch syndrome-related tumours exhibited MLH1 hypermethylation, and compare the methylation-sensitive high-resolution melting (MS-HRM) technology to the gold standard method of pyrosequencing, in view of performing routine MLH1 epimutation testing. We further ascertained epimutation of MLH1 by MS-HRM from a control group of 25 patients with known MMR germline pathogenic variant. RESULTS: MLH1 epimutation was detected in 6.8% of the comprehensive cohort (5/73). MS-HRM detected one positive case previously identified by pyrosequencing, along with two missed cases at very low allelic frequencies and allowed the identification of two additional positive patients, subsequently confirmed by pyrosequencing. No patients in the control group were found to have MLH1 epimutation. CONCLUSION: MS-HRM is a simple and sensitive real-time PCR method amenable to routinely detect MLH1 epimutation, with high sensitivity. Identifying patients with MLH1 epimutation is of paramount importance for patient care and genetic counselling. We further recommend performing this analysis systematically in discrete clinical settings herewith specified.