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Background: Methods to diagnose Hereditary Non Polyposis CRC (HNPCC/Lynch Syndrome) are described in this report. HNPCC is the most common CRC syndrome, characterized by defect in the DNA Mismatch repair system (MMR). We have recently introduced methods which enable us to discriminate between sporadic CRC and HNPCC. These methods are important tools to give the CRC patients the correct follow-up. Material and methods: The manuscript is based on the authors’ own experience and expertise in gene testing of HNPCC/Lynch syndrome and search in the database PubMed. Results and interpretation: The CRC-patient’s family history will indicate whether the disease may be caused by an inherited disease disposing gene variant. Tumour tissue from the patient is first analyzed by use of immunohistochemistry and microsatellite analysis. The results will indicate if there is a defect in the MMR system. In order to discriminate between sporadic CRC and HNPCC we analyze the tumour material for a specific BRAF mutation and for the presence of hypermethylation in the MMR gene MLH1. The BRAF mutation p.V600E and hypermethylation of the MLH1 promoter, which prevent expression of MLH1, identify sporadic microsatellite instable CRC. If HNPCC is still suspected, DNA and RNA from normal tissue (blood) are analyzed by methods like MLPA, HRM and sequencing. The identification of an abnormal gene variant in a MMR gene will confirm the HNPCC diagnosis.

MeSH