Techniques and strategies for identification of mutations predisposing to hereditary nonpolyposis colorectal cancer syndrome (HNPCC syndrome)

The strategy for identification of germline mutations in DNA mismatch repair (MMR) genes predisposing to HNPCC syndrome includes several factors, i.e., age and anamnestic criteria (Amsterdam criteria) as well as molecular criteria (microsatellite instability [MIN] and disease associated gene mutations). In young patients under 35 years of age the molecular criterion MIN divides our patients into those with marked instabilities (thus probable HNPCC patients with MMR gene mutations) and others without any instability. However, by means of Amsterdam criteria and MIN findings it is also possible to detect elder patients who are likely to be true HNPCC patients. The missense mutation (A > G transition) in base 67 of exon 8 of the MMR gene hMLH1 has been described before. It probably represents a mere polymorphism rather than a true mutation since it can be found in healthy individuals and in HNPCC patients with desease associated mutations of MMR genes. The meaning of the T > C transition at -6 SA site of exon 13 of hMSH2, which we found in two patients, is discussed controversely in the literature. This transition located at the intron/exon border may have a pathogenetic effect by inducing alternative splicing. However, this has to be confirmed by additional molecular tests such as the protein truncation test (PTT).