Assessment of pathogenicity criteria for constitutional missense mutationsof the hereditary nonpolyposis colorectal cancer genes MLH1 and MSH2

To determine the role played by MLH1 and MSH2 missense variants in cancer s usceptibility, we have investigated the following genetic and biological ch aracteristics associated with six MLH1 and four MSH2 missense changes ident ified in Italian hereditary nonpolyposis colorectal cancer (HNPCC) families : co-segregation with disease phenotype and/or bona fide pathogenetic mutat ions; presence of the variant in healthy control subjects; evolutionary con servation of the involved aminoacid and type of aminoacid change; and prese nce/absence of microsatellite instability (MSI) in tumour DNA, Overall, nin e variants did not fulfil greater than or equal to 2 pathogenicity criteria . MSI was investigated in tumour samples from carriers of nine different mi ssense mutations. Only 3/9 variants were associated with MSI in tumour DNA, In addition, four variants were not present in affected pedigree members, and five variants were observed in the control population. Based upon these results, we conclude that most MLH1 and MSH2 missense changes are unlikely to act as major causative factors in colorectal cancer susceptibility and development.