A missense germline mutation in exon 7 of the MSH2 gene in a HNPCC family from center-Italy

Introduction: Hereditary Non-Polyposis Colorectal Cancer (HNPCC) is an autosomal dominant inherited disease predisposing to the development of colorectal cancers and several other malignancies (endometrium, ovaries, stomach, small bowel, hepatobiliary and urinary tract). HNPCC is caused by germline mutations in any of the MisMatch Repair (MMR) genes. Mutations in MLH1 and MSH2 account for almost 90% of all identified ones. About 15% of mutations identified in MSH2 are missense ones. Patients and methods: We studied one family, fulfilling Amsterdam II criteria, referred to our Center for genetic counselling. The proband, and some of her relatives, have been investigated for microsatellite instability (MSI), immunohistochemical MMR protein staining and by direct sequencing and Multiplex Ligation-dependent Probe Amplification (MLPA). Results: All patients carried the same novel MSH2 germline missense mutation (R359S) in exon 7, which determines the substitution of an Arginine, which is a basic amino acid, with a polar Serine residue (R359S). The mutation was associated with lack of expression of MSH2 protein and high microsatellite instability in tumour tissues. The same mutation has been detected in one healthy relative. Conclusions: The mutation here reported shows a high correlation with phenotype. The mutation is located in an evolutionary conserved domain. Taken together, our findings suggest evidence that the amino acid substitution can be interpreted as pathogenetic.