[The first molecular analysis of a Hungarian HNPCC family: a novel MSH2 germline mutation].

Background: Hereditary nonpolyposis colorectal cancer is an inherited disease characterized by onset at an early age, an excess of synchronous and metachronous large bowel tumors and a variety of extracolorectal malignancies. Basal and squamous cell carcinomas of the skin are not customarily included in the tumor spectrum of the syndrome. The disease is caused by a germline mutation in one of the DNA mismatch repair genes, most commonly MSH2 or MLH1, and typically presents with microsatellite instability and frequent loss of mismatch repair protein expression in the tumor tissue.

Patient: The case of a 62-year old woman who had a history of colon cancer at the age of 46 years, endometrial cancer at the age of 56 years, baso-squamous, and squamous cell cancer of the face at the ages of 53, 54, 62 and 58 years, respectively, and rectal cancer at 60 is reported. Her family fulfills the Amsterdam criteria for the diagnosis of hereditary nonpolyposis colorectal cancer. The baso-squamous cell, the squamous cell, the endometrial and the rectal cancers were assessed for the microsatellite instability status and the expression of the MSH2 and MLH1 mismatch repair proteins, and the p53 tumor suppressor protein by immunohistochemistry. Mutational screening using an automated capillary DNA sequencer was performed by the direct genomic sequencing of 17 fragments of the MSH2 gene, which covers promoter, all exons and flanking intronic regions.

Results: All cancers displayed microsatellite instability and were positive for the p53 protein. The immunohistochemical staining in the baso-squamous cell, the squamous cell, the rectal and endometrial cancers were negative for MSH2 and positive for MLH1 proteins. DNA sequencing analysis revealed a mutation c.2292G > A in exon 14 of the MSH2 gene, which is altering the 764. amino acid, the tryptophan to STOP codon (p.W764X). Thus the MSH2 protein is presumably truncated by 171 aminoacids.

Conclusion: To the best of authors' knowledge, this is the first molecular characterization of a Hungarian hereditary nonpolyposis colorectal cancer family. According to the Human Mutation Database and International Collaborative Group of HNPCC Database, this mutation is novel, has not been reported previously. Cutaneous baso-squamous and squamous cell cancers may present as part of the HNPCC phenotype. Detection of the loss of mismatch repair protein expression and mismatch repair gene mutation mapping, represents a significant improvement of the diagnosis of this syndrome in Hungary. These examinations identify the mutation carriers who are at an increased risk of developing cancers.