The Clinical Characterization Of HNPCC Families From Northern Chinese Population And The Role Of HMLH3 And HEXO1 Germline Mutation In HNPCC

One of the important strategies in the prevention and cure of HNPCC is to find the proband and give the family genetic counseling.The clinical phenotypes are the most important indication to find HNPCC.Although Chinese criteria for HNPCC was established in 2003,we still need to know about the clinical characterization more widely.The purpose of collecting HNPCC families from northern Chinese population is to know more deeply about the clinical characterization of HNPCC families from northern Chinese population. Most patients of HNPCC family had the germline mutation of hMLH1 or hMSH2.Although MMR germline mutation commonly seen in HNPCC families,it still could not be found in some families.These families may be the HNPCC families or the suspected HNPCC families,and the MSI status of the tumours may be high.So it was supposed that there may be other pathogenetic genes.Another purpose of this study is to elucidate the role of the newly cloned hMLH3 and hEXO1 genes in these HNPCC families. Materials and methods 1. 69 families were analyzed by grouping and comparing with the sporadic colorectal cancer(SCRC).Among the 69 families,33 families fulfilled Amsterdam CriteriaⅡ(ACⅡ),24 families fulfilled Japan Criteria(JC) and 12 families fulfilled Bethesda Guideline(BG) 1 ～3 items.To investigate the numbers of these families,age of the first diagnosed cancer,sex distribution,and the characterization of tumour distribution, multiple colorectal cancers and tumor spectrum. 2.The second part of materials were 16 HNPCC families from the 69 families collected before. Among the 16 families,6 families fulfilled Amsterdam CriteriaⅡ(AC Ⅱ),7 families fulfilled Japan Criteria(JC) and 3 families fulfilled Bethesda Guideline(BG) 3～4 items,3 families fulfilled the BG items 3 or 4.All these fmilies had no pathogenetic germline mutations in hMLH1,hMSH2 and hMSH6.The germline mutations of hMLH3 and hEXO1 were detected by directly sequencing.And the methodology of molecule genetics and bioinformatics were used to analyse the data. Results 1. Among the 277 cancer patients,there were 213 colorectal cancer patients and 64 extra colorectal cancer patients.The median age of HNPCC cancer group was 46 years old,and the peak age of the HNPCC cancer group was between 40 to 49 years old.There were 65 families transmiting vertically more than two generations,accounting for 94.2% of all families.Patients whose cancers located proximal to the splenic flexure among the HNPCC group accounted for 62% of all colorectal cancer patients.There were 33 synchronous or metachronous multiple colorectal cancer patients,accounting for 11.9% of all cancer patients.There were 64 extra colorectal cancer patients,accounting for 23.1% of all cancer patients.Stomach and endometrium were the two most predominant locus for extra colorectal cancers. 2.10 kinds and 28 hMLH3 germline mutations were found.The detection rate was 69%.5 of the mutations were newly found;And the variants of C2615G,G2221T,A2533G and C2152T were not found in the normal controls,suggesting that they were associated with the disease.The C2615G was nonsense mutation,but it did not cosegregate with the family's disease. G2221T,A2533G and C2152T were missense mutations;Two LOHs were found in two families's tumour tissuses,and the mutation alleles were losed in these two LOHs.3.12 kinds and 52 hEXO1 germline mutations were found. The detection rate was 50%.9 of the mutations were newly found;All the four putative pathogenetic mutations were also found in the normal controls,and did not cosegregate with the diaease. Conclusions 1. Compared with the SCRC,HNPCC patients had the characteristics of early onsetting,having high incidence of extra colorectal cancer,wide tumor spectrum,frequent multiple colorectal cancers and the predominance of right-sided colorectal cancers.But there were some differences between Chinese HNPCC familiese and that of the western countries. 2. To our knowledge,it is the first report to elucidate the role of hMLH3 and hEXO1 germline mutations in HNPCC. 3. 5 new hMLH3 germline mutations were found;There was homogeny of hMLH3 variants between the northern Chinese population and the western population;The variation frequency of hMLH3 in Chinese population might be higher than that of western population. 4. hMLH3 may be one of the pathogenetic genes of the suspected HNPCC families from northern Chinese population.And hMLH3 may play a role in the pathogenesis of some individuals of the HNPCC family.The loss of the mutation allele of the target site may be the pathogenetic mode of hMLH3. 5. 5 new hEXO1 germline mutations were found;There was homogeny of hEXO1 variants between the northern Chinese population and the western population,but the variation frequencies were different between them. 6. No evidence was found between the germline variation of hEXO1 and the HNPCC families or the suspected HNPCC families,but the pathogenicity of hEXO1 could not be ruled out.