中国人遗传性非腺瘤病性结直肠癌家系hMSH2和hMLH1基因突变分析

目的 分析符合不同临床标准的中国遗传性非腺瘤病性结直肠癌(HNPCC)家系hMSH2和hMLH1基因种系突变状况,评价不同临床标准预示突变检测的敏感性。方法应用DNA直接测序对24个符合Amsterdam标准、15个符合日本标准家系先证者和19个符合Bethesda指导纲要患者(字系中仅1例患者)进行hMSH2和hMLH1基因种系突变检测。对检出突变的家系进行家庭成员的突变筛选。并对检出突变患者进行肿瘤组织突变的检测。结果在16例家系先证者中检测到6个hMSH2突变和11个hMLHl种系突变,其中12个突变是国际上尚未报道过的新突变。突变位于不同外显子中,其中6个突变位于hMLHl第14-16外显子。Amsterdam标准家系突变阳性率为50％(12／24),以日本标准所筛家系突变阳性率为3／15,以上两组家系以外的Bethesda指导纲要患者突变阳性率为1／19。突变类型包括移码突变、无义突变、剪接异常、框架内插入或缺失以及错义突变。基因突变与疾病共分离,检出突变家系先证者的肿瘤组织错配修复基因表现出3种不同基因型：(1)野生型等位基因丢失;(2)肿瘤组织基因型与生殖细胞一致;(3)突变型等位基因丢失。结论中国人HNPCC家系hMSH2和hMLHl突变谱广泛,突变类型多样,hMLHl突变较hMSH2突变多见,突变较为集中于hMLHl外显子14-16。不同临床标准预示突变的敏感性不同。突变基因型与疾病表现型共分离。家系成员中尚未发病的突变携带者应予密切监测。

Mutation analysis of hMSH2 and hMLH1 genes in Chinese hereditary nonpolyposis colorectal cancer families

OBJECTIVES: To determine the germ-line mutations of hMSH2 and hMLH1 genes in Chinese hereditary nonpolyposis colorectal cancer (HNPCC) families' probands or in patients fulfilling different clinical criteria or guidelines; to clarify the nature and distribution of the mutations; to evaluate the sensitivity of different clinical criteria in mutation prediction. METHODS: The entire coding regions (35 exons including exon-intron boundaries) of hMSH2 and hMLH1 genes were directly sequenced in 24 Amsterdam criteria (AC) probands, 15 Japanese criteria (JC) probands (except AC kindreds) and 19 Bethesda guidelines (BG) patients (except two former groups). All available affected and unaffected members from families of those with mutations were screened for mutation. RESULTS: In 16 unrelated families selected by the different clinical criteria, 17 germ-line mutations were found with 11 (64.7%) of hMLH1 and 6 (35.3%) of hMSH2. Two mutations were identified in one of the families. Among the 17 germ-line mutations, 12 had not been reported previously. A diversified mutation spectrum was found, but 6 hMLH1 mutations were found to be concentrated in the region encompassing exon 14, 15 and 16. There was a wide spectrum of mutation type including frame shift, nonsense, splice site mutation, in frame insertion or deletion and missense mutations. The mutation detection rate of hMSH2 and hMLH1 in the AC group was significantly higher than that in the JC group (12/24 vs. 3/15). On the other hand, a low mutation rate (1/19) was detected in 19 BG patients. The mutation cosegregated with disease. Besides, three different genotypes in tumors from probands of mutation-positive families were found. CONCLUSIONS: hMSH2 and hMLH1 mutations in Chinese HNPCC families show a wide spectrum. It seems that hMLH1 gene is involved more frequently than hMSH2 gene in Chinese HNPCC families. Different clinical criteria predict mutations with different sensitivities. The Amsterdam Criteria are most sensitive, while Japanese Criteria are highly practical and the Bethesda Guidelines are also practical to some extent. Gene mutations cosegregate with the disease phenotype. Carriers with no symptom in HNPCC families are most vulnerable groups, follow-ups are required for this group to get early diagnosis and to prevent the development of CRCs.