| About 5% ~ 15% of colorectal cancer are associated with the autosomal do-mintary Hereditary nonpolyposis colorectal cancer ( HNPCC). In 1913, Warthin first described some families with an excess of colorectal, uterine and gastric cancers. It took more than half a century before Lynch undertook the task of collecting data that led to accurate description of these cancer - prone families. According to the absence or presence of extracolonic malignancies, these families were divided into Lynch I syndrome and Lynch II syndrome. Later, the syndrome was specifically called HNPCC. So HNPCC is also called Lynch syndrome.Hereditary nonpolyposis colorectal cancer ( HNPCC) is the most frequent autosomal dominant predisposition to the development of colorectal cancer. Germline mutations of genes involved in postreplicative DNA mismatch repair (MMR), in particular hMSH2 hMLH1 hPMS1 hPMS2 hMSH3 and hMSH6, are thought to be responsible for HNPCC. MSH2 on chromosome 2p16, MLH1 on 3p21, MSH6 on 2pl5, and PMSl and PMS2 on 7p22. The vast majority of HNPCC - causing mutations have been reported in MSH2 and MLH1. Accordingly , mutations in these genes give rise to the " classical" HNPCC phenotype , whereas MSH6 mutations have been described in families with more atypical HNPCC. Only a few PMS2 germline mutations have been described so far. Cells with a defective DNA MMR demonstrate a mutation rate 100 - fold greater than that of normal cells, causing the accumulation of potentially deleterious mutations throughout the genome. These mutations preferentially affect repetitive DNA sequences and are responsible for the occurrence of microsatellite instability ( MSI). MSI has been detected in most MMR - deficient tumors and is consid-ered tibe the hallmark of HNPCC.Apart from a lifetime risk of colorectal cancer of 80% , individuals with an MMR gene mutation are characterized by an increased risk of tumors of the en-dometrium, stomach, small intestine, pancreas, hepatobiliary system, urinary tract, ovary, brain, and skin. Identification of HNPCC - causing MMR gene mutations enables at - risk relatives to be informed about their cancer risks and to benefit from intensive surveillance programs that have been proven to reduce their overall mortality by 65%.Knowledge of the causative mutation in a particular HNPCC family enables the identification of at risk family members by genetic testing. Clearly, the absence or presence of a mutation is of considerable medical and psychological significance. Subjects not carrying the mutation are relieved from a continuous anxiety and can be dismissed from medical surveillance, saving them trouble and reducing health care costs. Importantly, Subjects with the mutation can benefit from a medical surveillance programme.METHODS1. When the probands were verified, we investigated the more detailed family history of patients in the hospital or in the clinic through inquiry by telephone and mail. The tree of each family pedigree was drawn. 33HNPCC kindreds were reviewed retrospectively, Clinical characteristics and treatment were analyzed.2. Tissue Specimens. Peripherial blood and genomic DNA were extracted from family members who had provided informed consent. Surgical pathology specimens were collected and 5 ml of peripheral blood were routinely collected from each patient then kept at - 80.3. DNA Preparation.4. Premers were designed with the sequences downloaded from Genbank and synthesis in TaKaRa Biotechnology (Dalian) Co. ,Ltd.5. PCR Amplification. All 16 exons of MSH2 and all 19 exons of MLH1 were amplified from genomic DNA using primers. PCR and SSCP were used to screen coding regions of the hMLH1 and hMSH2 genes.6. Mutation Analysis. All 16 exons of MSH2 for 16 cases were sequenced by 377 DNA sequencer after purification.RESULTS1. Tumor frequency :The 33 families included 17 Lynch type I families and 16 Lynch type II families. A total of 187 patients developed malignant tumors, 103 males and 84 females. The median age at diagnosis was 50 years (range from 12 to 83 years). 96 patients (53 % ) developed malignant tumors below 50 years. The onset of the disease occurred earlier than expected with the passing of each generation within large kindreds.2. Of 109 patients with colorectal cancer 23 had metachronous colorectal cancer. 21% colorectal patients developed metachronous cancer within 7 years after initial operation and received re — operation. Synchronous and metachronous colorectal cancer occurred in 23 (21 % ) patients. 3. Extracolonic colorectal cancer; 85 extracolonic rumors were found, including 17 lung cancer , 14 stomach cancer, 12 endometric cancer and so on. Lung cancer is the most frequent extracolonic cancer in our series, accounting for 20 %.4. Sequencing showed that MSH2 mutation was located in exon 7 ,exonll, exonl3 and exonl5, three insert and one missense mutation. In 15 families,the overrall mutation rate of MSH2 gene was 25%.DISCUSSIONAmsterdam criteria I was adopted to diagnose HNPCC in this study. As the widely accepted criteria for diagnosis of HNPCC, the Amsterdam criteria were established by the International Collaborative Group on Hereditary Nonpolyposis Colorectal Cancer (ICG - HNPCC). But as clinical criteria, the Amsterdam criteria are too restrictive, thus leading to a number of limitations: (1) The failure to acknowledge the contribution of endometrial cancer and other extracolonic cancer to the HNPCC diagnosis. (2) Small family size or poor documentation of disease and cause of death limits the identification of many affected families.( 3) New mutations are not likely to be identified. Estimates of HNPCC frequency varied from country to country. On the one hand, a difference actually exists among different areas, ethnics, nationalities, etc. On the other hand, these studies were not based on uniform criteria. Amsterdam criteria I and II, Japanese criteria and other criteria for suspected HNPCC were used in different studies. According to the Amsterdam criteria, many population - based studies in foreign countries yielded the frequency at 1 - 6 %. To optimize mutation analysis in families with HNPCC and HNPCC - like disease, several clinical criteria have been formulated. Of these, the Amsterdam criteria, established by the International Collaborative Group on HNPCC, are now recognized as the gold standard in HNPCC clinical selection. Previously, MLH1 or MSH2 mutations have been found in only 45% -64% and 0% ~47% of the Amsterdam criteria - positive and - negative families, respectively. Since > 90% of HNPCC colorectal cancers display microsatellite instability (MSI) , in contrast to 12% 18% of the sporadic colorectal cancers, the "Bethesda guidelines" include MSI as an additional selection tool for MMR gene mutation analysis. However, although the application of the Bethesda guidelines does improve the mutation analysis sensitivity, it also results in a remarkable reduction of its specificity compared with the Amsterdam criteria, since a considerable number of families with more atypical phenotypes are included.Early age of cancer onset is one of the most striking features about HNPCC. The average age to develop colorectal cancer was 45 years, 20 years earlier than the sporadic colorectal cancer. The study involving 33 HNPCC kindreds and 187 HNPCC patients showed that the average age of onset was 50 years.HNPCC also predisposes individuals to multiple synchronous and metachro-unous colon cancer. The prevalence rate of synchronous and metachrounous colorectal cancer was about 35 %. A domestic investigation in China showed the percentage of synchronous and metachrounous colorectal cancers was 39. 5 %. All of them developed within ten years after surgery and needed reoperations. In our series, 23 (21%) of 109 patients presented with multiple cancers in the colorectum.extracolonic tumors are frequently seen in HNPCC patients and may con-tribute to the diagnosis of HNPCC. For this reason, extracolonic cancers were included in the Amsterdam criteria II. According to the reports of western countries, the endometrial and stomach cancers are the first and the second most common tumor in HNPCC, respectively. In our series, The three most common tumors were Lung cancer , stomach cancer, endometrial carcinoma. Different from the western countries and the other reported in China, The difference in extracolonic tumor spectrum between China and western countries may lie in many aspects. The small size of our sample may be one of the reasons. Besides, different types of mutation or mutation loci and interaction between environment, life style, ethnics and genotype may also contribute to the observed variation.CONCLUSIONHNPCC is an autosomal dominant disorder with special clinicopathological features:1. early onset ( average 50ys ) ;2. high frequency of cancers in colonrectum, ;3. excess of synchronous and metachronous tumors;4. development of extracolonic malignancies, It is often diagnosed by Amsterdam criteria, In our study, lung cancer, gastric cancer, endometrial cancer, were the three common extracolonic malignancies;5. The results indicate that the majority of missense mutations are pathogenic , although further characterization by functional assays is necessary before implementation in predictive testing programs.6. Sequencing showed that MSH2 mutation was located in exon 7 ,exonll, exonl3 and exonl5, three insert and one missense mutation.
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