Mutation Patterns In MMR Genes And Clinical Phenotypes Of HNPCC Families In The Northern Chinese Population

Background and aimsColorectal cancer (CRC) is a kind of malignant tumor that has a predominantly hereditary background. Nearly 30% of patients with colon cancer arise in the context of a family history of CRC. 20% of cases occur within familial aggregates. Of the hereditary colon cancer, HNPCC is the most commonly occurring familial CRC syndrome and may account for approximately 5% of all CRC. In recent years a lot of investigations have demonstrated that a defective DNA mismatch repair (MMR) may be basic pathogenesis of HNPCC. However no any defective MMR gene was found in a half of HNPCC tumors yet. In order to understand the genetic mechanism of HNPCC tumors International collaborative group for HNPCC and clinical criteria of diagnosis (Amsterdam â… /â…¡) were set up. Amsterdam criteria (AC) are a stricter standard. A parts of HNPCC families would be lost using the criteria. So many investigators recommended other criteria, such as Japan criteria (JC), Bethesda criteria. Up to now there was no any diagnostic criteria of HNPCC suitable to Chinese race. Our group conducted a comprehensive study of genetic pathogenesis. We collected 34 HNPCC families and studied their family history, clinical phenotypes and patterns of germline mutations in three MMR genes. The aims of the study were to analyze the availability of Amsterdam criteria and, new procedures suitable for screening HNPCC cases and clinical diagnostic criteria suitable for Chinese population.Materials and methods1.Based on Japan criteria and Amsterdam criteria 34 families who lived in north area of China were collected. Of whom, 21 met AC and 13 met JC. 120 sporadic colon cancer (CRC) were collected as a control .2.Except 8 families 26 HNPCC families wereexamined by Micro satellite (MS) analysis, immunohistochemical staining (hMSH2, hMLH1 and hMSH6) as well as direct DNA sequencing for detecting mutations in the MMR genes.Results 1) The clinical phenotypes of HNPCC: the median age of HNPCC probands and persons with CRC were 45.3 years and 59.3 years old respectively.62.1% of the cases suffered from HNPCC tumors were onset before 50 years. The peak of onset was 40-50 years of age. 34 families fulfilled autosomal dominantly inherited disease. The families included 140 patients and 612 members of families. The total lesions were 154; in which 31 were extra colon cancers (20.1%). Gastric cancers account for 41.9% in all extracolon cancers. Seventy-seven (66.4%) of 116 cases with colorectal cancers was in the right colon, thirty-nine cases (33.6%() in the left colon. Synchronous multiple primary cancers was in five and metachronous multiple primary cancers was in six. 2) Microsatellite instability (MSI) analysis: Based on Japan criteria twenty-two (84.62%) of the 26 cases showed MSI. Of MSI cases, MSI-H was at 80.77%(21/26); MSI-Lwas at 3.85%(1/26); MSS was at 15.38%(4/26). Of those fulfilled AC, MSI-H was at 84.21%. Five HNPCC families would be lost if we selected these families based on AC. 3) IHC(immunohistochemistry,IHC) analysis (hMSH2, hMLH1and hMSH6): Nineteen of 21cases with MSI-H tumors were observed the absence of protein expression. One case with MSI-L tumor showed absence of protein (hMSH6). Four MSS tumors had a normal protein expression. Fourteen of 19(73.68%) families fulfilled AC had absence of protein expression. Six of 7 families only fulfilled JC showed the absence of protein expression. Twenty of 26(76.9%) families fulfilled JC showed the absence of protein expression. 4) DNA sequencing for detecting germline mutations in the MMR genes: seven of 10 probands who had the absence of hMLH1 protein expression was found mutations in hMLH1 gene. Six of 9 probands who had the absence of hMSH2 protein expression was found mutations in hMSH2 gene. One proband who had the absence of hMSH6 protein expression showed missense mutation of hMSH6. Two probands with MSI-H tumors who had the normal proteins expressionof three MMR genes was found mutations in hMLH1 and hMSH2 genes. The frequency of MMR germline mutations wa...