Mutations In Mismatch Repair Gene Mutations Research Articles

Compound heterozygosity for two MSH2 mutations suggests mild consequences of the initiation codon variant c.1A>G of MSH2

Mono-allelic germline mutations in mismatch repair (MMR) genes lead to Lynch syndrome, an autosomal dominant syndrome with an increased risk of predominantly colorectal and endometrial cancers. Bi-allelic germline mutations in MMR genes predispose to haematological malignancies, brain tumours, gastrointestinal tumours, polyposis and features of neurofibromatosis type 1 in early childhood.We report a brother and a sister with bi-allelic germline mutations in MSH2; a pathogenic deletion of the first 6 exons and a variant of the initiation codon (c.1A>G (p.Met1?)), whereas their phenotypes (four colorectal cancers, small bowel carcinoma and 15 adenomas at age 39 and 48, and colorectal cancer, endometrial cancer and four adenomas at age 33 and 44, respectively) are more suggestive of a mono-allelic pathogenic MMR gene mutation. The carcinomas showed microsatellite instability in the presence of MLH1, PMS2, MSH2 and MSH6 proteins, indicating that the variant c.1A>G leads to an alternative protein with reduced activity that is retained in the tumours.Our data suggest that the MSH2 variant c.1A>G (p.Met1?) should not be considered as a regular pathogenic mutation that leads to a strongly increased cancer risk, though it possibly contributes to a more severe phenotype when combined with a truncating mutation on the other allele.

Discovering new drugs to target microsatellite instable (MSI) colorectal cancer (CRC) using the Connectivity Map (CMap)

11087 Background: MSI tumors represent approximately 15% of CRC. Several preclinical and clinical studies have identified differences in response to 5-Fluorouracil and Irinotecan between Microsatellite Stable (MSS) and MSI tumors. CMap is a systems biology tool which enables researchers to match a gene expression signature defining a biologic state of interest with a database containing expression data obtained from different cell lines after being exposed to a panel of 164 small molecules. Our objective was to identify new compounds to target MSI tumors using CMap and to evaluate these candidates in the preclinical setting. Methods: We have used gene expression data generated from MSI tumors included in the Molecular Epidemiology of Colorectal Cancer study and from 2 signatures published previously (Watanabe et al and Koinuma et al). In addition, an aggregated signature was generated from the common genes found to be up and downregulated through the 3 signatures. The most active compounds selected for cytotoxicity assays fulfilled the following criteria: ≥2 negative scores in the global analysis using the CMap; ≥50% negative scores; and compounds highly ranked in terms of a summary measure obtained from aggregating p-values across the different signatures. CRC cell lines showing MSI due to mutations in mismatch repair (MMR) genes, MSI due to hypermethylation of the promoter of MLH1, and MSS were selected to perform cytotoxicity experiments. Cells were seeded in 96-well plates and exposed to 7 different concentrations of drug over 5 days. Results: 17-Allyamino-Geldamycin (17- AAG), which targets hsp90, and Trichostatin, which acts through HDAC inhibition, are novel small molecules predicted to preferentially target MSI CRC based on expression profiles and the CMap. Cell lines with hypermethylation of MLH1 were more sensitive to 17-AAG than MSS and MSI cell lines harboring mutations in MMR genes. No differences in IC50 concentrations were observed for Trichostatin between any groups. Conclusions: We report the application of CMap systems biology tool for discovering new small molecules to specifically target MSI CRC. Further investigation of 17-AAG in combination with standard chemotherapeutic agents is warranted for MSI colorectal cancers. No significant financial relationships to disclose.

The −149C>T SNP within the ΔDNMT3B gene, is not associated with early disease onset in hereditary non-polyposis colorectal cancer

Hereditary non-polyposis colorectal cancer (HNPCC) is an autosomal dominantly inherited syndrome caused by germline mutations in mismatch repair (MMR) genes. HNPCC patients have a lifetime risk of 80% of developing colorectal cancer (CRC); however the likely age of onset is difficult to predict. A single C>T polymorphism located within the promoter region of the ΔDNMT3B gene has recently been reported to be associated with a significant increase to the risk of early onset CRC. In this study we determined the ΔDNMT3B genotype in 404 confirmed HNPCC participants (total of 194 CRC cases) from Australia (203) and Poland (201). From the total number of participants there were 194 diagnosed cases of CRC and 210 healthy MMR gene mutation carriers. The study was undertaken to assess whether the reported effect observed in a previous study of 146 HNPCC patients is consistent in a larger separate and unrelated participant cohort. Through the statistical tests of Kaplan–Meier survival analysis and Cox hazard regression models we did not observe any significant association between the ΔDNMT3B C>T SNP and early onset CRC in HNPCC patients.

Homozygous PMS2 germline mutations in two families with early-onset haematological malignancy, brain tumours, HNPCC-associated tumours, and signs of neurofibromatosis type 1

Heterozygous germline mutations in mismatch repair (MMR) genes MLH1, PMS2, MSH2, and MSH6 cause Lynch syndrome. New studies have indicated that biallelic mutations lead to a distinctive syndrome, childhood cancer syndrome (CCS), with haematological malignancies and tumours of brain and bowel early in childhood, often associated with signs of neurofibromatosis type 1. We provide further evidence for CCS reporting on six children from two consanguineous families carrying homozygous PMS2 germline mutations. In family 1, all four children had the homozygous p.I590Xfs mutation. Two had a glioblastoma at the age of 6 years and one of them had three additional Lynch-syndrome associated tumours at 15. Another sibling suffered from a glioblastoma at age 9, and the fourth sibling had infantile myofibromatosis at 1. In family 2, two of four siblings were homozygous for the p.G271V mutation. One had two colorectal cancers diagnosed at ages 13 and 14, the other had a Non-Hodgkin's lymphoma and a colorectal cancer at ages 10 and 11, respectively. All children with malignancies had multiple café-au-lait spots. After reviewing published cases of biallelic MMR gene mutations, we provide a concise description of CCS, revealing similarities in age distribution with carriers of heterozygous MMR gene mutations.

Hereditary Nonpolyposis Colorectal Cancer

Hereditary nonpolyposis colorectal cancer (HNPCC) is the most common form of hereditary colorectal cancer (CRC). The disease carries a >80% lifetime risk of CRC (mean age at diagnosis being 46 years). The CRCs that arise in HNPCC are usually right-sided and associated with synchronous and metachronous tumors. HNPCC is also associated with a high risk of extracolonic cancers, predominantly endometrial cancer. Predisposition to cancer in HNPCC has been attributed to mutations in mismatch repair (MMR) genes, over 95% of the identified mutations in HNPCC being in hMSH2 , hMLH1 , and hMSH6 . The abnormal MMR genes lead to instabilities in nucleotide repeat sequences (microsatellites) within the genome (MSI, microsatellite instability) that may lead to tumorigenesis and concerning pathologic features but improved clinical outcomes when compared with sporadic CRCs without MSI. Mutations in MMR genes are also associated with a host of other extraintestinal cancers. Each individual MMR gene has its own genotype-phenotype pattern of expression that can vary from individual to individual. As a result, this genetic information can be used to direct surveillance of affected and at-risk family members. Once the clinical criteria for HNPCC have been met and/or a gene mutation confirmed, affected patients show improved survival with cancer screenings every 1 to 2 years starting before age 25 years. Prophylactic colectomy for asymptomatic gene mutation carriers and the extent of colectomy when polyps or cancer arise in HNPCC remain the subject of debate. This issue will discuss our current understanding of the genetics of HNPCC, the various phenotypic expressions, genetic testing, surveillance, and current recommendations of management of this familial cancer syndrome.

GSTM1 Polymorphism Does Not Affect Hereditary Nonpolyposis Colorectal Cancer Age of Onset

<i>GSTM1</i> Polymorphism Does Not Affect Hereditary Nonpolyposis Colorectal Cancer Age of Onset

Methylation of the hMLH1 promoter but no hMLH1 mutations in sporadic gastric carcinomas with high-level microsatellite instability.

Microsatellite instability (MSI) in tumors from patients with hereditary non-polyposis colorectal cancer (HNPCC) is caused by germline mutations in mismatch repair (MMR) genes, principally hMSH2 and hMLH1. In contrast, somatic mutations in MMR genes are relatively rare in sporadic MSI(+) colon cancers. Rather, the majority of mutation-negative, MSI(+) cases involve hypermethylation of the hMLH1 promoter and subsequent lack of expression of hMLH1. The details of the mechanisms of this epigenetic gene silencing remain to be elucidated. In some colon cancer cell lines, hMLH1 promoter methylation is accompanied by mutation of 1 of the 2 alleles, whereas in other cell lines and tumors, such combinations have not been reported. To contribute to the characterization of MSI in gastric cancer and to directly investigate whether hMLH1 promoter methylation is accompanied by gene mutation in these cancers, we have analyzed 42 gastric tumors and corresponding normal tissue for MSI, hypermethylation of the hMLH1 promoter, and mutations in hMLH1 as well as hMSH2. We found that 10 (23.8%) of 42 cases of sporadic gastric cancer were MSI(+) and that 8 had at least 2 of 12 altered microsatellite loci. All samples with at least 2 altered loci exhibited methylation of the hMLH1 promoter region, but none had detectable mutations in hMLH1 or hMSH2. Our results confirm the importance of methylation of the hMLH1 promoter region in MSI(+) gastric tumors and suggest that methylation takes place in the absence of hMLH1 mutations in these tumors.

Microsatellite Instability in Adenomas as a Marker for Hereditary Nonpolyposis Colorectal Cancer

Hereditary nonpolyposis colorectal cancer (HNPCC) is the most common of the well-defined colorectal cancer syndromes, accounting for at least 2% of the total colorectal cancer burden and carrying a greater than 80% lifetime risk of cancer. Significant reduction in cancer morbidity and mortality can be accomplished by appropriate clinical cancer screening of HNPCC patients with mutations in mismatch repair (MMR) genes. Thus, it is desirable to identify individuals who are mutation-positive. In individuals with cancer, mutation detection can be accomplished relatively efficiently by germline mutation analysis of individuals whose cancers show microsatellite instability (MSI). This study was designed to assess the feasibility of screening colorectal adenoma patients for HNPCC in the same manner. Among 378 adenoma patients, six (1.6%) had at least one MSI adenoma. Five out of the six patients (83%) had a germline MMR gene mutation. We conclude that MSI analysis is a useful method of prescreening colorectal adenoma patients for HNPCC.

Microsatellite instability in early onset and familial colorectal cancer.

Hereditary non-polyposis colorectal cancer syndrome (HNPCC) is often considered to be the most common form of inherited colorectal cancer, although its precise incidence is unknown. The clinical diagnosis of HNPCC relies on a combination of family history and young age of onset of colorectal cancer, but as many familial aggregations of colorectal cancer do not fulfil the strict diagnostic criteria, HNPCC might be underdiagnosed. The majority of HNPCC families have germline mutations in mismatch repair (MMR) genes, such as MSH2 or MLH1, so that HNPCC cancers characteristically exhibit DNA replication errors (RERs) at microsatellite loci. Although an RER positive phenotype in tumours can also result from somatic mutations in an MMR gene, the prevalence of RER + tumours should provide a maximum estimate of the incidence of germline MMR gene mutations in patients with early onset and familial colorectal cancer. We investigated colorectal cancers for RERs from (1) a population based study of 33 patients with colorectal cancer aged 45 years or less, (2) 65 kindreds with familial colorectal cancer which only partially fulfilled the criteria for the diagnosis of HNPCC, and (3) 18 cancers from 12 HNPCC kindreds. Seven of 33 patients (21%) with colorectal cancer aged 45 years or less had an RER + cancer, with only two of these having a clear family history of HNPCC. A greater proportion of RER + tumours (5/7) occurred proximal to the splenic flexure than RER - tumours (4/26; chi2 = 6.14, p < 0.025). RERs were detected in all 18 cancers from HNPCC patients but in only six of 65 non-HNPCC familial colorectal cancer kindreds (9%; chi2 = 52.2, p < 0.0005). These findings suggest that most cancers in patients diagnosed at 45 years of age or less and familial aggregations of colorectal cancer which do not fulfil HNPCC diagnostic criteria do not have germline mutations in MSH2 and MLH1. Hence population screening for germline mutations in these genes is unlikely to be an efficient strategy for identifying people at high risk of developing colorectal cancer.