Recent studies suggest that MI in many cell lines or xenografts derived from sporadic colorectal carcinomas is not attributable to mutations in four known human DNA mismatch repair (MMR) genes (hMSH2, hMLH1, hPMS1, and hPMS2).
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.
Microsatellite instability (MSI) is intrinsic to most colorectal carcinomas (CRC) from patients with hereditary nonpolyposis colorectal cancer (HNPCC), reflecting germline mutations in the mismatch-repair (MMR) genes.
However, reports of mismatch repair (MMR) gene mutations in families not fulfilling the minimal diagnostic criteria point out the necessity to identify additional clinical parameters suggestive of genetic predisposition to colorectal cancer (CRC) related to MMR defects.
Microsatellite instability (MIN) due to defective mismatch repair (MMR) genes has been reported in a subset of sporadic colorectal carcinomas and in the majority of tumors from patients with hereditary nonpolyposis colorectal cancer (HNPCC) syndrome.
Further studies with newly diagnosed patients before they begin therapy will provide more convincing data about the role of MMR gene expression in the etiology of colorectal cancers in Egypt.
Thus, MSI and germline MMR gene mutation is present in a subset of young glioma patients, and these patients and their family members are at risk of developing other hereditary nonpolyposis colorectal cancer syndrome-related tumors, in particular colorectal carcinomas.
To investigate the frequency of germline alterations of the DNA MMR genes hMLH1 and hMSH2 among African Americans affected by HNPCC and early-age onset colorectal cancer.
Germline mutations in MMR genes are associated with Hereditary non-polyposis colorectal carcinoma (HNPCC) and somatic mutations in these genes are also found in a substantial fraction of colorectal cancers (CRC).
Lynch syndrome displays many curious features that cannot be accounted for by the prevailing concepts of carcinogenesis and genetics: (1) CRCs occur preferentially in the right side of the colon, whereas the majority of sporadic cases develop in the left colon; (2) the increased risk of CRC is not associated with an increased incidence of adenomatous polyps, which are necessary precancerous lesions in the development of common CRCs; (3) the tumor spectrum in Lynch syndrome is restricted to the colon and some extracolonic sites, whereas the responsible MMR genes are ubiquitously expressed; (4) the tumor risk, which is negligible during childhood, becomes significant during adulthood at the age of 25 and thereafter remains essentially constant throughout the ages.
The discovery of DNA mismatch repair (MMR) genes, inclusive of hMSH2, hMLH1, hPMS2, and hMSH6, has enabled the identification of who has and who does not have inordinately increased susceptibility to CRC as well as a litany of extracolonic cancers.
The MSI-H phenotype, observed in both hereditary nonpolyposis colon cancer-associated CRC and approximately 15% of sporadic CRC, generally results from mutational or epigenetic inactivation of the DNA mismatch repair (MMR) genes hMSH2 or hMLH1.
We identified 6 (17%) MSI-H tumors with germline mutations in mismatch repair (MMR) genes (tumors from patients with hereditary non-polyposis colorectal cancer (HNPCC) syndrome) and 29 (83%) MSI-H tumors without germline MMR mutations (sporadic MSI-H tumors).
A comprehensive analysis of somatic and germline mutations related to DNA mismatch-repair (MMR) genes can clarify the prevalence and mechanism of inactivation in colorectal carcinoma (CRC).
Hereditary nonpolyposis colorectal cancer (HNPCC) is the most frequent hereditary form of colorectal cancer and is caused by germline mutations in mismatch repair (MMR) genes.
In conclusion of our results and a critical review of literature, the prognostic importance of the MMR genes in sporadic colorectal carcinomas remains controversial.
The role of MSI in colorectal tumorigenesis was assessed further in this study by both microsatellite analysis of two CRC subsets [unselected patients (n = 215) and patients <50 years of age (n = 95)], and mutation screening of the two major MMR genes MLH1 and MSH2 among familial CRC cases.
Defects in the mismatch repair (MMR) genes hMLH1 and hMSH2 have been found in 10% to 20% of sporadic colorectal carcinomas and also many cases of hereditary nonpolyposis colorectal cancer syndrome.
Hereditary nonpolyposis colorectal cancer (HNPCC) represents 2-4% of colorectal cancers and is caused by a constitutional defect in a mismatch repair (MMR) gene, most commonly affecting the genes MLH1, MSH2, and MSH6.