Somatic mutations in the hMSH2 gene in microsatellite unstable colorectal carcinomas

Microsatellite instability is frequently seen in tumors from patients with hereditary nonpolyposis colorectal cancer (HNPCC). Germline mutations in the mismatch repair gene hMSH2 account for approximately 50% of these cases. Tumors from sporadic cases also exhibit this microsatellite instability phenotype, although at a lower frequency, and very few somatically derived mutations have so far been reported in such tumors. In this study DNA from 23 primary colorectal carcinomas (four familial and 19 sporadic cases) exhibiting microsatellite instability were screened for mutations in the hMSH2 gene using constant denaturant gel electrophoresis (CDGE). Among the sporadic cases, five (26%) were found to have somatically derived mutations. One tumor revealed two different mutations, possibly leading to a homozygous inactivation of the gene. One of the four familial cases was classified as having HNPCC, and a germline as well as a somatic mutation were found in this tumor. These results demonstrate that a considerable proportion of sporadic colorectal cancers with microsatellite instability, have somatic mutations in the hMSH2 gene.

Structure of the human MLH1 locus and analysis of a large hereditary nonpolyposis colorectal carcinoma kindred for mlh1 mutations

Hereditary nonpolyposis colorectal carcinoma is a major cancer susceptibility syndrome known to be caused by inheritance of mutations in at least four genes such as hMSH2, hMLH1, hPMS1, and hPMS2 which encode components of a DNA mismatch repair system. The hMLH1 genomic locus on chromosome 3p has been cloned and shown to cover approximately 58 kilobases of genomic DNA and contain 19 exons. The sequence of all of the intron-exon junctions has been determined and used to develop methods for analyzing each hMLH1 exon for mutations. Using these methods to analyze a 3p-linked hereditary nonpolyposis colorectal carcinoma kindred, we have demonstrated that cancer susceptibility in this family is due to the inheritance of a frame shift mutation in the hMLH1 gene.

Structure of the human MSH2 locus and analysis of two Muir-Torre kindreds for msh2 mutations

Hereditary nonpolyposis colorectal carcinoma (HNPCC) is a major cancer susceptibility syndrome known to be caused by inheritance of mutations in genes such as hMSH2 and hMLH1, which encode components of a DNA mismatch repair system. The MSH2 genomic locus has been cloned and shown to cover approximately 73 kb of genomic DNA and to contain 16 exons. The sequence of all the intron-exon junctions has been determined and used to develop methods for analyzing each MSH2 exon for mutations. These methods have been used to analyze two large HNPCC kindreds exhibiting features of the Muir-Torre syndrome and demonstrate that cancer susceptibility is due to the inheritance of a frameshift mutation in the MSH2 gene in one family and a nonsense mutation in the MSH2 gene in the other family.

Mutation in the DNA mismatch repair gene homologue hMLH1 is associated with hereditary non-polyposis colon cancer

The human DNA mismatch repair gene homologue hMSH2, on chromosome 2p is involved in hereditary non-polyposis colon cancer (HNPCC). On the basis of linkage data, a second HNPCC locus was assigned to chromosome 3p21-23 (ref. 3). Here we report that a human gene encoding a protein, hMLH1 (human MutL homologue), homologous to the bacterial DNA mismatch repair protein MutL, is located on human chromosome 3p21.3-23. We propose that hMLH1 is the HNPCC gene located on 3p because of the similarity of the hMLH1 gene product to the yeast DNA mismatch repair protein, MLH1, the coincident location of the hMLH1 gene and the HNPCC locus on chromosome 3, and hMLH1 missense mutations in affected individuals from a chromosome 3-linked HNPCC family.