These data suggest the involvement of mismatch repair deficiency in the premalignant stage of tumorigenesis in HNPCC cases, and suggest that mismatch repair genes (MSH2 or others) are defective in the germline of nearly all these patients.
In particular, hMSH2 and hMLH1 homologues of the bacterial DNA mismatch repair genes mutS and mutL, respectively, were shown to be mutated in a subset of HNPCC cases.
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.
Mutations in genes associated with the DNA mismatch repair system were considered to play important roles in predisposition to cancer, since hMSH2 and hMLH1, human homologues of yeast MSH2 and MLH1 as well as bacterial mutS and mutL genes, were found to be involved in hereditary nonpolyposis colorectal cancer (HNPCC).
Two susceptibility loci for hereditary nonpolyposis colorectal cancer (HNPCC) have been identified, and each contains a mismatch repair gene: MSH2 on chromosome 2p and MLH1 on chromosome 3p.
We have identified the source of the genetic instability in one ovarian tumor as a point mutation (R524P) in the human mismatch-repair gene MSH2 (Salmonella MutS homologue), which has recently been shown to be involved in hereditary nonpolyposis colorectal cancer.
In particular, hMSH2 and hMLH1 homologues of the bacterial DNA mismatch repair genes mutS and mutL, respectively, were shown to be mutated in a subset of HNPCC cases.
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.
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.
Mutations in genes associated with the DNA mismatch repair system were considered to play important roles in predisposition to cancer, since hMSH2 and hMLH1, human homologues of yeast MSH2 and MLH1 as well as bacterial mutS and mutL genes, were found to be involved in hereditary nonpolyposis colorectal cancer (HNPCC).
With the development of the International Hereditary Nonpolyposis Colorectal Cancer Collaborative Group, knowledge can be disseminated worldwide about the public health importance of HNPCC and the need to implement highly targeted surveillance and management strategies in all clinical practice settings.
Two (mismatch repair) genes (hMSH2 on chromosome 2p and hMLH1 on chromosome 3p) have recently been identified which appear to be involved in the development of cancer in most of the HNPCC families.
Of the remaining three families studied for linkage, one showed lod scores compatible with exclusion of both MSH2 and MLH1, while lod scores obtained in the other two families suggested exclusion of one HNPCC locus (MSH2 or MLH1) but were uninformative for markers flanking the other locus.