The Role Of HMLH3 In Familial Colorectal Cancer And Esophageal Cancer

To investigate the possible role of the newly identified mismatch repair gene hMLHS in familial colorectal and esophageal cancer.Methods70 index patients suggestive of a genetic predisposition for hereditary colorectal cancer ( HCRC) and 66 members from 10 familial esophageal cancers ( FEC) were screened for germline mutations in hMLHS with denaturing high performance liquid chromatography ( DHPLC ) , a newly developed method of comparative sequencing based on heteroduplex detection. For all samples exhibiting abnormal DHPLC profiles, sequence changes were evaluated by cycle sequencing. MSI status of all tumors had been established previously and germline mutations in hMLHl, hMSH2, and hMSH6 were excluded in all but two families (families 21 and 199). For any mutation of the index patient, we tested its presence or not in the family members, conducted segregation study, and compared its prevalence with that of sporadic colorectal cancer and sporadic esophageal cancers as well as in normal controls. Segregation of gene mutation with the occurrence of colorectal and esophageal cancers was evaluated.ResultsAll exons of hMLHS in all samples were successfully examined. (1) InHCRC, a total of one frameshift mutation, 10 missense mutations and 5 polymorphisms were identified in 16 index patients (23% ). Most families presented evidence against hMLH3 as a monogenic explanation for the familial aggregation of colorectal cancer, and most of the mutations were found in the low risk patients. In one family that the hMLHS mutation segregated with disease together with a missense mutation in hMSH2. No tumors with hMLH3 mutations showed micro-satellite instability. (2) In FEC, 4 missense mutations and 3 polymorphisms were identified in 4 families. hMLH3 missense mtations in family 9 and 10 may be pathogenic, with reduced penetrance. While in family 1 and 7, there were not sufficient evidence supporting the monogenic explanations of esophageal cancers in families. In most families, hMLH3 could not be the single causative gene of high risk. The mutations were found in 33% of high risk families and 50% of low risk families.Conclusions(1) In some families, hMLH3 could be a high risk gene with reduced penetrance.(2) while in most families, it acts as a low risk gene for colorectal cancer and esophageal cancer. The mutations of hMLH3 could work together with hM-SH2 in an additive manner and result in an elevated risk of colorectal tumors in one family.(3)Furthermore, hMLH3 does not make its contribution to carcinogenesis through an impaired DNA mismatch repair function.(4) DHPLC analysis is a very sensitive, robust and reproducible method for mutation screening.