IN-VITRO TRANSCRIPTION TRANSLATION ASSAY FOR THE SCREENING OF HMLH1 AND HMSH2 MUTATIONS IN FAMILIAL COLON-CANCER/

Background & Aims: Hereditary nonpolyposis colorectal cancer (HNPCC) h as been linked recently to a defect in repairing mismatched nucleotide s in DNA. The aim of this study was to screen for germline mutations t hat result in prematurely truncated proteins in two of the mismatch re pair genes identified at this time, hMLH1 and hMSH2, in a consecutive series of patients belonging to familial aggregations of colorectal ca ncer. Methods: Nineteen individuals with colorectal cancer from 19 fam ilies were consecutively referred because of a strong positive family history of colorectal cancer. Premature truncation mutations in hMLH1 and hMSH2 were sought from lymphocyte RNA by using an in vitro transcr iption/translation (IVTT) assay. Results: Protein truncating mutations in the hMLH1 or hMSH2 genes were found in 50% of families with HNPCC (6 of 12) but were not observed in any of the remaining familial aggre gations that did not fulfill the standard criteria for HNPCC. In some of the IVTT-positive samples, the mutations were characterized by geno mic sequencing. Conclusions: IVTT may be a practical method to accompl ish primary screening of germline mutations in DNA mismatch repair gen es in HNPCC; however, a broader approach is necessary to obtain a more complete picture of the mutational spectrum in HNPCC and other famili ar aggregations of colorectal cancer.