7 NEW MUTATIONS IN HMSH2, AN HNPCC GENE, IDENTIFIED BY DENATURING GRADIENT-GEL ELECTROPHORESIS

Hereditary nonpolyposis colorectal cancer (HNPCC) is a relatively comm on autosomal dominant cancer-susceptibility condition. The recent isol ation of the DNA mismatch repair genes (hMSH2, hMLH1, hPMS1, and hPMS2 ) responsible for HNPCC has allowed the search for germ-line mutations in affected individuals. In this study we used denaturing gradient-ge l electrophoresis to screen for mutations in the hMSH2 gene. Analysis of all the 16 exons of hMSH2, in 34 unrelated HNPCC kindreds, has reve aled seven novel pathogenic germ-line mutations resulting in stop codo ns either directly or through frameshifts. Additionally, nucleotide su bstitutions giving rise to one missense, two silent, and one useful po lymorphism have been identified. The proportion of families in which h MSH2 mutations were found is 21%. Although the spectrum of mutations s pread at the hMSH2 gene among HNPCC patients appears extremely heterog eneous, we were not able to establish any correlation between the site of the individual mutations and the corresponding tumor spectrum. Our results indicate that, given the genomic size and organization of the hMSH2 gene and the heterogeneity of its mutation spectrum, a rapid an d efficient mutation detection procedure is necessary for routine mole cular diagnosis and presymptomatic detection of the disease in a clini cal setup.