CHARACTERIZATION OF MSH2 AND MLH1 MUTATIONS IN ITALIAN FAMILIES WITH HEREDITARY NONPOLYPOSIS COLORECTAL-CANCER

Mismatch repair genes MSH2 and MLH1 are considered to be the two major genes that are responsible for hereditary nonpolyposis colorectal can cer (HNPCC). Germline heterozygous inactivating mutations of MSH2 and MLH1 have been identified previously in a substantial fraction of indi viduals who are predisposed genetically to colorectal carcinoma (CRC) and other tumors of the HNPCC spectrum. With the aim of determining th e relevance of these two genes in the Italian population, we submitted to mutational analysis a set of 17 HNPCC families, all of which fulfi lled the ''Amsterdam criteria'' A combination of different techniques, including reverse transcription-polymerase chain reaction (RT-PCR) of long fragments and single-strand conformation polymorphism (SSCP) on cDNA and genomic DNA, allowed the identification of ten molecular vari ants, seven of which are predicted to inactivate mismatch repair funct ion. The mutated predisposing gene was MSH2 in two families and MLH1 i n five other families. All of the mutations were characterized by DNA sequencing and appeared to involve different molecular mechanisms, suc h as short in-frame and out-of-frame deletions, splicing errors, and n onsense mutations. This study also demonstrates that, in the Italian p opulation, a considerable fraction of HNPCC families (at least 41%) is linked to MSH2 and MLH1 mutations. (C) 1997 Wiley-Liss, Inc.