Mutational analysis of the hMLH1 gene using an automated two-dimensional DNA typing system

Searching for mutations in DNA mismatch repair genes is important not only for presymptomatic diagnosis, but also for documenting the spectrum of mutations among families carrying predispositions to hereditary nonpolyposis colorectal cancer (HNPCC). We utilized an automated two-dimensional DNA typing system for mutational analysis of the hMLH1 gene and established optimal conditions for application of the technique to analysis of hMLH1. This approach enabled us to visualize 21 spots covering all 19 coding exons on a single gel and to envisage whether and where any mutations existed. All mutations that we had detected previously by other means in a panel of HNPCC patients and in one patient with sporadic endometrial cancer were also detectable by this method. Furthermore, using the 2-D system, we screened the entire coding regions of the hMLH1 gene in DNAs isolated from affected individuals belonging to two large HNPCC kindreds and four HNPCC-like kindreds, and from four patients with multiple primary cancers as well as eight sporadic colorectal cancers with replication error (RER)-positive phenotypes. We detected novel germline mutations in one HNPCC proband and one sporadic colorectal cancer with the RER-positive phenotype and one polymorphism in two HNPCC-like kindreds. This new diagnostic method is applicable to mutational analysis of any disease-causing gene, and it offers a major improvement over current approaches.