A large MSH2 Alu insertion mutation causes HNPCC in a German kindred

Hereditary non-polyposis colorectal cancer (HNPCC) syndrome is an autosomal, dominantly inherited disease accounting for about 1%-5% of all colorectal cancer cases. HNPCC predisposition is caused by germline mutations in at least five genes coding for DNA mismatch repair (MMR) proteins. More than 400 MMR gene mutations have been identified in HNPCC patients. About 90% of mutations affect the MLH1 and MSH2 genes. The mutational spectrum mainly includes point mutations and small deletions or insertions. Here, we report a large 184 base-pair Alu insertion mutation in exon 6 of the MSH2 gene in a German HNPCC family. The inserted sequence contains repetitive Alu sequence elements that present the highest homology with the old Alu J subfamily. The Alu J insertion was most likely derived from Alu-mediated recombination, since Alu J elements have been found close to the insertion site in adjacent introns, and since elements pivotal for Alu retrotransposition are missing. Our results suggest that the recombination event occurred at least one generation ago. This is the first report of an Alu insertion in the coding sequence of a MMR gene as the cause of HNPCC. Our data thus further extend the spectrum of MMR gene mutations causative for HNPCC.