In-frame deletions of BRCA1 may define critical functional domains

The identification of genomic rearrangements involving more than 0.5 kb of the BRCA1 gene has confirmed a more complex mutation spectrum than was initially appreciated. Genomic rearrangements in BRCA1 represent 15% of all mutations in a group of French and American breast and ovarian cancer families and 36% of all mutations in a group of Dutch families. The rearrangements described to date range in size from 510 bp to 23.8 kb, are found throughout the gene, and are most frequently attributable to homologous recombination. We describe the identification of rearrangements in two breast and ovarian cancer families that involve 3.4 and 11.5 kb of the BRCA1 gene and span multiple exons but maintain the reading frame. Both gene rearrangements appear to result from Alu-mediated homologous recombination and have been detected by using a combination of protein truncation analysis and Southern blot analysis. These rearrangements result in the loss of amino acids that lie at the carboxy-terminus of the protein and that have previously been shown to have functional significance. Because these rearrangements result in the deletion of exons but maintain the reading frame, they may provide insights into specific regions and amino acids that have functional significance for the BRCA1 protein.