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An Alu‐mediated 7.1 kb deletion of BRCA1 exons 8 and 9 in breast and ovarian cancer families that results in alternative splicing of exon 10

Constitutive large deletions and duplications of BRCA1 resulting from Alu‐mediated recombination account for a significant proportion of disease‐causing mutations in breast and/or ovarian cancer families. Using Southern blot analysis and a protein truncation test (PTT), we have identified a 7.1 kb germline deletion in two families with breast and ovarian cancer. This deletion, which includes exons 8 and 9 and leads to a frameshift at the mRNA level, appears to result from homologous recombination between closely related Alu repeats, one in intron 7 and one in intron 9. In addition to the transcript without exons 8 and 9, analysis of RNA by protein truncation test from individuals with the deletion also identified the presence of alternative splicing of exon 10 from the mutant allele, which results in a transcript that lacks exons 8, 9, and 10. Of interest is that the two American families who carry this deletion are of northern European ancestry and share a common haplotype, suggesting that this deletion may represent a founder mutation. Genes Chromosomes Cancer 28:300–307, 2000. © 2000 Wiley‐Liss, Inc.