Large BRCA1 and BRCA2 genomic rearrangements in Danish high risk breast-ovarian cancer families

BRCA1 and BRCA2 germ-line mutations predispose to breast and ovarian cancer. Large genomic rearrangements of BRCA1 account for 0–36% of all disease causing mutations in various populations, while large genomic rearrangements in BRCA2 are more rare. We examined 642 East Danish breast and/or ovarian cancer patients in whom a deleterious mutation in BRCA1 and BRCA2 was not detected by sequencing using the multiplex ligation-dependent probe amplification (MLPA) assay. We identified 15 patients with 7 different genomic rearrangements, including a BRCA1 exon 5–7 deletion with a novel breakpoint, a BRCA1 exon 13 duplication, a BRCA1 exon 17–19 deletion, a BRCA1 exon 3–16 deletion, and a BRCA2 exon 20 deletion with a novel breakpoint as well as two novel BRCA1 exon 17–18 and BRCA1 exon 19 deletions. The large rearrangements in BRCA1 and BRCA2 accounted for 9.2% (15/163) of all BRCA1 and BRCA2 mutations in East Denmark. Nine patients had the exon 3–16 deletion in BRCA1. By SNP analysis we find that the patients share a 5 Mb fragment of chromosome 17, including BRCA1, indicating that the exon 3–16 deletion represents a Danish founder mutation.