Haplotype analysis of two recurrent genomic rearrangements in the BRCA1 gene suggests they are founder mutations for the Greek population

The deletions of 4.4 and 3.2 kb identified in exons 24 and 20, respectively, are two of the four most common mutations in the BRCA1 gene in Greek breast cancer patients. They have been reported previously six and three times, respectively, in unrelated Greek families. A total of 11 more families have been identified in the present study. In order to characterize these recurrent mutations as founder mutations, it is necessary to identify the disease-associated haplotype and prove that it is shared by all the mutation carriers, suggesting that it occurred only once in a common ancestor. Haplotype analysis was performed on 24 mutation carriers and 66 healthy individuals using 10 short tandem repeat markers located within and flanking the BRCA1 gene locus, spanning a 5.9 Mb interval. Results indicate that most of the carriers of the exon 24 deletion share a common core haplotype '4-7-6-6-1-3' between markers D17S951 and D17S1299, for a stretch of 2.9 Mb, while the common haplotype for the exon 20 deletion is '6-7-4-2-6-7-1-3' between markers D17S579 and D17S1299, for a stretch of 3.9 Mb. Both genomic rearrangements in BRCA1 gene are Greek founder mutations, as carriers share the same, for each mutation, disease-associated haplotype, suggesting the presence of a distinct common ancestor for both mutations.