MLPA screening in the BRCA1 gene from 1,506 German hereditary breast cancer cases:: Novel deletions, frequent involvement of exon 17, and occurrence in single early-onset cases

We present a comprehensive analysis of 1,506 German families for large genomic rearrangements (LGRs) in the BRCA1 gene and of 450 families in the BRCA2 gene by the multiplex ligation-dependent probe amplification (MLPA) technique. A total of 32 pathogenic rearrangements in the BRCA1 gene were found, accounting for 1.6% of all mutations, but for 9.6% of all BRCA1 mutations identified in a total of 1,996 families, including 490 with small pathogenic BRCA1/2 mutations. Considering only high risk groups for hereditary breast/ovarian cancer, the prevalence of rearrangements is 2.1%. Interestingly, deletions involving exon 17 of the BRCA1 gene seem to be most frequent in Germany. Apart from recurrent aberrations like del ex 17, dupl ex 13, and del ex22, accounting for more than 50% of all BRCA1 LGRs, we could fully characterize 11 novel deletions. Moreover, one novel deletion involving exons 1-7 and one deletion affecting the entire BRCA1 gene were identified. All rearrangements were detected in families with: 1) at least two breast cancer cases prior to the age of 51 years; 2) breast and ovarian cancer cases; 3) ovarian cancer only families with at least two ovarian cancer cases; or 4) a single breast cancer case prior to the age of 36 years, while no mutations were detected in breast cancer only families with no or only one breast cancer case prior to the age of 51 years. Analysis for gross rearrangements in 412 high-risk individuals, revealed no event in the BRCA2 gene and only two known CHEK2 mutations. However, in an additional 38 high-risk families with cooccurrence of female breast/ovarian and male breast cancer, one rearrangement in the BRCA2 gene was found. In summary, we advise restricting BRCA1 MLPA screening to those subgroups that revealed LGRs and recommend BRCA2 MLPA screening only for families presenting with cooccurrence of female and male breast cancer.