An entire exon 3 germ-line rearrangement in the BRCA2 gene: pathogenic relevance of exon 3 deletion in breast cancer predisposition

<p>Abstract</p> <p>Background</p> <p>Germ-line mutations in the <it>BRCA1 </it>and <it>BRCA2 </it>genes are major contributors to hereditary breast/ovarian cancer. Large rearrangements are less frequent in the <it>BRCA2 </it>gene than in <it>BRCA1</it>. We report, here, the first total deletion of exon 3 in the <it>BRCA2 </it>gene that was detected during screening of 2058 index cases from breast/ovarian cancer families for <it>BRCA2 </it>large rearrangements. Deletion of exon 3, which is in phase, does not alter the reading frame. Low levels of alternative transcripts lacking exon 3 (Δ3 delta3 transcript) have been reported in normal tissues, which raises the question whether deletion of exon 3 is pathogenic.</p> <p>Methods</p> <p>Large <it>BRCA2 </it>rearrangements were analysed by QMPSF (Quantitative Multiplex PCR of Short Fluorescent Fragments) or MLPA (Multiplex Ligation-Dependent Probe Amplification). The exon 3 deletion was characterized with a "zoom-in" dedicated CGH array to the <it>BRCA2 </it>gene and sequencing. To determine the effect of exon 3 deletion and assess its pathogenic effect, three methods of transcript quantification were used: fragment analysis of FAM-labelled PCR products, specific allelic expression using an intron 2 polymorphism and competitive quantitative RT-PCR.</p> <p>Results</p> <p>Large rearrangements of <it>BRCA2 </it>were detected in six index cases out of 2058 tested (3% of all deleterious <it>BRCA2 </it>mutations). This study reports the first large rearrangement of the <it>BRCA2 </it>gene that includes all of exon 3 and leads to an <it>in frame </it>deletion of exon 3 at the transcriptional level. Thirty five variants in exon 3 and junction regions of <it>BRCA2 </it>are also reported, that contribute to the interpretation of the pathogenicity of the deletion. The quantitative approaches showed that there are three classes of delta3 <it>BRCA2 </it>transcripts (low, moderate and exclusive). Exclusive expression of the delta3 transcript by the mutant allele and segregation data provide evidence for a causal effect of the exon 3 deletion.</p> <p>Conclusion</p> <p>This paper highlights that large rearrangements and total deletion of exon 3 in the <it>BRCA2 </it>gene could contribute to hereditary breast and/or ovarian cancer. In addition, our findings suggest that, to interpret the pathogenic effect of any variants of exon 3, both accurate transcript quantification and co-segregation analysis are required.</p

Synthetic lethality of PARP inhibition in cancers lacking BRCA1 and BRCA2 mutations

Utilizing the concept of synthetic lethality has provided new opportunities for the development of targeted therapies, by allowing the targeting of loss of function genetic aberrations. In cancer cells with BRCA1 or BRCA2 loss of function, which harbor deficiency of DNA repair by homologous recombination, inhibition of PARP1 enzymatic activity leads to an accumulation of single strand breaks that are converted to double strand breaks but cannot be repaired by homologous recombination. Inhibition of PARP has therefore been advanced as a novel targeted therapy for cancers harboring BRCA1/2 mutations. Preclinical and preliminary clinical evidence, however, suggests a potentially broader scope for PARP inhibitors. Loss of function of various proteins involved in double strand break repair other than BRCA1/2 has been suggested to be synthetically lethal with PARP inhibition. Inactivation of these genes has been reported in a subset of human cancers and might therefore constitute predictive biomarkers for PARP inhibition. Here we discuss the evidence that the clinical use of PARP inhibition may be broader than targeting of cancers in BRCA1/2 germ-line mutation carriers