Characterization of a new BRCA1 rearrangement in an Italian woman with hereditary breast and ovarian cancer syndrome

We report a novel BRCA1 LGR, involving the complete duplication of exon 3, in an Italian patient with a strong family history of breast and ovarian cancer. Our purpose is to provide an effective characterization of this LGR using a combination of different methods able to establish the exact breakpoints of the duplication. MAQ assay was used as primary screening method in LGRs detection. Array CGH, RT-PCR, and Long-PCR were used for a careful characterization of rearrangement and breakpoint regions. The Repeat Masker program was employed to identify Alu sequences at breakpoint junctions. RNA analysis showed that this in tandem duplication of exon 3 causes an in frame insertion of 18 amino acids within the protein. Array CGH and Long-PCR strategies revealed that the duplication (g.100411_102863dup) involves exactly 2.452 nucleotides between intron 2 and intron 3 of the gene. In addition, while an Alu Sx sequence was identified at upstream breakpoint, no Alu repeats were found at downstream junction. This supports the hypothesis that the new duplication was the result of a non-homologous recombination event between Alu and Non-Alu sequences. Our strategy, which combines a comprehensive set of methodologies, has been able to characterize the new BRCA1 duplication confirming, as previously reported, that MAQ assay represents a reliable and effective method for a primary screening of BRCA rearrangements. We underline the relevance of incorporating quantitative methods for BRCA genes dosage testing into routine diagnostic practice.