Development and validation of a variant detection workflow for BRCA1 and BRCA2 genes and its clinical application based on the Ion Torrent technology

Abstract

Background: Breast cancer is the most common among women worldwide, and ovarian cancer is the most difficult gynecological tumor to diagnose and with the lowest chance of cure. Mutations in BRCA1 and BRCA2 genes increase the risk of ovarian cancer by 60% and breast cancer by up to 80% in women. Molecular tests allow a better orientation for patients carrying these mutations, affecting prophylaxis, treatment, and genetic counseling.

Results: Here, we evaluated the performance of a panel for BRCA1 and BRCA2, using the Ion Torrent PGM (Life Technologies) platform in a customized workflow and multiplex ligation-dependent probe amplification for detection of mutations, insertions, and deletions in these genes. We validated the panel with 26 samples previously analyzed by Myriad Genetics Laboratory, and our workflow showed 95.6% sensitivity and 100% agreement with Myriad reports, with 85% sensitivity on the positive control sample from NIST. We also screened 68 clinical samples and found 22 distinct mutations.

Conclusions: The selection of a robust methodology for sample preparation and sequencing, together with bioinformatics tools optimized for the data analysis, enabled the development of a very sensitive test with high reproducibility. We also highlight the need to explore the limitations of the NGS technique and the strategies to overcome them in a clinically confident manner.

Keywords: BRCA; Breast; Cancer; Ion Torrent; Ovarian.

Fig 1

Workflow for processing and analysis of samples in the validation design. PGM personal genome machine, VAF variant allele frequency, BAM bam file, VEP variant effect predictor

Fig 2

Coverage analysis report generated by Coverage Analysis plugin. a Coverage overview from the alignment regions of BRCA1 (chr17) and BRCA2 (chr13). b Reads distribution on the 167 targets of the Ion AmpliSeq BRCA1/2 panel, overlayed with target GC content for each read. Representative data from one of the samples sequenced in this validation

Fig 3

Distribution of the BRCA1 and BRCA2 mutations identified in the clinical cohort. The c.441+2T>A variant was not mapped, since it is an intronic variant.