BRCA Testing by Single-Molecule Molecular Inversion Probes.

BACKGROUND: Despite advances in next generation DNA sequencing (NGS), NGS-based single gene tests for diagnostic purposes require improvements in terms of completeness, quality, speed, and cost. Single-molecule molecular inversion probes (smMIPs) are a technology with unrealized potential in the area of clinical genetic testing. In this proof-of-concept study, we selected 2 frequently requested gene tests, those for the breast cancer genes BRCA1 and BRCA2, and developed an automated work flow based on smMIPs. METHODS: The BRCA1 and BRCA2 smMIPs were validated using 166 human genomic DNA samples with known variant status. A generic automated work flow was built to perform smMIP-based enrichment and sequencing for BRCA1, BRCA2, and the checkpoint kinase 2 (CHEK2) c.1100del variant. RESULTS: Pathogenic and benign variants were analyzed in a subset of 152 previously BRCA-genotyped samples, yielding an analytical sensitivity and specificity of 100%. Following automation, blind analysis of 65 in-house samples and 267 Norwegian samples correctly identified all true-positive variants (>3000), with no false positives. Consequent to process optimization, turnaround times were reduced by 60% to currently 10-15 days. Copy number variants were detected with an analytical sensitivity of 100% and an analytical specificity of 88%. CONCLUSIONS: smMIP-based genetic testing enables automated and reliable analysis of the coding sequences of BRCA1 and BRCA2. The use of single-molecule tags, double-tiled targeted enrichment, and capturing and sequencing in duplo, in combination with automated library preparation and data analysis, results in a robust process and reduces routine turnaround times. Furthermore, smMIP-based copy number variation analysis could make independent copy number variation tools like multiplex ligation-dependent probes amplification dispensable.

Identification of Novel Candidate Genes for Early-Onset Colorectal Cancer Susceptibility.

Approximately 25-30% of colorectal cancer (CRC) cases are expected to result from a genetic predisposition, but in only 5-10% of these cases highly penetrant germline mutations are found. The remaining CRC heritability is still unexplained, and may be caused by a hitherto-undefined set of rare variants with a moderately penetrant risk. Here we aimed to identify novel risk factors for early-onset CRC using whole-exome sequencing, which was performed on a cohort of CRC individuals (n = 55) with a disease onset before 45 years of age. We searched for genes that were recurrently affected by rare variants (minor allele frequency ≤ 0.001) with potentially damaging effects and, subsequently, re-sequenced the candidate genes in a replication cohort of 174 early-onset or familial CRC individuals. Two functionally relevant genes with low frequency variants with potentially damaging effects, PTPN12 and LRP6, were found in at least three individuals. The protein tyrosine phosphatase PTP-PEST, encoded by PTPN12, is a regulator of cell motility and LRP6 is a component of the WNT-FZD-LRP5-LRP6 complex that triggers WNT signaling. All variants in LRP6 were identified in individuals with an extremely early-onset of the disease (≤30 years of age), and two of the three variants showed increased WNT signaling activity in vitro. In conclusion, we present PTPN12 and LRP6 as novel candidates contributing to the heterogeneous susceptibility to CRC.

Translating sanger-based routine DNA diagnostics into generic massive parallel ion semiconductor sequencing.

BACKGROUND: Dideoxy-based chain termination sequencing developed by Sanger is the gold standard sequencing approach and allows clinical diagnostics of disorders with relatively low genetic heterogeneity. Recently, new next generation sequencing (NGS) technologies have found their way into diagnostic laboratories, enabling the sequencing of large targeted gene panels or exomes. The development of benchtop NGS instruments now allows the analysis of single genes or small gene panels, making these platforms increasingly competitive with Sanger sequencing. METHODS: We developed a generic automated ion semiconductor sequencing work flow that can be used in a clinical setting and can serve as a substitute for Sanger sequencing. Standard amplicon-based enrichment remained identical to PCR for Sanger sequencing. A novel postenrichment pooling strategy was developed, limiting the number of library preparations and reducing sequencing costs up to 70% compared to Sanger sequencing. RESULTS: A total of 1224 known pathogenic variants were analyzed, yielding an analytical sensitivity of 99.92% and specificity of 99.99%. In a second experiment, a total of 100 patient-derived DNA samples were analyzed using a blind analysis. The results showed an analytical sensitivity of 99.60% and specificity of 99.98%, comparable to Sanger sequencing. CONCLUSIONS: Ion semiconductor sequencing can be a first choice mutation scanning technique, independent of the genes analyzed.