Copy number variation in hereditary non-polyposis colorectal cancer

Determining the accuracy of next generation sequencing based copy number variation analysis in Hereditary Breast and Ovarian Cancer

BACKGROUND

Copy number variations (CNVs) are commonly associated with malignancies, including hereditary breast and ovarian cancers. Next generation sequencing (NGS) provides solutions for CNV detection in a single run. This study aimed to compare the accuracy of CNV detection by NGS analyzing tool against Multiplex Ligation Dependent Probe Amplification (MLPA).

RESEARCH DESIGN AND METHODS

In total, 1276 cases were studied by targeted NGS panels and 691 cases (61 calls in 58 NGS-CNV positive and 633 NGS-CNV negative cases) were validated by MLPA.

RESULTS

Twenty-eight (46%) NGS-CNV positive calls were consistent, whereas 33 (54%) calls showed discordance with MLPA. Two cases were detected as SNV by the NGS and CNV by the MLPA analysis. In total, 2% of the cases showed an MLPA confirmed CNV region in BRCA1/2. The results of this study showed that despite the high false positive call rate of the NGS-CNV algorithm, there were no false negative calls. The cases that were determined to be negative by the NGS and positive by the MLPA were actually carrying SNVs that were located on the MLPA probe binding sites.

CONCLUSION

The diagnostic performance of NGS-CNV analysis is promising; however, the need for confirmation by different methods remains.

Copy number variation analysis and targeted NGS in 77 families with suspected Lynch syndrome reveals novel potential causative genes

In many families with suspected Lynch syndrome (LS), no germline mutation in the causative mismatch repair (MMR) genes is detected during routine diagnostics. To identify novel causative genes for LS, the present study investigated 77 unrelated, mutation-negative patients with clinically suspected LS and a loss of MSH2 in tumor tissue. An analysis for genomic copy number variants (CNV) was performed, with subsequent next generation sequencing (NGS) of selected candidate genes in a subgroup of the cohort. Genomic DNA was genotyped using Illumina's HumanOmniExpress Bead Array. After quality control and filtering, 25 deletions and 16 duplications encompassing 73 genes were identified in 28 patients. No recurrent CNV was detected, and none of the CNVs affected the regulatory regions of MSH2. A total of 49 candidate genes from genomic regions implicated by the present CNV analysis and 30 known or assumed risk genes for colorectal cancer (CRC) were then sequenced in a subset of 38 patients using a customized NGS gene panel and Sanger sequencing. Single nucleotide variants were identified in 14 candidate genes from the CNV analysis. The most promising of these candidate genes were: (i) PRKCA, PRKDC, and MCM4, as a functional relation to MSH2 is predicted by network analysis, and (ii) CSMD1, as this is commonly mutated in CRC. Furthermore, six patients harbored POLE variants outside the exonuclease domain, suggesting that these might be implicated in hereditary CRC. Analyses in larger cohorts of suspected LS patients recruited via international collaborations are warranted to verify the present findings.

Germline copy number variations are associated with breast cancer risk and prognosis

Breast cancer is one of the most common cancers among women, and susceptibility is explained by genetic, lifestyle and environmental components. Copy Number Variants (CNVs) are structural DNA variations that contribute to diverse phenotypes via gene-dosage effects or cis-regulation. In this study, we aimed to identify germline CNVs associated with breast cancer susceptibility and their relevance to prognosis. We performed whole genome CNV genotyping in 422 cases and 348 controls using Human Affymetrix SNP 6 array. Principal component analysis for population stratification revealed 84 outliers leaving 366 cases and 320 controls of Caucasian ancestry for association analysis; CNVs with frequency > 10% and overlapping with protein coding genes were considered for breast cancer risk and prognostic relevance. Coding genes within the CNVs identified were interrogated for gene- dosage effects by correlating copy number status with gene expression profiles in breast tumor tissue. We identified 200 CNVs associated with breast cancer (q-value < 0.05). Of these, 21 CNV regions (overlapping with 22 genes) also showed association with prognosis. We validated representative CNVs overlapping with APOBEC3B and GSTM1 genes using the TaqMan assay. Germline CNVs conferred dosage effects on gene expression in breast tissue. The candidate CNVs identified in this study warrant independent replication.

Germline INDELs and CNVs in a cohort of colorectal cancer patients: their characteristics, associations with relapse-free survival time, and potential time-varying effects on the risk of relapse

INDELs and CNVs are structural variations that may play roles in cancer susceptibility and patient outcomes. Our objectives were a) to computationally detect and examine the genome‐wide INDEL/CNV profiles in a cohort of colorectal cancer patients, and b) to examine the associations of frequent INDELs/CNVs with relapse‐free survival time. We also identified unique variants in 13 Familial Colorectal Cancer Type X (FCCX) cases. The study cohort consisted of 495 colorectal cancer patients. QuantiSNP and PennCNV algorithms were utilized to predict the INDELs/CNVs using genome‐wide signal intensity data. Duplex PCR was used to validate predictions for 10 variants. Multivariable Cox regression models were used to test the associations of 106 common variants with relapse‐free survival time. Score test and the multivariable Cox proportional hazards models with time‐varying coefficients were applied to identify the variants with time‐varying effects on the relapse‐free survival time. A total of 3486 distinct INDELs/CNVs were identified in the patient cohort. The majority of these variants were rare (83%) and deletion variants (81%). The results of the computational predictions and duplex PCR results were highly concordant (93–100%). We identified four promising variants significantly associated with relapse‐free survival time (P < 0.05) in the multivariable Cox proportional hazards regression models after adjustment for clinical factors. More importantly, two additional variants were identified to have time‐varying effects on the risk of relapse. Finally, 58 rare variants were identified unique to the FCCX cases; none of them were detected in more than one patient. This is one of the first genome‐wide analyses that identified the germline INDEL/CNV profiles in colorectal cancer patients. Our analyses identified novel variants and genes that can biologically affect the risk of relapse in colorectal cancer patients. Additionally, for the first time, we identified germline variants that can potentially be early‐relapse markers in colorectal cancer.

Contribution of rare germline copy number variations and common susceptibility loci in Lynch syndrome patients negative for mutations in the mismatch repair genes

In colorectal carcinoma (CRC), 35% of cases are known to have a hereditary component, while a lower proportion (∼ 5%) can be explained by known genetic factors. In this study, copy number variations (CNVs) were evaluated in 45 unrelated patients with clinical hypothesis of Lynch syndrome (Amsterdam or Bethesda criteria); negative for MLH1, MSH2, MSH6, PMS2, CHEK2*1100delC and TP53 pathogenic mutations; aiming to reveal new predisposing genes. Analyses with two different microarray platforms (Agilent 180K and Affymetrix CytoScan HD) revealed 35 rare CNVs covering 67 known genes in 22 patients. Gains (GALNT6 and GALNT11) and losses (SEMA3C) involving the same gene families related to CRC susceptibility were found among the rare CNVs. Segregation analysis performed on four relatives from one family suggested the involvement of GALNT11 and KMT2C in those at risk of developing CRC. Notably, in silico molecular analysis revealed that 61% (41/67) of the genes covered by rare CNVs were associated with cancer, mainly colorectal (17 genes). Ten common SNPs, previously associated with CRC, were genotyped in 39 index patients and 100 sporadic CRC cases. Although no significant, an increased number of risk alleles was detected in the index cases compared with the sporadic CRC patients. None of the SNPs were covered by CNVs, suggesting an independent effect of each alteration in cancer susceptibility. In conclusion, rare germline CNVs and common SNPs may contribute to an increased risk for hereditary CRC in patients with mismatch repair proficiency.