Copy number variation and association over T-cell receptor genes--influence of DNA source

Rare germline copy number variants (CNVs) and breast cancer risk

Germline copy number variants (CNVs) are pervasive in the human genome but potential disease associations with rare CNVs have not been comprehensively assessed in large datasets. We analysed rare CNVs in genes and non-coding regions for 86,788 breast cancer cases and 76,122 controls of European ancestry with genome-wide array data. Gene burden tests detected the strongest association for deletions in BRCA1 (P = 3.7E-18). Nine other genes were associated with a p-value < 0.01 including known susceptibility genes CHEK2 (P = 0.0008), ATM (P = 0.002) and BRCA2 (P = 0.008). Outside the known genes we detected associations with p-values < 0.001 for either overall or subtype-specific breast cancer at nine deletion regions and four duplication regions. Three of the deletion regions were in established common susceptibility loci. To the best of our knowledge, this is the first genome-wide analysis of rare CNVs in a large breast cancer case-control dataset. We detected associations with exonic deletions in established breast cancer susceptibility genes. We also detected suggestive associations with non-coding CNVs in known and novel loci with large effects sizes. Larger sample sizes will be required to reach robust levels of statistical significance.

Genome-wide Analysis of Common Copy Number Variation and Epithelial Ovarian Cancer Risk

BACKGROUND

Germline DNA copy number variation (CNV) is a ubiquitous source of genetic variation and remains largely unexplored in association with epithelial ovarian cancer (EOC) risk.

METHODS

CNV was quantified in the DNA of approximately 3,500 cases and controls genotyped with the Illumina 610k and HumanOmni2.5M arrays. We performed a genome-wide association study of common (>1%) CNV regions (CNVRs) with EOC and high-grade serous (HGSOC) risk and, using The Cancer Genome Atlas (TCGA), performed in silico analyses of tumor-gene expression.

RESULTS

Three CNVRs were associated (P < 0.01) with EOC risk: two large (∼100 kb) regions within the 610k set and one small (<5 kb) region with the higher resolution 2.5M data. Large CNVRs included a duplication at LILRA6 (OR = 2.57; P = 0.001) and a deletion at CYP2A7 (OR = 1.90; P = 0.007) that were strongly associated with HGSOC risk (OR = 3.02; P = 8.98 × 10^-5). Somatic CYP2A7 alterations correlated with EGLN2 expression in tumors (P = 2.94 × 10^-47). An intronic ERBB4/HER4 deletion was associated with reduced EOC risk (OR = 0.33; P = 9.5 × 10^-2), and somatic deletions correlated with ERBB4 downregulation (P = 7.05 × 10^-5). Five CNVRs were associated with HGSOC, including two reduced-risk deletions: one at 1p36.33 (OR = 0.28; P = 0.001) that correlated with lower CDKIIA expression in TCGA tumors (P = 2.7 × 10^-7), and another at 8p21.2 (OR = 0.52; P = 0.002) that was present somatically where it correlated with lower GNRH1 expression (P = 5.9 × 10^-5).

CONCLUSIONS

Though CNV appears to not contribute largely to EOC susceptibility, a number of low-to-common frequency variants may influence the risk of EOC and tumor-gene expression.

IMPACT

Further research on CNV and EOC susceptibility is warranted, particularly with CNVs estimated from high-density arrays.

Rare CNVs in Suicide Attempt include Schizophrenia-Associated Loci and Neurodevelopmental Genes: A Pilot Genome-Wide and Family-Based Study

Suicidal behavior (SB) has a complex etiology involving genes and environment. One of the genetic components in SB could be copy number variations (CNVs), as CNVs are implicated in neurodevelopmental disorders. However, a recently published genome-wide and case-control study did not observe any significant role of CNVs in SB. Here we complemented these initial observations by instead using a family-based trio-sample that is robust to control biases, having severe suicide attempt (SA) in offspring as main outcome (n = 660 trios). We first tested for CNV associations on the genome-wide Illumina 1M SNP-array by using FBAT-CNV methodology, which allows for evaluating CNVs without reliance on CNV calling algorithms, analogous to a common SNP-based GWAS. We observed association of certain T-cell receptor markers, but this likely reflected inter-individual variation in somatic rearrangements rather than association with SA outcome. Next, we used the PennCNV software to call 385 putative rare (<1%) and large (>100 kb) CNVs, observed in n = 225 SA offspring. Nine SA offspring had rare CNV calls in a set of previously schizophrenia-associated loci, indicating the importance of such CNVs in certain SA subjects. Several additional, very large (>1MB) sized CNV calls in 15 other SA offspring also spanned pathogenic regions or other neural genes of interest. Overall, 45 SA had CNVs enriched for 65 medically relevant genes previously shown to be affected by CNVs, which were characterized by a neurodevelopmental biology. A neurodevelopmental implication was partly congruent with our previous SNP-based GWAS, but follow-up analysis here indicated that carriers of rare CNVs had a decreased burden of common SNP risk-alleles compared to non-carriers. In conclusion, while CNVs did not show genome-wide association by the FBAT-CNV methodology, our preliminary observations indicate rare pathogenic CNVs affecting neurodevelopmental functions in a subset of SA, who were distinct from SA having increased SNP risk-allele burden. These observations may open up new avenues in the genetic etiology of SB.

A Meta-Analysis of Retinoblastoma Copy Numbers Refines the List of Possible Driver Genes Involved in Tumor Progression

BACKGROUND

While RB1 loss initiates retinoblastoma development, additional somatic copy number alterations (SCNAs) can drive tumor progression. Although SCNAs have been identified with good concordance between studies at a cytoband resolution, accurate identification of single genes for all recurrent SCNAs is still challenging. This study presents a comprehensive meta-analysis of genome-wide SCNAs integrated with gene expression profiling data, narrowing down the list of plausible retinoblastoma driver genes.

METHODS

We performed SCNA profiling of 45 primary retinoblastoma samples and eight retinoblastoma cell lines by high-resolution microarrays. We combined our data with genomic, clinical and histopathological data of ten published genome-wide SCNA studies, which strongly enhanced the power of our analyses (N = 310).

RESULTS

Comprehensive recurrence analysis of SCNAs in all studies integrated with gene expression data allowed us to reduce candidate gene lists for 1q, 2p, 6p, 7q and 13q to a limited gene set. Besides the well-established driver genes RB1 (13q-loss) and MYCN (2p-gain) we identified CRB1 and NEK7 (1q-gain), SOX4 (6p-gain) and NUP205 (7q-gain) as novel retinoblastoma driver candidates. Depending on the sample subset and algorithms used, alternative candidates were identified including MIR181 (1q-gain) and DEK (6p gain). Remarkably, our study showed that copy number gains rarely exceeded change of one copy, even in pure tumor samples with 100% homozygosity at the RB1 locus (N = 34), which is indicative for intra-tumor heterogeneity. In addition, profound between-tumor variability was observed that was associated with age at diagnosis and differentiation grades.

INTERPRETATION

Since focal alterations at commonly altered chromosome regions were rare except for 2p24.3 (MYCN), further functional validation of the oncogenic potential of the described candidate genes is now required. For further investigations, our study provides a refined and revised set of candidate retinoblastoma driver genes.

Whole-Genome Sequencing of Salivary Gland Adenoid Cystic Carcinoma

Adenoid cystic carcinomas (ACC) of the salivary glands are challenging to understand, treat, and cure. To better understand the genetic alterations underlying the pathogenesis of these tumors, we performed comprehensive genome analyses of 25 fresh-frozen tumors, including whole-genome sequencing and expression and pathway analyses. In addition to the well-described MYB-NFIB fusion that was found in 11 tumors (44%), we observed five different rearrangements involving the NFIB transcription factor gene in seven tumors (28%). Taken together, NFIB translocations occurred in 15 of 25 samples (60%, 95% CI, 41%-77%). In addition, mRNA expression analysis of 17 tumors revealed overexpression of NFIB in ACC tumors compared with normal tissues (P = 0.002). There was no difference in NFIB mRNA expression in tumors with NFIB fusions compared with those without. We also report somatic mutations of genes involved in the axonal guidance and Rho family signaling pathways. Finally, we confirm previously described alterations in genes related to chromatin regulation and Notch signaling. Our findings suggest a separate role for NFIB in ACC oncogenesis and highlight important signaling pathways for future functional characterization and potential therapeutic targeting.

Copy number variations in multiple sclerosis and neuromyelitis optica

OBJECTIVE

To clarify the potential association of copy number variations (CNVs) with multiple sclerosis (MS) and neuromyelitis optica (NMO) in Japanese cases.

METHODS

Genome-wide association analyses of CNVs among 277 MS patients, 135 NMO/NMO spectrum disorder (NMOSD) patients, and 288 healthy individuals as a discovery cohort, and among 296 MS patients, 76 NMO/NMOSD patients, and 790 healthy individuals as a replication cohort were performed using high-density single nucleotide polymorphism microarrays.

RESULTS

A series of discovery and replication studies revealed that most identified CNVs were 5 to 50kb deletions at particular T cell receptor (TCR) gamma and alpha loci regions. Among these CNVs, a TCR gamma locus deletion was found in 16.40% of MS patients (p = 2.44E-40, odds ratio [OR] = 52.6), and deletion at the TCR alpha locus was found in 17.28% of MS patients (p = 1.70E-31, OR = 13.0) and 13.27% of NMO/NMOSD patients (p = 5.79E-20, OR = 54.6). These CNVs were observed in peripheral blood T-cell subsets only, suggesting the CNVs were somatically acquired. NMO/NMOSD patients carrying the CNV tended to be seronegative for anti-aquaporin-4 antibody or had significantly lower titers than those without CNV.

INTERPRETATION

Deletion-type CNVs at specific TCR loci regions contribute to MS and NMO susceptibility.

Genomic profile of a Li-Fraumeni-like syndrome patient with a 45,X/46,XX karyotype, presenting neither mutations in TP53 nor clinical stigmata of Turner syndrome

Li-Fraumeni syndrome (LFS) is a hereditary disorder that predisposes patients to several types of cancer and is associated with TP53 germline mutations. Turner syndrome (TS) is one of the most common aneuploidies in women. Patients with TS have a higher risk of developing cancer, although multiple malignant tumors are extremely rare. Herein, we describe a patient with a 45,X/46,XX karyotype with no classic phenotype of TS. She presented with a clinical diagnosis of Li-Fraumeni-like syndrome (LFL), showing papillary thyroid carcinoma and fibrosarcoma of the left flank, and had no TP53 germline mutations. Genome-wide analysis of copy number variations (CNVs) was assessed in DNA from peripheral blood cells and saliva. A total of 109 rare CNVs in the blood cells, including mosaic loss of the X chromosome (76% of cells), were identified. In saliva, three rare CNVs were detected, all of them were also detected in the blood cells: loss of 8q24.11 (EXT1), gain of 16q24.3 (PRDM7 and GAS8), and the mosaic loss of the X chromosome (50% of cells). Results of conventional G-banding confirmed the 45,X/46,XX karyotype. Surprisingly, the patient presented with an apparently normal phenotype. The PRDM and GAS8 genes are potential candidates to be associated with the risk of developing cancer in this LFL/TS patient.