Association Of Copy Number Variations Research Articles

Copy number variations and cancer

DNA copy number variations (CNVs) are an important component of genetic variation, affecting a greater fraction of the genome than single nucleotide polymorphisms (SNPs). The advent of high-resolution SNP arrays has made it possible to identify CNVs. Characterization of widespread constitutional (germline) CNVs has provided insight into their role in susceptibility to a wide spectrum of diseases, and somatic CNVs can be used to identify regions of the genome involved in disease phenotypes. The role of CNVs as risk factors for cancer is currently underappreciated. However, the genomic instability and structural dynamism that characterize cancer cells would seem to make this form of genetic variation particularly intriguing to study in cancer. Here, we provide a detailed overview of the current understanding of the CNVs that arise in the human genome and explore the emerging literature that reveals associations of both constitutional and somatic CNVs with a wide variety of human cancers.

Gene copy number variation throughout the Plasmodium falciparum genome

BackgroundGene copy number variation (CNV) is responsible for several important phenotypes of the malaria parasite Plasmodium falciparum, including drug resistance, loss of infected erythrocyte cytoadherence and alteration of receptor usage for erythrocyte invasion. Despite the known effects of CNV, little is known about its extent throughout the genome.ResultsWe performed a whole-genome survey of CNV genes in P. falciparum using comparative genome hybridisation of a diverse set of 16 laboratory culture-adapted isolates to a custom designed high density Affymetrix GeneChip array. Overall, 186 genes showed hybridisation signals consistent with deletion or amplification in one or more isolate. There is a strong association of CNV with gene length, genomic location, and low orthology to genes in other Plasmodium species. Sub-telomeric regions of all chromosomes are strongly associated with CNV genes independent from members of previously described multigene families. However, ~40% of CNV genes were located in more central regions of the chromosomes. Among the previously undescribed CNV genes, several that are of potential phenotypic relevance are identified.ConclusionCNV represents a major form of genetic variation within the P. falciparum genome; the distribution of gene features indicates the involvement of highly non-random mutational and selective processes. Additional studies should be directed at examining CNV in natural parasite populations to extend conclusions to clinical settings.

Association tests and software for copy number variant data

Recent studies have suggested that copy number variation (CNV) significantly contributes to genetic predisposition to several common disorders. These findings, combined with the imperfect tagging of CNVs by single nucleotide polymorphisms (SNPs), have motivated the development of association studies directly targeting CNVs. Several assays, including comparative genomic hybridisation arrays, SNP genotyping arrays, or DNA quantification through real-time polymerase chain reaction analysis, allow direct assessment of CNV status in cohorts sufficiently large to provide adequate statistical power for association studies. When analysing data provided by these assays, association tests for CNV data are not fundamentally different from SNP-based association tests. The main difference arises when the quality of the CNV assay is not sufficient to convert unequivocally the raw measurement into discrete calls -- a common issue, given the technological limitations of current CNV assays. When this is the case, association tests are more appropriately based on the raw continuous measurement provided by the CNV assay, instead of potentially inaccurate discrete calls, thus motivating the development of new statistical methods. Here, the programs available for CNV association testing for case control or family data are reviewed, using either discrete calls or raw continuous data.

Analysis of copy number variants and segmental duplications in the human genome: Evidence for a change in the process of formation in recent evolutionary history

Segmental duplications (SDs) are operationally defined as >1 kb stretches of duplicated DNA with high sequence identity. They arise from copy number variants (CNVs) fixed in the population. To investigate the formation of SDs and CNVs, we examine their large-scale patterns of co-occurrence with different repeats. Alu elements, a major class of genomic repeats, had previously been identified as prime drivers of SD formation. We also observe this association; however, we find that it sharply decreases for younger SDs. Continuing this trend, we find only weak associations of CNVs with Alus. Similarly, we find an association of SDs with processed pseudogenes, which is decreasing for younger SDs and absent entirely for CNVs. Next, we find that SDs are significantly co-localized with each other, resulting in a highly skewed "power-law" distribution and chromosomal hotspots. We also observe a significant association of CNVs with SDs, but find that an SD-mediated mechanism only accounts for some CNVs (<28%). Overall, our results imply that a shift in predominant formation mechanism occurred in recent history: approximately 40 million years ago, during the "Alu burst" in retrotransposition activity, non-allelic homologous recombination, first mediated by Alus and then the by newly formed CNVs themselves, was the main driver of genome rearrangements; however, its relative importance has decreased markedly since then, with proportionally more events now stemming from other repeats and from non-homologous end-joining. In addition to a coarse-grained analysis, we performed targeted sequencing of 67 CNVs and then analyzed a combined set of 270 CNVs (540 breakpoints) to verify our conclusions.

Identification of SNP markers for common CNV regions and association analysis of risk of subarachnoid aneurysmal hemorrhage in Japanese population

Copy number variation (CNV) is emerging as a new tool for understanding human genomic variation, but its relationship with human disease is not yet fully understood. The data for a total of 317,503 genotypes were collected for a genome-wide association study of subarachnoid aneurismal hemorrhage (SAH) in a Japanese population (cases and controls, n=497) using Illumina HumanHap300 BeadChip®. To identify multi-allelic CNV markers, we visually inspected all genotype clusters of 317,503 SNP markers covering the whole genome using Illumina’s BeadStudio 3.0® software. As a result, we identified 597 multi-allelic CNV markers for common (copy loss frequency>0.05) CNV regions in a Japanese population (n=497). The identified CNV markers shared the following characteristics: enrichment of Hardy–Weinberg disequilibria, Mendelian inconsistency among families, and high missing genotype rate. All annotated information for those markers is summarized in our database (http://www.snp-genetics.com/user/srch.htm). In addition, we performed case-control association analyses of identified multi-allelic CNV markers with the risk of subarachnoid aneurysmal hemorrhage. One SNP marker (rs1242541) within a CNV region neighboring the Sel-1 suppressor of lin-12-like protein (SEL1L) was significantly associated with a risk of SAH (P=0.0006). We also validated the CNV around rs1242541 using real-time quantitative polymerase chain reaction (PCR). Information and methods used in this study would be helpful for accurate genotyping of SNPs on CNV regions, which could be used for association analysis of SNP markers within CNV regions.

Detection, Imputation, and Association Analysis of Small Deletions and Null Alleles on Oligonucleotide Arrays

Copy-number variation (CNV) is a major contributor to human genetic variation. Recently, CNV associations with human disease have been reported. Many genome-wide association (GWA) studies in complex diseases have been performed with sets of biallelic single-nucleotide polymorphisms (SNPs), but the available CNV methods are still limited. We present a new method (TriTyper) that can infer genotypes in case-control data sets for deletion CNVs, or SNPs with an extra, untyped allele at a high-resolution single SNP level. By accounting for linkage disequilibrium (LD), as well as intensity data, calling accuracy is improved. Analysis of 3102 unrelated individuals with European descent, genotyped with Illumina Infinium BeadChips, resulted in the identification of 1880 SNPs with a common untyped allele, and these SNPs are in strong LD with neighboring biallelic SNPs. Simulations indicate our method has superior power to detect associations compared to biallelic SNPs that are in LD with these SNPs, yet without increasing type I errors, as shown in a GWA analysis in celiac disease. Genotypes for 1204 triallelic SNPs could be fully imputed, with only biallelic-genotype calls, permitting association analysis of these SNPs in many published data sets. We estimate that 682 of the 1655 unique loci reflect deletions; this is on average 99 deletions per individual, four times greater than those detected by other methods. Whereas the identified loci are strongly enriched for known deletions, 61% have not been reported before. Genes overlapping with these loci more often have paralogs (p = 0.006) and biologically interact with fewer genes than expected (p = 0.004).

Copy Number Variations in the Human Genome: Potential Source for Individual Diversity and Disease Association Studies

Abstract The widespread presence of large-scale genomic varia-tions, termed copy number variation (CNVs), has been recently recognized in phenotypically normal individuals. Judging by the growing number of reports on CNVs, it is now evident that these variants contribute significantly to genetic diversity in the human genome. Like single nucleotide polymorphisms (SNPs), CNVs are expected to serve as potential biomarkers for disease suscepti-bility or drug responses. However, the technical and practical concerns still remain to be tackled. In this re-view, we examine the current status of CNV DBs and research, including the ongoing efforts of CNV screening in the human genome. We also discuss the character-istics of platforms that are available at the moment and suggest the potential of CNVs in clinical research and application. Keywords: array-CGH, Copy number variation (CNV), Genome-wide association study (GWAS) Introduction Traditionally, large-scale genomic variants that are visi-ble in conventional karyotyping have been thought to be associated with early-onset, highly penetrant genetic disorders, while they are incompatible in normal, dis-ease-free individuals (Lupski, 1998; Stankiewicz and Lupski, 2002). The construction of the 'reference ge-nome' by the human genome sequencing project is based on the belief that human genome sequences are virtually identical, even in different individuals, except for well-known single nucleotide polymorphisms (SNP) or size-variants of tandem repeats such as mini- or micro-satellites (variable number of tandem repeats or VNTR) (Przeworski et al., 2000). This traditional concept has been recently challenged by the discovery that large structural variations are more prevalent than previously presumed (Check, 2005). Using high-resolution whole- genome scanning technologies such as array-based comparative genomic hybridization (array-CGH), two groups of pioneering scientists have identified wide-spread copy number variations (CNVs) in apparently healthy, normal individuals (Iafrate et al., 2004; Sebat et al., 2004). It proposes that our genome is more diverse than has ever been recognized, and subsequent studies have identified up to 11,000 CNVs across the whole ge-nome (Tuzun et al., 2005; Hinds et al., 2006; Mills et al., 2006; McCarroll et al., 2006; Conrad et al., 2006; Sharp et al., 2005; Wong et al., 2007; de Smith et al., 2007). Although the current understanding of CNVs is still limited for practical use and technical challenges still re-main to be tackled, recent studies already have demon-strated the potential association of CNVs with various diseases, suggesting plausible functional significances and highlighting the promising utility of CNVs. The current coverage of CNVs in the human genome already has exceeded that of SNPs (approximately 600 Mb comprising ∼12% of human genome) and is still in-creasing (Cooper et al., 2007). These large-scale struc-tural variants, in addition to SNPs, will serve as powerful sources to help our understanding of human genetic variation and of differences in disease susceptibility for various diseases. This paper reviews the current knowl-edge and future perspectives of CNVs.

Identification of a significant association of a single nucleotide polymorphism in TNXB with systemic lupus erythematosus in a Japanese population

Systemic lupus erythematosus (SLE) is one of the common autoimmune diseases, with complex genetic components. Here, we report on a case-control association study of 178 SLE patients and 899 control subjects, using genome-wide gene-based single nucleotide polymorphism (SNP) markers. An SNP, rs3130342, in a 5' flanking region of the TNXB gene revealed a significant association with SLE [P = 0.000000930, odds ratio (OR) 3.11, with 95% confidence interval (95%CI) of 1.89-5.28] in a Japanese population. This association was replicated independently with 203 cases and 294 controls (P = 0.0440, OR 1.52, with 95%CI of 1.01-2.78). Although a copy number variation (CNV) of the C4 gene adjacent to the TNXB gene was reported to be associated with SLE, our analysis on this CNV revealed that the association of CNV of the C4 gene was weaker than the SNP in the TNXB gene and likely to reflect the linkage disequilibrium between C4 CNV and this particular SNP. Stratified analysis also revealed that the association of SNP rs3130342 with SLE was independent of the HLA-DRB1*1501 allele that has been shown to be associated with SLE. Our findings strongly imply that the TNXB gene is a candidate gene susceptible to SLE in the Japanese population.

Methods and strategies for analyzing copy number variation using DNA microarrays

The association of DNA copy-number variation (CNV) with specific gene function and human disease has been long known, but the wide scope and prevalence of this form of variation has only recently been fully appreciated. The latest studies using microarray technology have demonstrated that as much as 12% of the human genome and thousands of genes are variable in copy number, and this diversity is likely to be responsible for a significant proportion of normal phenotypic variation. Current challenges involve developing methods not only for detecting and cataloging CNVs in human populations at increasingly higher resolution but also for determining the association of CNVs with biological function, recent human evolution, and common and complex human disease.

Cavitary pulmonary metastases.

<h3>Abstract</h3> <h3>Background</h3> The role of copy number variants (CNVs) in susceptibility to asthma is not well understood. This is, in part, due to the difficulty of accurately measuring CNVs in large enough sample sizes to detect associations. The recent availability of whole-exome sequencing (WES) in large biobank studies provides an unprecedented opportunity to study the role of CNVs in asthma. <h3>Methods</h3> We called common CNVs in 49,953 individuals in the first release of UK Biobank WES using ClinCNV software. CNVs were tested for association with asthma in a stage 1 analysis comprising 7,098 asthma cases and 36,578 controls from the first release of sequencing data. Nominally-associated CNVs were then meta-analysed in stage 2 with an additional 17,280 asthma cases and 115,562 controls from the second release of UK Biobank exome sequencing, followed by validation and fine-mapping. <h3>Results</h3> Five of 189 CNVs were associated with asthma in stage 2, including a deletion overlapping the <i>HLA-DQA1</i> and <i>HLA-DQB1</i> genes, a duplication of <i>CHROMR/PRKRA</i>, deletions within <i>MUC22</i> and <i>TAP2</i>, and a duplication in <i>FBRSL1</i>. The <i>HLA-DQA1, HLA-DQB1, MUC22</i> and <i>TAP2</i> genes all reside within the human leukocyte antigen (HLA) region on chromosome 6. <i>In silico</i> analyses demonstrated that the deletion overlapping <i>HLA-DQA1</i> and <i>HLA-DQB1</i> is likely to be an artefact arising from under-mapping of reads from non-reference HLA haplotypes, and that the <i>CHROMR/PRKRA</i> and <i>FBRSL1</i> duplications represent presence/absence of pseudogenes within the HLA region. Bayesian fine-mapping of the HLA region suggested that there are two independent asthma association signals. The variants with the largest posterior inclusion probability in the two credible sets were an amino acid change in <i>HLA-DQB1</i> (glutamine to histidine at residue 253) and a multi-allelic amino acid change in <i>HLA-DRB1</i> (presence/absence of serine, glycine or leucine at residue 11). <h3>Conclusions</h3> At least two independent loci characterised by amino acid changes in the <i>HLA-DQA1, HLA-DQB1</i> and <i>HLA-DRB1</i> genes are likely to account for association of SNPs and CNVs in this region with asthma. The high divergence of haplotypes in the HLA can give rise to spurious CNVs, providing an important, cautionary tale for future large-scale analyses of sequencing data.