Copy number variation-based gene set analysis reveals cytokine signalling pathways associated with psychiatric comorbidity in patients with inflammatory bowel disease.

BACKGROUND: Recent studies discovered many genetic variants associated with both psychiatric and inflammatory disorders, but the role of genetic factors in the development of psychiatric comorbidity (PC) in inflammatory bowel disease (IBD) is underexplored. Particularly, it has been shown that some of the genetic variants have been linked to the concentrations of circulating cytokines and symptoms of the inflammatory cytokine-associated depression. We analysed genomic features of individuals with IBD by comparing IBD patients with PC with those who have IBD but without PC. We hypothesized that cytokine related signalling pathways may be significantly associated with the psychiatric comorbidity in patients with IBD. METHODS: Individuals enrolled in the Manitoba IBD Cohort Study were separated to two groups accordingly to the presence of PC. A sample set comprising 97 IBD individuals with PC (IBD + PC) and 146 IBD individuals without PC (IBD) was first used to identify copy number variations (CNVs) from genome-wide genetic data using three different detection algorithms. IBD + PC and IBD groups were compared by the number of CNVs overlapping each gene; deletions and duplications were analysed separately. Gene set overrepresentation analysis was then conducted using CNV-overlapped genes and the candidate gene sets of neurological and immunological relevance. RESULTS: Medium-sized CNV (size between 100 and 500 kilobase pairs)-burden is significantly higher in IBD + PC than IBD groups. Gene-based CNV association analysis did not show significant differences between the two IBD groups. Gene set overrepresentation analysis demonstrated the significant enrichment of gene sets related to cytokine signalling pathways by the genes overlapped by deletions in the IBD individuals with PC. CONCLUSION: Our results confirm the role of cytokine signalling pathways in the development of PC in IBD. Additionally, our results warrant further study with a larger sample size focusing on cytokine SNPs to further understand the relationship between inflammatory and psychiatric disorders.

Genome-wide copy number variant data for inflammatory bowel disease in a caucasian population.

Genome-wide copy-number association studies offer new opportunities to identify the mechanisms underlying complex diseases, including chronic inflammatory, psychiatric disorders and others. We have used genotyping microarrays to analyse the copy-number variants (CNVs) from 243 Caucasian individuals with Inflammatory Bowel Disease (IBD). The CNV data was obtained by using multiple quality control measures and merging the results of three different CNV detection algorithms: PennCNV, iPattern, and QuantiSNP. The final dataset contains 4,402 CNVs detected by two or three algorithms independently with high confidence. This paper provides a detailed description of the data generation and quality control steps. For further interpretation of the data presented in this article, please see the research article entitled 'Copy number variation-based gene set analysis reveals cytokine signalling pathways associated with psychiatric comorbidity in patients with inflammatory bowel disease'.

Genome-wide analysis identifies rare copy number variations associated with inflammatory bowel disease.

BACKGROUND: Inflammatory bowel disease (IBD) is an idiopathic, chronic disorder of unclear etiology with an underlying genetic predisposition. Recent genome-wide association studies have identified more than 200 IBD susceptibility loci, but the causes of IBD remain poorly defined. We hypothesized that rare (<0.1% population frequency) gene copy number variations (CNVs) could play an important mechanism for risk of IBD. We aimed to examine changes in DNA copy number in a population-based cohort of patients with IBD and search for novel genetic risk factors for IBD. METHODS: DNA samples from 243 individuals with IBD from the Manitoba IBD Cohort Study and 2988 healthy controls were analyzed using genome-wide SNP microarray technology. Three CNV calling algorithms were applied to maximize sensitivity and specificity of CNV detection. We identified IBD-associated genes affected by rare CNV from comparing the number of overlapping CNVs in IBD samples with the number of overlapping CNVs in controls for each gene. RESULTS: 4,402 CNVs detected by two or three algorithms intersected 7,061 genes, in at least one analyzed sample. Four genes (e.g. DUSP22 and IP6K3) intersected by rare deletions and fourteen genes (e.g. SLC25A10, PSPN, GTF2F1) intersected by rare duplications demonstrated significant association with IBD (FDR-adjusted p-value < 0.01). Of these, ten genes were functionally related to immune response and intracellular signalling pathways. Some of these genes were also identified in other IBD related genome-wide association studies. These suggested that the identified genes may play a role in the risk of IBD. CONCLUSION: Our results revealed new genomic loci associated with IBD, which suggested the role of rare CNVs in IBD risk.

Implications of human genome structural heterogeneity: functionally related genes tend to reside in organizationally similar genomic regions.

BACKGROUND: In an earlier study, we hypothesized that genomic segments with different sequence organization patterns (OPs) might display functional specificity despite their similar GC content. Here we tested this hypothesis by dividing the human genome into 100 kb segments, classifying these segments into five compositional groups according to GC content, and then characterizing each segment within the five groups by oligonucleotide counting (k-mer analysis; also referred to as compositional spectrum analysis, or CSA), to examine the distribution of sequence OPs in the segments. We performed the CSA on the entire DNA, i.e., its coding and non-coding parts the latter being much more abundant in the genome than the former. RESULTS: We identified 38 OP-type clusters of segments that differ in their compositional spectrum (CS) organization. Many of the segments that shared the same OP type were enriched with genes related to the same biological processes (developmental, signaling, etc.), components of biochemical complexes, or organelles. Thirteen OP-type clusters showed significant enrichment in genes connected to specific gene-ontology terms. Some of these clusters seemed to reflect certain events during periods of horizontal gene transfer and genome expansion, and subsequent evolution of genomic regions requiring coordinated regulation. CONCLUSIONS: There may be a tendency for genes that are involved in the same biological process, complex or organelle to use the same OP, even at a distance of ~ 100 kb from the genes. Although the intergenic DNA is non-coding, the general pattern of sequence organization (e.g., reflected in over-represented oligonucleotide "words") may be important and were protected, to some extent, in the course of evolution.

Organizational heterogeneity of vertebrate genomes.

Genomes of higher eukaryotes are mosaics of segments with various structural, functional, and evolutionary properties. The availability of whole-genome sequences allows the investigation of their structure as "texts" using different statistical and computational methods. One such method, referred to as Compositional Spectra (CS) analysis, is based on scoring the occurrences of fixed-length oligonucleotides (k-mers) in the target DNA sequence. CS analysis allows generating species- or region-specific characteristics of the genome, regardless of their length and the presence of coding DNA. In this study, we consider the heterogeneity of vertebrate genomes as a joint effect of regional variation in sequence organization superimposed on the differences in nucleotide composition. We estimated compositional and organizational heterogeneity of genome and chromosome sequences separately and found that both heterogeneity types vary widely among genomes as well as among chromosomes in all investigated taxonomic groups. The high correspondence of heterogeneity scores obtained on three genome fractions, coding, repetitive, and the remaining part of the noncoding DNA (the genome dark matter--GDM) allows the assumption that CS-heterogeneity may have functional relevance to genome regulation. Of special interest for such interpretation is the fact that natural GDM sequences display the highest deviation from the corresponding reshuffled sequences.