Showing papers by "Alexandra Zhernakova published in 2011"

Dense genotyping identifies and localizes multiple common and rare variant association signals in celiac disease

Abstract: Using variants from the 1000 Genomes Project pilot European CEU dataset and data from additional resequencing studies, we densely genotyped 183 non-HLA risk loci previously associated with immune-mediated diseases in 12,041 individuals with celiac disease (cases) and 12,228 controls. We identified 13 new celiac disease risk loci reaching genome-wide significance, bringing the number of known loci (including the HLA locus) to 40. We found multiple independent association signals at over one-third of these loci, a finding that is attributable to a combination of common, low-frequency and rare genetic variants. Compared to previously available data such as those from HapMap3, our dense genotyping in a large sample collection provided a higher resolution of the pattern of linkage disequilibrium and suggested localization of many signals to finer scale regions. In particular, 29 of the 54 fine-mapped signals seemed to be localized to single genes and, in some instances, to gene regulatory elements. Altogether, we define the complex genetic architecture of the risk regions of and refine the risk signals for celiac disease, providing the next step toward uncovering the causal mechanisms of the disease.

Trans-eQTLs reveal that independent genetic variants associated with a complex phenotype converge on intermediate genes, with a major role for the HLA.

Abstract: For many complex traits, genetic variants have been found associated. However, it is still mostly unclear through which downstream mechanism these variants cause these phenotypes. Knowledge of these intermediate steps is crucial to understand pathogenesis, while also providing leads for potential pharmacological intervention. Here we relied upon natural human genetic variation to identify effects of these variants on trans-gene expression (expression quantitative trait locus mapping, eQTL) in whole peripheral blood from 1,469 unrelated individuals. We looked at 1,167 published trait- or disease-associated SNPs and observed trans-eQTL effects on 113 different genes, of which we replicated 46 in monocytes of 1,490 different individuals and 18 in a smaller dataset that comprised subcutaneous adipose, visceral adipose, liver tissue, and muscle tissue. HLA single-nucleotide polymorphisms (SNPs) were 10-fold enriched for trans-eQTLs: 48% of the trans-acting SNPs map within the HLA, including ulcerative colitis susceptibility variants that affect plausible candidate genes AOAH and TRBV18 in trans. We identified 18 pairs of unlinked SNPs associated with the same phenotype and affecting expression of the same trans-gene (21 times more than expected, P<10(-16)). This was particularly pronounced for mean platelet volume (MPV): Two independent SNPs significantly affect the well-known blood coagulation genes GP9 and F13A1 but also C19orf33, SAMD14, VCL, and GNG11. Several of these SNPs have a substantially higher effect on the downstream trans-genes than on the eventual phenotypes, supporting the concept that the effects of these SNPs on expression seems to be much less multifactorial. Therefore, these trans-eQTLs could well represent some of the intermediate genes that connect genetic variants with their eventual complex phenotypic outcomes.

Meta-analysis of genome-wide association studies in celiac disease and rheumatoid arthritis identifies fourteen non-HLA shared loci

Abstract: Epidemiology and candidate gene studies indicate a shared genetic basis for celiac disease (CD) and rheumatoid arthritis (RA), but the extent of this sharing has not been systematically explored. Previous studies demonstrate that 6 of the established non-HLA CD and RA risk loci (out of 26 loci for each disease) are shared between both diseases. We hypothesized that there are additional shared risk alleles and that combining genome-wide association study (GWAS) data from each disease would increase power to identify these shared risk alleles. We performed a meta-analysis of two published GWAS on CD (4,533 cases and 10,750 controls) and RA (5,539 cases and 17,231 controls). After genotyping the top associated SNPs in 2,169 CD cases and 2,255 controls, and 2,845 RA cases and 4,944 controls, 8 additional SNPs demonstrated P,5610 28 in a combined analysis of all 50,266 samples, including four SNPs that have not been previously confirmed in either disease: rs10892279 near the DDX6 gene (Pcombined=1.2610 212 ), rs864537 near CD247 (Pcombined=2.2610 211 ), rs2298428 near UBE2L3 (Pcombined=2.5610 210 ), and rs11203203 near UBASH3A (Pcombined =1.1610 28 ). We also confirmed that 4 gene loci previously established in either CD or RA are associated with the other autoimmune disease at combined P,5610 28 (SH2B3, 8q24, STAT4, and TRAF1-C5). From the 14 shared gene loci, 7 SNPs showed a genome-wide significant effect on expression of one or more transcripts in the linkage disequilibrium (LD) block around the SNP. These associations implicate antigen presentation and T-cell activation as a shared mechanism of disease pathogenesis and underscore the utility of cross-disease meta-analysis for identification of genetic risk factors with pleiotropic effects between two clinically distinct diseases.

Meta-analysis of genome-wide association studies in celiac disease and rheumatoid arthritis identifies fourteen non-HLA shared loci

Abstract: Background and objectives Epidemiology and candidate gene studies indicate a shared genetic basis for celiac disease (CD) and rheumatoid arthritis (RA), but the extent of this sharing has not been systematically explored. Previous studies demonstrate that 6 of the established non-human leucocyte antigen (HLA) CD and RA risk loci (out of 26 loci for each disease) are shared between both diseases. The authors hypothesised that there are additional shared risk alleles, and that combining genome-wide association study (GWAS) data from each disease would increase power to identify these shared risk alleles. Materials and methods The authors performed a meta-analysis of two published GWAS on CD (4533 cases and 10 750 controls) and RA (5539 cases and 17 231 controls), and genotyping the top associated single-nucleotide polymorphisms (SNPs) in independent set of 2169 CD cases and 2255 controls, and 2845 RA cases and 4944 controls. The authors used the gene-expression dataset of peripheral blood mononuclear cell of 1469 individuals to investigate the genotype-expression correlation of associated variants. The authors also analysed the results using various pathway analysis tools. Results Above already established six shared loci, eight additional SNPs demonstrated p −8 in a combined analysis of all 50 266 samples. From the 14 shared gene loci, 7 SNPs showed a genome-wide significant effect on expression of one or more transcripts in the linkage disequilibrium block around the SNP. Pathway analysis tools indicate remarkable overrepresentation of T cell signalling molecules among the shared genes. Conclusions The authors identified 14 shared CD-RA risk loci. These associations implicate antigen presentation and T cell activation as a shared mechanism of disease pathogenesis and underscore the utility of cross-disease meta-analysis for identification of genetic risk factors with pleiotropic effects between two clinically distinct diseases.

Haplotype-based Analysis of Ulcerative Colitis Risk Loci Identifies Both IL2 and IL21 as Susceptibility Genes in Han Chinese

Abstract: Background: The incidence of ulcerative colitis (UC) varies between Western and Eastern ethnicities. A distinct genetic background may play a role in the differences. Until now, very little was known of the UC genetics in Asian populations. Here we performed a haplotype-based analysis of six known UC susceptibility loci in Han Chinese patients. Methods: In all, 245 UC patients and 300 healthy controls of Han Chinese descent were genotyped for 27 single nucleotide polymorphisms (SNPs), which cover the major haplotypes of the chromosome regions containing IL10, IL2/IL21, MYO9B, ECM1, MST1, and IL23R in Han Chinese. Results: In contrast to the tight linkage disequilibrium (LD) block of the IL2/IL21 region in Caucasians, IL2 and IL21 reside in two independent LD blocks in Han Chinese. The IL2 SNP rs2069762 (P - 7.0 x 10(-4), odds ratio [OR] - 1.54, 95% confidence interval [CI] 1.20-1.99) and the IL21 SNP rs2055979 (P = 1.2 x 10(-4), OR = 1.50, 95% CI 1.17-1.92) were independently associated with UC. We identified one risk haplotype in IL2 and another independent risk haplotype in IL21. In addition to the IL2/IL21 locus, we observed association of the TT genotype of SNP rs1545620 in MYO9B with UC (P = 0.0169; OR = 0.29, 95% CI 0.11-0.78) and association of rs17375018 in IL23R with pancolitis in Chinese UC patients (P - 0.002; OR - 2.38, 95% CI 1.41-4.02). Conclusions: Our study confirmed the association of the IL2/IL21 region with UC in Han Chinese patients, and further implied both IL2 and IL21 as genetic risk factors for UC. Han Chinese UC patients share part of their genetic susceptibility with Caucasian patients. (Inflamm Bowel Dis 2011;17:2472-2479)

Multiple independent variants in 6q21-22 associated with susceptibility to celiac disease in the Dutch, Finnish and Hungarian populations

Abstract: Celiac disease is an inflammatory enteropathy caused by intolerance to gluten. Previous linkage studies in the Dutch, Finnish and Hungarian populations have revealed a locus on chromosome 6q21-22 conferring susceptibility to celiac disease. This locus has previously been implicated in susceptibility to other autoimmune diseases such as Crohn's disease and type 1 diabetes. We performed fine mapping on 446 independent individuals with celiac disease and 641 controls of Dutch origin, testing 872 tagging SNPs in a 22 Mb region of chromosome 6. The 12 most promising SNPs were followed up in 2071 individuals from 284 Finnish and 357 Hungarian celiac disease families to identify risk variants in this region. Multiple markers in the region were significantly associated with celiac disease in the Dutch material. Two SNPs, rs9391227 and rs4946111, were significantly associated with celiac disease in the Finnish population. The association to rs9391227 represents the strongest association signal found in the Finnish (P=0.003, OR 0.66) as well as the combined Dutch, Finnish and Hungarian populations (P=3.6 × 10−5, OR 0.76). The rs9391227 is situated downstream of the HECT domain and ankyrin repeat containing, E3 ubiquitin protein ligase 1 (HACE1) gene and is contained within a region of strong linkage disequilibrium enclosing HACE1. Two additional, independent, susceptibility variants in the 6q21-22 region were also found in a meta-analysis of the three populations. The 6q21-22 region was confirmed as a celiac disease susceptibility locus and harbors multiple independent associations, some of which may implicate ubiquitin-pathways in celiac disease susceptibility.