Ankylosing spondylitis is associated with the anthrax toxin receptor 2 gene (ANTXR2)

Abstract

Objectives: ANTXR2 variants have been associated with ankylosing spondylitis (AS) in two previous genome-wide association studies (GWAS) (p∼9×10(-8)). However, a genome-wide significant association (p<5×10(-8)) was not observed. We conducted a more comprehensive analysis of ANTXR2 in an independent UK sample to confirm and refine this association.

Methods: A replication study was carried out with 2978 cases and 8365 controls. Then, these were combined with non-overlapping samples from the two previous GWAS in a meta-analysis. Human leukocyte antigen (HLA)-B27 stratification was also performed to test for ANTXR2-HLA-B27 interaction.

Results: Out of nine single nucleotide polymorphisms (SNP) in the study, five SNPs were nominally associated (p<0.05) with AS in the replication dataset. In the meta-analysis, eight SNPs showed evidence of association, the strongest being with rs12504282 (OR=0.88, p=6.7×10(-9)). Seven of these SNPs showed evidence for association in the HLA-B27-positive subgroup, but none was associated with HLA-B27-negative AS. However, no statistically significant interaction was detected between HLA-B27 and ANTXR2 variants.

Conclusions: ANTXR2 variants are clearly associated with AS. The top SNPs from two previous GWAS (rs4333130 and rs4389526) and this study (rs12504282) are in strong linkage disequilibrium (r(2)≥0.76). All are located near a putative regulatory region. Further studies are required to clarify the role played by these ANTXR2 variants in AS.

Keywords: Ankylosing Spondylitis; Epidemiology; Gene Polymorphism; Inflammation; Spondyloarthritis.

Figure 1

Forest plots for overall meta-analysis of 9 single nucleotide polymorphisms (SNPs). Plots for SNPs with highly significant p-values, rs12504282 (p=6.7×10⁻⁹), rs4640621 (p=1.2×10⁻⁸), rs4333130 (p=2.5×10⁻⁸) and rs6534639 (p=4.5×10⁻⁶) show agreement across the studies with overlapping CIs. Two SNPs rs11098965 (I²=59%, Cochran's Q p=0.09) and rs4444471 (I²=54%, Cochran's Q p=0.11) exhibit some degree of heterogeneity, but this was not statistically significant (p>0.05).

Figure 2

Regional association plot showing ANTXR2 (CMG2) and all the single nucleotide polymorphisms (SNPs) in the study on the x-axis and their corresponding −log₁₀p values on the y-axis. Historic sex-averaged recombination rates are also shown in blue (top panel). Linkage disequilibrium (r², 1000 Genomes March 2012 European reference panel) between the top SNP rs12504282 (purple) and the other SNPs are also shown with colour-coding. ENCODE data showing that rs12504282 and the previous top genome-wide association studies (GWAS) SNPs are near a region of possible enhancer binding are presented in the bottom panel (A) Gene structure; (B) H3K27Ac mark, ie, often found near active regulatory elements; (C) DNaseI hypersensitivity clusters; (D) Transcription factor ChIP-seq; (E) Chromatin state segmentation; (F) Transcription factor binding sites by epitope-tag; G- Top SNPs from the previous GWAS (rs4333130 (TASC, 2010) and rs4389526 (WTCCC2, 2011)). These three top SNPs from three different studies are strongly correlated (rs4389526-rs4333130 r²=1.0, D′=1.0; rs4389526-rs12504282 r²=0.8, D′=1.0; rs4333130-rs12504282 r²=0.76, D′=1.0).