Background: Genetic factors are major determinants of ankylosing spondylitis (AS) risk. To date, 116 loci have been shown to be definitively associated with AS, collectively accounting for <30% of the total liability to disease. At many loci, the key associated genes and genetic variants remain unclear.

Objectives: To identify further genetic variants influencing AS-risk, and to pinpoint causative genes involved, using a large multi-ancestry genome-wide association study (GWAS).

Methods: GWAS was performed using SNP microarray data from 25,645 cases and 71,224 controls after quality control. This included cohorts of European ancestry (15,913 cases, 59,769 controls), East Asian ancestry (8,372 cases, 9,754 controls), and Iranian/Turkish ancestry (1,360 cases, 1,701 controls). Likely causative genes were identified using 2-sample Mendelian randomization (in UK Biobank genotype, whole blood mRNA and serum protein data) and Transcriptome-Wide Association Study (TWAS) and Proteome-Wide Association Study (PWAS) (OmicsPred) analyses in the overall dataset. Findings for 250 proteins were confirmed using Nulisa proteomic assays (Alamar Biosciences) in 298 European AS cases and 142 healthy controls.

Results: Excluding the MHC, the genomic inflation factors (λ ₁₀₀₀ ) were 1.007 (European), 1.019 (East Asian), and 1.004 (combined). A total of 71 genomewide significant (GWS; P<5x10 ^-8 ) loci were identified, including 32 novel loci. Whilst all novel loci were identified in the European-ancestry cohort, strong correlation was observed between European and east Asian ancestry findings (Pearson correlation of log (OR) for SNPs with P<5x10 ^-5 = 0.9), consistent with strong genetic correlation across ancestries. Novel GWS loci included ATG16L1 (an autophagy gene associated with Crohn’s disease) , SELE (E-selectin, expressed by activated enthothelial cells and involved in leukocyte migration into inflammed tissues), IL12A ( IL12B being a known AS-associated gene), GNLY (granulysin, produced by cytotoxic T-lymphocytes and NK cells with proinflammatory and antimicrobial functions), GPR55 (interacts with AHR , a known AS-gene, and involved in gut inflammation), TNFSF15 (TL1A, a marker of proinflammatory mononuclear phagocytes found in AS gut samples [1]), ABO (encoding ABO, the blood group antigens), and the telomerase genes, TERT and TERC . Imputation of blood group antigens revealed increased AS risk with blood type A amongst European cases (OR=1.064, P=0.0059). Association was also observed with FUT2 (fucosyltransferase 2), which determines secretor status (blood group H), the ability to secrete blood groups across mucosal surfaces, a form of mucosal innate immunity. Increased risk was observed in all ancestries with imputed non-secretor status (OR=1.13, P=1.11x10 ^-7 in Europeans; OR=1.21, P=3.59x10 ^-7 in east Asians). No interaction was observed between FUT2 and ABO on risk of AS. These findings provide further evidence supporting AS being driven by interactions between the gut microbiome and the host immune system. PWAS analysis identified association with 111 unique serum proteins and TWAS with 434 gene transcripts (false discovery rate <0.05). Considering cytokines and related gene products, increased levels of IL-10, IL-17F, IL-23R, IL-11RA, IL-34, IL-37 and reduced levels of IL-1R1 IL-6, IL-6R, IL-12A/B, IL-21, and IL-27RA protein were associated with increased disease risk. Amongst imputed mRNA levels, increased transcript levels of IL2RA, IL2RB, IL6ST, IRF5 and JAK2 were identified in AS cases, whereas mRNA levels of cytokine receptor genes IL7R and IL1RL1 were reduced. We found evidence to support B3GNT2 (β1,3-N-acetylglucosaminyltransferase 2) to be an AS-causative gene encoded at the previously reported chr 2p15 intergenic region. Using 2-sample MR, reduced levels of B3GNT2 mRNA were associated with increased risk of AS (β=-0.250, SE=0.034, P=3.20x10 ^-13 ). B3GNT2 mRNA levels were imputed to be lower in cases than controls (P=1.90x10 ^-32 ). B3GNT2 levels were also found to be lower in cases than controls in direct measurements (P=0.0076). The risk allele of the lead SNP at chr 2p15, rs4672505, is an eQTL for B3GNT2 (GTEX, whole blood normalised effect size 0.19, P=1.07x10 ^-29 ), the risk A allele being associated with reduced B3GNT2 transcription. B3GNT3 elongates cell surface long-chain poly-N-acetyl-lactosamine, leading to suppression of immune responses; B3GNT2-/- mice develop T- and B-cell hyperactivity [2].

Conclusion: This study identifies multiple novel genetic loci and pathways involved in AS pathogenesis, highlighting potential therapeutic targets. These findings underscore the role of gut immunity in the disease, and identify widespread genetically encoded dysregulation of cytokine expression as being involved in AS development.

REFERENCES: [1] Ciccia F, et al. Arthritis & rheumatology . 2018 Dec; 70(12):2003-2013.

[2] Togayachi A, et al. Methods Enzymol . 2010; 479:185-204.

Acknowledgements: NIL.

Disclosure of Interests: Zhixiu Li: None declared, Nicholas Harvey: None declared, Xin Wu: None declared, Jose Garrido-Mesa: None declared, Helena Marzo-Ortega: None declared, Dennis McGonagle: None declared, Ann Morgan: None declared, Nurullah Akkoc: None declared, Bora Nam: None declared, Handan Yarkan Tugsal: None declared, Gökçe Kenar Artin: None declared, Gary McFarlane: None declared, Gareth T. Jones: None declared, Paul Leo: None declared, Kate Zimmerman: None declared, Emma Duncan: None declared, Julia Brown: None declared, Mahdi Mahmoudi: None declared, Ahmadreza Jamshidi: None declared, Elham Farhadi: None declared, Nigil Haroon: None declared, Robert Inman: None declared, Maxime Breban: None declared, Michael M Ward: None declared, Michael H Weisman: None declared, Lianne S Gensler: None declared, David Evans: None declared, Tony Kenna: None declared, Tae-Hwan Kim: None declared, Paul Bryan Wordsworth: None declared, John D Reveille: None declared, Huji Xu: None declared, Matthew Brown No, Clementia, Grey Wolf, Incyte, Ipsen, Altis Medicines, UCB.

© The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.