rs1343151 — IL23R

Intronic IL23R variant whose minor A allele tags the protective haplotype for ankylosing spondylitis and Crohn's disease while representing an independent susceptibility signal for rheumatoid arthritis

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IL23R rs1343151 — A Haplotype Tag With Dual Immune Consequences

The interleukin-23 receptor (IL23R) gene encodes a key checkpoint in adaptive immunity. When IL-23 binds IL23R on T helper 17 (Th17) cells, it triggers STAT3 phosphorylation11 STAT3 phosphorylation
STAT3 is a transcription factor that, once activated, drives production of the inflammatory cytokines IL-17A and IL-22, sustaining chronic inflammation in the gut, spine, and skin. The rs1343151 variant sits in an intron of IL23R at chromosome 1 position 67,253,446 (GRCh38) and carries no direct amino acid change. Its clinical significance comes from two distinct properties: it tags the protective IL23R haplotype that dampens Th17 responses in ankylosing spondylitis (AS) and inflammatory bowel disease (IBD), and it carries an independent association with rheumatoid arthritis (RA) susceptibility that operates through a separate biological mechanism.

The Mechanism

As an intronic variant, rs1343151 does not directly alter the IL-23 receptor protein. Instead, it acts as a tag SNP22 tag SNP
a variant that is inherited together with nearby functional variants so frequently that knowing its allele predicts those of its neighbours; here rs1343151 co-inherits with rs11465804 and the functional missense variant rs11209026 (R381Q) for the AS and IBD associations. The biological engine is the R381Q substitution at rs11209026: replacing arginine with glutamine at position 381 in the cytoplasmic tail of IL23R partially uncouples the receptor from JAK2/STAT3 signalling, reducing IL-17A output in Th17 effector cells from approximately 36 pg/ml to 5.5 pg/ml under IL-23 stimulation — a 6.5-fold reduction.

The RA association, by contrast, appears to be at least partially independent of the R381Q haplotype. Hollis-Moffatt et al. 200933 Hollis-Moffatt et al. 2009
Ann Rheum Dis; 3,000+ Caucasian RA cases and 3,800+ controls found no association of rs11209026 with RA (OR 1.01) while rs1343151 showed an OR of 1.14 in the same dataset — an unusual dissociation that suggests rs1343151 is tagging a different regulatory element or haplotype block for RA than for IBD and AS.

The Evidence

For Crohn's disease and ulcerative colitis, the protective effect of the A allele is well-replicated in European populations. A New Zealand cohort study (Ferguson et al. 201144 (Ferguson et al. 2011
Gastroenterol Res Pract; 339 CD cases, 407 controls) found an allelic OR of 0.68 (P=0.001), with AA homozygotes showing an OR of 0.29 (95% CI 0.16–0.53) relative to GG individuals — a striking 71% reduction in CD odds. A subsequent meta-analysis of 15 studies55 meta-analysis of 15 studies
Ding et al. Sci Rep 2015 confirmed this with a pooled OR of 0.725 (95% CI 0.690–0.763) across Caucasian populations. Notably, no protective signal was detected in Asian populations, consistent with the low A allele frequency in East Asian cohorts (~8%).

For ankylosing spondylitis, a meta-analysis of 25 case-control studies66 meta-analysis of 25 case-control studies
Zhong et al. Expert Rev Clin Immunol 2018; 8,431 AS cases, 8,972 controls confirmed that the A allele frequency was significantly lower in AS patients than controls (P<0.001), ranking rs1343151 among four IL23R polymorphisms with consistent protective signals against AS. The study-level OR for rs1343151 in an earlier meta-analysis of ankylosing spondylitis cohorts was approximately 0.68 (95% CI 0.55–0.83).

For rheumatoid arthritis, the picture reverses: the A allele is associated with a modest increase in RA risk (OR ~1.11–1.14 in Caucasians), which has been independently replicated across multiple cohorts. This disease-direction reversal at the same allele — protective for gut and spine inflammation, risky for synovial inflammation — reflects the differential roles of IL-23/Th17 signalling in different tissue compartments and disease pathologies.

Practical Implications

For individuals concerned about IBD or spondyloarthritis, the A allele at rs1343151 is a protective marker. AA homozygotes have substantially lower lifetime odds of Crohn's disease and ankylosing spondylitis than GG homozygotes, in parallel with other IL23R protective variants. For RA, the relationship inverts — carriers of the A allele have slightly elevated susceptibility. However, the absolute risk difference conferred by this single variant for RA is small (OR ~1.11) compared with the protective effect on IBD and AS (OR ~0.68–0.72). IL-23 pathway targeting (with biologics such as risankizumab or guselkumab) is highly effective for AS and CD; carriers of the GG genotype at rs1343151 — lacking the protective haplotype — may be among those most likely to benefit from such therapies if they develop these conditions.

Interactions

rs1343151 is in moderate-to-strong linkage disequilibrium with several other IL23R variants on chromosome 1p31.3, including rs11465804, rs10489629, and the functional missense variant rs11209026 (R381Q). For the IBD and AS associations, these variants are largely interchangeable as they tag the same protective haplotype block; a person carrying the protective A allele at rs1343151 will almost always also carry the protective alleles at rs11465804 and rs10489629.

The RA signal at rs1343151, being independent of rs11209026, represents a distinct haplotype association and likely reflects different regulatory architecture in synovial versus intestinal/entheseal immune environments. The IL23R susceptibility variants rs2201841 and rs1004819 tag a separate, risk-conferring haplotype block and are tracked individually in this database.

Genotype Interpretations

What each possible genotype means for this variant.

GG Common Genotype Normal

Standard IL-23 receptor signalling — common genotype without protective IL23R haplotype

The G allele is the GRCh38 reference allele at this position (chr1:67,253,446). In European populations, the G allele frequency is approximately 66%, making GG homozygosity the most common genotype. While GG individuals lack the protective IL23R haplotype at this locus, they are not at elevated risk for IBD or AS — they simply represent the population-baseline reference group. Over 200 genetic loci contribute to IBD susceptibility, and the absence of protection at rs1343151 is only one factor. Environmental exposures, diet, gut microbiome composition, and other genetic variants all contribute substantially.

AA Full IL23R Protection Beneficial

Two protective A alleles — strongest IL23R haplotype protection against ankylosing spondylitis and IBD

The AA genotype carries maximum attenuation of IL-23-driven Th17 responses at this locus, consistent with an additive inheritance model. Both chromosomal copies carry the protective haplotype block, providing the same degree of IL-23 receptor hypomorphism as AA homozygotes at the functionally active rs11209026 (R381Q) locus. This translates to a dramatic reduction in Crohn's disease and ankylosing spondylitis risk in European populations.

The RA susceptibility signal is directionally opposite: each A allele contributes approximately OR 1.11–1.14 to RA risk independently of the R381Q haplotype, so AA individuals carry approximately OR 1.22–1.29 for RA relative to GG individuals by an additive model. This is a modest absolute risk elevation but worth noting in the context of family history or other RA risk factors.

AG Partial IL23R Protection Intermediate

One protective A allele — modestly reduced risk for ankylosing spondylitis and IBD

The A allele at rs1343151 is the ancestral allele (pre-dating the derived G allele) and represents the IL23R protective haplotype for intestinal and spondyloarthritis inflammation. Functional studies of the R381Q-tagged haplotype show that one copy of the protective allele meaningfully reduces IL-23-induced STAT3 phosphorylation and IL-17A output in Th17 cells — the additive model predicts intermediate attenuation between GG (none) and AA (maximum).

The RA counterassociation (A allele confers modest risk, OR ~1.11–1.14) reflects the complex tissue-specific roles of IL-23 signalling: in rheumatoid synovium, reduced IL-23/Th17 tone may paradoxically favour alternative immune pathways (e.g., Th1-dominant) that contribute to joint destruction. The net effect across all autoimmune diseases is not simply protective or risky — it depends on which tissue compartment and which disease is relevant to the individual.