rs1295686 — IL13 IL-13 Atopy Promoter Variant

IL-13 Atopy Haplotype Tag — Intronic Marker of the Th2 Cytokine Risk Block

Interleukin-13¹¹ Interleukin-13
IL-13 is a Th2 cytokine produced by mast cells, basophils, ILC2 innate lymphoid cells, and activated CD4+ helper T cells; it drives IgE class-switching in B cells, mucus hypersecretion in airway epithelium, airway smooth-muscle hyperresponsiveness, and suppression of epidermal barrier proteins including filaggrin is one of the most consequential mediators of allergic inflammation. At chromosome 5q31.1, a cluster of interrelated variants spans the IL13 gene and nearby regulatory elements, forming a haplotype block that has emerged as one of the strongest and most consistently replicated genetic loci in allergy genetics.

rs1295686 is an intronic variant within IL13 located at chr5:132,660,151 (GRCh38). It does not change the IL-13 protein sequence — its significance lies in the haplotype it marks. The minor T allele co-segregates tightly with rs20541 (the missense variant that produces the hyperactive Q130 form of IL-13) and rs1295685 (a 3'-UTR regulatory variant linked to enhanced mRNA stability). Together, these three variants — plus rs848 and rs847 — define the IL13 risk haplotype block at 5q31.1 that has been linked to atopic dermatitis, asthma, allergic rhinitis, elevated serum IgE, and IgE-mediated food allergy across dozens of independent studies.

The Mechanism

As an intronic variant, rs1295686 does not alter IL-13 protein function directly. Luciferase reporter and chromosome conformation capture experiments²² Luciferase reporter and chromosome conformation capture experiments
Li et al. Am J Respir Cell Mol Biol 2022 — identified functional SNPs at the locus as rs1295685, rs848, and rs847, which form a haplotype that interacts with the promoter of TH2LCRR, a long non-coding RNA with elevated expression in asthma patients show that the causal functional effect at this locus operates through a haplotype interacting with TH2LCRR — a long non-coding RNA elevated in asthmatic airways. rs1295686 lies in strong linkage disequilibrium with this functional haplotype and with rs20541, which changes amino acid 130 of the IL-13 protein from arginine (R, lower receptor affinity) to glutamine (Q, higher receptor engagement and enhanced signaling through IL-13Rα1).

When the T allele at rs1295686 is present, the carrier almost invariably also carries the rs20541-A (Q130) and rs1295685-A risk alleles. The combined effect of these co-inherited variants is higher constitutive IL-13 pathway activity: elevated circulating IL-13 protein with enhanced receptor engagement drives persistent IgE production in B cells, mucus hypersecretion and airway hyperresponsiveness in the lung, and epidermal barrier disruption through STAT6-mediated suppression of filaggrin and loricrin in the skin.

The Evidence

The 5q31.1 IL13/RAD50 locus is among the most robust signals in atopy genetics. A 2023 European and multi-ancestry GWAS meta-analysis³³ 2023 European and multi-ancestry GWAS meta-analysis
Budu-Aggrey et al. Nature Communications; ~21,000 cases and ~95,000 controls in European discovery, 2.9 million in 23andMe replication placed the IL13/SLC22A5 5q31 locus at P<10⁻³⁶ for atopic dermatitis — one of the most significant signals in human atopy genetics. rs1295686 lies within this haplotype block.

For food allergy specifically, a challenge-confirmed pediatric cohort study⁴⁴ challenge-confirmed pediatric cohort study
Ashley et al. Clin Exp Allergy 2017; discovery n=722 (367 food-allergic cases, 199 sensitized-tolerant, 156 controls) and replication n=533 (203 cases, 330 controls) found the T allele at rs1295686 associated with IgE-mediated food allergy at OR=1.75 (p=0.003) in discovery and OR=1.37 (p=0.03) in replication; the meta-analysis yielded OR=1.50 (p=0.0006). This study confirmed complete LD between rs1295686 and rs20541, establishing that the intronic tag and the coding functional variant travel together on the same risk haplotype.

For total serum IgE, a genome-wide association study in the Framingham Heart Study⁵⁵ genome-wide association study in the Framingham Heart Study
Granada et al. J Allergy Clin Immunol 2012; 6,819 Framingham participants plus 5 independent replication cohorts identified rs1295686 as one of three loci reaching genome-wide significance (P=3.55×10⁻⁸) for elevated total plasma IgE — alongside FCER1A (the high-affinity IgE receptor) and STAT6 (the primary IL-13 downstream transcription factor).

For asthma, analyses in Chinese pediatric and adult cohorts⁶⁶ Chinese pediatric and adult cohorts
Tang et al. Pediatr Allergy Immunol 2016; 903 asthmatic children, 1,205 controls; 479 adult asthmatics, 746 controls found rs1295686 associated with adult asthma (OR=1.64) and early-onset asthma (OR=1.92), confirming IL13 and GSDMB as replicated asthma genes. A study in Saudi Arabian adults⁷⁷ Saudi Arabian adults
Halwani et al. J Asthma 2018 found the T allele at rs1295686 conferred OR=1.69 (p=0.008) for symptomatic asthma, extending the association beyond European ancestry.

The African-ancestry T allele frequency is markedly higher (~66%) than in Europeans (~20%), reflecting population-specific LD patterns. This does not translate directly into higher atopic disease rates, as gene-environment interactions differ, but it does mean the risk allele is substantially more common in individuals of African descent — a factor relevant to genetic counseling in diverse populations.

Practical Implications

Carrying one or two copies of the T allele at rs1295686 indicates membership in the IL-13 high-activity haplotype. The practical consequence is a higher baseline Th2 bias: more IL-13 activity, higher IgE production, and increased susceptibility to the full atopic triad (eczema, allergic rhinitis, asthma) and IgE-mediated food allergy. Measuring serum total IgE quantifies how biologically active this IL-13 pathway is in the individual.

For those with active atopic disease inadequately controlled by topical or standard therapies, the IL-13/IL-4 pathway is the genetically-indicated target. IL-13-specific biologics (tralokinumab) and IL-4Rα inhibitors (dupilumab) directly neutralize the cytokine pathway this haplotype overactivates. Skin barrier protection with ceramide emollients addresses the downstream consequence — filaggrin suppression — of high IL-13 signaling.

Interactions

rs1295686 lies in near-complete linkage disequilibrium with rs20541⁸⁸ rs20541
IL-13 R130Q missense variant; Q130 form engages IL-13Rα1 with higher affinity, driving stronger JAK1/STAT6 signaling in B cells, airway epithelium, and skin keratinocytes and rs1295685⁹⁹ rs1295685
IL-13 3'-UTR variant affecting mRNA stability, on the same risk haplotype block. Carriers of the T allele at rs1295686 are thus almost invariably also carrying the rs20541-A and rs1295685-A risk alleles.

The downstream receptor partner for IL-13 signaling is IL-4Rα (encoded by IL4R, variant rs1801275). Carriers of both the IL-13 haplotype risk allele (rs1295686-T) and the IL4R risk allele may face compounding Th2 dysregulation — elevated IL-13 ligand activity meeting altered receptor signal transduction — with pharmacogenomic relevance to dupilumab response, which acts directly on the shared IL-4/IL-13 receptor subunit.

The upstream regulatory hub rs2040704 (in the RAD50/TH2LCRR region) coordinates expression of the IL-4/IL-5/IL-13 cytokine gene cluster. Combined risk allele status at both rs1295686 and rs2040704 may represent compounding Th2 amplification from different regulatory levels.