rs1295685 — IL13

IL-13 3'-UTR Variant — The Regulatory Tag on the Atopic Haplotype

Interleukin-13¹¹ Interleukin-13
IL-13 is a Th2 cytokine secreted by mast cells, basophils, ILC2 innate lymphoid cells, and activated CD4+ T cells; it drives IgE class switching, mucus hypersecretion, skin barrier remodeling, and airway smooth-muscle hyperresponsiveness is one of the most potent mediators of allergic inflammation in humans. While the better-known rs20541 variant changes the amino acid sequence of the IL-13 protein (p.Arg130Gln), rs1295685 sits 481 base pairs downstream at position chr5:132660753 in the 3' untranslated region (UTR) of the IL13 gene. It does not alter the protein — instead, it lies in a region of the mRNA that controls how long the transcript persists in cells and how efficiently it is translated. These 3'-UTR regulatory variants can influence gene expression as powerfully as coding changes, particularly for cytokines like IL-13 whose secretion is tightly gated by post-transcriptional regulation.

The Mechanism

The 3'-UTR of mRNA contains binding sites for microRNAs and RNA-binding proteins that collectively determine transcript stability and translation rate. A single-nucleotide variant in this region can disrupt or create a microRNA binding site, shifting the equilibrium of IL-13 production upward or downward across immune cells. rs1295685 lies within the IL13 3'-UTR on the plus strand (GRCh38 chr5:132660753), where the minor A allele is the GRCh38 reference but the population-major G allele (~80% globally) represents the baseline regulatory configuration. The A allele — present in approximately 20% of European chromosomes — is found almost exclusively on the same haplotype as the rs20541 Q130 risk allele, confirmed by haplotype analysis in Japanese cohorts²² haplotype analysis in Japanese cohorts
Lee et al. Ann Allergy Asthma Immunol 2020; fine-mapping of IL13 in 495 cases and 444 controls with independent replication in 757 cases and 1,620 controls; rs1295685 showed P=0.01 for AD association in the pilot study. This strong linkage disequilibrium means the two variants tag the same risk haplotype block rather than independently affecting IL-13 biology. The clinical consequence of carrying the A allele is the same as for rs20541-A: higher constitutive IL-13 pathway activity, measurably elevated serum IgE, and greater lifetime risk for atopic disease.

The Evidence

The IL13 5q31 locus is one of the most consistently replicated genomic regions in allergy genetics. A 2023 European and multi-ancestry GWAS meta-analysis³³ 2023 European and multi-ancestry GWAS meta-analysis
Budu-Aggrey et al., Nature Communications; European discovery: ~21,000 AD cases and ~95,000 controls; 23andMe replication: 2.9 million individuals placed the 5q31 IL13 locus at P<10⁻³⁶ for atopic dermatitis, one of the strongest genetic signals in all of human atopy genetics. rs1295685 sits within this implicated haplotype block. Fine-mapping work in [Japanese AD cohorts (495 cases, 444 controls pilot; 757 cases, 1,620 controls replication) | Lee et al. 2020](https://pubmed.ncbi.nlm.nih.gov/32371243/) established that both rs20541 and rs1295685 are significantly associated with atopic dermatitis, and that haplotypes containing both variants confer disease risk (minimum P=0.006). The same study confirmed strong LD between these two IL13 variants, locating the primary functional driver within the rs20541 coding change while acknowledging that rs1295685 marks the same risk haplotype. Fine-mapping of serum IgE loci in [>1,300 German children | Sharma et al. Allergy 2014](https://pubmed.ncbi.nlm.nih.gov/24930997/⁴⁴ https://pubmed.ncbi.nlm.nih.gov/24930997/) confirmed the 5q31 region — containing both IL13 variants — as a major susceptibility locus for elevated total serum IgE, the primary biological readout of sustained IL-13-driven B-cell class-switching.

Because rs1295685 is a 3'-UTR variant, it may also have a regulatory contribution that is independent of rs20541 at the mRNA level — 3'-UTR polymorphisms in cytokine genes frequently modulate transcript stability and production kinetics in ways that complement coding changes. However, the current evidence does not permit separating a 3'-UTR-specific regulatory effect from haplotype tagging; both mechanisms may contribute.

Practical Implications

The clinical implications of carrying the rs1295685 A allele are directly parallel to those of rs20541-A, because the variants co-segregate on the same haplotype in nearly all carriers. Elevated serum IgE, heightened susceptibility to atopic dermatitis, allergic rhinitis, and eczema, and a greater tendency to mount Th2 responses to environmental allergens are the principal consequences. For carriers with active atopic disease inadequately controlled by topical therapies, IL-13-pathway biologics (tralokinumab, dupilumab) represent a genetically rationale treatment pathway. Measuring serum total IgE and periostin provides a quantitative readout of how biologically active the IL-13 pathway is in the individual carrier, and documents eligibility for biologic therapy.

Interactions

rs1295685 lies in strong LD with rs20541 (IL13 R130Q) — these two variants tag the same risk haplotype. Carriers of the A allele at rs1295685 almost invariably also carry the A allele at rs20541, so the combined functional consequence represents compound within-gene effects on IL-13: one variant alters the protein surface charge (rs20541), the other potentially alters mRNA stability and translation rate (rs1295685).

The rs1801275 variant (IL-4Rα R576Q) alters the shared IL-4Rα signal transduction subunit used by both IL-4 and IL-13 receptors. Individuals carrying both rs1295685-A (IL13 UTR risk haplotype) and rs1801275 risk allele may face additive Th2 dysregulation — enhanced IL-13 production meeting altered receptor signal transduction — a mechanistic interaction relevant to dupilumab pharmacogenomics, since dupilumab targets IL-4Rα directly.

The rs2040704 variant in RAD50/TH2LCRR upstream of IL13 tags an enhancer hub that coordinates IL-4, IL-5, and IL-13 expression. Carriers of rs1295685-A alongside the rs2040704 risk haplotype may face compounding Th2 amplification via both cisregulatory (enhancer-level) and UTR-level effects on IL-13 expression.