rs2158177 — TH2LCRR RAD50/IL13 Region Variant

TH2LCRR rs2158177 — Inside the Th2 Locus Control Room

Tucked within TH2LCRR — T helper type 2 locus control region associated RNA — a long noncoding RNA¹¹ long noncoding RNA
lncRNA; a class of RNA molecules longer than 200 nucleotides that do not encode proteins but instead regulate chromatin structure, transcription, and gene expression in the cells where they are expressed that sits at the genomic address where some of the most replicated allergy genetics live — chromosome 5q31.1, position 132,648,366 (GRCh38). This locus is flanked upstream by RAD50²² RAD50
RAD50 double-strand break repair protein; at 5q31, RAD50's intronic sequences house the Th2 locus control region (TH2-LCR), a cluster of regulatory elements that coordinate IL-4, IL-5, and IL-13 expression in Th2-committed immune cells and downstream by IL13 and IL4 — the principal Th2 cytokines responsible for IgE class switching, airway remodeling, and eosinophil recruitment. rs2158177 lies within TH2LCRR's intronic sequence, embedded in one of the most replicated immune-regulation loci in human genetics.

The Mechanism

The intergenic and intronic space between RAD50 and IL13 is home to the Th2 locus control region (TH2-LCR)³³ Th2 locus control region (TH2-LCR)
a cluster of DNase I hypersensitive sites (RHS4–RHS7) that act as long-range chromatin enhancers; when a naive T cell commits to the Th2 lineage, these elements loop chromosomally to simultaneously activate IL-4, IL-5, and IL-13 transcription; allele-specific variants in RHS7 alter DNA methylation at the IL13 promoter — a set of chromatin regulatory elements that collectively determine how vigorously IL-4, IL-5, and IL-13 are transcribed when the immune system encounters allergens and shifts to a Th2 response.

TH2LCRR itself is a lncRNA whose expression is regulated by this same enhancer machinery. Li et al. (2022)⁴⁴ Li et al. (2022)
Li YK et al. Am J Respir Cell Mol Biol 2022; convergent evidence study combining GWAS data, eQTL analysis, and chromosomal conformation capture in human bronchial epithelial cells demonstrated that TH2LCRR expression is significantly elevated in asthma patients and is dependent on the genotype at this locus — with an enhancer containing functional SNPs physically looping to the TH2LCRR promoter, driving expression. rs2158177 is an intronic variant within TH2LCRR, positioned approximately 11 kb from rs2040704 (the established enhancer hub variant at the same locus). Whether rs2158177 itself has independent functional effects or tags the same regulatory haplotype as nearby variants remains to be fully resolved, but population data from the GWAS Catalog places its G allele (European frequency ~21%) in association with elevated blood eosinophil counts (beta=0.064, p=3×10⁻³⁸) — a direct readout of Th2/atopic activation state.

The Evidence

The 5q31 RAD50/TH2LCRR/IL13 locus has genome-wide significance for atopic disease in multiple independent cohorts. A GWAS of childhood-onset atopic dermatitis⁵⁵ GWAS of childhood-onset atopic dermatitis
Weidinger et al. Hum Mol Genet 2013; four loci identified: EDC on chromosome 1, LRRC32 on chromosome 11, RAD50/IL13 on chromosome 5, and MHC on chromosome 6 — Weidinger et al. (2013) — identified the RAD50/IL13 locus as one of only four genome-wide significant loci for childhood AD. Cross-ethnic replication from Jiang et al. (2017)⁶⁶ Jiang et al. (2017)
Jiang XY et al. Asian Pac J Allergy Immunol 2017; 3,013 AD cases and 5,483 controls from the Chinese Han population; two loci — 5q31 and 5q22.1 — both associated with JAK-STAT signaling pathway — analyzing 3,013 atopic dermatitis cases and 5,483 controls in a Chinese Han cohort — confirmed the same 5q31 locus via rs2158177 specifically (OR=1.15, P=1.08×10⁻³), with the dominant model reaching P=3.75×10⁻³. Both loci were functionally annotated to the JAK-STAT signaling pathway, confirming the immune-regulatory context.

A smaller Chinese Han asthma study⁷⁷ Chinese Han asthma study
Liang et al. 2015; 400 asthma cases and 200 controls in Qingdao; assessed both IL-13 and TNF-alpha polymorphisms found an opposite-direction signal for GG homozygotes specifically — fewer GG individuals in cases versus controls (OR=0.31). This result, from a sample a fraction of the size of the AD and eosinophil studies, likely reflects limited power, haplotype context differences between asthma and AD endpoints, or both; the eosinophil GWAS signal (p=3×10⁻³⁸, N=hundreds of thousands) and the AD replication (OR=1.15) in the same direction as the broader 5q31 evidence represent substantially stronger evidence for G allele risk.

Fine-mapping in >1,300 German children⁸⁸ >1,300 German children
Sharma et al. Allergy 2014 confirmed 5q31 as one of three major IgE-regulating loci — alongside 1q23 (FCER1A, the high-affinity IgE receptor) and 12q13 (STAT6) — with carriers of risk alleles at all three loci showing fourfold elevated IgE. The review by Potaczek & Kabesch (2012)⁹⁹ review by Potaczek & Kabesch (2012)
Potaczek DP, Kabesch M. Clin Exp Allergy 2012 places 5q31 within the consensus six-locus framework for IgE genetic architecture.

Practical Implications

The G allele at rs2158177 is a marker of elevated Th2 locus activity — the same biological axis that dupilumab (anti-IL-4Rα), tralokinumab (anti-IL-13), and anti-IL-5 biologics target. For carriers of one or two G alleles who develop refractory atopic conditions, the upstream genetic basis in IL-4/IL-13/IL-5 production provides mechanistic rationale for biologic therapy targeting this axis.

The eosinophil count elevation (beta=0.064 per G allele copy in the large GWAS) means G carriers will tend to have slightly higher baseline eosinophil counts — a readout of Th2 activation. This is clinically useful: an eosinophil count above 300 cells/µL in a symptomatic patient with G alleles supports Th2-driven inflammation and biologic candidacy.

Interactions

rs2158177 is in the same chromosomal region as rs2040704 — approximately 11 kb apart within the 5q31 TH2-LCR — and likely tags the same or an overlapping regulatory haplotype. Both variants are associated with elevated Th2 output; carrying risk alleles at both loci represents the highest local Th2-amplifying burden.

The IL13 coding variant rs20541 (R130Q), ~20 kb downstream, reduces IL-13 affinity for its decoy receptor, increasing IL-13 bioavailability independently of production. The combination of this production-amplifying locus (rs2158177/rs2040704 G allele) with reduced clearance (rs20541 A allele) constitutes a mechanistically coherent double hit on sustained IL-13 signaling.

Carriers who also have rs1801275 (IL-4Rα R576Q) or rs1837253 (TSLP upstream) risk alleles face additional Th2 amplification from receptor signaling efficiency and upstream alarmin cytokine production respectively — the most eosinophilic, IgE-high phenotype emerges from compound risk across production, clearance, receptor, and alarmin axes.