rs4537545 — IL6R IL6R intron variant

IL6R Intron Variant — A Genetic Tag for Cardiovascular Inflammation Risk

Interleukin-6 (IL-6) is one of the body's most powerful inflammatory messengers. When tissue is damaged, infected, or metabolically stressed, IL-6 floods the bloodstream, triggering C-reactive protein (CRP) production in the liver, activating immune cells, and — at chronically elevated levels — accelerating atherosclerosis and contributing to cardiovascular disease. The IL6R gene encodes the interleukin-6 receptor (IL-6R)¹¹ interleukin-6 receptor (IL-6R)
the cell-surface protein that binds IL-6 and initiates downstream JAK-STAT3 signaling cascades. A soluble form of this receptor (sIL-6R), shed from cell surfaces, enables "trans-signaling" — extending IL-6 activity to cells that do not themselves express membrane-bound IL-6R. rs4537545 is an intronic variant in IL6R whose C allele tags a haplotype associated with elevated inflammatory and lipid markers, and reduced protection from coronary heart disease.

The Mechanism

rs4537545 sits within intron 9 of IL6R on chromosome 1q21 and does not itself change the receptor's amino acid sequence. Its cardiovascular significance comes from linkage disequilibrium (LD)²² linkage disequilibrium (LD)
a statistical association between nearby genetic variants, meaning they are inherited together more often than chance would predict with the functional coding variant rs2228145 (Asp358Ala, p.Asp358Ala). The Asp358Ala substitution in the membrane-proximal domain of IL-6R alters the cleavage efficiency of the receptor's ectodomain by the metalloprotease ADAM17 (TACE), increasing release of sIL-6R into circulation. Higher circulating sIL-6R amplifies IL-6 trans-signaling in tissues that lack membrane-bound IL-6R — including vascular smooth muscle and endothelial cells — while paradoxically reducing classic IL-6 signaling in hepatocytes, which lowers CRP and fibrinogen production.

The rs4845625*T / rs4537545*C haplotype represents the pro-inflammatory configuration: reduced Asp358Ala activity, less sIL-6R shedding, stronger hepatic classic IL-6 signaling, and consequently higher circulating CRP and LDL cholesterol.

The Evidence

The most powerful evidence linking IL6R variants to cardiovascular disease comes from a Mendelian randomization meta-analysis coordinated by the IL6R MR Consortium³³ meta-analysis coordinated by the IL6R MR Consortium
Swerdlow DI et al., Lancet 2012, which combined data from 40 studies (up to 133,449 individuals for biomarker endpoints) and 25,458 coronary heart disease (CHD) cases alongside 100,740 controls across 25 studies. The Asp358Ala allele (tagged by rs4537545 through LD) was associated with a 9.45% increase in circulating IL-6 per allele (95% CI 8.34–10.57), an 8.35% decrease in CRP per allele (95% CI 7.31–9.38), and a 0.85% decrease in fibrinogen per allele — alongside a per-allele CHD odds ratio of 0.95 (95% CI 0.93–0.97, p=1.53×10⁻⁵). This inverse relationship — higher IL-6, lower CRP — reflects the sIL-6R shedding mechanism shifting IL-6 activity away from hepatic acute-phase protein synthesis. The genetic evidence parallels clinical trial findings for IL-6R-blocking biologics (tocilizumab, sarilumab), supporting IL-6R signaling as a causal cardiovascular target.

The specific haplotype containing rs4537545*C was directly linked to cardiovascular biomarker risk in a study by Arguinano et al.⁴⁴ study by Arguinano et al.
Arguinano AA et al., Genes Immun 2017, which examined two IL6R SNPs in French and Dutch cohorts. The rs4845625*T/rs4537545*C haplotype was simultaneously associated with elevated CRP (P=0.009), higher LDL-C (P=0.007), and elevated ApoB (P=0.009) — the full atherogenic triad. The rs4537545 T allele alone showed inverse associations with CRP (P=0.009), while the combination of risk alleles at both loci amplified the biomarker effect beyond either SNP alone.

In a prospective cohort of 559 Danish patients with severe chronic heart failure⁵⁵ 559 Danish patients with severe chronic heart failure
Hansen PR et al., Pharmacogenomics J 2019, IL6R pathway SNPs — including rs4537545 and the functionally linked rs2228145 — were among independent predictors of cardiovascular death and all-cause mortality over a mean 5-year follow-up (14-year observation window). Heterozygous carriers of related IL6R variants showed hazard ratios of 1.37–1.39 for cardiovascular death (p < 0.008), pointing to the prognostic importance of IL-6 signaling genetics in established heart disease.

Practical Actions

For individuals carrying the CC genotype, the actionable priorities are monitoring inflammatory cardiovascular biomarkers (hs-CRP and LDL-C), since this genotype is associated with higher baseline levels of both. Omega-3 fatty acids at pharmacological doses reduce CRP, and high-sensitivity statin trials show reductions in both CRP and cardiovascular events even at baseline LDL levels that clinical guidelines would not normally treat.

For individuals on IL-6R-targeting biologics (tocilizumab or sarilumab) for rheumatoid arthritis or other indications, IL6R genotype may influence receptor sensitivity and treatment response — a clinically relevant pharmacogenomic consideration to discuss with a prescriber.

Interactions

rs4537545 is in LD with rs2228145 (the Asp358Ala coding variant) and rs8192284, which have been the primary variants studied in GWAS and Mendelian randomization analyses. The rs4845625 variant shows strong haplotypic interaction with rs4537545: the combination of rs4845625*T and rs4537545*C produces a larger simultaneous effect on CRP, LDL-C, and ApoB than either variant alone, suggesting that IL6R haplotype-level analysis captures more cardiovascular risk than individual SNPs. Individuals who carry rs4537545*C alongside rs4845625*T represent the highest-risk configuration for these inflammatory and lipid biomarkers. Interaction with the CRP gene variants (rs1205, rs1800947) may further modulate baseline CRP levels beyond the IL6R pathway contribution.