rs1800787 — FGB -148C>T

The Fibrinogen Thermostat — How a Promoter Variant Turns Up Inflammation

Fibrinogen is not merely a clotting protein. Every gram per litre increase in plasma fibrinogen¹¹ Every gram per litre increase in plasma fibrinogen
Fibrinogen is synthesized in the liver and circulates at 2-4 g/L in healthy adults raises cardiovascular risk measurably — fibrinogen simultaneously thickens blood, fuels thrombus formation, and serves as a sensitive acute-phase reactant that spikes during infection, surgery, or chronic low-grade inflammation. The rs1800787 variant, a C-to-T substitution 148 base pairs upstream of the FGB transcription start site, quietly shifts the dial on this system — individuals carrying the T allele produce more fibrinogen at baseline and mount a larger inflammatory surge under stress.

The Mechanism

The FGB gene on chromosome 4q31 encodes the beta chain of fibrinogen, one of three chains (Aα, Bβ, γ) that assemble into the hexameric fibrinogen molecule. The -148 position lies in the promoter region, within transcription factor binding motifs that regulate how strongly the liver expresses the gene in response to interleukin-6 (IL-6) signaling — the master cytokine of the acute-phase response.

The T allele at -148 is thought to create a more accessible transcription factor binding site, leading to higher baseline FGB transcription and an amplified acute-phase response when IL-6 levels rise. The consequence is measurably elevated circulating fibrinogen: T allele carriers show approximately 8-10% higher preoperative fibrinogen compared to CC homozygotes, and a substantially larger CRP and IL-6 surge following surgical or inflammatory challenge.

The Evidence

The most direct clinical evidence comes from a 2012 Polish study of 243 consecutive patients undergoing coronary artery bypass grafting (CABG)²² 243 consecutive patients undergoing coronary artery bypass grafting (CABG)
Wypasek E et al. Fibrinogen beta-chain -C148T polymorphism is associated with increased fibrinogen, C-reactive protein, and interleukin-6 in patients undergoing coronary artery bypass grafting. Inflammation. 2012;35(2):429-35.. T allele carriers had significantly higher preoperative fibrinogen (4.42 ± 0.14 vs 4.07 ± 0.11 mg/L, p=0.04) and CRP (7.49 ± 1.2 vs 4.26 ± 1.0 mg/L, p=0.04). After surgery — a major inflammatory stress — T carriers showed greater CRP elevation (70.4 vs 51.6 mg/L, p=0.005) and higher IL-6 (22.34 vs 15.53 pg/mL, p=0.05). Strikingly, in-hospital non-fatal stroke occurred in 4% of T carriers versus 0% of CC homozygotes (p=0.02). The CT+TT genotype was an independent predictor of elevated pre- and postoperative CRP in multivariate analysis.

Population-level evidence for the fibrinogen-raising effect comes from the CARe consortium³³ CARe consortium
Wassel CL et al. Association of genomic loci from a cardiovascular gene SNP array with fibrinogen levels in European Americans and African-Americans from six cohort studies. Blood. 2011;117(10):2896-905., which examined 23,634 European Americans and 6,657 African Americans across six cohort studies. rs1800787 was consistently associated with fibrinogen concentration in both populations, establishing this as a cross-population effect rather than an ancestry-specific signal.

A study of 2,010 Black Africans⁴⁴ 2,010 Black Africans
Kotzé RC et al. Genetic polymorphisms influencing total and γ' fibrinogen levels and fibrin clot properties in Africans. Br J Haematol. 2015;170(2):253-63. found rs1800787 associated with fibrin fiber size and identified interactions between fibrinogen concentration and clot structure modulated by this variant — suggesting the SNP influences not only fibrinogen quantity but also the architecture of the resulting clot.

Practical Actions

The T allele does not cause disease directly, but it raises the baseline fibrinogen set point and amplifies inflammatory surges. Plasma fibrinogen is an independent predictor of cardiovascular and stroke risk; each 1 g/L increase in fibrinogen is associated with approximately 25% higher cardiovascular mortality risk in prospective cohorts.

For T allele carriers, cardiovascular risk stratification should explicitly include fibrinogen measurement alongside standard lipid panels and CRP. Elevated fibrinogen is addressed primarily through reducing the chronic low-grade inflammation that drives its production: targeted anti-inflammatory interventions — specifically omega-3 supplementation (EPA/DHA), tobacco elimination, and management of inflammatory conditions — have documented fibrinogen-lowering effects of clinical magnitude (0.2-0.5 g/L reductions).

Carriers scheduled for major surgery carry higher perioperative stroke risk based on the Wypasek data; this finding warrants disclosure to surgical teams so that perioperative anticoagulation and neuroprotective strategies can be considered.

Interactions

The -148C>T variant (rs1800787) sits in a haplotype block with other FGB promoter variants, most importantly rs1800790 (-455G>A) and rs1800789. The -455 variant is the better-studied promoter SNP associated with fibrinogen levels and cardiovascular risk — the two variants are often in linkage disequilibrium in European populations. The combined haplotype effect on fibrinogen production is larger than either SNP alone. Individuals carrying T alleles at both positions likely have substantially higher fibrinogen than those carrying risk alleles at only one site. See rs1800790 for the -455 variant profile.