rs2118181 — FBN1

Intronic FBN1 variant associated with elevated thoracic aortic dissection risk through altered fibrillin-1 microfibril structure and TGF-β1 bioavailability

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FBN1 rs2118181 — An Intronic Variant That Loosens the Aortic Wall's Scaffolding

Fibrillin-1 is the primary structural protein of extracellular microfibrils11 microfibrils
microscopic fibrous scaffolds in connective tissue, particularly important in the aortic wall — the elastic fibers that give the aortic wall its strength and flexibility. Mutations in FBN1 cause Marfan syndrome, but the gene also harbors common variants that, without causing Marfan syndrome, can subtly alter the mechanical properties of the aortic wall. rs2118181 is one such variant, an intronic polymorphism that affects how much functional fibrillin-1 protein the body produces — and by extension, how well the aorta can withstand the mechanical stress of blood pressure.

The Mechanism

The variant sits in an intron of FBN1 on chromosome 15. Although intronic variants do not change the protein sequence directly, they can alter mRNA splicing efficiency, expression levels, or the binding of regulatory proteins. The most direct evidence for a functional mechanism comes from a study of 269 individuals showing that carrying a single copy of the risk allele raised circulating TGF-β1 plasma levels by approximately 1 ng/mL22 carrying a single copy of the risk allele raised circulating TGF-β1 plasma levels by approximately 1 ng/mL
Sepetiene R, et al. Association between Fibrillin1 Polymorphisms and TGF-β1 Concentration. Medicina (Kaunas), 2015. This matters because fibrillin-1 normally sequesters TGF-β133 TGF-β1
transforming growth factor beta-1, a signaling protein that controls cell growth and tissue remodeling in the extracellular matrix. When fibrillin-1 function is subtly impaired, TGF-β1 is released into the circulation, where it drives smooth muscle cell dysfunction, aortic wall inflammation, and progressive structural weakening — the same pathophysiological cascade seen in severe Marfan syndrome, but at a lower magnitude.

The Evidence

The association between rs2118181 and thoracic aortic dissection (TAD) was established in a multicenter case-control study by Iakoubova et al. (PLoS One, 2014)44 Iakoubova et al. (PLoS One, 2014) involving 140 TAD cases, 497 non-dissecting thoracic aortic aneurysm (TAA) cases, and 275 controls from the US, Hungary, and Greece. C allele carriers had an adjusted odds ratio of 1.87 (95% CI 1.09–3.20) for TAD specifically — the life-threatening event where the aortic wall tears. Notably, the association was with dissection rather than aneurysm alone, suggesting the variant specifically affects the wall's resistance to acute mechanical failure rather than simply promoting dilation.

A Lithuanian study of 312 patients undergoing aortic surgery and 472 reference subjects replicated the association55 replicated the association
Lesauskaite V, et al. FBN1 polymorphisms in dilatative pathology of the ascending thoracic aorta. Int J Cardiol, 2015, finding OR 1.70 (95% CI 1.17–2.46) for Stanford Type A aortic dissection in an additive model. The risk allele also showed association with ascending aortic aneurysm (OR 1.67), extending the phenotype beyond pure dissection.

A 2024 study in 122 Chinese Han patients with sporadic TAAD confirmed rs2118181 as a risk factor66 confirmed rs2118181 as a risk factor and found it correlated with increased mortality specifically in male patients (dominant model, p = 0.009), adding a potential sex-specific dimension.

Importantly, the evidence base is still limited: these are small-to-moderate case-control studies, not large GWAS meta-analyses. The variant has not been replicated in genome-wide significant studies and does not appear in the GWAS Catalog as a confirmed hit. The effect is real but should be interpreted as an emerging risk signal.

Practical Actions

Carriers of the C allele — particularly those with two copies or additional cardiovascular risk factors — should be aware of aortic dissection warning signs and ensure aortic dimensions are assessed during routine cardiac imaging if available. Blood pressure control is the most modifiable risk factor: hypertension dramatically amplifies aortic wall stress, and the studies adjusted for it — meaning the FBN1 risk is present even at normal blood pressure, but uncontrolled hypertension compounds it substantially.

Interactions

rs2118181 is often co-inherited with rs1051917777 rs10519177
another intronic FBN1 variant identified in the same Iakoubova 2014 study, which showed a similar association with TAD. Both variants likely tag the same functional haplotype. rs1036477 is a third FBN1 polymorphism identified in the Zhejiang Han study and in the Lithuanian cohort as an independent contributor to aortic aneurysm susceptibility. Carrying multiple risk alleles across these variants may confer additive risk, though compound analyses have not been reported in the published literature.

Genotype Interpretations

What each possible genotype means for this variant.

TT Normal

No elevated fibrillin-1 aortic risk from this variant

You carry two copies of the T allele at rs2118181, the most common genotype globally. Approximately 73% of people share this genotype. You do not carry the C allele that has been associated with elevated thoracic aortic dissection risk in published studies. Your FBN1 microfibril scaffolding is not affected by this particular variant.

CT Intermediate

One copy of the aortic risk allele — modestly elevated dissection risk

The Iakoubova et al. 2014 multicenter study (PLoS One 9:e91437) found C allele carriers had an adjusted OR of 1.87 (95% CI 1.09–3.20) for thoracic aortic dissection specifically, with no significant association for non-dissecting aneurysm alone. A Lithuanian replication study (Lesauskaite et al., 2015) found OR 1.70 for Stanford Type A dissection. The mechanistic link is elevated TGF-β1 levels (approximately +1 ng/mL per risk allele copy), suggesting mildly impaired fibrillin-1 sequestration of TGF-β1 in the aortic extracellular matrix. The evidence is emerging rather than established — these are small case-control studies with no GWAS-level replication.

CC High Risk

Two copies of the aortic risk allele — elevated thoracic aortic dissection risk

The published studies used a dominant or additive genetic model, meaning most data reflect heterozygotes. Homozygous CC individuals were rare in the study populations (as expected given the ~11% C allele frequency in Europeans), and effect sizes for CC specifically were not reported separately. Extrapolating from the additive model, OR for CC would theoretically be approximately 1.87² ≈ 3.5 for thoracic aortic dissection versus TT homozygotes, though this estimate is speculative given the small sample size for CC homozygotes. The TGF-β1 elevation data (Sepetiene et al. 2015) showed a dose-response (~1 ng/mL per allele), suggesting CC carriers may have approximately 2 ng/mL higher TGF-β1 than TT carriers — enough to materially affect aortic wall biology. Evidence is emerging, not established clinical guideline level.