rs1036477 — FBN1

FBN1 rs1036477 — When the Aortic Wall's Structural Scaffolding Is Subtly Compromised

The aorta is not a passive tube — it is a living elastic structure that expands and recoils with every heartbeat, storing energy on expansion and releasing it to sustain diastolic flow. This elasticity¹¹ elasticity
the ability to stretch and return, critical for damping the pulsatile pressure wave from each heartbeat into steady forward flow depends on microfibrils: rope-like protein scaffolds made primarily from fibrillin-1, encoded by FBN1. When fibrillin-1 fails — most dramatically in Marfan syndrome — the aortic wall weakens progressively, diameters enlarge, and the risk of catastrophic rupture or dissection rises sharply. rs1036477 is a common intronic variant in FBN1 that, without causing Marfan syndrome, is associated with larger ascending aortic dimensions and modestly elevated risk of thoracic aortic aneurysm and dissection (TAAD).

The Mechanism

rs1036477 sits deep in an intron of FBN1 on chromosome 15q21.1 (the minus strand; plus-strand position 48,622,729 GRCh38). Intronic variants can alter mRNA splicing efficiency, transcription factor binding, or regulatory element activity, but the precise molecular mechanism of rs1036477 has not been resolved at the sequence level. The functional consequence follows from what fibrillin-1 does in the extracellular matrix (ECM): it forms the structural backbone for elastic microfibrils and, critically, sequesters latent TGF-β1²² latent TGF-β1
transforming growth factor beta-1, a signaling protein that when uncontrolled drives smooth muscle cell dysfunction and aortic wall remodeling in the ECM via latent TGF-β binding proteins (LTBPs). When fibrillin-1 function is impaired — even subtly through altered expression levels — TGF-β1 escapes sequestration and activates both canonical (SMAD) and noncanonical (ERK1/2) signaling cascades. This is the same TGF-β dysregulation that drives aortic root dilation in Marfan syndrome, but at a lower magnitude. The G allele at rs1036477 is associated with this downstream phenotype: measurably larger aortic dimensions at population scale.

The Evidence

The strongest evidence comes from large-scale genome-wide association studies of aortic imaging phenotypes. A deep learning GWAS by Pirruccello et al.³³ Pirruccello et al.
Deep learning enables genetic analysis of the human thoracic aorta. Nat Genet, 2022 analyzed cardiac MRI images from 39,688 UK Biobank participants and identified 82 loci associated with ascending thoracic aortic diameter — the FBN1 locus among them. A polygenic score derived from this GWAS predicted thoracic aortic aneurysm diagnosis with HR 1.43 per standard deviation (P=3.3×10⁻²⁰) in 385,621 participants. The GWAS Catalog records rs1036477 specifically with genome-wide significant associations for ascending aorta maximum area (P=1×10⁻¹⁶, β=−16.48 mm²) and ascending thoracic aortic diameter (P=6×10⁻¹⁵), from the Francis CM 2022 and Pirruccello JP 2021/2023 meta-analyses. An independent multi-ancestry GWAS by Tcheandjieu et al.⁴⁴ Tcheandjieu et al.
High heritability of ascending aortic diameter and trans-ancestry prediction of thoracic aortic disease. Nat Genet, 2022 confirmed FBN1 as one of 41 genome-wide significant loci for ascending aortic diameter in 36,021 UK Biobank individuals, with cross-ancestry replication.

Beyond imaging, blood pressure GWAS have independently flagged rs1036477: a meta-analysis in 321,262 individuals by Hoffmann TJ et al.⁵⁵ Hoffmann TJ et al.
Nat Genet, 2017 found genome-wide significant association with pulse pressure (P=2×10⁻²⁶). Wider pulse pressure reflects reduced aortic compliance — consistent with structural changes in the fibrillin-1 microfibril network increasing aortic stiffness.

Clinical case-control data provide the link to disease endpoints. A Lithuanian study by Lesauskaite et al.⁶⁶ Lesauskaite et al.
Eur J Cardiothorac Surg, 2015 of 312 patients undergoing aortic reconstructive surgery versus 472 controls found that rs1036477 minor allele frequencies were significantly higher in aortic aneurysm patients (P=0.007), with OR 1.67 (additive model). A more recent case-control study in 122 sporadic TAAD patients vs 98 controls⁷⁷ 122 sporadic TAAD patients vs 98 controls in a Chinese Han population confirmed rs1036477 as an independent risk factor for sTAAD (recessive model P=0.009) and found association with increased mortality in male sTAAD patients.

Practical Actions

The G allele — particularly homozygous GG — is associated with larger ascending aortic dimensions at the population level. For G allele carriers, the 2022 ACC/AHA Guideline for Aortic Disease⁸⁸ 2022 ACC/AHA Guideline for Aortic Disease
Circulation, 2022 framework applies: ascending aortic diameters ≥5.5 cm trigger surgical consideration, with lower thresholds (≥4.5 cm) for patients with heritable thoracic aortic disease and rapid expansion (>0.5 cm/year). Echocardiographic baseline measurement and periodic surveillance are the primary actionable steps for individuals with genetic risk factors at the FBN1 locus. Beta-blockers reduce the rate of aortic dilation and are a cornerstone of medical management in FBN1-related aortopathy.

Interactions

rs1036477 belongs to the FBN1 locus on chromosome 15q21, which also harbors rs2118181 — another intronic variant independently associated with thoracic aortic dissection (OR 1.87 per Iakoubova et al. 2014, PMID 24743685, and confirmed in the same Lesauskaite 2015 cohort). Both variants associate with elevated TGF-β1 plasma levels, suggesting that compound effects are biologically plausible when both risk alleles are carried. Additionally, variants in TGF-β signaling partners — particularly TGFβR2 (rs1036095, identified as a co-risk factor in the Yu 2024 sTAAD cohort) — likely interact additively with FBN1 variants to elevate sTAAD risk through the shared fibrillin-1/TGF-β axis.