rs216311 — VWF Thr1381Ala

VWF Thr1381Ala — A Common Variant That Turns Up the Volume on von Willebrand Factor

Von Willebrand factor¹¹ Von Willebrand factor
a large multimeric glycoprotein produced by endothelial cells and megakaryocytes that acts as both a platelet adhesion bridge at sites of vascular injury and a carrier protein for coagulation factor VIII in the bloodstream is one of the most potent modulators of bleeding and thrombosis risk in the human genome. Plasma VWF levels vary enormously between individuals — roughly four-fold from the 1st to the 99th percentile — and that variation is substantially heritable. The rs216311 variant at codon 1381 in the VWF D4 domain is one of the most studied common VWF coding polymorphisms, with robust evidence that the Ala allele raises circulating VWF concentrations above the Thr baseline, shifting the hemostatic balance toward higher platelet adhesion and clot formation.

The Mechanism

rs216311 is a missense variant in exon 28 of the VWF gene, substituting threonine (Thr) with alanine (Ala) at codon 1381 (c.4141A>G on the coding strand; T>C on the GRCh38 plus strand). This region falls within the VWF D4 domain²² VWF D4 domain
a structural domain implicated in VWF multimerization and regulated secretion from Weibel-Palade bodies in endothelial cells. Structural modeling predicts that the Thr→Ala substitution alters global VWF conformation, which could affect the efficiency of intracellular processing, multimer assembly, or clearance from the circulation — each a known mechanism by which VWF coding variants modulate plasma antigen levels.

The functional consequence is a consistent, dose-dependent shift in plasma VWF antigen levels: individuals homozygous for the Ala allele (CC genotype, ~44% of people globally) show the highest VWF levels, heterozygotes the intermediate, and Thr/Thr homozygotes (TT, ~12% globally) the lowest. This dose-response pattern across three studies in independent populations supports a direct, allele-additive effect rather than a statistical artifact.

The Evidence

The genotype-VWF level relationship was first described by Yuan et al. 2010³³ Yuan et al. 2010
Yuan ZH et al. Zhongguo Shi Yan Xue Ye Xue Za Zhi, 2010 in a cross-sectional study of 120 healthy young adults. Homozygous Ala carriers (AA in the original coding-strand notation; CC at the plus-strand level) had significantly higher plasma VWF than Thr homozygotes (p=0.003 and p=0.019 respectively vs. the two other genotype groups). The study also confirmed that ABO blood group modifies the genotype effect — a known major determinant of VWF levels that acts through a different mechanism (O-group individuals clear VWF faster). An important cross-ethnic replication came from Fu et al. 2012⁴⁴ Fu et al. 2012 in 841 Yugur, Tibetan, and Han Chinese participants: the Ala homozygote consistently associated with the highest plasma VWF levels, with genotype frequency distribution differing significantly across the three groups (p<0.01), suggesting population-level differences in the variant's contribution to VWF variability.

A natural experiment across varying Beijing air quality periods (Yuan et al. 2013)⁵⁵ (Yuan et al. 2013) in 114 healthy medical students confirmed the genotype hierarchy at six blood draws over three months: Thr/Thr homozygotes had the lowest VWF across all time points, Ala/Ala homozygotes the highest, and heterozygotes intermediate — a finding that held even as overall VWF levels fluctuated with pollution levels, ruling out genotype-pollution confounding as the sole explanation. In a case-control study of 104 coronary heart disease patients vs. 96 controls (Yuan et al. 2011)⁶⁶ (Yuan et al. 2011), plasma VWF was highly elevated in CHD patients overall (p<0.001), and heterozygotes showed a trend toward higher VWF than Ala homozygotes in CHD patients — though the SNP alone did not significantly predict CHD susceptibility (OR=1.26; 95% CI 0.70–2.26; p=0.44), indicating the variant contributes to VWF level variation without independently determining cardiovascular disease risk in isolation.

Structural analysis of VWF missense variants in COVID-19 coagulopathy (Elek et al. 2023)⁷⁷ (Elek et al. 2023) found that rs216311 T allele carriers showed enhanced INR. In silico modeling predicted that Thr1381 variants alter global VWF conformation, potentially affecting secretion efficiency and plasma stability, supporting a structural rather than purely regulatory mechanism.

The evidence level is assessed as moderate: the genotype-VWF level association is replicated across independent populations and biological contexts, the dose-response pattern is consistent, and a structural mechanism is plausible. However, the studies are primarily from Chinese cohorts with limited total sample sizes (<1,000 subjects each), and the downstream cardiovascular consequences of the VWF elevation are not yet established for this variant independently of ABO blood group and other confounders.

Practical Actions

For CC homozygotes (the most common genotype, ~44% globally), elevated VWF is a pro-coagulant state that increases the efficiency of platelet plug formation and fibrin clot initiation — clinically relevant in the context of atrial fibrillation, prolonged immobility, surgery, or concurrent thrombophilic variants. Monitoring VWF antigen levels directly provides a genotype-personalized cardiovascular biomarker. Endurance exercise acutely raises VWF but chronically trained athletes often maintain lower resting levels; high-intensity exercise is likely unfavorable acutely for high-VWF individuals at thrombotic risk.

CT heterozygotes carry one Ala allele and have intermediate VWF levels — actionable primarily in the presence of other thrombotic risk factors or family history of VTE or arterial thrombosis.

TT homozygotes (Thr/Thr) have the lowest VWF levels of the three genotypes. While modestly lower VWF in the normal range is generally protective against thrombosis, very low VWF levels approach type 1 von Willebrand disease territory. This genotype is not a disease state but warrants awareness of potential mild bleeding tendency, particularly before surgical procedures.

Interactions

VWF levels are powerfully modified by ABO blood group: O-group individuals have ~25% lower VWF than non-O individuals regardless of rs216311 genotype, because O-type glycans on VWF increase clearance rate. The combination of CC genotype (high VWF expression) with non-O blood group (slow VWF clearance) produces the highest VWF levels of any genotype-blood group combination and may represent an additive thrombotic risk state worth monitoring. Conversely, O-group TT individuals likely have the lowest VWF levels and the greatest susceptibility to surgical bleeding or VWD-like symptoms under stress.

Additional VWF variants at rs1063856 (5'UTR) and rs7965413 affect VWF transcription and secretion through independent mechanisms. The combination of rs216311 CC with promoter or clearance-receptor variants may compound VWF elevation beyond what either variant produces alone.