Friedman RK, Heath AS, Huffman JE, et al. Genetic study of von Willebrand factor antigen levels ≤ 50 IU/dL identifies variants associated with increased risk of von Willebrand disease and bleeding. J Thromb Haemost. 2025. doi:10.1016/j.jtha.2025.04.029
Clinical Question
Which genetic variants are linked to von Willebrand factor antigen (VWF:Ag) levels at or below 50 IU/dL across diverse populations, and how do these variants relate to a clinical diagnosis of von Willebrand disease (VWD), bleeding phenotypes, and thrombotic risk?
Background
Von Willebrand Disease (VWD) is the most common inherited bleeding disorder, yet its genetic architecture remains a complex clinical mystery. Type 1 VWD, accounting for 70% to 80% of all cases, is defined by a quantitative deficiency in von Willebrand factor (VWF), currently diagnosed at biochemical thresholds of VWF:Ag <30 IU/dL, or between 30 and 50 IU/dL when coupled with a significant bleeding history. While approximately 41% of Type 1 cases demonstrate a clear monogenic inheritance pattern due to pathogenic variants in the VWF gene, the majority of cases are multifactorial, likely driven by a combination of rare variants and common polygenic modifiers. Despite extensive research on loci associated with continuous VWF levels in the general population, a critical knowledge gap exists regarding how these genetic determinants specifically relate to the lower limit of normal (≤50 IU/dL) and why a profound “disconnect” exists between biochemically low levels and formal clinical diagnosis.
Guidlines
Current diagnostic frameworks from the International Society on Thrombosis and Haemostasis (ISTH), the American Society of Hematology (ASH), and the British Society for Haematology (BSH) emphasize the following:
- Diagnostic Thresholds: Type 1 VWD is diagnosed when VWF:Ag levels are less than 30 IU/dL regardless of symptoms, or between 30 and 50 IU/dL in individuals with clinically significant bleeding.
- ABO Reference Ranges: Despite the well-known influence of blood group on VWF levels (where O-group individuals have roughly 25% lower levels), guidelines explicitly do not recommend the use of ABO-specific reference ranges.
- Role of Genetic Testing: Molecular analysis is not a routine requirement for VWD diagnosis, especially in mild Type 1 cases. Its utility is currently reserved for specialized scenarios where it may inform subtype classification or familial counseling.
Study Design
- Primary Analysis: A cross-population genome-wide association study (GWAS) was performed utilizing whole-genome sequencing (WGS) data from the NHLBI Trans-Omics for Precision Medicine (TOPMed) Freeze 6. The cohort included 926 cases (VWF:Ag ≤50 IU/dL) and 12,846 controls (>50 IU/dL) across European, African, Hispanic/Latino, and Asian ancestry groups.
- Secondary Analyses: A meta-analysis of five large-scale biobanks (UK Biobank, FinnGen, Michigan Genomics Initiative [MGI], BioVU, and the Million Veteran Program [MVP]) was conducted to evaluate clinical VWD diagnosis. Specific bleeding and thrombotic phenotypes (Heavy Menstrual Bleeding, Iron Deficiency Anemia, Intrapartum Hemorrhage, GI Bleeding, Deep Vein Thrombosis, and Intracranial Hemorrhage) were assessed within the FinnGen cohort (n=306,833).
- Polygenic Risk Score (PRS): Two PRSs – one including the ABO locus and one excluding it were constructed using 16 VWF-decreasing variants in the MVP cohort (n=461,177) to assess the cumulative risk of clinical VWD diagnosis.
Populations
- Inclusion criteria:
- Available whole-genome sequencing data
- Measured VWF:Ag level (IU/dL)
- Case: VWF:Ag ≤50 IU/dL
- Control: VWF:Ag >50 IU/dL
- Baseline Characteristics
- Mean Age: 49.5 years
- Sex: 59% Female
- VWF:Ag ≤50
- Prevalence (Ancestry): African (11.4%), Hispanic (7.3%), European (5.8%), Asian (2.3%)
Outcomes
Key Genetic Variants
Two primary loci achieved genome-wide significance for association with VWF:Ag levels ≤50 IU/dL:
- VWF locus (p.Tyr1584Cys / rs1800386): A rare missense variant (0.22%) with a profound effect on low VWF levels (OR 78.58) and clinical VWD diagnosis (OR 7.16).
- ABO locus (rs529565): A common intronic variant linked to blood group O, demonstrating a more modest effect on low VWF levels (OR 2.52) and clinical VWD (OR 1.57).
Penetrance and Age-Dependence
The study highlights a major disconnect between biochemistry and clinical manifestation. For individuals heterozygous for p.Tyr1584Cys, the penetrance for VWF:Ag ≤50 IU/dL was 24.2%. In contrast, the penetrance for a formal VWD diagnosis was remarkably low at 0.30%, representing an absolute risk difference of 0.25% compared to the 0.05% risk seen in T-allele homozygotes. Penetrance was highly age-dependent: among those <60 years, penetrance for VWF:Ag ≤50 IU/dL was 51.8%, but this plummeted to 5.0% in those ≥60 years, reflecting the physiological rise of VWF with age.
Clinical Phenotypes and PRS
- Bleeding and Thrombosis (FinnGen): The p.Tyr1584Cys variant significantly increased the risk of intrapartum hemorrhage (OR 2.20), iron deficiency anemia (OR 1.55), and heavy menstrual bleeding (OR 1.27), while providing protection against deep vein thrombosis (OR 0.54).
- PRS Results: The cumulative burden of common alleles significantly drove clinical risk. The PRS, including the ABO locus, showed an OR of 1.71 per SD increase, whereas the PRS excluding ABO showed an OR of 1.40 per SD. Individuals in the top 1% of the PRS including ABO had 4.90 times the odds of a VWD diagnosis compared to the rest of the population (vs. OR 2.77 for the top 1% of the PRS excluding ABO).
Commentary
Pathogenicity Classification
Based on these population-based data, there is a compelling case for reclassifying p.Tyr1584Cys (rs1800386) from “variant of uncertain significance” to a “low-penetrance pathogenic” variant. The biochemical impact is grounded in clear functional consequences: the substitution of tyrosine with cysteine introduces a unique thiol sidechain, promoting disulfide bond switching and aberrant tertiary protein structure. This leads to increased intracellular VWF retention and degradation. Furthermore, the variant increases the susceptibility of VWF multimers to proteolytic cleavage by ADAMTS13, explaining its impact on bleeding risk even when antigen levels are only modestly reduced.
Clinical Utility
The identified associations with iron deficiency anemia and heavy menstrual bleeding support a sex-specific hypothesis: the variant’s impact on iron stores is largely mediated through increased menstrual blood loss in women. While not replacing biochemical testing, PRSs may eventually clarify the “enigma” of VWD in families lacking standard monogenic variants, helping to predict penetrance and risk across the lifespan.
Strengths and Limitations
- Strengths:
- Leveraged whole-genome sequencing to capture rare, high-impact variants like p.Tyr1584Cys.
- Multi-ancestry cohort design enhances the generalizability of the findings beyond European populations.
- The use of five large biobanks allowed for the first robust quantification of absolute risk and penetrance in a population setting.
- Limitations:
- Reliance on ICD-code-based phenotypes in biobanks likely results in significant underreporting and underdiagnosis.
- The study could not distinguish between VWD subtypes (e.g., Type 1 vs. Type 2).
- Bleeding phenotype analyses were restricted to the FinnGen cohort.
These findings confirm that von Willebrand disease exists on a genetic spectrum rather than being a strictly monogenic trait. The clinical phenotype is determined by a complex interplay between rare, low-penetrance variants like p.Tyr1584Cys, and the cumulative burden of common polygenic modifiers. This study underscores the need for diagnostic frameworks to move beyond binary biochemical thresholds toward a more integrated genetic and clinical risk assessment.
Hasan Tahsin Özpolat, MD, is a hematology fellow at the University of Washington/Fred Hutchinson Cancer Center. He completed medical school and internal medicine residency at Istanbul University, followed by postdoctoral research training at the Bloodworks Northwest Research Institute in Seattle. He then completed a nephrology fellowship at the University of Arizona, focusing on glomerular disease and thrombotic microangiopathies. His clinical and research interests center on classical hematology, with particular emphasis on thrombotic microangiopathies.
