rs61754010 — VWF N528S

VWF N528S — When the Protein Cannot Pack Itself Away

Von Willebrand factor (VWF) is the first responder at a vascular injury — a multimeric protein that bridges damaged endothelium to platelets and chauffeurs factor VIII through the bloodstream. Its effectiveness depends critically on two things: being built into large multimers, and being stored in Weibel-Palade bodies¹¹ Weibel-Palade bodies
endothelial storage organelles that release VWF on demand when a blood vessel is damaged. The rs61754010 variant — encoding the N528S substitution in the VWF propeptide²² N528S substitution in the VWF propeptide
asparagine-to-serine change at position 528 in the D2 domain — disrupts both processes, producing a qualitative deficiency classified as von Willebrand disease type 2A³³ von Willebrand disease type 2A
a subtype characterised by loss of large and intermediate VWF multimers with reduced platelet-dependent function.

The Mechanism

The VWF propeptide (domains D1-D2) acts as a chaperone: it guides the nascent VWF chain through multimerization in the Golgi and escorts the assembled multimers into Weibel-Palade bodies. Position 528 sits in the D2 domain close to a CGLC disulfide-isomerase consensus sequence⁴⁴ CGLC disulfide-isomerase consensus sequence
a short protein motif that orchestrates disulfide bond formation during VWF assembly. The N528S substitution introduces an additional N-glycosylation site (at Asn-526, two residues upstream) by creating the consensus sequence Asn-X-Ser. The extra sugar chain attached at this site physically interferes with the propeptide-VWF interaction needed for normal multimerization and for targeting the assembled protein to storage granules.

Haberichter et al. demonstrated in expression studies⁵⁵ Haberichter et al. demonstrated in expression studies
using heterologous cell lines expressing wild-type and N528S VWF constructs that the mutant VWF is neither properly multimerized nor trafficked to storage granules. The propeptide itself folds and traffics normally — only the mature VWF chain is misdirected. The result, as seen in the Turkish family where this mutation was first characterised, is VWD phenotype IIC: absent triplet structure in plasma multimers, complete absence of platelet VWF multimers beyond protomers, and a near-zero response to desmopressin.

The Evidence

The N528S mutation was identified in a consanguineous Turkish family with several affected homozygous members⁶⁶ consanguineous Turkish family with several affected homozygous members
three documented homozygous patients with significant mucocutaneous and joint bleeding. ClinVar classifies it as Pathogenic for VWD type 2A with four-star expert panel review status (ClinGen VWD Variant Curation Expert Panel, last reviewed August 2024), making it one of the highest-confidence VWF pathogenic classifications in the database.

For type 2A VWD broadly, the evidence on management is well established. Federici & Mannucci reviewed VWD management across subtypes⁷⁷ Federici & Mannucci reviewed VWD management across subtypes
including outcomes data for desmopressin and VWF concentrate use by subtype, establishing that desmopressin has variable and often insufficient efficacy in type 2A and that plasma-derived VWF concentrates are the mainstay of treatment for significant bleeding. A 100-patient Italian cohort study of plasma VWF/FVIII concentrate⁸⁸ 100-patient Italian cohort study of plasma VWF/FVIII concentrate
across all VWD types including type 2A showed excellent or good haemostatic responses in 95% of spontaneous bleeding episodes and 97% of surgical procedures, with no serious adverse events across 370 treatments.

For heterozygous carriers of dominant type 2A mutations, the phenotypic range is wide: some have only laboratory abnormalities (reduced VWF:RCo relative to VWF:Ag), while others have clinically significant bleeding — nosebleeds, heavy menstrual bleeding, prolonged wound bleeding, and post-procedural haemorrhage. The quantitative burden of rare VWF missense variants predicts VWF antigen levels with extreme significance⁹⁹ quantitative burden of rare VWF missense variants predicts VWF antigen levels with extreme significance
P = 1.62 × 10⁻²¹, n = 737 subjects, supporting the pathogenic role of each individual rare coding variant.

Practical Actions

The core clinical step for heterozygous carriers is a formal laboratory assessment: VWF antigen (VWF:Ag), VWF ristocetin cofactor activity (VWF:RCo), and the VWF:RCo/VWF:Ag ratio. In type 2A, the ratio falls below 0.6 — the hallmark of a qualitative defect rather than a simple quantitative one. Multimer analysis shows loss of large multimers. This panel should be performed at a haemostasis specialist centre rather than a routine laboratory, as multimer gels require specific expertise. A desmopressin trial¹⁰¹⁰ desmopressin trial
a controlled 0.3 µg/kg infusion to test VWF release from Weibel-Palade bodies is recommended to document response before using it clinically; for N528S specifically, the storage defect makes desmopressin unreliable and VWF concentrate is the preferred treatment.

For homozygous individuals (an extremely rare scenario given the near-zero population frequency of the C allele), management is as for severe type 2A: VWF concentrate infusion for all bleeding episodes and pre-procedural cover, with desmopressin contraindicated given the absent Weibel-Palade body stores.

Interactions

ABO blood group is a significant modifier of VWF levels in all carriers of VWF variants. Blood group O independently reduces VWF antigen by approximately 25% through enhanced ADAMTS13- mediated clearance, which can compound the qualitative deficit in type 2A and push measurable VWF:RCo activity to levels requiring treatment. Co-inheritance of other VWF variants (compound heterozygosity with a second pathogenic allele on the opposite chromosome) can produce a more severe phenotype than either allele alone. Thrombocytopenia from any cause — including liver disease or immune platelet destruction — further worsens bleeding in VWF- deficient individuals because VWF-platelet co-function is already impaired.