rs61754011 — VWF Gly550Arg

VWF Gly550Arg — A Propeptide Mutation That Stops Multimer Assembly

Von Willebrand factor is the scaffold protein of primary hemostasis: it bridges platelets to exposed collagen at a vascular injury site, and it ferries coagulation factor VIII through the bloodstream. To function, VWF must assemble into massive chain-like multimers¹¹ multimers
Ultra-large VWF multimers can span hundreds of individual VWF subunits and are far more effective at capturing platelets under the high shear stress of arterial blood flow than small multimers. rs61754011 disrupts that assembly at its very first step.

The Mechanism

The VWF gene encodes a precursor protein (pro-VWF) that begins with a large propeptide — the D1 and D2 domains — that acts as a chaperone. Inside the Golgi apparatus²² Golgi apparatus
The cellular organelle where VWF propeptides dimerize and then oligomerize into multimers before being packaged for secretion, the D2 domain orchestrates disulfide-linked end-to-end joining of VWF dimers into the high molecular weight (HMW) multimer chains that give VWF its clotting efficacy. The Gly550Arg substitution — a glycine replaced by the bulkier, charged arginine — disrupts this multimerization step. The resulting VWF is secreted but lacks its largest, most hemostatically active multimers.

This mechanism defines VWD type 2A: qualitative VWF deficiency with selective loss of HMW multimers and a VWF activity-to-antigen ratio below 0.7. Factor VIII levels are typically normal to mildly reduced. On electrophoretic multimer analysis, the large multimer bands are absent or greatly diminished.

The rs61754011 variant shows autosomal recessive inheritance³³ autosomal recessive inheritance
Heterozygous family members of the index case were phenotypically normal or only mildly affected; the full VWD type 2A phenotype required homozygosity. This recessive pattern distinguishes it from most VWD type 2A mutations, which are dominant — the Gly550Arg D2 domain defect impairs multimerization when present in both alleles, but a single wild-type allele produces sufficient functional propeptide to support normal multimer assembly.

The Evidence

The Gly550Arg mutation was first identified by Schneppenheim et al. in 1995⁴⁴ first identified by Schneppenheim et al. in 1995
In a German kindred, the proband was homozygous Gly550Arg with epistaxis, easy bruising, and menorrhagia; heterozygous relatives were phenotypically normal or borderline-abnormal. Laboratory findings in the homozygote included absent HMW multimers on electrophoresis and a reduced VWF ristocetin cofactor (VWF:RCo) activity disproportionate to VWF antigen level (VWF:Ag) — the hallmark ratio of type 2 VWD. The variant was originally classified as VWD type IIC (propeptide-defective multimerization) and was re-classified as VWD type 2A under the current Sadler 2006 nosology⁵⁵ Sadler 2006 nosology
The updated classification unified VWD subtypes IIA, IIC, IID, IIE, and related propeptide-defect types under the single "type 2A" umbrella.

Because the variant is exceedingly rare in population databases (not detected in gnomAD or the ALFA population dataset across >10,000 chromosomes), population-level frequency estimates are unavailable. The recessive inheritance means most carriers (CT genotype) are unknown to themselves and require clinical investigation only if they have a consanguineous pedigree or a homozygous affected family member. ClinVar classifies the Gly550Arg allele as Pathogenic (VCV000000305) for VWD type 2A based on functional and clinical evidence.

Practical Actions

For homozygous carriers (TT), the clinical picture is von Willebrand disease type 2A — a moderate qualitative bleeding disorder. The cardinal symptoms are mucocutaneous bleeds: frequent or prolonged nosebleeds, easy bruising, gum bleeds, and in women, heavy menstrual periods. Joint bleeds are uncommon.

Management of VWD type 2A focuses on two therapeutic tools: Desmopressin (DDAVP) releases stored VWF from endothelial Weibel-Palade bodies, transiently raising VWF levels 3–5-fold. In type 2A it may provide partial benefit for minor bleeds, but the released VWF still lacks HMW multimers (because the defect is in propeptide-mediated assembly, not in release), so response is typically incomplete. A desmopressin trial under clinical supervision is necessary before relying on it for procedural prophylaxis. VWF concentrate (plasma-derived, e.g. Humate-P, Wilate) delivers functional VWF with a full multimer distribution and is the definitive treatment for major bleeds, surgery, and procedures when desmopressin response is insufficient.

Heterozygous carriers (CT) are typically clinically normal, though mildly reduced VWF:RCo values may appear on sensitive laboratory testing. No treatment is usually indicated, but formal assessment before elective surgery or invasive procedures is prudent.

Interactions

Because this variant follows autosomal recessive inheritance, the clinical risk in heterozygous carriers becomes significant primarily in the context of consanguinity (two carrier parents produce a 25% probability of a homozygous child). ABO blood group (rs505922 / ABO locus) is a major modifier of VWF levels in everyone: blood group O individuals have ~25% lower VWF than non-O, which can compound mild VWF quantitative reductions. However, for the Gly550Arg defect — which is a qualitative structural problem, not a quantitative one — ABO modulation is a secondary consideration. Clinicians managing affected individuals should assess the full coagulation profile including FVIII activity, VWF:Ag, VWF:RCo, and multimer electrophoresis to characterise individual phenotype severity.