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Zorluk: Çok zorHematology and Oncology

A 24-year-old female undergoes comprehensive coagulation testing for a lifelong history of mucocutaneous bleeding and menorrhagia. Her hematologist suspects a variant of von Willebrand disease (vWD) and orders a full diagnostic panel, including vWF antigen (vWF:Ag), vWF ristocetin cofactor activity (vWF:RCo), Factor VIII activity, ristocetin-induced platelet aggregation (RIPA), and multimer analysis. Match the specific laboratory profiles below with their exact underlying molecular pathophysiology.

  • vWF:RCo to vWF:Ag ratio < 0.7; absent high-molecular-weight multimers; enhanced platelet agglutination at low-dose ristocetin (RIPA); mild thrombocytopenia.Gain-of-function mutation causing excessive spontaneous binding of vWF to platelet glycoprotein Ib
  • Normal vWF:Ag and vWF:RCo; normal multimer pattern; markedly decreased Factor VIII activity; clinically mimics Hemophilia A.Mutation severely impairing vWF's carrier binding affinity for a specific coagulation factor, accelerating its degradation
  • Proportionately decreased vWF:Ag and vWF:RCo (ratio > 0.7); normal multimer distribution; normal platelet count.Heterozygous mutation causing a partial quantitative deficiency of structurally and functionally normal vWF
  • vWF:RCo to vWF:Ag ratio < 0.7; absent high-molecular-weight multimers; markedly decreased or absent ristocetin-induced platelet aggregation (RIPA); normal platelet count.Mutation rendering vWF highly susceptible to cleavage by ADAMTS13 or impairing normal multimer assembly

Cevap

The laboratory profiles map to vWD subtypes as follows: enhanced RIPA/thrombocytopenia matches the gain-of-function glycoprotein Ib binding (Type 2B); isolated low Factor VIII matches impaired carrier binding (Type 2N); proportionate decrease matches partial quantitative deficiency (Type 1); and decreased RIPA matches ADAMTS13 susceptibility/assembly defect (Type 2A).
Precise classification of von Willebrand disease subtypes is critical because their management differs drastically. For example, administering desmopressin (DDAVP) is a standard treatment for Type 1, but it is contraindicated in Type 2B because it can exacerbate spontaneous platelet agglutination and worsen thrombocytopenia. The distinct laboratory findings provided in the stem directly reflect the underlying molecular pathophysiology for each subtype, allowing for definitive matching.

Adım Adım Çözüm

1
Identify the quantitative variant (proportionate decrease, ratio > 0.7).
Matches the partial quantitative deficiency of functionally normal vWF (Type 1).
In Type 1 vWD, the defect affects the amount of vWF, not its structure or function, preserving the ratio.
2
Isolate the variant mimicking Hemophilia A (low Factor VIII, normal vWF parameters).
Matches the mutation impairing vWF's carrier binding affinity (Type 2N).
vWF acts as a protective carrier protein for Factor VIII. When this binding site is defective, Factor VIII is rapidly degraded in the plasma.
3
Distinguish between the two variants with absent large multimers (ratio < 0.7). Evaluate the profile with markedly decreased RIPA and a normal platelet count.
Matches the mutation rendering vWF susceptible to ADAMTS13 cleavage or impairing assembly (Type 2A).
Without large multimers, normal platelet agglutination fails, resulting in decreased RIPA.
4
Evaluate the remaining multimer-deficient profile showing enhanced RIPA at low-dose ristocetin and mild thrombocytopenia.
Matches the gain-of-function mutation causing excessive spontaneous binding to glycoprotein Ib (Type 2B).
The hyperactive vWF spontaneously binds platelets in vivo, clearing large multimers and platelets from circulation, which explains both the enhanced in vitro aggregation to minimal ristocetin and the in vivo thrombocytopenia.

Anahtar Kavram

Pathophysiology and advanced laboratory differentiation of von Willebrand Disease (vWD) subtypes

Alternatif Yöntem

When evaluating vWD panels, always look at the vWF:RCo to vWF:Ag ratio first. If > 0.7, it is a quantitative defect (Type 1 or 3). If < 0.7, it is a qualitative defect (Type 2A, 2B, or 2M). From there, use RIPA and multimer analysis to differentiate the Type 2 variants.
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Hematology and Oncology

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