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Zorluk: ZorHemodynamic and Coagulation Processes

A 19-year-old woman is evaluated in the hematology clinic prior to a scheduled wisdom tooth extraction. She has a history of heavy menstrual bleeding and frequent epistaxis since childhood. Her older brother and mother have similar bleeding tendencies. Laboratory studies show:

Hemoglobin: 11.2 g/dL11.2 \text{ g/dL}
Platelet count: 165,000/mm3165,000/\text{mm}^3
Prothrombin time (PT): 11 seconds (Normal: 11-15 s)
Activated partial thromboplastin time (aPTT): 39 seconds (Normal: 25-35 s)
Ristocetin cofactor activity: decreased

A test dose of intravenous desmopressin (DDAVP) is administered to determine if it can be used for hemostatic prophylaxis during her dental procedure. Thirty minutes after the infusion, her platelet count is rechecked and has fallen to 38,000/mm338,000/\text{mm}^3. Which of the following best describes the underlying molecular pathophysiology of this patient's bleeding disorder?

  1. Gain-of-function mutation leading to enhanced affinity of a circulating glycoprotein for platelet glycoprotein IbCevap
  2. B
    Partial quantitative deficiency of a carrier protein leading to rapid proteolytic clearance of factor VIII
  3. C
    Decreased metalloproteinase cleavage of ultra-large multimeric hemostatic proteins
  4. D
    Absence of a functional platelet membrane receptor complex resulting in impaired adhesion to the subendothelium
  5. E
    Immune-mediated destruction of platelets by drug-dependent antibodies targeting surface glycoproteins

Cevap

Gain-of-function mutation leading to enhanced affinity of a circulating glycoprotein for platelet glycoprotein Ib
The correct answer describes the pathophysiology of Type 2B von Willebrand disease (VWD). This patient's presentation of mucocutaneous bleeding (epistaxis, heavy menses), autosomal dominant inheritance, mildly prolonged aPTT, and decreased ristocetin cofactor activity establishes a baseline diagnosis of VWD. The critical distinguishing feature in this vignette is the development of acute, severe thrombocytopenia following the administration of desmopressin (DDAVP). DDAVP stimulates the release of stored von Willebrand factor (VWF) from endothelial Weibel-Palade bodies. In Type 2B VWD, a gain-of-function mutation in the VWF gene produces a mutant protein with an abnormally high affinity for the platelet glycoprotein Ib (GPIb) receptor. When a massive amount of this mutant VWF is suddenly released into the circulation by DDAVP, it spontaneously binds to the patient's platelets, causing widespread in vivo platelet aggregation and subsequent rapid clearance by the reticuloendothelial system. Consequently, DDAVP is contraindicated in patients with Type 2B VWD.

Adım Adım Çözüm

1
Identify the baseline bleeding disorder
The patient has a history of mucocutaneous bleeding, an autosomal dominant inheritance pattern, a mildly prolonged aPTT, and decreased ristocetin cofactor activity. This constellation of findings is consistent with von Willebrand disease (VWD).
Establishing the baseline diagnosis is necessary to contextualize the adverse reaction to the medication.
2
Analyze the adverse response to DDAVP
Administration of desmopressin (DDAVP) caused acute, severe thrombocytopenia. DDAVP's mechanism of action involves stimulating the release of stored von Willebrand factor (VWF) from endothelial Weibel-Palade bodies.
Understanding the pharmacodynamic effect of DDAVP explains the sudden change in the patient's platelet count.
3
Determine the specific VWD subtype
Acute thrombocytopenia immediately following DDAVP administration is the classic hallmark of Type 2B VWD, making DDAVP contraindicated in these patients.
Different subtypes of VWD require drastically different management strategies.
4
Identify the underlying molecular pathophysiology
Type 2B VWD is caused by a gain-of-function mutation in the VWF gene. This results in a mutant VWF protein with an abnormally high affinity for the platelet glycoprotein Ib (GPIb) receptor, causing spontaneous platelet aggregation and rapid clearance.
The question specifically asks for the molecular mechanism driving the disorder.

Anahtar Kavram

Type 2B von Willebrand disease is characterized by a gain-of-function mutation in VWF that increases its affinity for platelet GPIb, leading to paradoxical thrombocytopenia when DDAVP is administered.
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Konular

Hemodynamic and Coagulation Processes

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