von Willebrand disease Flashcards
T/F: vWD is the most common inherited bleeding diathesis overall.
True
-Hemophilia A is considered the most common cause of SEVERE hemophila
vWD is a simultaneous impairment of the coagulation cascade and platelet function.
- Coagulation effect?
- Platelet function effect?
- vWF maintains high levels of circulating factor 8 (VIII)
- vWF is operant in the formation of platelet thrombi
Where does synthesis of vWF occur? (2)
- Endothelial cells
- Megakaryocytes
Where in endothelial cells is vWF stored?
Weibel-Palade bodies
Where in megakaryocytes is vWF stored?
alpha granules
vWF is secreted by endothelial cells into underlying basement membrane. What happens when the basement is exposed?
vWF is bound by platelet GPIb
How is GPIb activated?
- In vivo
- In vitro
- In vivo - shear stress
- In vitro - Ristocetin
*vWF is also referred to as ristocetin cofactor
vWF is also secreted into circulation, what breaks it down?
ADAMTS-13
-variably sized multimers, most commonly dimers
What does vWF do in circulation?
Complexes with F8 (VIII) and protects it from degradation
*vWF is sometimes called F8 related antigen
What is the most common type of vWD?
-Second MC
Type I (70%) -Type IIa (10-15%)
Type I vWD severity?
Mild QUANTITATIVE defect
Type I vWD lab findings:
- Platelet count
- PT
- aPTT
- Bleeding time
- PFA-100
Type I vWD lab findings:
- Platelet count - Normal
- PT - Normal
- aPTT - Prolonged
- Bleeding time - Prolonged
- PFA-100 - Prolonged
What are the levels in Type I vWD?
- Factor 8
- vWF Ag
- vWF activity
- Factor 8 - Decreased
- vWF antigen - Decreased
- vWF activity - Decreased
*Ratio of vWF activity to vWF antigen approaches 1 (always >0.7)
Type IIa vWD severity?
Moderate to severe bleeding
Type IIa vWD mutation.
vWF gene on exon 28
-Missense mutation
What is the abnormality in Type IIa vWD?
Absence of large multimers (abnormal multimer pattern)
Prolonged aPTT
What are the levels in Type IIa vWD?
- Factor 8
- vWF Ag
- vWF activity
- Factor 8 - Normal/-
- vWF Ag - Normal/-
- vWF activity - Decreased (Markedly; <50%)
What is the ratio of vWF antigen to vWF activity in Type IIa vWD?
<0.7
Type I vWD:
- Multimer pattern
- Genetics
- Normal
- Unknown genetics
Type IIb vWD mutation.
Gain-of-Function mutation in GPIb binding domain of vWF
What is the abnormality in type IIb vWD?
Decreased large multimers
How is Type IIb vWD unique? (3)
- Enhanced Ristocetin induced platelet aggregation
- DDAVP causes profound thrombocytopenia and bleeding
- Spontaneous binding of vWF to platelets
What must Type IIb vWD be distinguished from?
Platelet type vWD
what is the mutation in Platelet type vWD?
Gain of function mutation in the gene that encodes he platelet GPIb receptor