Von Willebrand Disease
vWD is due to an abnormality ,either quantitative ,absence or qualitative of the vWf.
vWf is a large multimeric glycoprotein that function as :
1.the factor Vlll carrier protein (vWf protect factor Vlll from degradation).
2. required for normal platelet adhesion (vWf binds on platelet to its specific receptor glycoprotein lb & acts as adhesive bridge between the platelet & damaged sub-endothelium at the site of vascular injury

vWf is composed of dimeric subunits that are linked by disulfide bonds to form complex multimers of low ,intermediate & high molecular weights .
The small multimers function mainly as carriers for factor Vlll.

High molecular weight multimers have higher numbers of platelet-binding sites & greater adhesive properties .
Each multimeric subunit has binding sites for the receptor glycoprotein lb on non-activated platelets & the receptor glycoprotein llb/llla on activated platelets,
this facilitates both platelet adhesion & aggregation

Acquired forms of vWD
1. Wilm’s tumor.
2. Congenital hear disease.
3. Systemic lupus erythmatosus.
4. Angiodysplasia.
5. Seizures disorders treated with valproate.
6. Hypothyroidism.

Aortic-valve Stenosis can be complicated by bleeding that is associated with acquired type 2A von Willebrand syndrome . However, the prevalence & cause of the haemostatic abnormality in aortic Stenosis are unknown .
We enrolled 50 consecutive patients with aortic Stenosis, who completed a standardized screening questionnaire to detect a H/O bleeding. 42 patients with sever aortic Stenosis underwent valve replacement.
Platelets function under conditions of high shear stress, vWf collagen-binding activity & Ag levels, & the multimeric structure of vWf were assessed @ base line & 1 day, 7 days, & six months post-operatively.

Results:
Skin or mucosal bleeding occurred in 21% of the patients with sever aortic Stenosis. Platelets-function abnormalities under condition of high shear stress, decreased vWf collagen-binding activity & the loss of the largest multimers, or a combination of these was present in 67 – 92 % of patients with sever aortic Stenosis & correlated significantly with the severity of valve Stenosis.

Conclusions:
Type 2A vW Syndrome is common in patients with sever aortic Stenosis.
vWf abnormalities are directly related to the severity of aortic Stenosis & are improved by valve replacement in the absence of mismatch between patient & prosthesis.

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