Inherited qualitative platelet disorders are those in which platelet function is impaired usually due to an
Disorders of Adhesion von Willebrand's Disease
The most important disease of platelet adhesion is von Willebrand disease (vWD). Discovered in 1926 by Dr. Eric von Willebrand, vWD is the most prevalent inherited bleeding disorder worldwide, affecting 1% to 3% of the world population by conservative estimates. In random studies of children investigated for epistaxis and women investigated for menorrhagia, vWD was the most frequent cause of bleeding.14,15 von Willebrand initially described a family of 12 children of which 10 had excessive nosebleeds, gum bleeds, and menorrha-gia. One of the youngest girls died at age 13 during her fourth menstrual cycle of uncontrollable bleeding. vWD is an autosomal dominant disorder marked by easy bruising, nosebleeds, heavy menses, and excessive bleeding after tooth extraction or dental procedures. Type O individuals have a lower plasma concentration of vWF than other blood types. For many patients, the variabilities in clinical symptoms and laboratory presentations have contributed to the underdiagnosis of this disorder. Women may represent a significant yet under-served subset of individuals affected by vWD, since menorrhagia is a frequent presenting feature of this disease. According to Luscher, vWD may be the underlying cause in 9% to 11% of cases of menorrhagia,16 yet it is often not considered as a possible diagnosis by obstetricians and gynecologists.
As a disease entity, vWD is fairly complex with few clear-cut and consistent diagnostic clues. The basic pathophysiology in vWD is a qualitative or quantitative defect in vWF. vWF is a large multimeric glycoprotein derived from two sources: endothelial cells and megakaryocytes (Table 16.3). This protein is coded for by chromosome 12 and is carried into plasma circulation by factor 8, one of the clotting factors. vWF serves as an intermediary for platelet adhesion, providing a receptor molecule for GP Ib of the platelets and the subendothe-lium. With this platform in place, platelets, once activated by injury, adhere to the subendothelium forming a platelet plug, recruiting more platelets to the site of injury and eventually leading to platelet aggregation and the formation of an insoluble fibrin clot. Without a fully functioning vWF, platelet adhesion is impaired. Addi
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