VON WILLEBRAND'S DISEASE

also called Pseudohemophilia B, Vascular Hemophilia, or Angiohemophilia, inherited hemorrhagic disorder characterized by a prolonged bleeding time and a deficiency of antihemophilic factor (factor VIII), which is an important blood clotting agent. This disorder is due to deficiencies in von Willebrand factor (vWF), a molecule that facilitates platelet adhesion and is a plasma carrier for factor VIII. Von Willebrand's disease (vWD) types 1 and 2 are milder forms and are inherited as autosomal dominant traits; type III, the most severe form, is recessive and requires that the trait be inherited from both parents. Symptoms usually include abnormal bruising, bleeding from mucosal surfaces such as the gums and the gastrointestinal tract, and prolonged bleeding from any break in the skin or during surgery. The level of vWF and the severity of the disease vary over time, often as a result of hormonal or immune responses elevating the level of vWF. Inherited forms of vWD respond to cryoprecipitate, a plasma rich in vWF. Acquired forms of vWD, in which antibodies are formed against the vWF, have occasionally developed after multiple transfusions and in autoimmune or lymphoproliferative disorders, and treatment focuses on the underlying disorder because treatment with cryoprecipitate is ineffective. See also thrombocytopathy.