Von Willebrand Disease
(Von Willebrand's Disease)
Von Willebrand disease is a hereditary deficiency or abnormality of the blood protein von Willebrand factor, which affects platelet function.
The von Willebrand factor is found in plasma, platelets, and the walls of blood vessels. Platelets are cell fragments that circulate in the bloodstream and help blood clot (see also Overview of Platelet Disorders). When the factor is missing or defective, platelets cannot adhere to the vessel wall at the site of an injury. As a result, bleeding does not stop as quickly as it should.
There are three types of von Willebrand disease, all of which are inherited. The types differ on the degree of deficiency of the factor. People with the greatest deficiency have a higher risk of bleeding.
Often, a person with von Willebrand disease has a parent who has a history of bleeding problems. Typically, a child bruises easily or bleeds excessively after a cut, tooth extraction, or surgery. A young woman may have increased menstrual bleeding. Bleeding may worsen at times. On the other hand, hormonal changes, stress, pregnancy, inflammation, and infections may stimulate the body to increase production of von Willebrand factor and temporarily improve the capacity of platelets to stick to the blood vessel wall and stop bleeding.
Laboratory tests typically show that the platelet count and the standard tests of blood clotting (such as the PT and PTT) are normal. Doctors usually order tests that measure the amount of von Willebrand factor in the blood and determine how well the von Willebrand factor functions. Because von Willebrand factor is the protein that carries an important clotting factor (factor VIII) in the blood, the level of factor VIII in the blood may also be decreased.
Many people with von Willebrand disease never need treatment. If excessive bleeding occurs, a transfusion of concentrated blood clotting factors containing von Willebrand factor (intermediate-purity factor VIII concentrates) may be given. For some mild forms of the disease, drug treatment with desmopressin may be given to increase the amount of von Willebrand factor long enough for surgery or dental procedures to be done without transfusions. For women with heavy menstrual bleeding due to von Willebrand disease, a brief period of treatment with tranexamic acid by mouth may decrease bleeding.