vonWillebrand Disease
Von Willebrand Disease is a bleeding disorder caused by a defect or deficiency of a blood clotting protein, called von Willebrand Factor. The disease is estimated to occur in 1% to 2% of the population. The disease was first described by Erik von Willebrand, a Finnish physician who reported a new type of bleeding disorder among island people in Sweden and Finland.
Von Willebrand Factor is a protein critical to the initial stages of blood clotting. This glue-like protein, produced by the cells that line the blood vessel walls, interacts with blood cells called platelets to form a plug which prevents the blood from flowing at the site of injury. People with von Willebrand Disease are unable to make this plug because they do not have enough von Willebrand Factor or their factor is abnormal.
Most fall into the following classifications:
- Type I: This is the most common and mildest form of von Willebrand Disease. Levels of von Willebrand factor are lower than normal, and levels of factor VIII may also be reduced.
- Type II: In these people, the von Willebrand factor itself has an abnormality. Depending on the abnormality, they may be classified as having Type IIa or Type IIb. In Type IIa, the level of von Willebrand factor is reduced, as is the ability of platelets to clump together. In Type IIb, although the factor itself is defective, the ability of platelets to clump together is actually increased.
- Type III: This is severe von Willebrand disease. These people may have a total absence of von Willebrand factor, and factor VIII levels are often less than 10%.
- Pseudo (or platelet-type) von Willebrand disease: This disorder resembles Type IIb von Willebrand disease, but the defects appear to be in the platelets, rather than the von Willebrand factor.