von Willebrand Disease

von Willebrand disease is a hereditary deficiency or abnormality of the von Willebrand factor in the blood, a protein that affects platelet function. It’s the most common hereditary disorder of platelet function, affecting both women and men. 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.

In von Willebrand disease, blood platelets don’t stick to holes in blood vessel walls. Platelets are tiny particles in the blood that clump together at the site of an injury to prepare for the formation of a blood clot. von Willebrand factor causes them to bind to areas of a blood vessel that are damaged. If there is too little von Willebrand factor, or the factor is defective, platelets do not gather properly when a blood vessel is injured. von Willebrand factor is found in plasma, platelets, and blood vessel walls. When the factor is missing or defective, the first step in plugging a blood vessel injury (platelets adhere to the vessel wall at the site of the injury) doesn’t take place. As a result, bleeding doesn’t stop as quickly as it should, although it usually stops eventually.

There are no racial or ethnic associations with the disorder. A family history of a bleeding disorder is the primary risk factor.

Researchers have identified many variations of the disease, but most fall into the following classifications:

Most common and mildest form of von Willebrand disease. Levels of von Willebrand factor are lower than normal. Levels of factor VIII may also be reduced.

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.

Severe von Willebrand disease. These people may have a total absence of von Willebrand factor and factor VIII levels are often less than 10%.