von Willebrand Disease Causes & Risks

Causes

vWD is caused by a reduced amount of a protein called von Willebrand factor (vWF) or an abnormality in this protein. This protein helps blood to clot. When a person is bleeding, blood cells called platelets form a plug to stop the bleeding. Normally, vWF allows platelets to adhere to the cells that line the inside of the blood vessels (endothelium), a process necessary for successful clotting. If there is not enough vWF or if it is defective, platelets cannot properly grip onto the injured area and bleeding does not stop as quickly as it should.

VWF has a separate function of protecting against the break down of another protein involved in clotting—factor VIII:C. The relative absence of functioning vWF, therefore, can lead to minor clotting problems through this mechanism as well.

von Willebrand disease can often be traced through several generations in a family. Some have symptoms, while others just carry the gene. Most people with vWD inherit only one gene with the vWD defect. They have one of the milder forms of the disorder—either type 1 or type 2. This means they have some blood clotting ability. The small percentage of people who inherit two defective genes—type 3 vWD—have little clotting ability and experience severe bleeding episodes.

Types 1 and 2 are usually inherited in what is known as a "dominant" pattern. A man or woman with the disease has a 50% chance of passing the gene to his or her child. This means that if even one parent has the gene and passes it to a child, the child gets the disease. Whether the child has no symptoms, mild symptoms, or, less commonly, severe symptoms, he or she definitely has the disease. Regardless of severity of the symptoms, the child can still pass the gene to his or her own offspring.

Type 3 von Willebrand disease, however, is usually inherited in a "recessive" pattern. This type occurs when the child inherits the gene from both parents. Even if both parents have mild or asymptomatic disease, their children are likely to be severely affected.

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition. The only risk factor for vWD is having family members with this disease.