Causes

The usual cause of von Willebrand disease is an inherited abnormal gene that controls von Willebrand factor — a protein that plays a key role in blood clotting.

When you have low levels of this protein or it doesn't work as it should, small blood cells called platelets cannot stick together properly nor attach themselves normally to the blood vessel walls when an injury has occurred. This interferes with the clotting process and can sometimes cause uncontrolled bleeding.

Many people with von Willebrand disease also have low levels of factor VIII, another protein that helps in clotting.

Factor VIII is involved in another inherited clotting disorder called hemophilia. But unlike hemophilia, which mainly affects males, von Willebrand disease affects males and females and is usually milder.

Rarely, von Willebrand disease can develop later in life in people who didn't inherit an abnormal gene from a parent. This is known as acquired von Willebrand syndrome, and it's likely caused by an underlying medical condition.