The usual cause of von Willebrand disease is an inherited defect in the gene that controls von Willebrand factor, a protein that plays a key role in your blood-clotting process. When von Willebrand factor is scarce — or not functioning properly because of structural abnormalities — small blood cells called platelets cannot stick together properly, nor can they attach themselves normally to the blood vessel walls when an injury has occurred. The result is interference with the clotting process, and uncontrolled bleeding may persist.

Von Willebrand factor carries an additional substance, called factor VIII, that helps stimulate clotting. Many people with von Willebrand disease also have low levels of factor VIII.

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 disease. The exact cause of this type of von Willebrand disease isn't clear. It may be an autoimmune disease, or it may be linked to a slow thyroid gland (hypothyroidism) or to certain medications, such as the anti-seizure medication valproic acid (Depakene) or the antibiotic ciprofloxacin (Cipro).

Jan. 02, 2014