Von Willebran disease (vWD) is the most common hereditary coagulation abnormality described in humans, although it can also be acquired as a result of other medical conditions. It arises from a qualitative or quantitative deficiency of von Willebrand factor (vWF), a multimeric protein that is required for platelet adhesion. It is known to affect humans and dogs. There are four types of hereditary vWD. Other factors including ABO blood groups may also play a part in the severity of the condition.