What Is Type 1 von Willebrand Disease?

Von Willebrand disease (vWD) is an enigmatic hemorrhagic disorder. A diagnosis of type 3 vWD is readily established in people who lack the von Willebrand factor (vWF); those with a qualitatively abnormal factor have type 2 disease. People with low levels of normal vWF do not fall into either of these categories and are said to have type 1 disease. However, a complicating aspect is that people with the O blood type sometimes exhibit depressed levels of vWF and mild bleeding propensity, and are suspected of having type 1 vWD. This raises the possibility that vWD is overdiagnosed. To clarify the molecular basis of type 1 vWD, two groups (European and Canadian) evaluated people with suspected type 1 vWD based on bleeding symptoms, family histor…