Clinical Information

von Willebrand disease (VWD) is a bleeding disorder due to quantitative or qualitative defects in von Willebrand factor (VWF), which results from disease-causing alterations in the VWF gene. VWD constitutes 1 of the 2 most common bleeding disorders. Most subtypes of VWD are inherited as autosomal dominant traits, although autosomal recessive variants occur.

In hemostasis, there are 2 essential roles for VWF. The first is its ability to promote platelet adhesion to damaged vessel walls, and the second is to function as a carrier protein for Factor VIII (FVIII). Thus, noncovalent binding of FVIII to VWF is necessary for normal survival of FVIII in the blood circulation. In patients with severe VWD, the circulating half-life of endogenous or infused FVIII is shorter than expected. Disease-causing alterations within the FVIII binding domain of VWF may result in an isolated 'deficiency' of FVIII associated with a clinically mild to moderate bleeding disorder that may be misdiagnosed as Hemophilia A (HA).

Abnormal binding of FVIII to VWF can be detected with a binding assay. Since its initial description in patients from the Normandy region of France, more recent studies suggest that VWD type 2N or Normandy (VWD2N) has been associated with a more severe phenotype among patients who are homozygous for pathogenic alterations within the FVIII binding domain of VWF.

In an international survey, FVIII binding defect was detected in 58 out of 1198 (4.8%) patients with mild HA. Other studies confirm these findings and reveal that 1.5% to 16.6% of patients with VWD Type 1 have the FVIII binding defect. The diagnosis of VWD2N has 2 main implications:

-Genetic counseling differs considerably from that for X-linked recessive HA since the inheritance of VWD2N is autosomal recessive.

-Optimal treatment or prophylaxis of bleeding requires factor replacement therapy with products containing functional VWF.