Platelet-type von Willebrand disease and type 2B von Willebrand disease: a story of nonidentical twins when two different genetic abnormalities evolve into similar phenotypes.

Platelet-type von Willebrand disease (PT-VWD, or pseudo-VWD) and type 2B VWD share a common bleeding phenotype with different etiologies. Both PT-VWD and type 2B VWD represent an enhanced binding between the plasma von Willebrand factor (VWF) to its platelet ligand, glycoprotein Ib alpha ( GP1BA). However, type 2B VWD results from a functionally abnormal VWF molecule, whereas PT-VWD is caused by hyperresponsive platelets due to defects in the platelet GP1BA gene. The laboratory discrimination between the two disorders can be a challenge because simple phenotypic testing will not differentially identify the disorders, and the more complex testing approaches are often poorly applied. Definitive diagnosis is critical for treatment decisions and can be most definitively achieved by identifying the gene defect at either the VWF or GP1BA loci. A systematic international molecular genetic study would be helpful to address the question of whether PT-VWD is being misdiagnosed as type 2B VWD. Such a study can be facilitated by an international online database/disease registry to enhance international awareness about this otherwise long-recognized diagnostic dilemma.