Evaluation of an automated screening assay for von Willebrand disease type 2N

Evaluating the factor VIII (FVIII) binding activity of von Willebrand factor (VWF) is an important step in the diagnostic work-up of families affected by apparent mild haemophilia A. In von Willebrand's disease (VWD) type 2N (Normandy), mutations at the N-terminal end of the mature VWF subunit gene prevent the binding of FVIII. Individuals heterozygous for type 2N VWD are generally asymptomatic. Homozygotes and compound heterozygotes present with a clinical picture which mimics haemophilia A, with a markedly reduced FVIII : C activity and VWF within the normal range, but instead of exhibiting X-linked inheritance they show an autosomal recessive inheritance pattern. The distinction between haemophilia A and VWD type 2N has important implications for therapy and genetic counselling. We present a highly specific enzyme-linked immunosorbent assay screening method for the Normandy variant, which measures VWF : FVIII binding activity in parallel with VWF antigen, using monoclonal capture and detection antibodies. The assay is fully automated using a robotic microtitre plate processor, requiring minimal user intervention and providing the capacity to screen large numbers of patients.