Genetic variants of von Willebrand's disease.

A specific antiserum against an antihaemophilic factor (AHF)-related plasma protein was raised in rabbits. A quantitative immunochemical method was used to determine the amount of this protein present in the plasma of 33 patients with haemophilia A and 70 patients with von Willebrand's disease. The protein probably consisted of AHF residing in or complexed with the von Willebrand factor. The patients with von Willebrand's disease were shown to fall into two separate genetic groups, one with decreased and one with normal amounts of the AHF-related protein. The patients with haemophilia A had normal amounts of the protein in their plasma.