Further studies of canine von Willebrand's disease.

Additional characterization of von Willebrand's disease (VWD) in a family of German shepherd dogs is presented. Genetic studies of three generations of affected dogs indicate that about 50% of the progeny are affected if one parent has VWD and about 60% if both parents have the defect. Some of these progeny manifested an incomplete form of VWD, suggesting autosomal dominant inheritance with variable expressivity. The disease become progressively less severe with advancing age and repeated pregnancies. Ristocetin-induced platelet aggregation was significantly reduced in VWD dogs as compared with normal, thrombopathic, and hemophilic carrier dogs. Immunodiffusion and electroimmunodiffusion studies with rabbit anticanine factor VII showed the level of factor VII-related antigen to be low in VWD dogs but present in increased amounts in hemophilic dogs. VWD affected dogs had markedly delayed hemostatic plug formation, but their plugs appeared normal by light and electron microscopy. Their platelet nucleotides, ATP/ADP ration, and platelet protein content were normal. Platelet and fibrinogen survival times with [75Se] selenomethionine were also normal, although platelets from VWD dogs incorporated more radioactivity than did those from normal dogs or from dogs with incomplete VWD.