Detection of heterozygotes in both parents of homozygous patients with Von Willebrand's disease.

Three patients with severe Von Willebrand's disease are shown to be homozygotes. They were born from unaffected parents. New techniques using a factor-VIII-related antigen assay by the Laurell method and a ristocetin-induced platelet aggregation assay demonstrated abnormalities in these two tests in both parents of the probands. Factor-VIII-related of heterogotes could not be differentiated from normal factor-VIII-related antigen by the immunodiffusion technique, crossed immunoelectrophoresis, and filtration on a sepharose 4b column.