Hereditary thrombocytopathy: a familial bleeding disorder due to impaired platelet coagulant activity.

A family with a bleeding disorder due to congenital thrombocytopenic thrombocytopathy is described, with ten affected members in three generations. The disorder is inherited as an autosomal dominant trait and is characterized by thrombocytopenia, morphologically abnormal platelets, prolonged bleeding time, platelet coagulant activity deficiency and abnormal platelets, prolonged bleeding time, platelet coagulant activity deficiency and abnormal platelet aggregation. Patients' platelets adhered to collagen, but aggregation was reversible and the release of platelet constituents was minimal. Aggregation with ADP was similarly reversible, but the platelet response to thrombin was normal. These defects in platelet aggregation and release were not corrected by addition of normal plasma indicating an intrinsic abnormality of platelets. By definition thrombocytopathy consists of a deficiency in platelet coagulant activity. It was shown that the deficiency of platelet coagulant activity caused a delay and decrease in the conversion of prothrombin to thrombin, and it is proposed that the lack of thrombin accounts for the defective release reaction and the reversible aggregation. An adequate haemostatic plug due to decreased release of ADP, together with instability of the plug provide an explanation for the bleeding tendency in thrombocytopathy.