Thrombotic thrombocytopenic purpura in 2 siblings: defective platelet function and plasma factor deficiency occurring...

In 2 siblings with recurring attacks of thrombotic thrombocytopenic purpura, platelet aggregation was found to be decreased during attacks. In contrast with reported observations in other patients, aggregation was found decreased also in symptom-free periods. ATP/ADP ratio in platelet rich plasma was normal. The cause of decreased aggregation was not uraemia, alcohol or drugs. In a healthy sister, platelet aggregation induced by ADP was subnormal. The attacks in 1 of the patients responded to infusion of fresh frozen plasma.