Platelet dysfunction in Noonan's syndrome. A case with a platelet cyclooxygenase-like deficiency and chronic idiopathic thrombocytopenic purpura.

Individuals with Noonan's syndrome are likely to have one or more coagulation abnormalities: complex platelet function defects, partial Factor XI deficiency, or von Willebrand's disease. A distinctive platelet function defect has not been identified. The authors describe a 24-year-old women with Noonan's syndrome, chronic idiopathic thrombocytopenic purpura (ITP), and a platelet function defect characterized by a greater than 15-minute bleeding time, failure of aggregation and release with 10 microM ADP, 10 microM epinephrine, 750 microM arachidonic acid or 0.019 g/L collagen. A mixture of aspirin-treated platelets with the patient's platelets failed to correct the defect. Addition of 2.5 microM U46619 (a PGG2 analogue) corrected the aggregation and release defect. An electron microscopic analysis failed to reveal structural abnormalities. Thus, the platelet function defect in this patient appears to be a functional deficiency of cyclooxygenase. The presence of autoantiplatelet antibodies in a clinical setting consistent with chronic ITP raises the possibility that the defect may be acquired.