Metsel et al. (1980) found biochemical evidence of defective thromboxane A2 synthetase (TBXAS1; 274180) in a 3-year-old girl with massive gastrointestinal bleeding. Petechiae and bruises had been noted soon after birth, and nosebleeds and hematuria subsequently. Platelet counts ... Metsel et al. (1980) found biochemical evidence of defective thromboxane A2 synthetase (TBXAS1; 274180) in a 3-year-old girl with massive gastrointestinal bleeding. Petechiae and bruises had been noted soon after birth, and nosebleeds and hematuria subsequently. Platelet counts were normal, but aggregation of platelets was defective, even with exposure to prostaglandin H2. No thromboxane B2 was detected in the patient's plasma. Her father and 2 sibs had a milder bleeding disorder. Defreyn et al. (1981) reported 3 patients from 3 successive generations with a moderate bleeding tendency due to platelet dysfunction. Clinical features included cutaneous ecchymoses and bleeding following dental extractions in 1 patient. Laboratory studies showed no platelet aggregation with arachidonic acid, but there was a response to treatment with thromboxane analogs. Thromboxane B2 and malondialdehyde levels were about 50% of normal, suggesting a heterozygous state. Levels of several prostaglandins, particularly prostaglandin D2, were increased. The findings were compatible with partial primary thromboxane synthetase deficiency in patients' platelets.