The prevalence of plasma thromboplastin antecedent (PTA, factor XI) deficiency.

By W. Angus Muir and Oscar D. Ratnoff P LASMA TH ROM BOPLASTIN antecedent (PTA, Factor X I) deficiency is an inherited disorder of blood coagulation characterized by a defect of the intrinsic pathway of thrombin formation and a mild to moderate bleeding tendency. Since the original description by Rosenthal, Dreskin, and Rosenthal,’ it has been reported in this country and in Europe to occur with especial frequency in Jewish individuals.2 The mode of inheritance of PTA deficiency has been disputed,3 but the bulk ofdata suggest that it is transmitted as an autosomal recessive trait.4 Since the prevalence of PTA deficiency and of the carrier state is unknown, we have reviewed our experience with PTA deficiency in Cuyahoga County, Ohio, of which Cleveland is the county seat. The patients participating in this study were referred to us either because of a mild to moderate bleeding diathesis, revealed by dental extractions or by minor surgical procedures, or because a prolonged partial thromboplastin time was found during routine studies. None of the patients bled spontaneously, and the extent of bleeding was limited to local oozing for 3-14 days after surgical procedures. All patients had a prolonged partial thromboplastin time. The concentration of PTA in different patients ranged from 0.01 to 0.08 U/mI of plasma; pooled normal plasma contains 1 .0 U/mI, while the PTA content of individual normal plasmas varies from 0.55 to 1.85 U/ml as tested in this laboratory. All available close relatives of PTA-deficient patients were tested for PTA activity. We have identified seven patients with PTA deficiency in Cuyahoga County, all of Jewish origin; two of the patients were sibs. The pattern of inheritance was not always established in these cases due to a paucity of family data. In one parent and eight offspring of PTA-deficient individuals, the concentration of PTA varied from 0.33 to 0.96 U/mI, averaging 0.49 U/mI. Similar data were obtained in a carefully studied family from a nearby county. These data are consistent with the assumption that in most instances PTA deficiency is inherited as an autosomal recessive trait. A recent estimate5 indicates that in 1973, 83,000 individuals in Cuyahoga County were identified as Jewish. Accepting this figure, the minimal prevalence of homozygous PTA deficiency is approximately 1/12,000. Using the principle