• A black man with a prolonged partial thromboplastin time had a severe deficiency of plasma thromboplastin antecedent (PTA) (factor XI) measured both in clotting assays and immunoassays, suggesting a diagnosis of homozygous PTA deficiency. His offspring seemed to be heterozygous carriers of PTA deficiency. Additionally, the proband and two of his children had decreased Hageman factor (factor XII) levels consistent with those of heterozygous carriers of Hageman trait. To our knowledge, this is the first case known of PTA deficiency in a black person. Its pattern of inheritance was independent of that of factor XII deficiency.
(Arch Intern Med 1981;141:936-937)