The Mode of Inheritance of PTA Deficiency: Evidence for the Existence of Major PTA Deficiency and Minor PTA Deficiency

Plasma thromboplastin antecedent (PTA) activity was measured with aquantitative assay in the available members of the families of eight propositiwith severe PTA deficiency. PTA deficiency was found to exist in two forms:major PTA deficiency, characterized by PTA levels of up to 20 per cent of ourstandard reference plasma and by the potential for serious surgical bleeding,and minor PTA deficiency, characterized by PTA levels between 30 and 65per cent of our standard reference plasma and by the absence of significantsurgical bleeding. Minor PTA deficiency was found in parents and childrenof subjects with major PTA deficiency.

It would appear that the gene for PTA deficiency is an incompletely recessive or "intermediate" gene which produces major PTA deficiency in the homozygote and minor PTA deficiency in the heterozygote.

Submitted on March 27, 1961 Accepted on May 16, 1961