Nature of the Defect in Congenital Factor V Deficiency: Study in a Patient With an Acquired Circulating Anticoagulant

An 8-yr-old girl with congenital factor V deficiency and sporadic hemorrhagic episodes developed an anticoagulant to transfused factor V. This clinical complication, not previously reported, was associated with a severe bleeding episode that subsided when the anticoagulant level decreased. Anticoagulant activity was neutralized by antihuman IgG antiserum but not by anti-IgA or anti-IgM, indicating that the anticoagulant was an immunoglobulin of the IgG class. After 6 mo, anticoagulant activity was no longer detectable. At this time, neutralization studies were performed using the patient’s anticoagulant. Normal plasma and serum contained antigenic activity that neutralized the anticoagulant. Such activity was absent from the remission plasma. Thus, the genetic lesion in the case was characterized by parallel diminution of antigenically and functionally active factor V.