Acquired coagulation inhibitor delaying fibrinopeptide release.

A 14-yr-old girl Down syndrome developed a unique type of circulating inhibitor causing a mild bleeding tendency and interfering strongly with coagulation tests, including reptilase time, and with the reaction of purified fibrinogen and thrombin. The concentration of all coagulation factors was normal. The inhibitor had no direct effect on thrombin activity or on the aggregation of fibrin monomer in plasma. Chromatography on DEAE-cellulose and neutralization by immune sera revealed that the inhibitor was an immunoglobulin of IgG class with both kappa and lambda determinants. Isolated inhibitor delayed the release of fibrinopeptide A from a normal fibrinogen reacting with thrombin and retarded the onset of visible clotting, but had no effect on the the final degree of clottability. The clinical and laboratory features of this patient resemble those of patients with congenital dysfibrinogenemia associated with abnormal fibrinopeptide release.