A new, autosomally inherited abnormal fibrinogen associated with hypofibrinogenemia has been described in several members of a family. Plasma fibrinogen measured either as thrombin-clottable protein or by immunodiffusion revealed a fibrinogen level ranging between 60 and 90 mg/100 ml. The thrombin time of plasma or purified fibrinogen was prolonged and only partially corrected by the addition of calcium. Purified fibrinogen prolonged the thrombin time of normal plasma. Fibrinopeptide release by thrombin was normal in rate and amount, but fibrin monomer aggregation was grossly disturbed, especially in a high ionic strength medium. We have designated this fibrinogen "fibrinogen Philadelphia." Acrylamide gel electrophoresis of mixtures of [121I]normal and [125I]abnormal fibrinogens revealed a slight increase in the anodal mobility of fibrinogen Philadelphia. Similarly, DEAE-cellulose chromatography showed slightly stronger binding of fibrinogen Philadelphia than normal. To elucidate the mechanism responsible for the low plasma fibrinogen concentration, simultaneous metabolic studies of autologous (patient) and homologous (normal) fibrinogen, labeled with 125I and 121I, respectively, were performed in two affected subjects. Autologous fibrinogen half-life was short and the fractional catabolic rate was markedly increased in both family members. In contrast, homologous fibrinogen half-life and fractional catabolic rate were normal. These metabolic studies demonstrate that rapid degradation of fibrinogen Philadelphia is largely responsible for the depressed levels of a plasma fibrinogen. This represents the first example of a mutant plasma protein in which the molecular defect is associated with an altered catabolism.
J Martinez, R R Holburn, S S Shapiro, A J Erslev