Dysfibrinogenemia and thrombosis.

Congenital abnormal fibrinogen molecules (dysfibrinogenemias) are due to structural defects in the molecule. The molecular structure of the fibrinogen molecule is to a great extent known and this has allowed identification of the abnormalities at a molecular level. While most patients with dysfibrinogenemia are clinically asymptomatic, some present with a bleeding diathesis, others with thrombophilia, and occasionally with both, bleeding and thromboembolism. In principle, the dysfibrinogenemias are due to either impaired release of the fibrinopeptides, defective fibrin polymerization, or abnormal cross-linking by factor XIIIa. Dysfibrinogenemias associated with thrombophilia have been reported in those related to abnormal fibrinopeptide release or defective polymerization. In addition, abnormal interactions with platelets, defective fibrinolysis, defective assembly of the fibrinolytic system, and abnormal calcium binding have been described. The presently identified dysfibrinogenemias associated with thrombosis and their molecular defects are described in this review. It must also be recognized that some patients with abnormal fibrinogen molecules have additional hemostasis defects, such as abnormalities of antithrombin, protein C, protein S, factor V Leiden, and others. On rare occasions, dysfibrinogenemias can be associated with hypofibrinogenemia.