PKa can activate FXII, plasminogen, and urokinase-type plasminogen activator.4During HAE attacks, both the coagulation cascade and fibrinolytic system seem to be activated as evidenced by elevated prothrombin fragment 1 + 2 and D-dimer levels.5Either way, HAE patients do not have a prothrombotic tendency.6, Fig. 1gives an overview of the functions of PKa in the kallikrein/kinin, intrinsic coagulation, and fibrinolysis systems. The gene discussed is KLK4; the disease is hereditary angioedema.