Fibrinogen and Clot Structure is Affected by Eculizumab in Patients with Paroxysmal Nocturnal Haemoglobinuria

Background Paroxysmal nocturnal haemoglobinuria (PNH) is a haematopoietic stem cell disorder in which an acquired somatic mutation of the PIGA gene in a haematopoietic stem cell results in the deficiency of key complement regulatory molecules, namely CD59 and CD55, from the surface of blood cells leading to an increased susceptibility of blood cells to complement-mediated activation +/- intravascular haemolysis and thrombosis. Thrombosis has been the leading cause of death in PNH. Multiple mechanisms of thrombosis in PNH have been proposed, including cross talk between the coagulation and complement system. This may lead to denser clots which are more resistant to fibrinolysis. Treatment with eculizumab, which inhibits complement factor C5 and thereby prevents terminal complement activation, reduces thromboembolic events in PNH, indicating that complement activation plays a significant role in the pathophysiology of thrombosis in this disease. Patients with other thrombotic disorders are known to form denser fibrin clots that incur greater resistance to fibrinolysis. It has not previously been explored whether changes to clot architecture contribute to thrombosis in PNH. Furthermore, the role of eculizumab in clot architecture is undocumented.