Eculizumab, a humanized anti-C5 antibody, is the lead anti-complement drug but to date has only been approved for two rare disorders, paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS) and recently for Myasthenia Gravis. Here, C5 is linked to paroxysmal nocturnal hemoglobinuria.