Many recent studies have confirmed the efficacy of eculizumab in the treatment of aHUS and demonstrated that treatment with eculizumab early in the course of illness improves preservation of renal function.7, -9 Eculizumab is an anti-C5 monoclonal antibody that acts by preventing cleavage of C5, thereby preventing the formation of the membrane attack complex, which is composed of C5b-C9.10 It is currently approved for adult and pediatric patients for treatment of aHUS; however, its use in typical HUS is not well established. The gene discussed is C5; the disease is hemolytic-uremic syndrome.