Atypical haemolytic–uraemic syndrome (aHUS) is characterized by endothelial damage leading to renal failure. aHUS has a proven genetic background [1]. To date, underlying genetic factors have been identified in complement components and complement regulators among∼ 50% of aHUS patients [2, 3]. The disease-associated genes include C3 and factor B, which form the complement amplification convertase C3bBb and the regulators factor H (CFH, a plasma gycoprotein), membrane cofactor protein (CD46, MCP) and factor I (a plasma serine protease) which concur to controlling C3 convertase activity (Figure 1). In addition, autoantibodies recognizing factor H have been identified as being associated with haemolytic–uraemic syndrome (HUS)[4]. Over the last decade, a clear link has been demonstrated between this disorder and a defective regulation of the complement system components [5]. Thus, it is generally accepted that aHUS is a disease of excessive complement activation in the kidney glomerular and arteriolar cells. Following yet not well-identified triggering events, endothelial cells lose their integrity and become a target for an uncontrolled complement attack. The release of C5a and the inactive form—in terms of cytolytic effect—of the membrane attack complex (MAC) C5b-9 induces a procoagulant phenotype. This deleterious triggering of the complement and the coagulation cascades leads to the development of the thrombotic microangiopathy (TMA) that characterizes aHUS [6]. aHUS is a severe and frequently relapsing disorder comprising a typical triad of thrombocytopaenia, haemolysis and acute renal failure, in the absence of Shiga toxinproducing Escherichia coli infection, and detectable ADAMST13 in the serum. It portends a dismal prognosis. More than 50% of patients with aHUS progress to chronic renal failure and 10% die from complications of the disease. The disease can affect patients of all ages and its prognosis correlates to a certain extent with the identified genetic defects. Patients with CFH mutations carry the worst prognosis [7]. At the end of the first year following the onset of aHUS, 60% of patients with CFH mutations die or progress to dialysis dependency. In addition, when renal transplantation is undertaken, loss of the graft occurs in over 50% of renal transplants, due to HUS recurrence [8]. Despite the fact that plasma exchanges are the treatment of choice in severe thrombotic thrombocytopaenic purpura [9], their efficacy in aHUS is not guaranteed. Therefore, other therapeutic procedures, in particular complement-blocking agents, may be of benefit, and considering the severity of this condition are fully justified. As the activation of C5 plays a pivotal role in the pathophysiology of aHUS, the newly elaborated complement antagonist eculizumab represents a reasonable hope as a promising treatment for the disease [10].

Eculizumab (Soliris; Alexion) is a humanized monoclonal antibody indicated for the treatment of paroxysmal nocturnal haemoglobinuria [11]. It binds specifically and with high affinity to the complement protein C5, thereby preventing the release of the anaphylatoxin C5a and the assembly of the terminal complement complex C5b-9. To this day,> 50 cases of patients who received eculizumab for aHUS have been published or included in an international multicentre prospective Phase II trial [8, 12–24, 25]. Eculizumab was used in patients who had experienced aHUS in their native kidney, in order to rescue or prevent post-transplant recurrence. There are still few reports indicating that the C5 mAb antagonist eculizumab may be an effective form of treatment for aHUS. The results of clinical trials have …