Familial hemolytic uremic syndrome associated with complement factor H deficiency

Pharmacological Management of Atypical Hemolytic Uremic Syndrome in Pediatric Patients: Current and Future

Atypical hemolytic uremic syndrome is a thrombotic microangiopathy characterized by hemolysis, thrombocytopenia, and acute kidney injury, usually caused by alternative complement system overactivation due to pathogenic genetic variants or antibodies to components or regulatory factors in this pathway. Previously, a lack of effective treatment for this condition was associated with mortality, end-stage kidney disease, and the risk of disease recurrence after kidney transplantation. Plasma therapy has been used for atypical hemolytic uremic syndrome treatment with inconsistent results. Complement-blocking treatment changed the outcome and prognosis of patients with atypical hemolytic uremic syndrome. Early administration of eculizumab, a monoclonal C5 antibody, leads to improvements in hematologic, kidney, and systemic manifestations in patients with atypical hemolytic uremic syndrome, even with apparent dialysis dependency. Pre- and post-transplant use of eculizumab is effective in the prevention of atypical hemolytic uremic syndrome recurrence. Evidence on eculizumab use in secondary hemolytic uremic syndrome cases is controversial. Recent data favor the restrictive use of eculizumab in carefully selected atypical hemolytic uremic syndrome cases, but close monitoring for relapse after drug discontinuation is emphasized. Prophylaxis for meningococcal infection is important. The long-acting C5 monoclonal antibody ravulizumab is now approved for atypical hemolytic uremic syndrome treatment, enabling a reduction in the dosing frequency and improving the quality of life in patients with atypical hemolytic uremic syndrome. New strategies for additional and novel complement blockage medications in atypical hemolytic uremic syndrome are under investigation.

Renal diseases and the role of complement: Linking complement to immune effector pathways and therapeutics

The complement system is an ancient and phylogenetically conserved key danger sensing system that is critical for host defense against pathogens. Activation of the complement system is a vital component of innate immunity required for the detection and removal of pathogens. It is also a central orchestrator of adaptive immune responses and a constituent of normal tissue homeostasis. Once complement activation occurs, this system deposits indiscriminately on any cell surface in the vicinity and has the potential to cause unwanted and excessive tissue injury. Deposition of complement components is recognized as a hallmark of a variety of kidney diseases, where it is indeed associated with damage to the self. The provenance and the pathophysiological role(s) played by complement in each kidney disease is not fully understood. However, in recent years there has been a renaissance in the study of complement, with greater appreciation of its intracellular roles as a cell-intrinsic system and its interplay with immune effector pathways. This has been paired with a profusion of novel therapeutic agents antagonizing complement components, including approved inhibitors against complement components (C)1, C3, C5 and C5aR1. A number of clinical trials have investigated the use of these more targeted approaches for the management of kidney diseases. In this review we present and summarize the evidence for the roles of complement in kidney diseases and discuss the available clinical evidence for complement inhibition.

Atypical Hemolytic-Uremic Syndrome: An Update on Pathophysiology, Diagnosis, and Treatment

Atypical hemolytic uremic syndrome (aHUS), a rare variant of thrombotic microangiopathy, is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and renal impairment. The condition is associated with poor clinical outcomes with high morbidity and mortality. Atypical HUS predominantly affects the kidneys but has the potential to cause multi-organ system dysfunction. This uncommon disorder is caused by a genetic abnormality in the complement alternative pathway resulting in over-activation of the complement system and formation of microvascular thrombi. Abnormalities of the complement pathway may be in the form of mutations in key complement genes or autoantibodies against specific complement factors. We discuss the pathophysiology, clinical manifestations, diagnosis, complications, and management of aHUS. We also review the efficacy and safety of the novel therapeutic agent, eculizumab, in aHUS, pregnancy-associated aHUS, and aHUS in renal transplant patients.

Podocytes are new cellular targets of haemoglobin-mediated renal damage

Recurrent and massive intravascular haemolysis induces proteinuria, glomerulosclerosis, and progressive impairment of renal function, suggesting podocyte injury. However, the effects of haemoglobin (Hb) on podocytes remain unexplored. Our results show that cultured human podocytes or podocytes isolated from murine glomeruli bound and endocytosed Hb through the megalin-cubilin receptor system, thus resulting in increased intracellular Hb catabolism, oxidative stress, activation of the intrinsic apoptosis pathway, and altered podocyte morphology, with decreased expression of the slit diaphragm proteins nephrin and synaptopodin. Hb uptake activated nuclear factor erythroid-2-related factor 2 (Nrf2) and induced expression of the Nrf2-related antioxidant proteins haem oxygenase-1 (HO-1) and ferritin. Nrf2 activation and Hb staining was observed in podocytes of mice with intravascular haemolysis. These mice developed proteinuria and showed podocyte injury, characterized by foot process effacement, decreased synaptopodin and nephrin expression, and podocyte apoptosis. These pathological effects were enhanced in Nrf2-deficient mice, whereas Nrf2 activation with sulphoraphane protected podocytes against Hb toxicity both in vivo and in vitro. Supporting the translational significance of our findings, we observed podocyte damage and podocytes stained for Hb, HO-1, ferritin and phosphorylated Nrf2 in renal sections and urinary sediments of patients with massive intravascular haemolysis, such as atypical haemolytic uraemic syndrome and paroxysmal nocturnal haemoglobinuria. In conclusion, podocytes take up Hb both in vitro and during intravascular haemolysis, promoting oxidative stress, podocyte dysfunction, and apoptosis. Nrf2 may be a potential therapeutic target to prevent loss of renal function in patients with intravascular haemolysis. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Clopidogrel-induced Thrombotic Microangiopathy in a Patient with Hypocomplementemia

Clopidogrel was administered to a 67-year-old Japanese man to prevent the recurrence of cerebral infarction. Twelve weeks later, he was admitted to our hospital with acute renal failure, hemolytic anemia and thrombocytopenia, and was diagnosed with clopidogrel-induced thrombotic microangiopathy. Clopidogrel was immediately discontinued and corticosteroid and plasma exchange therapy were administered simultaneously. Thereafter, the patient's condition gradually improved. The patient had a decreased serum complement C3 level. This suggests that the activated alternative pathway is related to thrombotic microangiopathy (TMA). TMA is a critical drug-associated adverse reaction that clinicians should always be vigilant about, because clopidogrel is widely prescribed.

Complement genetics and susceptibility to inflammatory disease. Lessons from genotype-phenotype correlations

Different genome-wide linkage and association studies performed during the last 15 years have associated mutations and polymorphisms in complement genes with different diseases characterized by tissue damage and inflammation. These are complex disorders in which genetically susceptible individuals usually develop the pathology as a consequence of environmental triggers. Although complement dysregulation is a common feature of these pathologies, how the disease phenotype is determined is only partly understood. One way to advance understanding is to focus the research in the analysis of the peculiar genotype-phenotype correlations that characterize some of these diseases. I will review here how understanding the functional consequences of these disease-associated complement genetic variants is providing us with novel insights into the underpinning complement biology and a better knowledge of the pathogenic mechanisms underlying each of these pathologies. These advances have important therapeutic and diagnostic implications.

Podocyte dysfunction in atypical haemolytic uraemic syndrome

Genetic or autoimmune defects that lead to dysregulation of the alternative pathway of complement have been associated with the development of atypical haemolytic uraemic syndrome (aHUS), which is characterized by thrombocytopenia, haemolytic anaemia and acute kidney injury. The relationship between aHUS, podocyte dysfunction and the resultant proteinuria has not been adequately investigated. However, the report of mutations in diacylglycerol kinase ε (DGKE) as a cause of recessive infantile aHUS characterized by proteinuria, highlighted podocyte dysfunction as a potential complication of aHUS. DGKE deficiency was originally thought to trigger aHUS through pathogenetic mechanisms distinct from complement dysregulation; however, emerging findings suggest an interplay between DGKE and complement systems. Podocyte dysfunction with nephrotic-range proteinuria can also occur in forms of aHUS associated with genetic or autoimmune complement dysregulation without evidence of DGKE mutations. Furthermore, proteinuric glomerulonephritides can be complicated by aHUS, possibly as a consequence of podocyte dysfunction inducing endothelial injury and prothrombotic abnormalities.

Eculizumab in neonatal hemolytic uremic syndrome with homozygous factor H deficiency

BACKGROUND

Neonatal atypical hemolytic uremic syndrome (aHUS) is a rare but severe disease that is mainly due to methylmalonic aciduria or genetic complement abnormalities. Traditional management of aHUS includes plasma infusion/exchange, but in small or unstable infants, plasma exchange can be challenging because of high extracorporeal volume and difficulty to obtain an adequate venous access. The C5 complement blocker eculizumab has become a cornerstone of first-line management of aHUS due to complement deregulation in older patients. However, little data are available on its use in neonatal aHUS.

CASE-DIAGNOSIS/TREATMENT

We report on an 11-day-old neonate with severe aHUS (myocardial impairment, respiratory failure, acute kidney disease requiring hemodiafiltration) due to homozygous factor-H deficiency. She received early treatment with eculizumab as first-line therapy and completely recovered within 5 days. A second dose of eculizumab was administered 7 days after the first infusion, followed by a dose every 2 weeks for 2 months and then every 3 weeks, at the same dosage (300 mg). With more than 24 months of follow-up, renal function remains normal.

CONCLUSIONS

We report on the long-term efficacy and safety of eculizumab as first-line therapy in neonatal aHUS. However its use still requires optimization in terms of indications and administration (frequency, dosage).

Anesthetic management of living donor liver transplantation for complement factor H deficiency hemolytic uremic syndrome: a case report

We experienced a living donor liver transplantation for a 26-month-old girl with complement factor H deficiency. Complement factor H is a plasma protein that regulates the activity of the complement pathway. Complement overactivity induced by complement factor H deficiency is associated with atypical hemolytic uremic syndrome. Liver transplantation can be the proper treatment for this condition. During the liver transplantation of these patients, prevention of the complement overactivation is necessary. Minimizing complement activation, through the use of modalities such as plasma exchange before the surgery and transfusion of fresh frozen plasma throughout the entire perioperative period, may be the key for successful liver transplantation in these patients.

Use of eculizumab and plasma exchange in successful combined liver-kidney transplantation in a case of atypical HUS associated with complement factor H mutation

BACKGROUND

Atypical hemolytic uremic syndrome (aHUS) evolves into end-stage renal failure in nearly half of affected patients and is associated with defective regulation of the alternative complement pathway. Patients with a complement factor H (CFH) mutation have a 30-100% risk of graft loss due to aHUS recurrence or graft thrombosis. Since CFH is produced predominantly by the liver, combined liver-kidney transplant is a curative treatment option. One major unexpected risk includes liver failure secondary to uncontrolled complement activation. We report a successful combined liver-kidney transplantation with perioperative plasma exchange and use of the humanized anti-C5 monoclonal antibody eculizumab.

CASE DIAGNOSIS/TREATMENT

An 11-month-old female presented with oliguric renal failure after 3 weeks of flu-like symptoms in the absence of diarrhea. Following the identification of Escherichia coli 0157:H7 in her stool, she was discharged home on peritoneal dialysis with a diagnosis of Shiga toxin-associated HUS. Three months later, she developed severe anemia, thrombocytopenia, and neurological involvement. aHUS was diagnosed and confirmed, and genetic testing revealed a mutation in CFH SCR20. Once donor organs became available, she received preoperative plasma exchange followed by eculizumab infusion with intra-operative fresh frozen plasma prior to combined liver-kidney transplant. At 19 months post-transplant, she continues to have excellent allograft and liver function without signs of disease recurrence.

CONCLUSION

Perioperative use of eculizumab in conjunction with plasma exchange during simultaneous liver-kidney transplant can be used to inhibit terminal complement activity, thereby optimizing successful transplantation by reducing the risk of graft thrombosis.

Hemolytic uremic syndrome

Hemolytic uremic syndrome (HUS) is a thrombotic microangiopathy defined by thrombocytopenia, nonimmune microangiopathic hemolytic anemia, and acute renal failure. The most frequent form is associated with infections by Shiga-like toxin-producing bacteria (STEC-HUS). Rarer cases are triggered by neuraminidase-producing Streptococcus pneumoniae (pneumococcal-HUS). The designation of aHUS is used to refer to those cases in which an infection by Shiga-like toxin-producing bacteria or S. pneumoniae can be excluded. Studies performed in the last two decades have documented that hyperactivation of the complement system is the pathogenetic effector mechanism leading to the endothelial damage and the microvascular thrombosis in aHUS. Recent data suggested the involvement of the complement system in the pathogenesis of STEC-HUS and pneumococcal-HUS as well. Clinical signs and symptoms may overlap among the different forms of HUS; however, pneumococcal-HUS and aHUS have a worse prognosis compared with STEC-HUS. Early diagnosis and identification of underlying pathogenetic mechanism allows instating specific support measures and therapies. In clinical trials in patients with aHUS, complement inhibition by eculizumab administration leads to a rapid and sustained normalization of hematological parameters with improvement in long-term renal function. This review summarizes current concepts about the epidemiological findings, the pathological and clinical aspects of STEC-HUS, pneumococcal-HUS, and aHUS, and their diagnosis and management.

Therapeutic plasma exchange for the treatment of pediatric renal diseases in 2013

Therapeutic plasma exchange is an extracorporeal treatment modality that removes systemic circulating pathologic factors or replaces absent plasma components and plays a role in many nephrologic conditions. It presents a number of technical challenges in the pediatric population but has become an increasingly common practice in pediatric nephrology over the past several decades. While prospective evidence is often lacking, our increased understanding of the molecular pathogenesis underlying many pediatric renal diseases provides sound reasoning for the use of plasma exchange in treating these conditions. This review will present the currently accepted indications for plasma exchange in children, the technical aspects of the procedure and its potential complications.

Monogenic diseases that can be cured by liver transplantation

While the prevalence of most diseases caused by single-gene mutations is low and defines them as rare conditions, all together, monogenic diseases account for approximately 10 in every 1000 births according to the World Health Organisation. Orthotopic liver transplantation (LT) could offer a therapeutic option in monogenic diseases in two ways: by substituting for an injured liver or by supplying a tissue that can replace a mutant protein. In this respect, LT may be regarded as the correction of a disease at the level of the dysfunctional protein. Monogenic diseases that involve the liver represent a heterogeneous group of disorders. In conditions associated with predominant liver parenchymal damage (i.e., genetic cholestatic disorders, Wilson's disease, hereditary hemochromatosis, tyrosinemia, α1 antitrypsin deficiency), hepatic complications are the major source of morbidity and LT not only replaces a dysfunctional liver but also corrects the genetic defect and effectively cures the disease. A second group includes liver-based genetic disorders characterised by an architecturally near-normal liver (urea cycle disorders, Crigler-Najjar syndrome, familial amyloid polyneuropathy, primary hyperoxaluria type 1, atypical haemolytic uremic syndrome-1). In these defects, extrahepatic complications are the main source of morbidity and mortality while liver function is relatively preserved. Combined transplantation of other organs may be required, and other surgical techniques, such as domino and auxiliary liver transplantation, have been attempted. In a third group of monogenic diseases, the underlying genetic defect is expressed at a systemic level and liver involvement is just one of the clinical manifestations. In these conditions, LT might only be partially curative since the abnormal phenotype is maintained by extrahepatic synthesis of the toxic metabolites (i.e., methylmalonic acidemia, propionic acidemia). This review focuses on principles of diagnosis, management and LT results in both paediatric and adult populations of selected liver-based monogenic diseases, which represent examples of different transplantation strategies, driven by the understanding of the expression of the underlying genetic defect.

Complement dysregulation and disease: from genes and proteins to diagnostics and drugs

During the last decade, numerous studies have associated genetic variations in complement components and regulators with a number of chronic and infectious diseases. The functional characterization of these complement protein variants, in addition to recent structural advances in understanding of the assembly, activation and regulation of the AP C3 convertase, have provided important insights into the pathogenic mechanisms involved in some of these complement related disorders. This knowledge has identified potential targets for complement inhibitory therapies which are demonstrating efficacy and generating considerable expectation in changing the natural history of these diseases. Comprehensive understanding of the genetic and non-genetic risk factors contributing to these disorders will also result in targeting of the right patient groups in a stratified medicine approach through better diagnostics and individually tailored treatments, thereby improving management of patients.

STEC-HUS, atypical HUS and TTP are all diseases of complement activation

Haemolytic uraemic syndrome (HUS) and thrombotic thrombocytopaenic purpura (TTP) are diseases characterized by microvascular thrombosis, with consequent thrombocytopaenia, haemolytic anaemia and dysfunction of affected organs. Advances in our understanding of the molecular pathology led to the recognition of three different diseases: typical HUS caused by Shiga toxin-producing Escherichia coli (STEC-HUS); atypical HUS (aHUS), associated with genetic or acquired disorders of regulatory components of the complement system; and TTP that results from a deficiency of ADAMTS13, a plasma metalloprotease that cleaves von Willebrand factor. In this Review, we discuss data indicating that complement hyperactivation is a common pathogenetic effector that leads to endothelial damage and microvascular thrombosis in all three diseases. In STEC-HUS, the toxin triggers endothelial complement deposition through the upregulation of P-selectin and possibly interferes with the activity of complement regulatory molecules. In aHUS, mutations in the genes coding for complement components predispose to hyperactivation of the alternative pathway of complement. In TTP, severe ADAMTS13 deficiency leads to generation of massive platelet thrombi, which might contribute to complement activation. More importantly, evidence is emerging that pharmacological targeting of complement with the anti-C5 monoclonal antibody eculizumab can effectively treat not only aHUS for which it is indicated, but also STEC-HUS and TTP in some circumstances.

Management of hemolytic uremic syndrome

2011 has been a special year for hemolytic uremic syndrome (HUS): on the one hand, the dramatic epidemic of Shiga toxin producing E. coli -associated HUS in Germany brought the disease to the attention of the general population, on the other hand it has been the year when eculizumab, the first complement blocker available for clinical practice, was demonstrated as the potential new standard of care for atypical HUS. Here we review the therapeutic options presently available for the various forms of hemolytic uremic syndrome and show how recent knowledge has changed the therapeutic approach and prognosis of atypical HUS.

Genetics of hemolytic uremic syndromes

Hemolytic uremic syndrome (HUS) is a very rare disease (two cases per year per 1 million population) but represents the most common cause of acute renal failure in young children that require dialysis. The majority of cases in childhood (90%) is caused by Shiga toxin producing Escherichia coli infection. This typical form of the disease does not relapse and has a good prognosis if the acute status can be managed successfully. Atypical HUS (aHUS) is a severe and frequently relapsing disorder with the same triad of thrombocytopenia, hemolysis and acute renal failure in the absence of Shiga toxin E. coli infection. More than 50% of patients with atypical HUS progress to chronic renal dysfunction and 10% die due to complications of the disease. Atypical HUS appears to have a genetic basis. Mutations in genes coding for components of the alternative complement pathway are found in about 60% of cases. The clinical presentation of aHUS overlaps with that of other thrombotic microangiopathies, rendering the diagnosis on clinical grounds alone extremely difficult. In recent years, genetic testing has opened the way for molecular diagnostics and helped establishing therapeutically and prognostically useful genotype-phenotype correlations. This review summarizes recent findings regarding the genetic basis of the HUS. The pathophysiology of the disease and the implication of genetic abnormalities in the complement system for the different types of HUS are discussed.

Atypical hemolytic uremic syndrome

Hemolytic uremic syndrome (HUS) is defined by the triad of mechanical hemolytic anemia, thrombocytopenia and renal impairment. Atypical HUS (aHUS) defines non Shiga-toxin-HUS and even if some authors include secondary aHUS due to Streptococcus pneumoniae or other causes, aHUS designates a primary disease due to a disorder in complement alternative pathway regulation. Atypical HUS represents 5 -10% of HUS in children, but the majority of HUS in adults. The incidence of complement-aHUS is not known precisely. However, more than 1000 aHUS patients investigated for complement abnormalities have been reported. Onset is from the neonatal period to the adult age. Most patients present with hemolytic anemia, thrombocytopenia and renal failure and 20% have extra renal manifestations. Two to 10% die and one third progress to end-stage renal failure at first episode. Half of patients have relapses. Mutations in the genes encoding complement regulatory proteins factor H, membrane cofactor protein (MCP), factor I or thrombomodulin have been demonstrated in 20-30%, 5-15%, 4-10% and 3-5% of patients respectively, and mutations in the genes of C3 convertase proteins, C3 and factor B, in 2-10% and 1-4%. In addition, 6-10% of patients have anti-factor H antibodies. Diagnosis of aHUS relies on 1) No associated disease 2) No criteria for Shigatoxin-HUS (stool culture and PCR for Shiga-toxins; serology for anti-lipopolysaccharides antibodies) 3) No criteria for thrombotic thrombocytopenic purpura (serum ADAMTS 13 activity > 10%). Investigation of the complement system is required (C3, C4, factor H and factor I plasma concentration, MCP expression on leukocytes and anti-factor H antibodies; genetic screening to identify risk factors). The disease is familial in approximately 20% of pedigrees, with an autosomal recessive or dominant mode of transmission. As penetrance of the disease is 50%, genetic counseling is difficult. Plasmatherapy has been first line treatment until presently, without unquestionable demonstration of efficiency. There is a high risk of post-transplant recurrence, except in MCP-HUS. Case reports and two phase II trials show an impressive efficacy of the complement C5 blocker eculizumab, suggesting it will be the next standard of care. Except for patients treated by intensive plasmatherapy or eculizumab, the worst prognosis is in factor H-HUS, as mortality can reach 20% and 50% of survivors do not recover renal function. Half of factor I-HUS progress to end-stage renal failure. Conversely, most patients with MCP-HUS have preserved renal function. Anti-factor H antibodies-HUS has favourable outcome if treated early.

Atypical hemolytic uremic syndrome

Hemolytic uremic syndrome (HUS) is defined by the triad of mechanical hemolytic anemia, thrombocytopenia and renal impairment. Atypical HUS (aHUS) defines non Shiga-toxin-HUS and even if some authors include secondary aHUS due to Streptococcus pneumoniae or other causes, aHUS designates a primary disease due to a disorder in complement alternative pathway regulation. Atypical HUS represents 5 -10% of HUS in children, but the majority of HUS in adults. The incidence of complement-aHUS is not known precisely. However, more than 1000 aHUS patients investigated for complement abnormalities have been reported. Onset is from the neonatal period to the adult age. Most patients present with hemolytic anemia, thrombocytopenia and renal failure and 20% have extra renal manifestations. Two to 10% die and one third progress to end-stage renal failure at first episode. Half of patients have relapses. Mutations in the genes encoding complement regulatory proteins factor H, membrane cofactor protein (MCP), factor I or thrombomodulin have been demonstrated in 20-30%, 5-15%, 4-10% and 3-5% of patients respectively, and mutations in the genes of C3 convertase proteins, C3 and factor B, in 2-10% and 1-4%. In addition, 6-10% of patients have anti-factor H antibodies. Diagnosis of aHUS relies on 1) No associated disease 2) No criteria for Shigatoxin-HUS (stool culture and PCR for Shiga-toxins; serology for anti-lipopolysaccharides antibodies) 3) No criteria for thrombotic thrombocytopenic purpura (serum ADAMTS 13 activity > 10%). Investigation of the complement system is required (C3, C4, factor H and factor I plasma concentration, MCP expression on leukocytes and anti-factor H antibodies; genetic screening to identify risk factors). The disease is familial in approximately 20% of pedigrees, with an autosomal recessive or dominant mode of transmission. As penetrance of the disease is 50%, genetic counseling is difficult. Plasmatherapy has been first line treatment until presently, without unquestionable demonstration of efficiency. There is a high risk of post-transplant recurrence, except in MCP-HUS. Case reports and two phase II trials show an impressive efficacy of the complement C5 blocker eculizumab, suggesting it will be the next standard of care. Except for patients treated by intensive plasmatherapy or eculizumab, the worst prognosis is in factor H-HUS, as mortality can reach 20% and 50% of survivors do not recover renal function. Half of factor I-HUS progress to end-stage renal failure. Conversely, most patients with MCP-HUS have preserved renal function. Anti-factor H antibodies-HUS has favourable outcome if treated early.

Hemolytic uremic syndrome: new developments in pathogenesis and treatment

Hemolytic uremic syndrome is defined by the characteristic triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure. In children, most cases of HUS are caused by Shiga-toxin-producing bacteria, especially Escherichia coli O157:H7. Common vehicles of transmission include ground beef, unpasteurized milk, and municipal or swimming water. Shiga-toxin-associated HUS is a main cause of acute renal failure in young children. Management remains supportive as there is at present no specific therapy to ameliorate the prognosis. Immediate outcome is most often favourable but long-term renal sequelae are frequent due to nephron loss. Atypical HUS represents 5% of cases. In the past 15 years, mutations in complement regulators of the alternative pathway have been identified in almost 60% of cases, leading to excessive complement activation. The disease has a relapsing course and more than half of the patients either die or progress to end-stage renal failure. Recurrence after renal transplantation is frequent.

aHUS caused by complement dysregulation: new therapies on the horizon

Atypical hemolytic uremic syndrome (aHUS) is a heterogeneous disease that is caused by defective complement regulation in over 50% of cases. Mutations have been identified in genes encoding both complement regulators [complement factor H (CFH), complement factor I (CFI), complement factor H-related proteins (CFHR), and membrane cofactor protein (MCP)], as well as complement activators [complement factor B (CFB) and C3]. More recently, mutations have also been identified in thrombomodulin (THBD), an anticoagulant glycoprotein that plays a role in the inactivation of C3a and C5a. Inhibitory autoantibodies to CFH account for an additional 5-10% of cases and can occur in isolation or in association with mutations in CFH, CFI, CFHR 1, 3, 4, and MCP. Plasma therapies are considered the mainstay of therapy in aHUS secondary to defective complement regulation and may be administered as plasma infusions or plasma exchange. However, in certain cases, despite initiation of plasma therapy, renal function continues to deteriorate with progression to end-stage renal disease and renal transplantation. Recently, eculizumab, a humanized monoclonal antibody against C5, has been described as an effective therapeutic strategy in the management of refractory aHUS that has failed to respond to plasma therapy. Clinical trials are now underway to further evaluate the efficacy of eculizumab in the management of both plasma-sensitive and plasma-resistant aHUS.

Treatment with human complement factor H rapidly reverses renal complement deposition in factor H-deficient mice

Total deficiency of complement factor H (CFH) is associated with dense deposit disease and atypical hemolytic uremic syndrome. CFH is the major regulator of the alternative pathway of complement activation and its complete deficiency results in uncontrolled C3 activation through this pathway and secondary C3 deficiency. Plasma infusion, as a source of CFH, has been used with variable success to treat renal disease associated with its deficiency. However, the risks of volume and protein overload limit this therapeutic approach. In this study, we investigated the efficacy of a purified human CFH (hCFH) preparation in Cfh-gene knockout mice. These mice spontaneously develop both secondary plasma C3 deficiency and a renal abnormality characterized by massive accumulation of C3 along the glomerular basement membrane. The renal lesion is analogous to human dense deposit disease. Treatment of knockout mice with hCFH resulted in rapid normalization of plasma C3 levels and resolution of the glomerular basement membrane C3 deposition. Long-term treatment of mice with hCFH was not possible because of the development of an immune response against hCFH. Hence, we suggest that hCFH can be an effective alternative therapy to plasma infusions in patients with renal disease associated with CFH deficiency.

KDIGO clinical practice guideline for the care of kidney transplant recipients

The 2009 Kidney Disease: Improving Global Outcomes (KDIGO) clinical practice guideline on the monitoring, management, and treatment of kidney transplant recipients is intended to assist the practitioner caring for adults and children after kidney transplantation. The guideline development process followed an evidence-based approach, and management recommendations are based on systematic reviews of relevant treatment trials. Critical appraisal of the quality of the evidence and the strength of recommendations followed the Grades of Recommendation Assessment, Development, and Evaluation (GRADE) approach. The guideline makes recommendations for immunosuppression, graft monitoring, as well as prevention and treatment of infection, cardiovascular disease, malignancy, and other complications that are common in kidney transplant recipients, including hematological and bone disorders. Limitations of the evidence, especially on the lack of definitive clinical outcome trials, are discussed and suggestions are provided for future research.

Renal manifestations of systemic illness in children

Kidney disease may be associated with a systemic disorder or found in isolation. With advances in the understanding of the pathophysiology of glomerular disorders, the distinction between primary and secondary glomerular disease is no longer valid. A wide spectrum of glomerular, vascular, and tubulointerstitial diseases may accompany autoimmune disorders, nephritogenic pharmaceuticals, infections, or complement dysregulation. This article focuses on renal manifestations of systemic diseases such as vasculitis, drug- and infection-related tubulointerstitial injury, and thrombotic disorders.

Hemolytic uremic syndrome due to homozygous factor H deficiency

The majority of complement factor H mutations associated with atypical hemolytic uremic syndrome (HUS) are heterozygous. Homozygous mutations causing atypical hemolytic uremic syndrome are rare. We report a 7-month-old boy with HUS, severe hypocomplementemia (low C3 and normal C4 levels), and extremely low circulating levels of factor H. Genetic analysis showed homozygous 4 bp deletion in the gene encoding factor H in the patient, with his parents being carriers. The patient showed progression to end-stage renal disease and is presently on chronic ambulatory peritoneal dialysis.

Guideline for the investigation and initial therapy of diarrhea-negative hemolytic uremic syndrome

This guideline for the investigation and initial treatment of atypical hemolytic uremic syndrome (HUS) is intended to offer an approach based on opinion, as evidence is lacking. It builds on the current ability to identify the etiology of specific diagnostic sub-groups of HUS. HUS in children is mostly due to infection, enterohemorrhagic Escherichia coli (EHEC), Shigella dysenteriae type 1 in some geographic regions, and invasive Streptococcus pneumoniae. These sub-groups are relatively straightforward to diagnose. Their management, which is outside the remit of this guideline, is related to control of infection where that is necessary and supportive measures for the anemia and acute renal failure. A thorough investigation of the remainder of childhood HUS cases, commonly referred to as "atypical" HUS, will reveal a risk factor for the syndrome in approximately 60% of cases. Disorders of complement regulation are, numerically, the most important. The outcome for children with atypical HUS is poor, and, because of the rarity of these disorders, clinical experience is scanty. Some cases of complement dysfunction appear to respond to plasma therapy. The therapeutic part of this guideline is the consensus of the contributing authors and is based on limited information from uncontrolled studies. The guideline proposes urgent and empirical plasmapheresis replacement with whole plasma fraction for the first month after diagnosis. This should only be undertaken in specialized pediatric nephrology centers where appropriate medical and nursing skills are available. The guideline includes defined terminology and audit points so that the early clinical effectiveness of the strategy can be evaluated.

Hemolytic uremic syndrome recurrence after renal transplantation

About 60% of non-Stx-associated aHUS are due to the defect of protection of endothelial cells from complement activation, secondary to mutations in the genes of CFH, MCP, IF, BF, or C3. In addition, 10% of patients have anti-CFH antibodies. While the risk of post-transplant recurrence is less than 1% in Stx-HUS patients, it is approximately 80% in CFH or IF-mutated patients, 20% in MCP-mutated patients, and 30% in patients with no mutation. Patients with anti-CFH antibodies probably also are at risk of recurrence. While MCP-mutated patients can reasonably go to transplantation, recent reports suggest that plasmatherapy started before surgery and maintained life-long may prevent recurrence in CFH-mutated patients. Four successful liver-kidney transplantation utilizing plasmatherapy in CFH-mutated children have been reported recently. In summary, the risk of post-transplant recurrence can now be approached according to genotype. Therefore, aHUS patients should undergo complement determination, screening for anti-CFH antibodies, and genotyping before transplantation. Kidney or kidney + liver transplantation with concomitant plasmatherapy need to be evaluated by prospective trials in patients with hereditary complement abnormalities.

Efficacy of plasma therapy in atypical hemolytic uremic syndrome with complement factor H mutations

Atypical hemolytic uremic syndrome (aHUS) frequently results in end-stage renal failure and can be lethal. Several studies have established an association between quantitative or qualitative abnormalities in complement factor H and aHUS. Although plasma infusion and exchange are often advocated, guidelines have yet to be established. Long-term outcome for patients under treatment is still unknown. We describe a patient who, at 7 months of age, presented with aHUS associated with combined de novo complement factor H mutations (S1191L and V1197A) on the same allele. Laboratory investigations showed normal levels of complements C4, C3 and factor H. Plasma exchanges and large-dose infusion therapy resulted in a resolution of hemolysis and recovery of renal function. Three recurrences were successfully treated by intensification of the plasma infusion treatment to intervals of 2 or 3 days. This patient showed good response to large doses of plasma infusions and her condition remained stable for 30 months with weekly plasma infusions (30 ml/kg). Long-term tolerance and efficacy of such intensive plasma therapy are still unknown. Reported secondary failure of plasma therapy in factor H deficiency warrants the search for alternative therapeutic approaches.

Complement and the atypical hemolytic uremic syndrome in children

Over the past decade, atypical hemolytic uremic syndrome (aHUS) has been demonstrated to be a disorder of the regulation of the complement alternative pathway. Among approximately 200 children with the disease, reported in the literature, 50% had mutations of the complement regulatory proteins factor H, membrane cofactor protein (MCP) or factor I. Mutations in factor B and C3 have also been reported recently. In addition, 10% of children have factor H dysfunction due to anti-factor H antibodies. Early age at onset appears as characteristic of factor H and factor I mutated patients, while MCP-associated HUS is not observed before age 1 year. Low C3 level may occur in patients with factor H and factor I mutation, while C3 level is generally normal in MCP-mutated patients. Normal plasma factor H and factor I levels do not preclude the presence of a mutation in these genes. The worst prognosis is for factor H-mutated patients, as 60% die or reach end-stage renal disease (ESRD) within the first year after onset of the disease. Patients with mutations in MCP have a relapsing course, but no patient has ever reached ESRD in the first year of the disease. Half of the patients with factor I mutations have a rapid evolution to ESRD, but half recover. Early intensive plasmatherapy appears to have a beneficial effect, except in MCP-mutated patients. There is a high risk of graft loss for HUS recurrence or thrombosis in all groups except the MCP-mutated group. Recent success of liver-kidney transplantation combined with plasmatherapy opens this option for patients with mutations of factors synthesized in the liver. New therapies such as factor H concentrate or complement inhibitors offer hope for the future.

Translational mini-review series on complement factor H: therapies of renal diseases associated with complement factor H abnormalities: atypical haemolytic uraemic syndrome and membranoproliferative glomerulonephritis

Genetic and acquired abnormalities in complement factor H (CFH) have been associated with two different human renal diseases: haemolytic uraemic syndrome and membrano proliferative glomerulonephritis. The new genetic and pathogenetic findings in these diseases and their clinical implications for the management and cure of patients are reviewed in this paper.

Where next with atypical hemolytic uremic syndrome?

Hemolytic uremic syndrome (HUS) is a systemic disease characterized by damage to endothelial cells, erythrocytes and kidney glomeruli. A "typical" form of HUS follows gastrointestinal infection with enterohemorrhagic E. coli (e.g. O157:H7). Atypical HUS (aHUS) is not associated with gastrointestinal infections but is sporadic or familial in nature. Approximately 50% of aHUS cases are associated with a mutation in one or more genes coding for proteins involved in regulation or activation of the alternative pathway of complement. The link between the disease and the mutations shows the important balance of the alternative pathway between activation and regulation on host cell surfaces. It also demonstrates the power of this pathway in destroying cellular targets in general. In this review we discuss the current knowledge on pathogenesis, classification, diagnostics and management of this disease. We indicate a comprehensive diagnostic approach for aHUS based on the latest knowledge on complement dysregulation to gain both immediate and future patient benefit by assisting in choosing more appropriate therapy for each patient. We also indicate directions in which therapy of aHUS might improve and indicate the need to re-think the terminology and categorisation of the HUS-like diseases so that any advantage in the understanding of complement regulatory problems can be applied to patients accurately.

Differential impact of complement mutations on clinical characteristics in atypical hemolytic uremic syndrome

Mutations in factor H (CFH), factor I (IF), and membrane cofactor protein (MCP) genes have been described as risk factors for atypical hemolytic uremic syndrome (aHUS). This study analyzed the impact of complement mutations on the outcome of 46 children with aHUS. A total of 52% of patients had mutations in one or two of known susceptibility factors (22, 13, and 15% of patients with CFH, IF, or MCP mutations, respectively; 2% with CFH+IF mutations). Age <3 mo at onset seems to be characteristic of CFH and IF mutation-associated aHUS. The most severe prognosis was in the CFH mutation group, 60% of whom reached ESRD or died within <1 yr. Only 30% of CFH mutations were localized in SCR20. MCP mutation-associated HUS has a relapsing course, but none of the children reached ESRD at 1 yr. Half of patients with IF mutation had a rapid evolution to ESRD, and half recovered. Plasmatherapy seemed to have a beneficial effect in one third of patients from all groups except for the MCP mutation group. Only eight (33%) of 24 kidney transplantations that were performed in 15 patients were successful. Graft failures were due to early graft thrombosis (50%) or HUS recurrence. In conclusion, outcome of HUS in patients with CFH mutation is catastrophic, and posttransplantation outcome is poor in all groups except for the MCP mutation group. New therapies are urgently needed, and further research should elucidate the unexplained HUS group.

Transient severe metastatic calcification in acute renal failure

Metastatic calcification, a known complication of prolonged end-stage renal disease, is herein described for the first time in a 10-month-old boy with acute renal failure, manifesting as a painful and swollen arm. Imaging revealed diffuse calcification and technetium-99 methylene diphosphonate (99Tc-MDP) uptake around the humerus and axilla. Calcium and vitamin D restriction, followed by intravenous administration of sodium thiosulfate caused a full symptomatic, radio- and scintigraphic improvement.

[Incomplete hemolytic uremic syndrome associated with partial factor H deficiency]

Hemolytic uremic syndrome (HUS) consists of the association of hemolytic anemia, thrombocytopenia and renal failure. Most cases are related to toxins (verotoxins) produced by Escherichia coli 0157:H7 and generally have good renal prognosis. Atypical forms can occur, with a less favorable prognosis, and can be due to mutations in the gene codifying factor H, a protein that regulates activation of the alternative complement pathway, among other causes. Factor H deficiency produces continuous complement activation, causing injury to capillary endothelial cells. We report a case of incomplete (absence of thrombocytopenia and uremia), atypical HUS in which hypocomplementemia secondary to partial factor H deficiency was detected, with favorable outcome. Prior to symptom onset, the patient had a Campylobacter infection, precipitating the symptoms. Genetic analysis showed a heterozygous mutation (C846T) located in the SCR4 domain, generating an amino acid change in the factor H molecule (Pro240Leu). This mutation may have been the cause of the partial factor H deficiency and the patient's symptoms on admission.

Renal transplantation in HUS patients with disorders of complement regulation

Haemolytic uraemic syndrome (HUS) is the primary diagnosis of 4.5% of children on chronic renal replacement therapy. Approximately 5% of all HUS cases have an "atypical" or recurrent course. Atypical HUS is an inadequate term that applies to a heterogeneous group of conditions. We describe this group as non-diarrhoeal (D-) ), non-EHEC (EHEC - ) HUS. Patients in the non-diarrhoeal, non-EHEC, relapsing group are much more likely to exhibit severe hypertension, histological findings of arterial as well as arteriolar disease, chronic and end-stage renal failure. In general, these patients have an alarmingly high risk of graft loss from disease recurrence or thrombosis ranging from 60-100%. Family history is crucial, and where family members have relapsing disease, transplantation is a very high risk procedure (recurrence 100%). Patients with (D-)HUS need very careful consideration before transplantation, including molecular investigation of complement regulators (and von Willebrandt protease (ADAMTS13) activity, although this goes beyond the scope of this review). Guidelines are accessible under http://www.espn.ucwm.ac.uk . On no account should live related donation take place unless the risks of graft loss are understood. International collaboration to identify safer ways of transplanting these challenging patients is urgently needed.

Secondary failure of plasma therapy in factor H deficiency

We report a patient with homozygous factor H deficiency leading to permanent alternate complement activation and early onset of the hemolytic uremic syndrome. He was successfully treated with weekly infusions of fresh frozen plasma over 4 years, displaying normal blood pressure while only treated with an angiotensin converting enzyme (ACE) inhibitor, a steady level of haptoglobin, low-range proteinuria and normal creatinine clearance. By the end of the fourth year of treatment, he dramatically developed a relapse of hemolytic and uremic syndrome, displaying undetectable haptoglobin, nephrotic range proteinuria and progressive renal failure. Despite a ten-fold increase in the dosage of plasma infusion through daily plasma exchange, haptoglobin remained undetectable while circulating antigenic factor H levels reached 22-24% (normal values 65-140%). Three months following the biological onset of the relapse, a bilateral nephrectomy was performed owing to uncontrolled hypertension and rapidly progressive renal failure. The molecular mechanism of plasma resistance remained unclear while antifactor H antibodies were not detected in the plasma. We suggest that protracted administration of exogenous factor H might not be a long-term strategy in homozygous factor H deficiency.

Thrombotic microangiopathy after kidney transplantation

Two forms of post-transplant thrombotic microangiopathy (TMA) may be recognized: recurrent TMA and de novo TMA. Recurrent TMA may occur in patients who developed a nondiarrhoeal form of haemolytic uraemic syndrome (HUS) being particularly frequent in patients with autosomal recessive or dominant HUS. The recurrence is almost the rule in patients with mutation in complement factor H gene. Most patients eventually lose the graft. Treatment with plasma infusions or plasmapheresis is often disappointing, but few cases may be rescued. Intravenous immunoglobulins and rituximab have also been successful in anedoctic cases. De novo TMA is rarer. A number of factors including viral infection may be responsible of de novo TMA, but in most cases TMA is triggered by calcineurin inhibitors or mTOR inhibitors. The clinical presentation of de novo TMA may be variable with some patients showing clinical and laboratory features of HUS while others showing only a progressive renal failure. The prognosis is less severe than with recurrent TMA. Complete withdrawal of the offending drug may lead to improvement in many cases. The addition of plasma exchange may result in graft salvage in about 80% of cases.

Genetic kidney diseases in the pediatric population of southern Israel

Genetic kidney diseases (GKDs) are an important and well-known entity in pediatric nephrology. In the past decade advances in genetic and molecular approaches have enabled elucidation of the underlying molecular defects in many of these disorders. Herein we summarize the progress that has been made over the past decade in disclosing the molecular basis of several novel GKDs, which were characterized in our area and include Bartter syndrome type IV, type II Bartter syndrome and transient neonatal hyperkalemia, cystinuria and mental retardation, familial hypomagnesemia with secondary hypocalcemia, infantile nephronophthisis, familial hemolytic uremic syndrome with factor H deficiency, and non-cystic autosomal dominant nephropathy. Retrospective analysis of our data reveals that GKDs are over-represented among the pediatric population in southern Israel. GKDs are seen four-times more often than end-stage renal disease (ESRD) and comprise 38% of all cases of ESRD in our area. This high rate of GKDs is mainly due to the high frequency of consanguineous marriages that prevails in this area. Understanding of the genetic and molecular background of these diseases is a result of a fruitful collaboration between the pediatric nephrologists and scientists, and has a direct implication on the diagnosis and treatment of the affected families.

A classification of hemolytic uremic syndrome and thrombotic thrombocytopenic purpura and related disorders

The diagnostic terms hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP) are based on historical and overlapping clinical descriptions. Advances in understanding some of the causes of the syndrome now permit many patients to be classified according to etiology. The increased precision of a diagnosis based on causation is important for considering logical approaches to treatment and prognosis. It is also essential for research. We propose a classification that accommodates both a current understanding of causation (level 1) and clinical association in cases for whom cause of disease is unclear (level 2). We tested the classification in a pediatric disease registry of HUS. The revised classification is a stimulus to comprehensive investigation of all cases of HUS and TTP and is expected to increase the proportion of cases in whom a level 1 etiological diagnosis is confirmed.

A case of atypical hemolytic uremic syndrome with a transient decrease in complement factor H

We report a case of sporadic atypical hemolytic uremic syndrome (HUS) with a transient decrease in complement factor H. Referred for hemolysis and azotemia without diarrhea prodrome, this 31-month-old boy showed a decreased complement 3 (C3) and complement factor H (FH) level. However, the factor H gene (HF1) mutation was missing. After the hemolysis was controlled with plasma infusion, the C3 and FH levels recovered. The patient's renal function fully recovered and remained normal, and there was no recurrence of the HUS.

Binding of complement factor H to endothelial cells is mediated by the carboxy-terminal glycosaminoglycan binding site

Factor H (FH), the major fluid phase regulator of the alternative complement pathway, mediates protection of plasma-exposed host structures. It has recently been shown that short consensus repeats 19 to 20 of FH are mutational hot spots associated with atypical hemolytic uremic syndrome (aHUS), a disease with endothelial cell damage. Domain 20 of FH contains binding sites for heparin, C3b, and the cleavage product C3d. To study the role of these binding sites in target recognition, we performed site-directed mutagenesis in domain 20 and assayed the resulting recombinant proteins. The mutant FH15-20A (substitutions R1203E, R1206E, and R1210S) bound neither heparin nor endothelial cells. Similarly, an aHUS-derived mutant FH protein (E1172Stop, lacking domain 20) failed to bind endothelial cells and showed impaired binding to heparin. Binding of FH to endothelial cells was inhibited by heparin and a specific monoclonal antibody that inhibited heparin but not C3d binding, demonstrating that the heparin site on domains 19 to 20 mediates interaction of FH to endothelial cells. Binding of FH15-20 to heparin was inhibited by several cell surface- and basement membrane-associated glycosaminoglycans, suggesting that binding site specificity is not restricted to heparin. Thus, defective heparin/glycosaminoglycan-binding site on domains 19 to 20 of FH most probably mediates complement-induced endothelial cell damage in aHUS.

The hemolytic uremic syndromes

PURPOSE OF REVIEW

Recent studies have provided a better understanding of the molecular mechanisms responsible for hemolytic uremic syndromes. In this review, we summarize biochemical and genetic data that may lead to new clinical approaches.

RECENT FINDINGS

The structures and modes of action of Shiga toxins have been deciphered. Patients with non-Shiga-like toxin hemolytic uremic syndrome have been found to carry mutations in three genes that encode for regulators of the complement system (factor H, membrane cofactor protein, and factor I).

SUMMARY

Shiga-like toxin-1 and Shiga-like toxin-2 regulate genes that encode for chemokines, cytokines, cell adhesion molecules, and transcription factors involved in immune response and apoptosis. Mutations in factor H, membrane cofactor protein and factor I have recently been identified. Reduced expression of compliment regulators might prevent restriction of complement deposition on glomerular endothelial cells, leading to microvascular cell damage and tissue injury. Shiga-like toxin hemolytic uremic syndrome in children has a favorable prognosis in 90% of cases; kidney transplantation shows a good graft survival rate (80%) in children who progress to end stage renal disease. As for non-Shiga-like toxin hemolytic uremic syndrome, treatment with plasma infusion or exchange has been used with controversial effects. Kidney transplantation is not recommended in those patients with mutations in factor H and factor I; however, a kidney transplant corrects membrane cofactor protein dysfunction. These findings vividly underscore the clinical heterogeneity of outcomes depending upon the nature of the underlying cause of the disease.

Posttransplantation cytomegalovirus-induced recurrence of atypical hemolytic uremic syndrome associated with a factor H mutation: successful treatment with intensive plasma exchanges and ganciclovir

Atypical hemolytic uremic syndrome (HUS) can recur after renal transplantation and often leads to graft loss. In some series of familial HUS, the risk of early graft loss due to recurrence of HUS approaches 100% despite any therapy. This led some authors to claim that kidney transplantation is contraindicated in those patients. The authors describe an 8-year-old girl with end-stage renal failure owing to familial atypical HUS with a factor H mutation who underwent successful transplantation using continuous prophylactic plasma exchange (PE). Twenty-four months after transplantation, plasma creatinine level is 1.2 mg/dL (106 micromol/L) despite 2 recurrences of HUS contemporaneous to 2 cytomegalovirus infections, which resolved with PE intensification and ganciclovir. This strongly suggests that cytomegalovirus infection may trigger posttransplant recurrent HUS. The feasibility of kidney transplantation in case of atypical HUS related to factor H mutation using continuous prophylactic PE intensified during relapses should be confirmed in prospective studies.