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.     

Analysis of 66 children with atypical hemolytic uremic syndrome

Objective To summarize the clinical data of atypical hemolytic uremic syndrome (aHUS) and analyze the treatment and prognosis. Methods A prospective cohort study was conducted on 66 cases in Beijing Children's Hospital affiliated to Capital Medical University from January 2011 to December 2017. The children were divided into positive and negative auto-antibody groups according to the results of anti-factor H autoantibody test. The clinical characteristics, treatment plan and prognosis of the two groups were compared. Results Among the 66 children who met the inclusion criteria, there were 43 cases (65.2%) in the positive group, with an average onset age of (8.0±2.9) years. There were 23 cases (34.8%) in the negative group, with an average onset age of (3.0±2.6) years. On the basis of plasma treatment, in the positive group, the usage rate of hormone was 83.3%(35/42) and the usage rate of immunosuppressive agents was 42.9%(18/42), while in the negative group, the rates were 63.6%(14/22) and 13.6%(3/22) respectively. The average follow-up time was 19.3 months. One child in each group was lost to follow-up. In the positive group, 8 cases recurred (19.0%) and the average recurrence interval time was 16.1 months. In the negative group, 7 cases recurred (31.8%) and the average recurrence interval time was 9.3 months. And the recurrent interval time in the positive group was more longer than the negative group (P＜0.05). A total of 85.9%(55/64) children had complete hemolysis control and complete recovery of renal function, in which the positive group was 85.7%(36/42) and negative group was 86.4%(19/22). However, 7.8%(5/64) children had abnormal renal function, in which the positive group was 9.5%(4/42) and the negative group was 4.5%(1/22). And 4.7%(3/64) children died, in which the positive group was 2.4%(1/42) and the negative group was 9.1%(2/22). The one left (1.6%) showed dialysis dependence, which was positive for the auto-antibody. Multifactor Cox regression analysis showed that the age of less than 3 years old was the risk factor of poor prognosis (HR=4.651, 95%CI 0.988-21.898, P=0.047). Conclusions The positive proportion of anti-factor H autoantibody in children with aHUS is high. The age of these children is older. Individualized therapy based on anti-factor H autoantibody and immunosuppressive therapy is of great significance for disease remission, preventing recurrence and improving the prognosis. Age less than 3 years old is the risk factor for poor prognosis.     

Clinical grand rounds: atypical hemolytic uremic syndrome

Atypical hemolytic uremic syndrome (aHUS) is a rare, lifethreatening, chronic, genetic disease of uncontrolled alternative pathway complement activation. The understanding of the pathophysiology and genetics of this disease has expanded over recent decades and promising new developments in the management of aHUS have emerged. Regardless of the cause of aHUS, with or without a demonstrated mutation or autoantibody, blockade of terminal complement activation through C5 is of high interest as a mechanism to ameliorate the disease. Eculizumab, an existing monoclonal antibody directed against C5 with high affinity, prevents the perpetuation of the downstream activation of the complement cascade and the damage caused by generation of the anaphylotoxin C5a and the membrane attack complex C5b-9, by blocking C5 cleavage. We report the successful use of eculizumab in a patient after kidney transplantation and discuss the disease aHUS.     

Clinical guides for atypical hemolytic uremic syndrome in Japan

Atypical hemolytic uremic syndrome (aHUS) is a rare disease characterized by the triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. In 2013, we developed diagnostic criteria to enable early diagnosis and timely initiation of appropriate treatment for aHUS. Recent clinical and molecular findings have resulted in several proposed classifications and definitions of thrombotic microangiopathy and aHUS. Based on recent advances in this field and the emerging international consensus to exclude secondary TMAs from the definition of aHUS, we have redefined aHUS and proposed diagnostic algorithms, differential diagnosis, and therapeutic strategies for aHUS.     

Eculizumab in the treatment of atypical hemolytic uremic syndrome in infants

A 28-day-old male newborn weighing 3.6 kg was given a diagnosis of atypical hemolytic-uremic syndrome, new-onset thrombotic microangiopathy (TMA; hemoglobin, 7.7 g/dL; schistocytes, 9%), thrombocytopenia (platelets, 49 × 10(3)/μL [49 × 10(9)/L]), and acute kidney failure (serum creatinine, 1.13 mg/dL [99.8 μmol/L], corresponding to estimated glomerular filtration rate [eGFR] of 15 mL/min/1.73 m(2) [0.25 mL/s/1.73 m(2)]). Repeated high-volume plasma infusions were ineffective. Plasma exchange was attempted, but not tolerated. The patient required mechanical ventilation and continuous renal replacement therapy. He developed multiple intestinal perforations and leg skin necrosis due to systemic TMA. A low C3 level (36 mg/dL) suggested complement activation. Eculizumab, 300 mg, was administered, and within 48 hours the patient recovered from acute kidney failure, with complete hematologic remission 2 weeks later. The infant, 14 months old at the time of writing, continues to receive eculizumab, 300 mg, every 3 weeks; he is free of disease activity and has a normal creatinine level of 0.2 mg/dL (17.68 μmol/L; corresponding to eGFR of 110 mL/min/1.73 m(2) [1.83 mL/s/1.73 m(2)]), but mild proteinuria (urinary protein-creatine ratio, 1 mg/g). Results of additional studies, including probing for cobalamin anomalies and measuring levels of ADAMTS13, complement factor H (CFH), factor I (CFI), and membrane cofactor protein (MCP), were unremarkable. Antibodies to CFH were undetectable, and mutation testing of the genes for CFH, CFI, and MCP gave negative results. Treatment with eculizumab was life saving, and with continued treatment, the patient showed sustained freedom from clinical TMA complications.     

Neonatal atypical hemolytic uremic syndrome due to methylmalonic aciduria and homocystinuria

BACKGROUND: Inborn errors of cobalamin (Cbl) absorption and metabolism form a large group of rare diseases that include Cbl-C disorder. Among the renal complications of Cbl-C disorder, atypical hemolytic uremic syndrome (HUS) is the least common and has been described only in a small number of cases. CASE-DIAGNOSIS/TREATMENT: Four patients were admitted to our clinic after 15-30 days of life with vomiting associated with poor sucking, failure to thrive, lethargy and hypotonia. Examinations showed thrombocytopenia and microangiopathic hemolytic anemia associated with renal damage. The neonates had high blood homocysteine levels, increased urinary levels of both homocystine and methylmalonic acid, increased propionylcarnitine (C3) levels and an increased C3/acetylcarnitine ratio. Homozygosity for c.271-272dupA (p.Arg91LysfsX14) of the MMACHC gene was detected in three patients, and heterozygosity for c.271-272dupA and c.666C > A(p.Tyr222X) in one patient, which confirmed the diagnosis of Cbl-C disorder. Treatment with parenteral hydroxycobalamin in combination with folic acid and betaine gradually normalized the metabolic test findings and hematological and renal parameters after about 1 week. CONCLUSIONS: Atypical HUS in neonates with Cbl-C disorder may be associated with mild to moderate renal involvement also in early-onset disease, and early adequate therapy can reverse renal damage.     

Prophylactic eculizumab prior to kidney transplantation for atypical hemolytic uremic syndrome

Atypical hemolytic uremic syndrome (aHUS) in childhood is a rare disease associated with high morbidity and mortality. Most cases progress to end-stage renal failure. In approximately 50% of affected patients, mutations in genes encoding complement proteins are causative of the impairment in the regulation of the complement alternative pathway. This leads to deficient host cell protection and inappropriate complement activation on platelets and endothelial cells, particularly in the kidneys. Complement factor H (FH) heterozygosity induces unregulated activation of the membrane attack complex (MAC) C5b-9. Present therapeutic strategies for aHUS include lifelong plasmapheresis and renal dialysis. Unfortunately, kidney transplantation is frequently an unsatisfactory intervention due to the high rate of post-transplantation HUS recurrence, particularly in patients with FH mutation. Combined liver-kidney transplantation is also associated with poor outcome, mostly as a result of premature liver failure secondary to uncontrolled complement activation. Eculizumab is a complement C5 antibody that inhibits complement factor 5a (C5a) and the formation of the MAC. Thus, this antibody may be a promising new agent for patients with an aHUS undergoing kidney transplantation. We present the first case of a young patient with aHUS who received eculizumab as prophylactic treatment prior to a successful kidney transplantation.     

Anti-Factor H autoantibodies associated with atypical hemolytic uremic syndrome

Several studies have demonstrated genetic predisposition in non-shigatoxin-associated hemolytic uremic syndrome (HUS), involving regulatory proteins of the complement alternative pathway: Factor H (FH) and membrane co-factor protein (CD46). Regarding the observations of thrombotic thrombocytopenic purpura patients, in whom a von Willebrand factor protease (ADAMST-13) deficiency may be inherited or acquired secondary to IgG antibodies, it was speculated that HUS might occur in a context of an autoimmune disease with the development of anti-FH antibodies leading to an acquired FH deficiency. The presence of FH autoantibodies was investigated by an ELISA method using coated purified human FH in a series of 48 children who presented with atypical HUS and were recruited from French university hospitals. Anti-FH IgG antibodies were detected in the plasma of three children who presented with recurrent HUS. The anti-FH specificity was conserved by the Fab'2 fraction. The plasma FH activity was found to be decreased, whereas plasma FH antigenic levels and FH gene analysis were normal, indicating that the presence of anti-FH antibodies led to an acquired functional FH deficiency. This report supports for the first time that HUS may occur in a context of an autoimmune disease with the development of anti-FH-specific antibody leading to an acquired FH deficiency. This new mechanism of functional FH deficiency may lead to the design of new approaches of diagnosis and treatment with a particular interest in plasma exchanges or immunosuppressive therapies.     

Long-term eculizumab improves clinical outcomes in atypical hemolytic uremic syndrome

Background

Atypical hemolytic uremic syndrome (aHUS) is a rare genetic disorder caused by chronic uncontrolled complement activation.

Case-diagnosis/treatment

We present a 4-year-old girl with aHUS who had multiple severe clinical manifestations of thrombotic microangiopathy (TMA) including acute kidney injury, dilated cardiomyopathy, and cardiorespiratory arrest. She was managed with intensive plasma exchange and hemodialysis, which could not halt the progression of TMA. The initial single dose of eculizumab only temporarily improved the clinical symptoms of TMA. Sustained improvement of renal, hematological, and cardiac values were only achieved upon institution of chronic treatment with eculizumab. During long-term treatment with eculizumab (>2.5 years), she has had no further clinical manifestations of TMA, and required neither plasma exchange nor hemodialysis.

Conclusion

Chronic eculizumab treatment was associated with control of complement-mediated TMA and sustained long-term improvement in renal and cardiac function.     

Neurological involvement in a child with atypical hemolytic uremic syndrome

We report the case of a 4-year-old boy, diagnosed with atypical hemolytic uremic syndrome (HUS) due to a hybrid factor H. He progressed to end-stage renal failure despite plasmatherapy and underwent bilateral nephrectomy because of uncontrolled hypertension. Three days after, he had partial complex seizures with normal blood pressure, normal blood count and normal magnetic resonance imaging (MRI), which recurred 1 month later. Eight months later, he had a third episode of seizures, with hemoglobin of 10 g/dl without schizocytes, low haptoglobin of 0.18 g/l, and moderate thrombocytopenia (platelets 98 × 10⁹/l). He remained hypertensive and deeply confused for 2 days. The third MRI showed bilateral symmetrical hyperintensities of the cerebral pedunculas, caudate nuclei, putamens, thalami, hippocampi, and insulae suggesting thrombotic microangiopathy secondary to a relapse of HUS rather than reversible posterior leukoencephalopathy syndrome (RPLS), usually occipital and asymmetrical. Plasmatherapy led to a complete neurological recovery within 2 days although hypertension had remained uncontrolled. The fourth MRI 10 weeks after, on maintenance plasmatherapy, was normal and clinical examination remained normal, except for high blood pressure. In conclusion, brain MRI allows differentiating thrombotic microangiopathy lesions from RPLS in atypical HUS, which is crucial since lesions may be reversible with plasmatherapy.     

Macrovascular involvement in a child with atypical hemolytic uremic syndrome

Background

Atypical hemolytic uremic syndrome (aHUS) is a disorder of the complement system which leads to thrombotic microangiopathy. It is caused by either acquired or hereditary defects in the activation or regulation of the alternative complement pathway and is therefore considered to be a disease of local complement dysregulation in microvasculature with predominantly renal involvement. However, extrarenal manifestations are observed in approximately one-fifth of aHUS patients, with the myocardium and central nervous system (CNS) being involved most often. Additionally, there have been a few reports of aHUS with cerebral artery stenoses or periphereal gangrene, suggesting the possibility of ‘macrovascular’ involvement in aHUS.

Case-diagnosis/treatment

We present a child with early onset aHUS and a C3 gain-of-function mutation who developed cerebral artery stenoses, leading ultimately to death due to a massive stroke 9 days after successful renal transplantation under prophylactic eculizumab treatment. Similar cases described in the literature are also briefly summarized.

Conclusions

The disease course in our patient with aHUS confirms that dysregulated complement activation can induce arterial steno-occlusive lesions in the absence of acute episodes of HUS. Further studies are required to document the frequency of such macrovascular complications and the role of eculizumab treatment in preventing their development and progression.     

Current aspects of hemolytic uremic syndrome in children

The authors are approaching the problem of hemolytic uremic syndrome, a common cause of acute renal failure in children. This review present an update about the pathophysiology of typical hemolytic uremic syndrome, useful for understanding the clinical picture and the base for some modern therapeutical models. Concerning the evolution, the authors underline the importance of identifying the risk factors for acute phase, the extrarenal manifestations being considered of vital risk. The atypical hemolytic uremic syndrome still has some uncertainties; the article try to make a synthesis of ethiopathogeneity, clinical manifestations, evolution and therapeutical modern approaches.     

Management of diarrhea-associated hemolytic uremic syndrome in children

Most cases of diarrhea-associated hemolytic uremic syndrome (D+HUS) are caused by Shiga toxin-producing bacteria. Shiga toxin-producing Escherichia coli (STEC) O157:H7 has the strongest association worldwide with HUS. A massive outbreak of E. coli O157:H7 infections in Sakai, Osaka, Japan, in 1996 raised public and medical awareness of STEC. However, most cases are sporadic or occur in small clusters. Indeed, more than 100 sporadic or small cluster cases of D+HUS occur every year in Japan. The use of antibiotics in patients with definite or possible enteric STEC infections is controversial; however, there has been no randomized controlled trial to date showing the effectiveness of antibiotics for the prevention of the development of HUS. Thus, most investigators in western countries believe that antibiotics should not be administered to patients with such infections, and the management of HUS remains supportive. There are no specific therapies to ameliorate the course of the disease, and vascular injury leading to HUS is likely to be well under way by the time infected patients seek medical attention for diarrhea. The best way to prevent HUS is to prevent primary infection by Shiga toxin-producing bacteria.     

Mutations in complement factor I predispose to development of atypical hemolytic uremic syndrome

Mutations in the plasma complement regulator factor H (CFH) and the transmembrane complement regulator membrane co-factor protein (MCP) have been shown to predispose to atypical hemolytic uremic syndrome (HUS). Both of these proteins act as co-factors for complement factor I (IF). IF is a highly specific serine protease that cleaves the alpha-chains of C3b and C4b and thus downregulates activation of both the classical and the alternative complement pathways. This study looked for IF mutations in a panel of 76 patients with HUS. Mutations were detected in two patients, both of whom had reduced serum IF levels. A heterozygous bp change, c.463 G>A, which results in a premature stop codon (W127X), was found in one, and in the other, a heterozygous single base pair deletion in exon 7 (del 922C) was detected. Both patients had a history of recurrent HUS after transplantation. This is in accordance with the high rate of recurrence in patients with CFH mutations. Patients who are reported to have mutations in MCP, by contrast, do not have recurrence after transplantation. As with CFH- and MCP-associated HUS, there was incomplete penetrance in the family of one of the affected individuals. This study provides further evidence that atypical HUS is a disease of complement dysregulation.     

The successful treatment of atypical hemolytic uremic syndrome with plasmapheresis

A seven and a half-year-old boy presented with idiopathic atypical hemolytic uremic syndrome (HUS). He initially appeared to respond to plasma infusions. When he became refractory to plasma infusion, plasmapheresis was initiated. The treatment with plasmapheresis dramatically reversed the deterioration in glomerular filtration rate and platelet count. The use of plasma infusion and plasmapheresis in HUS is discussed. The authors advise the use of plasmapheresis in idiopathic atypical HUS.