Clinico-pathological findings in diarrhoea-negative haemolytic uraemic syndrome

Clinical value of the renal pathologic scoring system in complement-mediated thrombotic microangiopathy

OBJECTIVES

This study was initiated to establish a renal thrombotic microangiopathy (TMA) scoring system based on clinical needs and investigate its predictive value for patients' long-term outcomes.

METHODS

Kidney biopsy-proven Complement-mediated TMA (C-TMA) patients from January 2000 to December 2017 in Peking University First Hospital were retrospectively studied. Both acute and chronic TMA-related lesions, including 15 pathologic indices, were semiquantitatively scored. The interobserver and intraobserver reproducibility and correlation between the pathologic indices and clinical parameters were analyzed. Furthermore, the patients were divided into 2 groups by dialysis use at baseline, and the association of these pathologic indices with their prognostic outcomes was assessed between the two groups.

RESULTS

Ninety-two patients with renal biopsy-proven C-TMA were enrolled. All fifteen included pathology indices showed good or moderate interobserver and intraobserver reproducibility and correlated well with several clinical parameters. Several clinicopathological indices were worse in the dialysis group than in the nondialysis group, such as serum creatinine, hemoglobin, platelet count, and estimated glomerular filtration rate. Moreover, morphologic features in the dialysis group presented with more severe vascular lesions. Interstitial fibrosis and chronic tubulointerstitial lesions were related to a trend of high risk of continuous dialysis in the dialysis group. Based on univariate and multivariable Cox regression analysis, more severe glomerular lesions, including glomerular mesangiolysis, glomerular basement membrane double contours and glomerular mesangial proliferation, were identified as risk factors predicting worse prognosis.

CONCLUSIONS

Our renal C-TMA semiquantitative scoring system is reliable with good reproducibility and prognostic value in clinical practice, which needs further validation.

Modeling complement activation on human glomerular microvascular endothelial cells

Introduction

Atypical hemolytic uremic syndrome (aHUS) is a rare kidney disease caused by dysregulation of the complement alternative pathway. The complement dysregulation specifically leads to damage to the glomerular endothelium. To further understand aHUS pathophysiology, we validated an ex vivo model for measuring complement deposition on both control and patient human glomerular microvascular endothelial cells (GMVECs).

Methods

Endothelial cells were incubated with human test sera and stained with an anti-C5b-9 antibody to visualize and quantify complement depositions on the cells with immunofluorescence microscopy.

Results

First, we showed that zymosan-activated sera resulted in increased endothelial C5b-9 depositions compared to normal human serum (NHS). The levels of C5b-9 depositions were similar between conditionally immortalized (ci)GMVECs and primary control GMVECs. The protocol with ciGMVECs was further validated and we additionally generated ciGMVECs from an aHUS patient. The increased C5b-9 deposition on control ciGMVECs by zymosan-activated serum could be dose-dependently inhibited by adding the C5 inhibitor eculizumab. Next, sera from five aHUS patients were tested on control ciGMVECs. Sera from acute disease phases of all patients showed increased endothelial C5b-9 deposition levels compared to NHS. The remission samples showed normalized C5b-9 depositions, whether remission was reached with or without complement blockage by eculizumab. We also monitored the glomerular endothelial complement deposition of an aHUS patient with a hybrid complement factor H (CFH)/CFH-related 1 gene during follow-up. This patient had already chronic kidney failure and an ongoing deterioration of kidney function despite absence of markers indicating an aHUS flare. Increased C5b-9 depositions on ciGMVECs were observed in all samples obtained throughout different diseases phases, except for the samples with eculizumab levels above target. We then tested the samples on the patient's own ciGMVECs. The C5b-9 deposition pattern was comparable and these aHUS patient ciGMVECs also responded similar to NHS as control ciGMVECs.

Discussion

In conclusion, we demonstrate a robust and reliable model to adequately measure C5b-9-based complement deposition on human control and patient ciGMVECs. This model can be used to study the pathophysiological mechanisms of aHUS or other diseases associated with endothelial complement activation ex vivo.

Copy number variation analysis using next-generation sequencing identifies the CFHR3/CFHR1 deletion in atypical hemolytic uremic syndrome: a case report

OBJECTIVES

Atypical hemolytic uremic syndrome (aHUS) is characterized by a triad of thrombocytopenia, microangiopathic hemolytic anemia, and acute renal failure resulting from platelet thrombi in the microcirculation of the kidney and other organs, in the absence of a preceding diarrheal illness. This report describes a case in which copy number variation (CNV) analysis using next-generation sequencing (NGS) identified the CFHR3/CFHR1 deletion in a patient with aHUS.

METHODS

A 49-year-old Korean female was diagnosed with aHUS based on clinical findings, including schistocytes in peripheral blood and marked thrombocytopenia, suggesting the presence of thrombotic microangiopathy, elevated serum lactate dehydrogenase, and acute kidney injury. Sequence variants and CNV generated from NGS data were estimated to determine if there was a potential genetic cause. Multiplex ligation-dependent probe amplification (MLPA) was conducted to confirm the CFHR3/CFHR1 deletion identified by NGS with CNV analysis.

RESULTS

No known or novel pathogenic single nucleotide variant or small insertion/deletion that would be predicted to have damaging effects that could lead to aHUS were identified. However, CNV analysis of NGS data identified the heterozygous CFHR3/CFHR1 deletion. MLPA confirmed this loss of one copy number between the CFHR3 and the CFHR1 genes on chromosome 1q31.3.

CONCLUSION

We genetically diagnosed a Korean woman harboring a heterozygous CFHR3/CFHR1 deletion of a known causative gene for aHUS. Our report emphasizes the need for CNV analysis of NGS data and gene dosage assays, such as MLPA, to evaluate large-scale deletions or duplications and generate hybrid CFH genes in patients with suspected aHUS.

Complement Mediated Endothelial Damage in Thrombotic Microangiopathies

Thrombotic microangiopathies (TMA) constitute a group of different disorders that have a common underlying mechanism: the endothelial damage. These disorders may exhibit different mechanisms of endothelial injury depending on the pathological trigger. However, over the last decades, the potential role of the complement system (CS) has gained prominence in their pathogenesis. This is partly due to the great efficacy of complement-inhibitors in atypical hemolytic syndrome (aHUS), a TMA form where the primary defect is an alternative complement pathway dysregulation over endothelial cells (genetic and/or adquired). Complement involvement has also been demonstrated in other forms of TMA, such as thrombotic thrombocytopenic purpura (TTP) and in Shiga toxin-producing Escherichia coli hemolytic uremic syndrome (STEC-HUS), as well as in secondary TMAs, in which complement activation occurs in the context of other diseases. However, at present, there is scarce evidence about the efficacy of complement-targeted therapies in these entities. The relationship between complement dysregulation and endothelial damage as the main causes of TMA will be reviewed here. Moreover, the different clinical trials evaluating the use of complement-inhibitors for the treatment of patients suffering from different TMA-associated disorders are summarized, as a clear example of the entry into a new era of personalized medicine in its management.

Cerebral Microangiopathy in Two Dogs with Cutaneous and Renal Glomerular Vasculopathy

Cutaneous and renal glomerular vasculopathy (CRGV) is an emerging disease in the UK, but its aetiology remains unclear. It is considered a thrombotic microangiopathy (TMA) in which the kidney and skin are the most commonly affected organs. We now document two cases of CRGV with brain lesions, which may have accounted for neurological signs displayed by these animals. The histopathological brain lesions were similar to TMA lesions in humans with thrombotic thrombocytopaenic purpura (TTP) and complement-mediated haemolytic uraemic syndrome (CM-HUS), in which the neurological signs are more associated with TMA than with any systemic disease or electrolyte imbalance. Fibrinoid necrosis in brain arterioles and associated lesions in these dogs were similar to those in human CM-HUS, indicating that the alternative complement pathway may play an important role in the pathophysiology of CRGV.

Atypical hemolytic uremic syndrome and acute tubular necrosis induced by complement factor B gene (CFB) mutation: A case report

RATIONALE

Atypical hemolytic uremic syndrome (aHUS) is an uncommon and serious disease that manifests hemolytic anemia, thrombocytopenia, and acute kidney injury. Genetic complement abnormalities have been shown to be responsible. Compared with the aHUS caused by other mutated genes, aHUS secondary to CFB mutation in adults is extremely rare. We report an adult with CFB mutation developing aHUS.

PATIENT CONCERNS

A 56-year-old man was admitted for 4-day history of nausea and fatigue, anuria for 2 days, and unconsciousness for 10 hours.

DIAGNOSES

The patient presented with life-threatening anemia, thrombocytopenia, acute kidney injury, and nervous system abnormalities. The patient had schistocytes on the peripheral blood smear, increased lactate dehydrogenase (LDH), and plasma-free hemoglobin levels. The patient was later found to harbor a pathogenic variant in the CFB gene (C.1598A>G), and was diagnosed with aHUS and acute kidney injury.

INTERVENTION

The patient was treated by plasmapheresis, continuous renal replacement therapy, blood transfusion, and anti-infective and antihypertensive treatment.

OUTCOMES

After the treatment, the patient's consciousness returned to normal, and the hemoglobin, platelet, and serum creatinine recovered. The disease activity remained quiescent during the follow-up.

LESSONS

A rare heterozygous variant c.1598A>G p.Lys 533Arg in the CFB gene, which was associated with adult-onset aHUS, was described and successfully treated. This case can help in understanding the early diagnosis and effective therapies of this rare disease.

Atypical Hemolytic Uremic Syndrome: New Challenges in the Complement Blockage Era

Atypical hemolytic uremic syndrome (aHUS) is a rare cause of thrombotic microangiopathy (TMA), characterized by microangiopathic hemolytic anemia, consumptive thrombocytopenia, and multisystem end organ involvement, most commonly affecting the kidney. Diagnosis is clinical, after exclusion of other TMA causes. Primary aHUS arises from genetic abnormalities, resulting in uncontrolled complement activity, while a variety of clinical scenarios cause secondary aHUS, including infection, pregnancy, malignancy, autoimmune disease, and medications. They can also induce a temporary complement deregulation with an overlap between both scenarios, which can make differential diagnosis difficult. Primary aHUS can be sporadic or familial and is associated with a high rate of progression to ESRD. Many aHUS patients relapse in the native or transplanted kidneys, leading to kidney failure. The introduction of eculizumab has changed the prognosis of aHUS, by inducing hematologic remission, improving or stabilizing kidney functions, and preventing graft failure. The early institution of appropriate therapy can prevent multiorgan damage, so is essential to recognize and differentiate the TMA syndromes. Eculizumab is considered now the first-line treatment, and it is recommended lifelong therapy. However, the high cost of therapy has led to make efforts to develop precise complement functional and genetic studies that help physicians to determine the appropriate duration of eculizumab therapy. Nowadays, more studies are needed to select candidates to adjustment of therapy.

Renal Biopsy Prognostic Findings in Children With Atypical Hemolytic Uremic Syndrome

BACKGROUND

The aim of this study was to investigate the histopathological findings in kidney biopsies in children with atypical hemolytic uremic syndrome (aHUS) and to determine whether specific pathological findings in aHUS have a prognostic value.

METHODS

Renal biopsy specimens of 29 patients who were recorded in the national Turkish aHUS registry database were available for review. Histopathological findings were compared with the clinical and laboratory features at the presentation and the final outcome.

RESULTS

The mean age at presentation and follow-up period was 4.9 ± 3.9 and 3.9 ± 3.0 years, respectively. The median time interval from the first symptom to biopsy was 10 days. Vascular thrombosis and interstitial fibrosis were significantly related to chronic kidney disease (CKD) requiring dialysis or kidney transplantation during follow-up (5.6-fold, for both). Glomerular necrosis, cortical necrosis, and glomerular sclerosis were markedly associated with CKD without dialysis (6.2-fold, 13.3-fold, and 8.8-fold, respectively). However, presence of endothelial swelling, subendothelial widening, and fragmented erythrocytes was found to be correlated with a favorable final outcome.

CONCLUSIONS

Presence of vascular thrombosis, cortical necrosis, and glomerular sclerosis in histopathological evaluation correlated with developing CKD. Chronic changes in the interstitial compartment were also related to poor prognosis, a finding that has been shown for the first time in pediatric aHUS cases.

Is eculizumab indicated in patients with atypical hemolytic uremic syndrome already on prolonged dialysis? A case report and review of the literature

BACKGROUND

Eculizumab has caused a revolution in the treatment and prognosis of atypical hemolytic uremic syndrome. Early initiation of treatment is recommended to increase chances of renal recovery.

CASE-DIAGNOSIS/TREATMENT

We describe a boy with atypical hemolytic uremic syndrome who started eculizumab therapy after being on dialysis for 4.5 months, with complete anuria. With treatment, he was weaned off dialysis.

CONCLUSION

We review the evidence in the literature and discuss the possible mechanism by which eculizumab induces renal recovery even in patients already on prolonged dialysis. This case report highlights the importance of a treatment trial with eculizumab, even in patients already on prolonged dialysis.

A rare case of Alport syndrome, atypical hemolytic uremic syndrome and Pauci-immune crescentic glomerulonephritis

Background

Renal thrombotic microangiopathy (TMA) is occasionally seen in biopsies with pauci-immune necrotizing crescentic glomerulonephritis (PCGN). Recent study indicated that the complement activation is more prominent in the ANCA-negative glomerulonephritis.

Case presentation

We report a case of concurrent TMA and PCGN without ANCA positivity. Interestingly, our patient also had biopsy features supportive of Alport syndrome (AS). Genetic studies identified variants and polymorphisms in alternative complement pathway genes that confer substantial risk of developing atypical hemolytic uremic syndrome (aHUS).

Conclusions

Abnormal activation in complement pathway may represent a common pathogenic link between these three distinct entities.

Drug-induced Thrombotic Microangiopathy Caused by Gemcitabine

Hemolytic uremic syndrome (HUS) is the triad of nonimmune (Coombs negative) hemolytic anemia, low platelet count, and renal impairment. HUS has been associated with a variety of gastrointestinal malignancies and chemotherapeutic agents. We present a patient with pancreatic cancer treated with gemcitabine for palliation who developed gemcitabine-induced HUS (GiHUS) which responded to some extent to blood and platelet transfusions. With the increase in the use of gemcitabine therapy for pancreatic and other malignancies, it is essential to accurately and timely diagnose GiHUS to avoid the life-threatening complications.

Hemolytic-uremic syndrome: Findings of post-acute renal failure in light and electron microscopy

The blood count test results of six patients (five male adolescents and one female adult) who were diagnosed with the hemolytic-uremic syndrome are presented. Certain diverse lesions and especially, their different intensity, were observed. They were referred to the clinical process and the time from syndrome occurrence to biopsy.

Critical appraisal of eculizumab for atypical hemolytic uremic syndrome

The biology of atypical hemolytic uremic syndrome has been shown to involve inability to limit activation of the alternative complement pathway, with subsequent damage to systemic endothelial beds and the vasculature, resulting in the prototypic findings of a thrombotic microangiopathy. Central to this process is the formation of the terminal membrane attack complex C5b-9. Recently, application of a monoclonal antibody that specifically binds to C5, eculizumab, became available to treat patients with atypical hemolytic uremic syndrome, replacing plasma exchange or infusion as primary therapy. This review focuses on the evidence, based on published clinical trials, case series, and case reports, on the efficacy and safety of this approach.

Hemoconcentration: a major risk factor for neurological involvement in hemolytic uremic syndrome

BACKGROUND

Shigatoxin-associated hemolytic uremic syndrome (STEC-HUS) is a common thrombotic microangiopathy (TMA) in which central nervous system (CNS) involvement is responsible for the majority of deaths and for severe long-term sequelae. We have analyzed the role of hemoconcentration in disease severity.

METHODS

This was a retrospective review of the records and laboratory data at presentation of all patients with STEC-HUS cases (n = 61) over a 10-year period. The patients were grouped into three severity classes: group A, comprising patients who did not require dialysis; group B, patients who were dialyzed without CNS involvement; group C, patients with CNS involvement.

RESULTS

Patients with CNS involvement (group C) had a higher mean hemoglobin level (11.2 ± 2.3 g/dL) than those of group A or B ( 9.4 ± 2.1 and 7.5 ± 1.9 g/dL, respectively; p < 0.0001). We also observed that the higher the initial hemoglobin level, the more severe the long-term renal damage (p < 0.007).

CONCLUSIONS

In patients with STEC-HUS, hemoconcentration and hypovolemia may be responsible for more severe ischemic organ damage (both short and long term) at disease onset, and these signs should be regarded as risk factors for CNS damage and for more severe TMA. Therefore, we recommend that hydration status should be actively monitored in HUS patients and that dehydration, when diagnosed, should be promptly corrected.

Atypical hemolytic uremic syndrome recurrence after kidney transplantation

BACKGROUND

Atypical hemolytic uremic syndrome (aHUS) is a rare disease with a high recurrence rate after kidney transplantation. In most cases, aHUS are caused by genetic mutations of components of the complement alternative pathway. In this single-center series, we present our data of 12 consecutive patients with aHUS and the outcome after kidney transplantation.

METHODS

In this 10-year retrospective study, we identified 12 patients with aHUS who were managed in our center since 2003. We reviewed clinical data, including genetic testing, posttransplant course and response to therapy including the prophylactic use of eculizumab.

RESULTS

Overall, eight patients are women. Six of our patients have at least one genetic mutation causing aHUS, including 4 with complement factor H mutations. Nine patients had at least one previous kidney transplant that failed secondary to recurrent aHUS (75% of our patients). Three patients were treated with eculizumab and plasmapheresis for recurrent aHUS after kidney transplantation; two of them responded to the therapy. Four patients received prophylactic eculizumab; three of them received 6 months and one has been on life long therapy. No signs of recurrence have been observed in these 4 patients so far.

CONCLUSION

Genetic mutations of the complement alternative pathway were confirmed in half of our patients, most of those mutations are in CHF. We demonstrate that treatment or prophylaxis with eculizumab was effective in reversing or preventing aHUS whether or not genetic complement mutations were identified.

Making sense of the spectrum of glomerular disease associated with complement dysregulation

Over recent years, complement has emerged as a major player in the development of a number of glomerular diseases, including atypical haemolytic uraemic syndrome, membranoproliferative glomerulonephritis and the recently described C3 glomerulonephritis. Some patients and pedigrees show overlapping features of these conditions. Intriguingly, a few complement gene mutations are common to different disease phenotypes. In this review, we explore the evidence for complement dysregulation in these diseases and the clinical interface between them, and present a hypothesis to explain the variable phenotype associated with dysregulation of the alternative complement pathway.

Atypical Hemolytic Uremic Syndrome: Differential Diagnosis from TTP/HUS and Management

Atypical hemolytic uremic syndrome (aHUS) is a rare form of thrombotic microangiopathy (TMA). It has an unfavorable outcome with death rates as high as 25% during the acute phase and up to 50% of cases progressing to end-stage renal failure. Uncontrolled complement activation through the alternative pathway is thought to be the main underlying pathopysiology of aHUS and corresponds to all the deleterious findings of the disease. Thrombotic thrombocytopenic purpura (TTP) and Shiga toxin-associated HUS are the 2 other important TMA diseases. Although differentiating HUS from TTP is relatively easy in children with a preceding diarrheal illness or invasive S. pneumoniae, differentiating aHUS from TTP or other microangiopathic disorders can present a major diagnostic challenge in adults. ADAMTS13 analysis is currently the most informative diagnostic test for differentiating TTP, congenital TTP, and aHUS. Today empiric plasma therapy still is recommended by expert opinion to be used as early as possible in any patient with symptoms of aHUS. The overall treatment goal remains restoration of a physiological balance between activation and control of the alternative complement pathway. So it is a reasonable approach to block the terminal complement complex with eculizumab in order to prevent further organ injury and increase the likelihood organ recovery. Persistence of hemolysis or lack of improvement of renal function after 3-5 daily plasmaphereses have to be regarded as the major criteria for uncontrolled TMA even if platelet count has normalized and as an indication to switch the treatment to eculizumab. Eculizumab has changed the future perspectives of patients with aHUS and both the FDA and the EMA have approved it as life-long treatment. However, there are still some unresolved issues about the follow-up such as the optimal duration of eculizumab treatment and whether it can be stopped or how to stop the therapy.

Diagnosis of Streptococcus pneumoniae-associated hemolytic uremic syndrome

BACKGROUND

Hemolytic uremic syndrome related to pneumococcal infection (P+HUS) can be difficult to diagnose due to the lack of a specific test and the absence of a consensus for definite diagnostic criteria.

METHODS

A retrospective study was conducted on the cases that have been considered as P+HUS in the participating centers during the past 10 years. Diagnostic strategy and criteria used for the diagnosis of P+HUS were evaluated and compared with a review of literature data.

RESULTS

A total of 17 children were studied. Tests ruling out other causes of HUS were performed in 94% of cases. Direct confirmatory tests for P+HUS were done in a minority of cases as Thomsen-Friedenreich antigen testing using lectin assay were done in only 2 patients (11%). Retrospectively, the diagnosis of P+HUS was confirmed in 28% to 89% of cases depending on the already published criteria used. A literature review focused on the last 15 years confirmed these diagnostic difficulties due to variable definition criteria and bring a new light on the potential usefulness of tests used to reveal T activation in this setting.

CONCLUSION

To date, in a context of suspicion of P+HUS, no precise, practical and consensual strategy exists for T-antigen exposure diagnosis. The T-antigen activation test using peanut lectin might be the most appropriate test for a direct diagnosis of P+HUS. A large prospective study is required to confirm this hypothesis. However, before such data are available, its use could be of help when a suspicion of P+HUS is present given the therapeutic impact of such a diagnosis.

Trends in US hospital stays for Streptococcus pneumoniae-associated hemolytic uremic syndrome

BACKGROUND

Hemolytic uremic syndrome (HUS) is usually associated with diarrheal illness but can also occur in children with Streptococcus pneumoniae infection (SpHUS), particularly those with complicated pneumonia. Based on recent reports that hospital discharges for complicated pneumococcal pneumonia are increasing in US children, we studied whether discharges for SpHUS might also be increasing.

METHODS

We used the Kids' Inpatient Database samples from 1997, 2000, 2003, 2006 and 2009 to estimate trends in US hospital discharges of children (0-18 years) for whom diagnosis codes indicated invasive pneumococcal disease, HUS, or both (SpHUS). Univariate and multivariate analyses were based on 2009 discharges.

RESULTS

During the 5 study years, annual numbers of US hospital discharges for SpHUS approximately doubled (P = 0.025 for linear trend) and cumulatively totaled an estimated 211 discharges. In 2009, SpHUS accounted for 4.6% (95% confidence interval [CI]: 3.0%-6.7%) of HUS discharges, 0.7% (95% CI: 0.5%-1.0%) of invasive pneumococcal disease discharges and 3.0% (95% CI: 2.0%-3.9%) of discharges for complicated pneumococcal pneumonia. Discharges for SpHUS were more likely than those for other invasive pneumococcal disease to occur in children <3 years of age and to incur longer length of stay and greater hospital charges. SpHUS was independently associated with pneumococcal sepsis/bacteremia (age-adjusted odds ratio 3.8; 95% CI: 1.9-7.8) and complicated pneumonia (odds ratio 9.2; 95% CI: 4.1-20.7).

CONCLUSIONS

SpHUS is an uncommon but severe illness that primarily affects young children and is strongly associated with complicated pneumococcal pneumonia. US hospital stays for SpHUS appear to be increasing along with those for complicated pneumococcal pneumonia.

Escherichia coli O157:H7 in Ecuador: animal reservoirs, yet no human disease

Escherichia coli O157:H7 is frequently isolated from cases of diarrhea in many industrialized countries; however, it is seldom found in developing countries. The present manuscript reports the presence of E. coli O157:H7 in Ecuadorian livestock, a country where enterohemorrhagic E. coli disease in humans has never been reported. The Ecuadorian isolates were genetically related to some strains linked to clinical cases in the United States as assessed by multiple-locus variable number tandem repeat (VNTR) analysis.

Combined complement gene mutations in atypical hemolytic uremic syndrome influence clinical phenotype

Several abnormalities in complement genes reportedly contribute to atypical hemolytic uremic syndrome (aHUS), but incomplete penetrance suggests that additional factors are necessary for the disease to manifest. Here, we sought to describe genotype-phenotype correlations among patients with combined mutations, defined as mutations in more than one complement gene. We screened 795 patients with aHUS and identified single mutations in 41% and combined mutations in 3%. Only 8%-10% of patients with mutations in CFH, C3, or CFB had combined mutations, whereas approximately 25% of patients with mutations in MCP or CFI had combined mutations. The concomitant presence of CFH and MCP risk haplotypes significantly increased disease penetrance in combined mutated carriers, with 73% penetrance among carriers with two risk haplotypes compared with 36% penetrance among carriers with zero or one risk haplotype. Among patients with CFH or CFI mutations, the presence of mutations in other genes did not modify prognosis; in contrast, 50% of patients with combined MCP mutation developed end stage renal failure within 3 years from onset compared with 19% of patients with an isolated MCP mutation. Patients with combined mutations achieved remission with plasma treatment similar to patients with single mutations. Kidney transplant outcomes were worse, however, for patients with combined MCP mutation compared with an isolated MCP mutation. In summary, these data suggest that genotyping for the risk haplotypes in CFH and MCP may help predict the risk of developing aHUS in unaffected carriers of mutations. Furthermore, screening patients with aHUS for all known disease-associated genes may inform decisions about kidney transplantation.

A new era in the diagnosis and treatment of atypical haemolytic uraemic syndrome

The haemolytic uraemic syndrome (HUS) is characterised by haemolytic anaemia, thrombocytopenia and acute renal failure. The majority of cases are seen in childhood and are preceded by an infection with Shiga-like toxin producing Escherichia coli (STEC-HUS; so-called typical HUS). Non-STEC or atypical HUS (aHUS) is seen in 5 to 10% of all cases and occurs at all ages. These patients have a poorer outcome and prognosis than patients with STEC-HUS. New insights into the pathogenesis of aHUS were revealed by the identification of mutations in genes encoding proteins of the alternative pathway of the complement system in aHUS patients. Specific information of the causative mutation is important for individualised patient care with respect to choice and efficacy of therapy, the outcome of renal transplantation, and the selection of living donors. This new knowledge about the aetiology of the disease has stimulated the development of more specific treatment modalities. Until now, plasma therapy was used with limited success in aHUS, but recent clinical trials have demonstrated that patients with aHUS can be effectively treated with complement inhibitors, such as the monoclonal anti-C5 inhibitor eculizumab.

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.

Update on evaluating complement in hemolytic uremic syndrome

PURPOSE OF REVIEW

The last few years have seen the decoding of the genetic basis for atypical hemolytic uremic syndrome.

RECENT FINDINGS

Mutations in complement factor H were the first to be associated with atypical hemolytic uremic syndrome. These mutations cluster in the C-terminus of complement factor H. This year has seen the publication of a transgenic mouse model lacking the C-terminus of complement factor H, which spontaneously develops atypical hemolytic uremic syndrome. This mouse model regulated C3 activation in plasma but failed to bind to endothelial cells in an analogous manner to the mutations seen in atypical hemolytic uremic syndrome patients. This year has also seen the emergence of genotype-phenotype correlations in atypical hemolytic uremic syndrome. Patients with membrane cofactor protein mutations have a good prognosis and in those who do develop endstage renal disease, recurrence after transplantation is rare. By contrast, the outcome for patients with complement factor H and complement factor I mutations is poor and the rate of recurrence after transplantation is high. New complement genes associated with atypical hemolytic uremic syndrome have also been described in the past year including factor B, C3, C4b-binding protein, FHR1 and FHR3.

SUMMARY

Genetic screening is now providing prognostically significant information in predicting survival, renal recovery and transplant outcome. It paves the way for the use of complement inhibitors in 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.

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.

Pathogenesis and prognosis of thrombotic microangiopathy

Thrombotic microangiopathy (TMA) is a clinicopathological syndrome characterized by thrombosis formation in the microvasculature of various organs. Included in the broad category of TMA are the hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP). Typical HUS is caused by Escherichia coli O157:H7, which produces the Shiga-like toxins; Stx-1 and Stx-2. In addition to damaging endothelial cells via the inhibition of protein synthesis, Shiga-like toxins also activate endothelial cells to produce inflammatory mediators, amplifying the prothrombogenic state. Although most patients with typical HUS recover renal functions, recent analysis has shown that typical HUS is not a benign disease in the long term. Genetic abnormalities of complement regulatory proteins predispose patients to atypical HUS. Mutations in factor H, membrane cofactor protein, and factor I are known to be associated with atypical HUS. Atypical HUS forms have a poor outcome and show recurrent and progressive courses. Autoimmune IgG inhibitors of a disintegrin and metalloprotease, with thrombospodin-1-like domains (ADAMTS) 13 and mutations of the ADAMTS13 gene lead to the development of TTP. Without treatment, TTP is associated with a very high mortality rate. As it is for atypical HUS, plasma exchange is currently the most feasible treatment for TTP. Etiological diagnosis at the bedside and the development of disease-specific therapeutic modalities will enable us to optimize the management of patients with TMA and improve their prognosis in the future.

Unusual clinical severity of complement membrane cofactor protein-associated hemolytic-uremic syndrome and uniparental isodisomy

Atypical hemolytic-uremic syndrome (aHUS; OMIM 235400) is genetically and clinically heterogeneous. Mutations in membrane cofactor protein (MCP; CD46), a widely expressed complement regulator, predispose to recurrent forms of the disease. Patients carrying MCP mutations have a favorable clinical outcome in comparison to those with factor H (CFH) or factor I (IF) mutations, which lead in most cases to end-stage renal failure. We identified 1 patient who presented at 1 year of age with a first episode of aHUS requiring dialysis therapy. After 2 recurrences of the disease, the patient developed end-stage renal failure. No mutation in the CFH and IF genes was found. A novel homozygous mutation (IVS10+2 T-->C) in the splice-donor of exon 10 encoding the transmembrane region of the MCP gene was associated with dramatically decreased cell-surface expression of MCP. Because the nucleotide substitution was inherited from the patient's father, but not her mother, a large deletion or uniparental disomy was suspected. Both karyotyping and cytogenetic analysis of chromosome 1q32 were performed, for which MCP maps showed no abnormalities. Subsequent genotype analysis using microsatellite markers spanning chromosome 1 showed that the affected child was homozygous for the entire series of markers tested and that all alleles originated from the father. Complete paternal uniparental isodisomy of chromosome 1 is a novel mechanism resulting in severe deficiency of MCP expression. The outcome of the disease reported here indicates that MCP mutation and complete paternal uniparental disomy of chromosome 1 could have an additive effect in determining the severity of the HUS phenotype.

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.

Modeling how CD46 deficiency predisposes to atypical hemolytic uremic syndrome

Mutations in complement regulatory proteins predispose to the development of aHUS. Approximately 50% of patients bear a mutation in one of three complement control proteins, factor H, factor I, or membrane cofactor protein (MCP; CD46). Another membrane regulator that is closely related to MCP, decay accelerating factor (DAF; CD55) thus far has shown no association with aHUS and continues to be investigated. The goal of this study was to compare the regulatory profile of MCP and DAF and to assess how alterations in MCP predispose to complement dysregulation. We employed a model system of complement activation on Chinese hamster ovary (CHO) cell transfectants. The four regularly expressed isoforms of MCP and DAF inhibited C3b deposition by the alternative pathway. DAF, but not MCP, inhibited the classical pathway. Most patients with MCP-aHUS are heterozygous and express only 25-50% of the wild-type protein. We, therefore, analyzed the effect of reduced levels of wild-type MCP and found that cells with lowered expression levels were less efficient in inhibiting alternative pathway activation. Further, a dysfunctional MCP mutant, expressed at normal levels and identified in five patients with aHUS (S206P), failed to protect against C3b amplification on CHO cells, even if expression levels were increased 10-fold. Our results add new information relative to the necessity for appropriate expression levels of MCP and further implicate the alternative pathway in disease processes such as aHUS.

Genetics of HUS: the impact of MCP, CFH, and IF mutations on clinical presentation, response to treatment, and outcome

Hemolytic uremic syndrome (HUS) is a thrombotic microangiopathy with manifestations of hemolytic anemia, thrombocytopenia, and renal impairment. Genetic studies have shown that mutations in complement regulatory proteins predispose to non-Shiga toxin-associated HUS (non-Stx-HUS). We undertook genetic analysis on membrane cofactor protein (MCP), complement factor H (CFH), and factor I (IF) in 156 patients with non-Stx-HUS. Fourteen, 11, and 5 new mutational events were found in MCP, CFH, and IF, respectively. Mutation frequencies were 12.8%, 30.1%, and 4.5% for MCP, CFH, and IF, respectively. MCP mutations resulted in either reduced protein expression or impaired C3b binding capability. MCP-mutated patients had a better prognosis than CFH-mutated and nonmutated patients. In MCP-mutated patients, plasma treatment did not impact the outcome significantly: remission was achieved in around 90% of both plasma-treated and plasma-untreated acute episodes. Kidney transplantation outcome was favorable in patients with MCP mutations, whereas the outcome was poor in patients with CFH and IF mutations due to disease recurrence. This study documents that the presentation, the response to therapy, and the outcome of the disease are influenced by the genotype. Hopefully this will translate into improved management and therapy of patients and will provide the way to design tailored treatments.

Outcome of renal transplantation in patients with non-Shiga toxin-associated hemolytic uremic syndrome: prognostic significance of genetic background

More than 50% of patients with non-Shiga toxin-associated hemolytic uremic syndrome (non-Stx-HUS) progress to ESRD. Kidney transplant failure for disease recurrence is common; hence, whether renal transplantation is appropriate in this clinical setting remains a debated issue. The aim of this study was to identify possible prognostic factors for renal transplant outcome by focusing on specific genetic abnormalities associated with the disease. All articles in literature that describe renal transplant outcome in patients with ESRD secondary to non-Stx-HUS, genotyped for CFH, MCP, and IF mutations, were reviewed, and data of patients who were referred to the International Registry of Recurrent and Familial HUS/TTP and data from the Newcastle cohort were examined. This study confirmed that the overall outcome of kidney transplantation in patients with non-Stx-HUS is poor, with disease recurring in 60% of patients, 91.6% of whom developed graft failure. No clinical prognostic factor that could identify patients who were at high risk for graft failure was found. The presence of a factor H (CFH) mutation was associated with a high incidence of graft failure (77.8 versus 54.9% in patients without CFH mutation). Similar results were seen in patients with a factor I (IF) mutation. In contrast, graft outcome was favorable in all patients who carried a membrane co-factor protein (MCP) mutation. Patients with non-Stx-HUS should undergo genotyping before renal transplantation to help predict the risk for graft failure. It is debatable whether a kidney transplant should be recommended for patients with CFH or IF mutation. Reasonably, patients with an MCP mutation can undergo a kidney transplant without risk for recurrence.

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.