Disseminated Cryptococcosis Following Eculizumab Therapy: Insight Into Pathogenesis

Eculizumab, a recombinant humanized monoclonal antibody (mAb), is used for the treatment of patients (both adults and children) with paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome. This mAb binds to complement protein 5 (C5), thereby inhibiting its cleavage. On the other hand, one of the C5 cleavage products, C5a, is a potent anaphylatoxin with proinflammatory properties, involved in antimicrobial surveillance. Administration of eculizumab has been reported to make patients more susceptible to infection by encapsulated bacteria. Here, we are reporting an adult case of disseminated infection due to the encapsulated yeast Cryptococcus neoformans following eculizumab therapy and discuss its pathogenesis.

Ex Vivo Test for Measuring Complement Attack on Endothelial Cells: From Research to Bedside

As part of the innate immune system, the complement system plays a key role in defense against pathogens and in host cell homeostasis. This enzymatic cascade is rapidly triggered in the presence of activating surfaces. Physiologically, it is tightly regulated on host cells to avoid uncontrolled activation and self-damage. In cases of abnormal complement dysregulation/overactivation, the endothelium is one of the primary targets. Complement has gained momentum as a research interest in the last decade because its dysregulation has been implicated in the pathophysiology of many human diseases. Thus, it appears to be a promising candidate for therapeutic intervention. However, detecting abnormal complement activation is challenging. In many pathological conditions, complement activation occurs locally in tissues. Standard routine exploration of the plasma concentration of the complement components shows values in the normal range. The available tests to demonstrate such dysregulation with diagnostic, prognostic, and therapeutic implications are limited. There is a real need to develop tools to demonstrate the implications of complement in diseases and to explore the complex interplay between complement activation and regulation on human cells. The analysis of complement deposits on cultured endothelial cells incubated with pathologic human serum holds promise as a reference assay. This ex vivo assay most closely resembles the physiological context. It has been used to explore complement activation from sera of patients with atypical hemolytic uremic syndrome, malignant hypertension, elevated liver enzymes low platelet syndrome, sickle cell disease, pre-eclampsia, and others. In some cases, it is used to adjust the therapeutic regimen with a complement-blocking drug. Nevertheless, an international standard is lacking, and the mechanism by which complement is activated in this assay is not fully understood. Moreover, primary cell culture remains difficult to perform, which probably explains why no standardized or commercialized assay has been proposed. Here, we review the diseases for which endothelial assays have been applied. We also compare this test with others currently available to explore complement overactivation. Finally, we discuss the unanswered questions and challenges to overcome for validating the assays as a tool in routine clinical practice.

Activation de la voie alterne du complément dans les formes sévères de COVID-19

Introduction

Le SARS-CoV-2 est désormais responsable de plus de 4 millions de décès dans le monde. Les formes sévères de COVID-19 sont caractérisées par un état d’hyperinflammation, et l’utilisation de la corticothérapie a réduit significativement la mortalité. Des thérapies complémentaires plus spécifiques pourraient permettre d’améliorer la prise en charge des patients présentant des formes sévères. Dans ce contexte, les voies de signalisation en lien avec le système du complément semblent etre une cible idéale : on retrouve une surreprésentation des voies du compléments dans les cellules épithéliales pulmonaires, une élévation des marqueurs d’activation de la cascade du complément dans le plasma des patients atteints de COVID-19, et des déficits congénitaux dans les protéines de régulation du complément ont été associées à des formes plus sévères de la maladie. Cependant, nos connaissances des voies spécifiques activées du complément et leur lien avec la sévérité de la maladie restent limitées.

Patients et méthodes

Durant la première vague épidémique en France, nous avons recueilli les prélèvements de 32 patients COVID-19 présentant des niveaux de sévérité différents de la maladie. Nous avons déterminé l’expression ARN de 28 gènes du système du complément et les concentrations sériques de 6 protéines, représentant les trois voies du complément.

Résultats

L’expression des gènes du complément étaient régulées de façon différentielle selon la gravité de la COVID-19 : alors que la voie classique était activée chez tous les patients infectés, la forme sévère de la maladie était associée à une suractivation de la voie de la lectine et de la voie alterne, dont l’expression corrélait avec les marqueurs de l’inflammation et de coagulation. De plus, la properdine, régulateur positif majeur de la voie alterne, était exprimé à des niveaux élevés (ARN) chez les patients les plus graves, tandis que leurs niveaux protéiques étaient diminués, suggérant une consommation importante et la déposition au niveau des sites de l’activation du complément. De façon intéressante, les concentrations sériques basses de properdine étaient significativement associées au recours à la ventilation mécanique.

Conclusion

Cette étude apporte un éclairage sur le rôle potentiel de la voie alterne du complément dans les formes graves de COVID-19. Bien que des études histologiques et mécanistiques ainsi qu’une confirmation de ces résultats sur une plus grande cohorte soient nécessaires, ces résultats sont en faveur d’essais ciblant la voie alterne du complément chez les patients présentant des formes sévères de COVID-19.

Identification of Distinct Immunophenotypes in Critically Ill Coronavirus Disease 2019 Patients

Background

Severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infection causes direct lung damage, overwhelming endothelial activation, and inflammatory reaction, leading to acute respiratory failure and multi-organ dysfunction. Ongoing clinical trials are evaluating targeted therapies to hinder this exaggerated inflammatory response. Critically ill coronavirus disease 2019 (COVID-19) patients have shown heterogeneous severity trajectories, suggesting that response to therapies is likely to vary across patients.

Research Question

Are critically ill COVID-19 patients biologically and immunologically dissociable based on profiling of currently evaluated therapeutic targets?

Study Design and Methods

We did a single-center, prospective study in an ICU department in France. Ninety-six critically ill adult patients admitted with a documented SARS-CoV-2 infection were enrolled. We conducted principal components analysis and hierarchical clustering on a vast array of immunologic variables measured on the day of ICU admission.

Results

We found that patients were distributed in three clusters bearing distinct immunologic features and associated with different ICU outcomes. Cluster 1 had a “humoral immunodeficiency” phenotype with predominant B-lymphocyte defect, relative hypogammaglobulinemia, and moderate inflammation. Cluster 2 had a “hyperinflammatory” phenotype, with high cytokine levels (IL-6, IL-1β, IL-8, tumor necrosis factor-alpha [TNF⍺]) associated with CD4+ and CD8+ T-lymphocyte defects. Cluster 3 had a “complement-dependent” phenotype with terminal complement activation markers (elevated C3 and sC5b-9).

Interpretation

Patients with severe COVID-19 exhibiting cytokine release marks, complement activation, or B-lymphocyte defects are distinct from each other. Such immunologic variability argues in favor of targeting different mediators in different groups of patients and could serve as a basis for patient identification and clinical trial eligibility.

Cobalamin c deficiency associated with antifactor h antibody-associated hemolytic uremic syndrome in a young adult

Background

Thrombotic microangiopathy (TMA) syndromes are characterized by the association of hemolytic anemia, thrombocytopenia and organ injury due to arteriolar and capillary thrombosis.

Case presentation

We report the first case of adult onset cobalamin C (Cbl C) disease associated with anti-factor H antibody-associated hemolytic uremic syndrome (HUS).

A 19-year-old woman was admitted to the nephrology department owing to acute kidney failure, proteinuria, and hemolytic anemia with schizocytes.

TMA was diagnosed and plasma exchanges were started in emergency.

Exhaustive analyses showed 1) circulating anti factor H antibody and 2) hyperhomocysteinemia, hypomethioninemia and high levels of methylmalonic aciduria pointing towards Clb C disease. Cbl C disease has been confirmed by methylmalonic aciduria and homocystinuria type C protein gene sequencing revealing two heterozygous pathogenic variants.

The kidney biopsy showed 1) intraglomerular and intravascular thrombi 2) noticeable thickening of the capillary wall with a duplication aspect of the glomerular basement membrane and a glomerular capillary wall IgM associated with Cbl C disease related TMA.

We initiated treatment including hydroxycobalamin, folinic acid, betaine and levocarnitine and Eculizumab. Rituximab infusions were performed allowing a high decrease in anti-factor H antibody rate.

Six month after the disease onset, Eculizumab was weaning and vitaminotherapy continued. Outcome was favorable with a dramatic improvement in kidney function.

Conclusion

TMA with renal involvement can have a complex combination of risk factors including anti-FH autoantibody in the presence of cblC deficiency.

Structural Basis for Properdin Oligomerization and Convertase Stimulation in the Human Complement System

Properdin (FP) is a positive regulator of the immune system stimulating the activity of the proteolytically active C3 convertase C3bBb in the alternative pathway of the complement system. Here we present two crystal structures of FP and two structures of convertase bound FP. A structural core formed by three thrombospondin repeats (TSRs) and a TB domain harbors the convertase binding site in FP that mainly interacts with C3b. Stabilization of the interaction between the C3b C-terminus and the MIDAS bound Mg2+ in the Bb protease by FP TSR5 is proposed to underlie FP convertase stabilization. Intermolecular contacts between FP and the convertase subunits suggested by the structure were confirmed by binding experiments. FP is shown to inhibit C3b degradation by FI due to a direct competition for a common binding site on C3b. FP oligomers are held together by two sets of intermolecular contacts, where the first is formed by the TB domain from one FP molecule and TSR4 from another. The second and largest interface is formed by TSR1 and TSR6 from the same two FP molecules. Flexibility at four hinges between thrombospondin repeats is suggested to enable the oligomeric, polydisperse, and extended architecture of FP. Our structures rationalize the effects of mutations associated with FP deficiencies and provide a structural basis for the analysis of FP function in convertases and its possible role in pattern recognition.

C3 glomerulopathy - understanding a rare complement-driven renal disease

The C3 glomerulopathies are a group of rare kidney diseases characterized by complement dysregulation occurring in the fluid phase and in the glomerular microenvironment, which results in prominent complement C3 deposition in kidney biopsy samples. The two major subgroups of C3 glomerulopathy - dense deposit disease (DDD) and C3 glomerulonephritis (C3GN) - have overlapping clinical and pathological features suggestive of a disease continuum. Dysregulation of the complement alternative pathway is fundamental to the manifestations of C3 glomerulopathy, although terminal pathway dysregulation is also common. Disease is driven by acquired factors in most patients - namely, autoantibodies that target the C3 or C5 convertases. These autoantibodies drive complement dysregulation by increasing the half-life of these vital but normally short-lived enzymes. Genetic variation in complement-related genes is a less frequent cause. No disease-specific treatments are available, although immunosuppressive agents and terminal complement pathway blockers are helpful in some patients. Unfortunately, no treatment is universally effective or curative. In aggregate, the limited data on renal transplantation point to a high risk of disease recurrence (both DDD and C3GN) in allograft recipients. Clinical trials are underway to test the efficacy of several first-generation drugs that target the alternative complement pathway.

Both Monoclonal and Polyclonal Immunoglobulin Contingents Mediate Complement Activation in Monoclonal Gammopathy Associated-C3 Glomerulopathy

C3 glomerulopathy (C3G) results from acquired or genetic abnormalities in the complement alternative pathway (AP). C3G with monoclonal immunoglobulin (MIg-C3G) was recently included in the spectrum of “monoclonal gammopathy of renal significance.” However, mechanisms of complement dysregulation in MIg-C3G are not described and the pathogenic effect of the monoclonal immunoglobulin is not understood. The purpose of this study was to investigate the mechanisms of complement dysregulation in a cohort of 41 patients with MIg-C3G. Low C3 level and elevated sC5b-9, both biomarkers of C3 and C5 convertase activation, were present in 44 and 78% of patients, respectively. Rare pathogenic variants were identified in 2/28 (7%) tested patients suggesting that the disease is acquired in a large majority of patients. Anti-complement auto-antibodies were found in 20/41 (49%) patients, including anti-FH (17%), anti-CR1 (27%), anti-FI (5%) auto-antibodies, and C3 Nephritic Factor (7%) and were polyclonal in 77% of patients. Using cofactor assay, the regulation of the AP was altered in presence of purified IgG from 3/9 and 4/7 patients with anti-FH or anti-CR1 antibodies respectively. By using fluid and solid phase AP activation, we showed that total purified IgG of 22/34 (65%) MIg-C3G patients were able to enhance C3 convertase activity. In five documented cases, we showed that the C3 convertase enhancement was mostly due to the monoclonal immunoglobulin, thus paving the way for a new mechanism of complement dysregulation in C3G. All together the results highlight the contribution of both polyclonal and monoclonal Ig in MIg-C3G. They provide direct insights to treatment approaches and opened up a potential way to a personalized therapeutic strategy based on chemotherapy adapted to the B cell clone or immunosuppressive therapy.

C3 glomerulopathy and eculizumab: a report on four paediatric cases

BACKGROUND

Eculizumab may be used to treat C3-glomerulopathy (C3G), a rare but severe glomerular disease.

DIAGNOSIS AND TREATMENT

Patients 1, 2 and 3 were diagnosed with nephritic syndrome with alternative complement pathway activation (low C3, C3Nef-positive) and C3G at the age of 9, 13 and 12 years, respectively. Treatment with eculizumab normalized proteinuria within 1, 2 and 7 months, respectively. Proteinuria relapsed when eculizumab was withdrawn, but the re-introduction of eculizumab normalized proteinuria. Patient 4 was diagnosed with C3G at 9 years of age, with progression to end-stage renal disease within 2 years, followed by a first renal transplantation (R-Tx) with early disease recurrence and graft loss within 39 months. After a second R-Tx, she rapidly presented with biological and histological recurrence: therapy with eculizumab was started, with no effect on proteinuria after 5 months, in a complex clinical setting (i.e. association of C3G recurrence, humoral rejection and BK nephritis). Eculizumab was withdrawn due to multiple viral reactivations, but the re-introduction of the drug a few months later enabled a moderate decrease in proteinuria.

CONCLUSION

These cases illustrate the efficacy of eculizumab, at least on native kidneys, in paediatric C3G. However, larger international studies are warranted to confirm the benefit and safety of eculizumab therapy.

Infections Revealing Complement Deficiency in Adults: A French Nationwide Study Enrolling 41 Patients

Complement system is a part of innate immunity, its main function is to protect human from bacterial infection. As genetic disorders, complement deficiencies are often diagnosed in pediatric population. However, complement deficiencies can also be revealed in adults but have been poorly investigated. Herein, we describe a case series of infections revealing complement deficiency in adults to study clinical spectrum and management of complement deficiencies.A nationwide retrospective study was conducted in French university and general hospitals in departments of internal medicine, infectious diseases enrolling patients older than 15 years old who had presented at least one infection leading to a complement deficiency diagnosis.Forty-one patients included between 2002 and 2015 in 19 different departments were enrolled in this study. The male-to-female ratio was 1.3 and the mean age at diagnosis was 28 ± 14 (15-67) years. The main clinical feature was Neisseria meningitidis meningitis 75% (n = 31/41) often involving rare serotype: Y (n = 9) and W 135 (n = 7). The main complement deficiency observed was the common final pathway deficiency 83% (n = 34/41). Half of the cohort displayed severe sepsis or septic shock at diagnosis (n = 22/41) but no patient died. No patient had family history of complement deficiency. The mean follow-up was 1.15 ± 1.95 (0.1-10) years. Half of the patients had already suffered from at least one infection before diagnosis of complement deficiency: meningitis (n = 13), pneumonia (n = 4), fulminans purpura (n = 1), or recurrent otitis (n = 1). Near one-third (n = 10/39) had received prophylactic antibiotics (cotrimoxazole or penicillin) after diagnosis of complement deficiency. The vaccination coverage rate, at the end of the follow-up, for N meningitidis, Streptococcus pneumonia, and Haemophilius influenzae were, respectively, 90% (n = 33/37), 47% (n = 17/36), and 35% (n = 14/34).This large study emphasizes that complement deficiencies can be revealed in adults by infectious episodes. Most of them were meningococcal infections revealing common final pathway deficiency. To avoid undiagnosis or late diagnosis, adult displaying first episode of N meningitidis infection should be tested for complement deficiency.

Anti-factor H autoantibodies in C3 glomerulopathies and in atypical hemolytic uremic syndrome: one target, two diseases

Autoantibodies targeting factor H (FH), which is a main alternative complement pathway regulatory protein, have been well characterized in atypical hemolytic uremic syndrome (aHUS) but have been less well described in association with alternative pathway-mediated glomerulopathies (GP). In this study, we studied 17 patients presenting with GP who were positive for anti-FH IgG. Clinical data were collected and biological characteristics were compared with those of patients presenting with anti-FH Ab-associated aHUS. In contrast to the aHUS patients, the GP patients had no circulating FH-containing immune complexes, and their anti-FH IgG had a weaker affinity for FH. Functional studies demonstrated that these Abs induced no perturbations in FH cell surface protection or the binding of FH to its ligand. However, anti-FH IgG samples isolated from three patients were able to affect the factor I cofactor activity of FH. Epitope mapping identified the N-terminal domain of FH as the major binding site for GP patient IgG. No homozygous deletions of the CFHR1 and CFHR3 genes, which are frequently associated with the anti-FH Ab in aHUS patients, were found in the GP patients. Finally, anti-FH Abs were frequently associated with the presence of C3 nephritic factor in child GP patients and with monoclonal gammopathy in adult GP patients, who frequently showed Ig Lchain restriction during reactivity against factor H. These data provide deeper insights into the pathophysiological differences between aHUS and GP, demonstrating heterogeneity of anti-FH IgG.

Detection of C3d-binding donor-specific anti-HLA antibodies at diagnosis of humoral rejection predicts renal graft loss

Antibody-mediated rejection (AMR) is a major cause of kidney graft loss, yet assessment of individual risk at diagnosis is impeded by the lack of a reliable prognosis assay. Here, we tested whether the capacity of anti-HLA antibodies to bind complement components allows accurate risk stratification at the time of AMR diagnosis. Among 938 kidney transplant recipients for whom a graft biopsy was performed between 2004 and 2012 at the Lyon University Hospitals, 69 fulfilled the diagnosis criteria for AMR and were enrolled. Sera banked at the time of the biopsy were screened for the presence of donor-specific anti-HLA antibodies (DSAs) and their ability to bind C1q and C3d using flow bead assays. In contrast with C4d graft deposition, the presence of C3d-binding DSA was associated with a higher risk of graft loss (P<0.001). Despite similar trend, the difference did not reach significance with a C1q-binding assay (P=0.06). The prognostic value of a C3d-binding assay was further confirmed in an independent cohort of 39 patients with AMR (P=0.04). Patients with C3d-binding antibodies had worse eGFR and higher DSA mean fluorescence intensity. In a multivariate analysis, only eGFR <30 ml/min per 1.73 m(2) (hazard ratio [HR], 3.56; 95% confidence interval [CI], 1.46 to 8.70; P=0.005) and the presence of circulating C3d-binding DSA (HR, 2.80; 95% CI, 1.12 to 6.95; P=0.03) were independent predictors for allograft loss at AMR diagnosis. We conclude that assessment of the C3d-binding capacity of DSA at the time of AMR diagnosis allows for identification of patients at risk for allograft loss.

Adult-onset eculizumab-resistant hemolytic uremic syndrome associated with cobalamin C deficiency

A 20-year-old man was hospitalized for malignant hypertension, mechanical hemolysis, and kidney failure. Kidney biopsy confirmed glomerular and arteriolar thrombotic microangiopathy. Etiologic analyses, which included ADAMTS13 activity, stool culture, complement factor proteins (C3, C4, factor H, factor I, and MCP [membrane cofactor protein]), anti-factor H antibodies, HIV (human immunodeficiency virus) serology, and antinuclear and antiphospholipid antibodies, returned normal results. Malignant hypertension was diagnosed. Ten months later, we observed a relapse of acute kidney injury and mechanical hemolysis. Considering a diagnosis of complement dysregulation-related atypical hemolytic uremic syndrome (HUS), we began treatment with eculizumab. Despite the efficient complement blockade, the patient's kidney function continued to decline. We performed additional analyses and found that the patient's homocysteine levels were dramatically increased, with no vitamin B12 (cobalamin) or folate deficiencies. We observed very low plasma methionine levels associated with methylmalonic aciduria, which suggested cobalamin C disease. We stopped the eculizumab infusions and initiated specific treatment, which resulted in complete cessation of hemolysis. MMACHC (methylmalonic aciduria and homocystinuria type C protein) sequencing revealed compound heterozygosity for 2 causative mutations. To our knowledge, this is the first report of adult-onset cobalamin C-related HUS. Considering the wide availability and low cost of the homocysteine assay, we suggest that it be included in the diagnostic algorithm for adult patients who present with HUS.

Genetics and outcome of atypical hemolytic uremic syndrome: a nationwide French series comparing children and adults

BACKGROUND AND OBJECTIVES

Atypical hemolytic uremic syndrome (aHUS) is a rare complement-mediated kidney disease that was first recognized in children but also affects adults. This study assessed the disease presentation and outcome in a nationwide cohort of patients with aHUS according to the age at onset and the underlying complement abnormalities.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A total of 214 patients with aHUS were enrolled between 2000 and 2008 and screened for mutations in the six susceptibility factors for aHUS and for anti-factor H antibodies.

RESULTS

Onset of aHUS occurred as frequently during adulthood (58.4%) as during childhood (41.6%). The percentages of patients who developed the disease were 23%, 40%, 70%, and 98% by age 2, 18, 40, and 60 years, respectively. Mortality was higher in children than in adults (6.7% versus 0.8% at 1 year) (P=0.02), but progression to ESRD after the first aHUS episode was more frequent in adults (46% versus 16%; P<0.001). Sixty-one percent of patients had mutations in their complement genes. The renal outcome was not significantly different in adults regardless of genetic background. Only membrane cofactor protein (MCP) and undetermined aHUS were less severe in children than adults. The frequency of relapse after 1 year was 92% in children with MCP-associated HUS and approximately 30% in all other subgroups.

CONCLUSION

Mortality rate was higher in children than adults with aHUS, but renal prognosis was worse in adults than children. In children, the prognosis strongly depends on the genetic background.

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.

Membranoproliferative glomerulonephritis with C3NeF and genetic complement dysregulation

The development of membranoproliferative glomerulonephritis (MPGN) is associated with uncontrolled activation of the complement alternative pathway. This dysregulation is related either to C3 nephritic factor (C3NeF), an auto-antibody directed against the alternative C3 convertase, or to homozygous loss-of-function mutation of the complement regulatory protein factor H. Heterozygous mutations in the genes coding for factor H, or for the other alternative pathway inhibitory proteins factor I and membrane cofactor protein, have recently been identified in a small number of patients with MPGN with exclusive C3 deposits. We report three hypocomplementemic children with dense deposit disease (n=1) or immune-complex-mediated MPGN type I (n=2), associated with both C3NeF activity and heterozygous mutation of factor H or factor I. These observations highlight the possible combination of genetic and acquired defect in complement control in various subtypes of MPGN, a finding that may influence the treatment strategy in some patients.

Atypical hemolytic uremic syndrome and mutation analysis of factor H gene in two Tunisian families

We carried out a protein and genetic investigation of the factor H gene mutations within two families presenting with a diagnostic suspicion of atypical hemolytic uremic syndrome (aHUS). The results within the patients of the first family revealed a factor H-deficiency. Direct sequencing allowed the detection of a 4-nucleotide deletion in the factor H gene. This deletion was found as the homozygote form in the proband and as the heterozygote form in the parents. Protein and functional analyses of the complement system were normal in all members of the second family. However, the molecular investigation for the father showed the presence of an amino acid substitution in the FH gene. Unfortunately, his two affected children died without being investigated for mutations. The functional consequences of these abnormal proteins are still to be demonstrated.

Non-atheromatous arterial stenoses in atypical haemolytic uraemic syndrome associated with complement dysregulation

BACKGROUND

A child, who presented atypical haemolytic uraemic syndrome (aHUS) at the age of 1 month, developed cerebral ischaemic events at the age of 10 years.

RESULTS

Stenoses of both carotid arteries, left subclavian and vertebral arteries, several intracranial, right humeral, several coronary, and all pulmonary arteries were demonstrated. At the age of 13 years, left subclavian and right cervical carotid arteries were occluded. Right carotid recanalization induced intracranial dissection and death. The child had a Lys350Asp factor B mutation.

CONCLUSION

Arterial steno-occlusive lesions appear as potential complications of dysregulated complement activation in aHUS. Endovascular treatment should be considered cautiously in this setting.

Varicella as a trigger of atypical haemolytic uraemic syndrome associated with complement dysfunction: two cases

We report two cases of children who presented with haemolytic uraemic syndrome following varicella infection. One of them had a membrane cofactor protein mutation, and the other had anti-factor H antibodies. These observations show that infectious agents such as varicella-zoster virus may be the trigger of haemolytic uraemic syndrome in patients with complement dysregulation.

[Hemolytic-uremic syndrome: what is the mechanism?]

Many data suggest that improper regulation of the alternative complement pathway is involved in the pathophysiology of atypical hemolytic-uremic syndrome. Until a few years ago, research exclusively focused on protein assays, which did not help to identify precise genetic factors predisposing to atypical hemolytic-uremic syndrome. In this context, the introduction of gene study considerably accelerated advances.