C3 Mutation Research Articles

Analysis of genetic and predisposing factors in Japanese patients with atypical hemolytic uremic syndrome

Hemolytic uremic syndrome (HUS) is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and renal impairment. Approximately 10% of cases are classified as atypical due to the absence of Shiga toxin-producing bacteria as a trigger. Uncontrolled activation of the complement system plays a role in the pathogenesis of atypical HUS (aHUS). Although many genetic studies on aHUS have been published in recent years, only limited data has been gathered in Asian countries. We analyzed the genetic variants of 6 candidate genes and the gene deletion in complement factor H (CFH) and CFH-related genes, examined the prevalence of CFH autoantibodies and evaluated the genotype-phenotype relationship in 10 Japanese patients with aHUS. We identified 7 causative or potentially causative mutations in CFH (p.R1215Q), C3 (p.R425C, p.S562L, and p.I1157T), membrane cofactor protein (p.Y189D and p.A359V) and thrombomodulin (p.T500M) in 8 out of 10 patients. All 7 of the mutations were heterozygous and four of them were novel. Two patients carried CFH p.R1215Q and 3 other patients carried C3 p.I1157T. One patient had 2 causative mutations in different genes. One patient was a compound heterozygote of the 2 MCP mutations. The patients carrying mutations in CFH or C3 had a high frequency of relapse and a worse prognosis. One patient had CFH autoantibodies. The present study identified the cause of aHUS in 9 out of 10 Japanese patients. Since the phenotype-genotype correlation of aHUS has clinical significance in predicting renal recovery and transplant outcome, a comprehensively accurate assessment of molecular variation would be necessary for the proper management of aHUS patients in Japan.

Echocardiographic study of double mutations of myosin-binding protein C3 gene in Chinese patients with familial hypertrophic cardiomyopathy

To determine the associated mutations in myosin-binding protein C3 (MYBPC3) in Chinese patients with family hypertrophic cardiomyopathy (FHCM) and to analyze the genotype and phenotype correlation. One family with 27 family members affected with FHCM was chosen for the study. The full encoding exons of MYBPC3 were amplified with PCR and the products were sequenced. The clinical data and echocardiography were collected. Two missense mutations in the family were identified: one was C.2526C>G mutation which caused a tyrosine (Tyr) to terminator exchange at amino acid residue 842 and the other was C.2971G>A mutation which resulted in a valine (Val) to methionine (Met) exchange at amino acid residue 991. Four patients in the family suffered from HCM with asymmetric interventricular septal hypertrophy. The left ventricular diastolic function was significantly reduced. Signs of regional diastolic abnormalities occurred in some mutation carriers. Severe hypertrophy and diastolic dysfunction of the disease are compatible with the presence of double mutations in MYBPC3. Signs of regional diastolic abnormalities suggest a primary response to the mutations of MYBPC3 expression.

Peripheral Gangrene in Children With Atypical Hemolytic Uremic Syndrome

Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy with severe clinical manifestation, frequent recurrence, and poor long-term prognosis. It is usually caused by abnormalities in complement regulation. We report 2 cases of children affected by a catastrophic extrarenal complication. A 4-year-old Indian girl developed gangrene of the finger tips 2 days after initial presentation of aHUS. Factor H autoantibodies were identified. Renal function continued to decline despite daily plasma exchanges, and she was started on peritoneal dialysis 5 days after admission. The distal tips of the left hand remained gangrenous with a line of demarcation. Three weeks later, she did not return for follow-up and died at home because of dialysis-related complications. An Arabic girl developed end-stage renal disease due to aHUS in the fourth month after birth. A de novo activating C3 mutation was found. At age 9 months, she suddenly developed ischemic changes in fingers of both hands and several toes. The lesions progressed, and several finger tips became gangrenous despite intense plasma exchange therapy. The decision was made to administer complement blocking therapy with the C5 antibody eculizumab. All nonnecrotic digits rapidly regained perfusion. The 3 already gangrenous fingers healed with loss of the end phalanges. During maintenance, eculizumab aHUS activity subsided completely and some late recovery of renal function was observed. aHUS may present by thrombotic macroangiopathy of small peripheral arteries. Eculizumab appears effective in preserving tissue viability if administered before gangrene occurs and should be considered as first-line rescue therapy in such cases.

CH50 Activity Correlates with Residual Intravascular Hemolysis in Pts with Paroxysmal Nocturnal Hemoglobinuria Treated by Eculizumab

AbstractAbstract 3193 Background:Paroxysmal Nocturnal Hemoglobinuria (PNH) is an acquired hemolytic anemia characterized by intravascular hemolysis, which is effectively controlled with eculizumab. However, in some cases, unexplained upper limit lactate dehydrogenase levels (LDH), as well as low haptoglobin levels are not unusual under treatment, suggesting residual low-level hemolysis. C3-mediated clearance of PNH red blood cells has been recently suggested in patients (pts) under eculizumab (Risitano Blood 2010). We hypothesized residual hemolysis may also be due to incomplete C5 blockage under treatment. CH50 activitiy (residual functional C5 activity) as well as C3 deposition on PNH red blood cells were assessed among eculizumab-treated pts. We also examined the hypothesis that mutations in complement genes are implicated in residual hemolytic process. Patients and Methods:From October 2010 to February 2012, 22 pts (7 male, median age 42 years range 21 to 72) with hemolytic PNH treated with eculizumab (900 mg intravenously every 14±2 days) were prospectively followed systematically every 2 weeks. Before each Eculizumab infusion, clinical data (abdominal pain, thrombosis events and transfusion requirements) as well as complete blood count, LDH, bilirubin levels and reticulocytes were systematically collected. Concomitantly, CH50 using sensibilized sheep red blood cells, C3d deposition on red blood cells using flow cytometry as well as C3 and C4 circulating levels were also studied. Complete C5 blockage was defined by a CH50 activity ≤10% (as for pts with hereditary complete C5 deficiency). All pts included in the study have at least 6 months follow-up under treatment. Only measurements performed after at least 6 months of treatment were considered. Residual intravascular hemolysis was defined by upper limit LDH level before eculizumab injection. CH50 was analyzed with a longitudinal tobit regression model accounting for repeated sampling and the limit of detection. The model was fit in a Bayesian framework, so no p-values are presented. Results:Before starting eculizumab, 21 pts were transfusion-dependent with a mean of 7 red blood cell (RBC) transfusions per year and 9 pts had a significant PNH-related complication (9 thrombosis and 7 with a previous history of aplastic anemia). During the study period, 6 pts received at least one transfusion (mean of 3 RBC transfusions per year) and 1 patient presented a deep vein thrombosis. All pts were analyzed for CH50 activity (412 samples; median 19 per patient; range, 4 to 31). Overall, CH50 measurements showed substantial variability for most pts (Figure 1). Residual CH50 activity (>10%) was significantly associated with higher LDH levels whereas pts who were still transfused (as well as pts with lower hemoglobin level and higher reticulocytes counts) tended to have higher CH50. Type III PNH red blood cell C3d deposition (assessed in all but 1 patient; 277 samples; median 14 per patient; range, 2 to 21) was found in all pts evaluated during the study period (Fig. 1). However, we did not find any correlation between C3 opsonization and clinical or biological signs of hemolysis. The association between CH50 and higher C3 deposition was weak (on average −0.8% CH50 per 10%) more C3 deposition (95%CI −1.7 to 0.2) (Fig. 1). Those results were confirmed in the subset of 15 patients with pure hemolytic PNH (no history of aplastic anemia). C3 and C4 circulating levels were in the normal range during the study period in all but one patient (pts#15, Fig. 1), who carry a complement factor H (CFH) mutation, leading to a quantitative Factor H deficiency. Systematic screening was positive for 2 other pts (CFH, pts#1; C3 mutation, pts#14) but with no phenotypical consequence. Conclusion:Our results confirm the excellent overall clinical and biological response of hemolytic PNH pts to eculizumab. We found that unblocked CH50 activity, reflecting the residual C5 activity, was significantly associated with residual intravascular hemolysis while the selective C3d deposition of PNH red cells (found in all pts under treatment) was not. We also identified mutations in C3 and factor H genes. Whether incomplete C5 blockade is due to low residual level of eculizumab, complement mutations or polymorphisms, or other mechanisms are under investigation. [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Analysis of Genetic and Predisposing Factors in Japanese Patients with Atypical Hemolytic Uremic Syndrome

AbstractAbstract 3337 Introduction:Hemolytic uremic syndrome (HUS) is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and renal impairment. Approximately 10% of the cases are classified as atypical due to the absence of Shiga toxin-producing bacterial infection as a trigger. Compared to typical HUS, atypical HUS (aHUS) has a much poorer prognosis, with up to half of the patients progressing to end-stage renal disease, and a higher mortality. Uncontrolled activation of the complement system plays a role in the pathogenesis of aHUS. More than half of the patients with aHUS have the mutations of genes involved in the alternative pathway of the complement system. Mutations with loss-of-function of regulators (CFH, CFI, MCP and THBD) and gain-of-function of key of complement components (C3 and CFB) have been found to predispose to aHUS. In addition, genomic deletion of CFHR3 and CFHR1 has been linked to a risk of aHUS, sometimes together with the presence of CFH autoantibodies. Although many genetic studies on aHUS have been published in recent years, the Asian data are rare so far. It is important to perform genetic screening in patients with aHUS, because genotype-phenotype correlations have clinical significance in predicting renal recovery and transplant outcome. In this study, we analyzed 10 Japanese aHUS patients and the genotype-phenotype relationship was evaluated. Patients and Methods:Ten Japanese patients in Japan-Nara registry of thrombotic microangiopathy (TMA) with aHUS were investigated in this study; eight of them were sporadic and the other two were from one family. Diagnosis of aHUS was made by the simultaneous occurrence of microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure without association to Shiga toxin. The CFH antigen level was analyzed by a rocket-immunoelectrophoresis method, and hemolytic assay was performed using sheep red blood cells (Sanchez-Corral P, et al. Mol Immunol 2004). Genomic DNA was extracted from peripheral blood leukocytes of patients and their family members. The genetic mutations of 6 candidate genes and the gene deletion in complement factor H (CFH) and CFH-related genes were analyzed.Results: (1) Clinical features and laboratory data:Plasma ADAMTS13 activity was not severely decreased in all patients (29–119% of the normal). The first episode of aHUS occurred at childhood (≤10 yr) in 7 patients. Nine cases had probable triggering events. The plasma C3 level was low in 4 patients. Three patients showed apparent hemolytic activity against the sheep erythrocytes. Five patients had experienced relapses by the most recent follow-up. Five patients progressed to end-stage renal disease and could not be maintained without hemodialysis or peritoneal dialysis. (2) The result of gene analysis:We identified 7 causative or potentially causative mutations in 8 of these patients, and these mutations were heterozygous. Three of the mutations, p.R1215Q in CFH, p.I1157T in C3, and p.Y189D in MCP, were identified previously, indicating that these mutations are definitely causative for aHUS. The remaining 4 missense mutations, p.A359V in MCP, p.S562L and p.R425C in C3, and p.T500M in THBD, were novel. We considered them as potentially causative mutations based on the available information, including the PolyPhen-2 prediction, a search of the literature, and the position of the missense mutation in the three-dimensional structure. Two patients, who showed apparently an enhanced hemolytic activity, carried CFH p.R1215Q and 3 other patients carried C3 p.I1157T. One patient had 2 causative mutations in different genes. One patient was a compound heterozygote of the 2 MCP mutations. The patients carrying mutations in CFH or C3 had a high frequency of relapse and a worse prognosis. Conclusion:In this study, we identified the cause of aHUS in 8 out of 10 patients. Since the phenotype-genotype correlation of aHUS has clinical significance in predicting renal recovery and transplant outcome, a comprehensively accurate assessment of molecular variation would be necessary as part of the clinical management for aHUS patients. Such an assessment system would facilitate aHUS phenotype- genotype studies in Japan. Disclosures:Matsumoto:Alexion Pharma: Membership on an entity's Board of Directors or advisory committees. Fujimura:Baxter BioScience: Membership on an entity's Board of Directors or advisory committees; Alexion Pharma: Membership on an entity's Board of Directors or advisory committees.

Novel C3 mutation p.Lys65Gln in aHUS affects complement factor H binding

BackgroundAtypical hemolytic uremic syndrome (aHUS) is associated with mutations affecting complement proteins and regulators and with autoantibodies against complement factor H (CFH). Approximately half of the aHUS patients progress to end-stage renal disease. DNA analysis of the risk factor genes is important for prognosis of aHUS recurrence after renal transplantation.MethodsMutational screening of C3 encoding the central complement component was performed by Sanger sequencing in 70 aHUS patients. Mutated and wild type recombinant C3b proteins were produced and their affinity to CFH was analyzed by ELISA.ResultsA single novel missense change p.Lys65Gln in C3 was found in 3 aHUS patients. The alteration leads to decreased binding of C3b to CFH in vitro. All three patients acquired the illness as adults and had a first aHUS episode after renal transplantation or suffered recurrence of the disease after transplantation.ConclusionsThe novel C3 change was found in 3 aHUS patients. It results in decreased C3b binding to CFH and thus might lead to impaired C3b inactivation in vivo. The p.Lys65Gln is likely to be associated with aHUS after kidney transplantation and, therefore, might be an important prognostic factor.

A prevalent C3 mutation in aHUS patients causes a direct C3 convertase gain of function

AbstractAtypical hemolytic uremic syndrome (aHUS) is a rare renal thrombotic microangiopathy commonly associated with rare genetic variants in complement system genes, unique to each patient/family. Here, we report 14 sporadic aHUS patients carrying the same mutation, R139W, in the complement C3 gene. The clinical presentation was with a rapid progression to end-stage renal disease (6 of 14) and an unusually high frequency of cardiac (8 of 14) and/or neurologic (5 of 14) events. Although resting glomerular endothelial cells (GEnCs) remained unaffected by R139W-C3 sera, the incubation of those sera with GEnC preactivated with pro-inflammatory stimuli led to increased C3 deposition, C5a release, and procoagulant tissue-factor expression. This functional consequence of R139W-C3 resulted from the formation of a hyperactive C3 convertase. Mutant C3 showed an increased affinity for factor B and a reduced binding to membrane cofactor protein (MCP; CD46), but a normal regulation by factor H (FH). In addition, the frequency of at-risk FH and MCP haplotypes was significantly higher in the R139W-aHUS patients, compared with normal donors or to healthy carriers. These genetic background differences could explain the R139W-aHUS incomplete penetrance. These results demonstrate that this C3 mutation, especially when associated with an at-risk FH and/or MCP haplotypes, becomes pathogenic following an inflammatory endothelium-damaging event.

Inclusion body myositis coexisting with hypertrophic cardiomyopathy: An autopsy study

Inclusion body myositis is an inflammatory myopathy characterized pathologically by rimmed vacuoles and the accumulation of amyloid-related proteins. Autopsy studies in these patients, including histochemical examinations of multiple skeletal muscles, have not yet been published. In this paper, we describe the autopsy findings of a patient with inclusion body myositis and hypertrophic cardiomyopathy. A 69-year-old man, who was a human T lymphotropic virus type 1 carrier, exhibited slowly progressive muscle weakness and atrophy, predominantly affecting the scapular, quadriceps femoris, and forearm flexor muscles. His disease course was more rapidly progressive than that typically observed; the patient died suddenly of arrhythmia 5years after diagnosis. Autopsy findings revealed that multiple muscles, including the respiratory muscles, were involved. Longitudinal studies revealed an increased frequency of rimmed vacuoles and p62/sequestosome 1- and/or TAR DNA-binding protein 43-positive deposits in autopsied muscles, although the amount of inflammatory infiltrate appeared to be decreased. We speculated that muscle degeneration may be more closely involved in disease progression compared with autoimmunity. Genetic analysis revealed a myosin binding protein C3 mutation, which is reportedly responsible for familial hypertrophic cardiomyopathy. This mutation and human T lymphotropic virus type 1 infection may have affected the skeletal muscles of this patient.

A Novel C3 Mutation Causing Increased Formation of the C3 Convertase in Familial Atypical Hemolytic Uremic Syndrome

Atypical hemolytic uremic syndrome has been associated with dysregulation of the alternative complement pathway. In this study, a novel heterozygous C3 mutation was identified in a factor B-binding region in exon 41, V1636A (4973 T > C). The mutation was found in three family members affected with late-onset atypical hemolytic uremic syndrome and symptoms of glomerulonephritis. All three patients exhibited increased complement activation detected by decreased C3 levels and glomerular C3 deposits. Platelets from two of the patients had C3 and C9 deposits on the cell surface. Patient sera exhibited more C3 cleavage and higher levels of C3a. The C3 mutation resulted in increased C3 binding to factor B and increased net formation of the C3 convertase, even after decay induced by decay-accelerating factor and factor H, as assayed by surface plasmon resonance. Patient sera incubated with washed human platelets induced more C3 and C9 deposition on the cell surface in comparison with normal sera. More C3a was released into serum over time when washed platelets were exposed to patient sera. Results regarding C3 and C9 deposition on washed platelets were confirmed using purified patient C3 in C3-depleted serum. The results indicated enhanced convertase formation leading to increased complement activation on cell surfaces. Previously described C3 mutations showed loss of function with regard to C3 binding to complement regulators. To our knowledge, this study presents the first known C3 mutation inducing increased formation of the C3 convertase, thus explaining enhanced activation of the alternative pathway of complement.

Thrombotic microangiopathy mimicking membranoproliferative glomerulonephritis

A 4-year-old boy presented with proteinuria and developed progressive renal failure over 6 years. In the patient's family, five individuals were affected with atypical haemolytic uraemic syndrome (aHUS) but not the patient. Renal biopsies (n = 3) showed glomerular basement membrane thickening with double contours, endothelial swelling and deposits of C3 and C1q. Electron microscopy revealed mesangial and subendothelial electron-dense deposits. Complement mutations in membrane cofactor protein (Y155D) and C3 (R713W and G1094R) were detected in all affected family members. The patient also had transient autoantibodies to factor H. The findings suggest that aHUS and glomerulopathy resembling membranoproliferative glomerulonephritis may have a common molecular background.

Three novel C3 mutations in atypical haemolytic uraemic syndrome: Two ways to hyperactive C3 convertase

Three novel C3 mutations in atypical haemolytic uraemic syndrome: Two ways to hyperactive C3 convertase

Subclinical echocardiographic abnormalities in phenotype-negative carriers of myosin-binding protein C3 gene mutation for hypertrophic cardiomyopathy

Early diastolic myocardial tissue Doppler velocities have reported to be reduced in mutation-positive patients with hypertrophic cardiomyopathy (HCM) in some studies even in the absence of left ventricular hypertrophy (LVH). Strain is a sensitive tool in detecting early systolic abnormalities in patients with HCM. Our goal is to examine novel echocardiographic characteristics of phenotype-negative carriers for a known sarcomeric gene mutation for HCM. We evaluated 41 consecutive subjects with a known myosin-binding protein C3 (MYBPC3) mutation (c.3330+2T>G). Subjects who were mutation positive without LVH (G+/LVH-, n = 35) were compared with healthy controls (n = 30) regarding tissue Doppler and segmental longitudinal strain measures. The G+/LVH- group was similar to the healthy controls with respect to chamber size, left ventricular mass index, and most diastolic filling parameters, including tissue Doppler-derived early diastolic annular velocities. Global longitudinal strain was similar for both groups (20.3 ± 2.1 vs 19.8 ± 1.8, P = .36), although regional segment analysis showed a notable reduction in the basal septum (16.8 ± 3.1 vs 19.0 ± 4.0%, P = .02) and increase in the basal posterior (22.5 ± 5.2 vs 17.9 ± 5.2, P = .001) as well as mid posterior (21.8 ± 4.7 vs 18.2 ± 3.0, P = .001) walls. In our cohort of phenotype-negative carriers of a specific MYBPC3 mutation, there were minimal differences in conventional 2-dimensional, Doppler, and speckle-tracking-derived parameters of systolic and diastolic function compared with that of healthy subjects. The presence of regional alterations in strain indicative of the presence of underlying subclinical disease requires further validation.

Disease-associated N-terminal Complement Factor H Mutations Perturb Cofactor and Decay-accelerating Activities

Many mutations associated with atypical hemolytic uremic syndrome (aHUS) lie within complement control protein modules 19–20 at the C terminus of the complement regulator factor H (FH). This region mediates preferential action of FH on self, as opposed to foreign, membranes and surfaces. Hence, speculation on disease mechanisms has focused on deficiencies in regulation of complement activation on glomerular capillary beds. Here, we investigate the consequences of aHUS-linked mutations (R53H and R78G) within the FH N-terminal complement control protein module that also carries the I62V variation linked to dense-deposit disease and age-related macular degeneration. This module contributes to a four-module C3b-binding site (FH1–4) needed for complement regulation and sufficient for fluid-phase regulatory activity. Recombinant FH1–4V62 and FH1–4I62 bind immobilized C3b with similar affinities (KD = 10–14 μm), whereas FH1–4I62 is slightly more effective than FH1–4V62 as cofactor for factor I-mediated cleavage of C3b. The mutant (R53H)FH1–4V62 binds to C3b with comparable affinity (KD ∼12 μm) yet has decreased cofactor activities both in fluid phase and on surface-bound C3b, and exhibits only weak decay-accelerating activity for C3 convertase (C3bBb). The other mutant, (R78G)FH1–4V62, binds poorly to immobilized C3b (KD >35 μm) and is severely functionally compromised, having decreased cofactor and decay-accelerating activities. Our data support causal links between these mutations and disease; they demonstrate that mutations affecting the N-terminal activities of FH, not just those in the C terminus, can predispose to aHUS. These observations reinforce the notion that deficiency in any one of several FH functional properties can contribute to the pathogenesis of this disease.

Syndrome hémolytique et urémique lié à des anomalies du complément

Hemolytic uremic syndrome (HUS) is a thrombotic microangiopathy (TMA) disorder characterised by the association of haemolytic anaemia, thrombocytopenia and acute renal failure. Atypical forms (non-shigatoxin related forms) may be familial or sporadic, frequently with relapses and most of them lead to end stage renal failure. During the last years, different groups have demonstrated genetic predisposition to atypical HUS (aHUS) involving five genes encoding for complement components which play a role in the activation or control of the alternative pathway: encoding factor H (CFH), accounting for 30% of aHUS; CD46 (encoding membrane cofactor protein [MCP]) accounting for approximately 10% of aHUS; CFI (encoding factor I) accounting for an estimated 5-15% of patients; C3 (encoding C3) accounting for approximately 10% of aHUS; and rarely CFB (encoding factor B). Predisposition to aHUS is inherited with incomplete penetrance. It is admitted that mutations confer a predisposition to develop aHUS rather than directly causing the disease and that a second event (genetic or environmental) is required for disease manifestation. HUS onset follows a triggering event in most cases (frequently banal seasonal infection and pregnancy). Uncontrolled C3 convertase leads to increased deposition of C3b on vascular endothelium and participates to the prothrombotic state. The phenotype of aHUS is variable ranging from mild forms, with complete recovery of renal function to severe forms with end stage renal disease within the first year after the onset. Overall, the outcome is severe with a mortality rate of 10% and with more than 60% of patients on dialysis. The most severe prognosis was in the CFH mutation group. There is a high risk of recurrence of the disease after renal transplantation in patients with mutations in CFH, CFI, CFB and C3. Plasma therapy may allow complete haematological remission but frequently with persistent renal damage. Some patients are plasma resistant and some are plasma dependent. The recent progress in the determination of the susceptibility factors for aHUS, have allowed to propose new diagnostic tests including a molecular genetic testing and may permit to consider some new specific treatments in this disease (human plasma-derived CFH or complement inhibitors).

Transplantation in Atypical Hemolytic Uremic Syndrome

Atypical hemolytic uremic syndrome (aHUS) is a disease characterized by overactivation of complement. Recurrence following renal transplantation is determined by a genetic predisposition. Genetic screening of all individuals with aHUS should be performed prior to listing for transplantation. Individuals with isolated mutations in MCP have a low risk of recurrence and may be considered for kidney transplantation alone. In individuals with CFH and CFI mutations, the risk of recurrence following renal transplantation is high. Combined liver/kidney transplantation has been used successfully in individuals with CFH mutations following the introduction of perioperative plasma exchange; however, such a procedure is not without its risks. Liver/kidney transplantation has yet to be performed on individuals with CFI and C3 mutations but may be predicted to be successful. In individuals with CFH autoantibodies, a reduction in titer through plasma exchange and rituximab has been successful. Clinical trials of the complement C5 inhibitor eculizumab may improve prospects for isolated renal transplantation in individuals with complement protein mutations.

Novel C3 convertase gain of function in atypical haemolytic uraemic syndrome, caused by a frequent mutation in C3

Novel C3 convertase gain of function in atypical haemolytic uraemic syndrome, caused by a frequent mutation in C3

Functional characterization of mutations in complement C3 that predispose to aHUS

Functional characterization of mutations in complement C3 that predispose to aHUS

Human C3 mutation associated with Dense Deposit Disease unravels distinct structural requirements for factor H, MCP and DAF regulation

Human C3 mutation associated with Dense Deposit Disease unravels distinct structural requirements for factor H, MCP and DAF regulation

Relative Role of Genetic Complement Abnormalities in Sporadic and Familial aHUS and Their Impact on Clinical Phenotype

Hemolytic uremic syndrome (HUS) is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and renal impairment. Most childhood cases are caused by Shiga toxin-producing bacteria. The other form, atypical HUS (aHUS), accounts for 10% of cases and has a poor prognosis. Genetic complement abnormalities have been found in aHUS. We screened 273 consecutive patients with aHUS for complement abnormalities and studied their role in predicting clinical phenotype and response to treatment. We compared mutation frequencies and localization and clinical outcome in familial (82) and sporadic (191) cases. In >70% of sporadic and familial cases, gene mutations, disease-associated factor H (CFH) polymorphisms, or anti-CFH autoantibodies were found. Either mutations or CFH polymorphisms were also found in the majority of patients with secondary aHUS, suggesting a genetic predisposition. Familial cases showed a higher prevalence of mutations in SCR20 of CFH and more severe disease than sporadic cases. Patients with CFH or THBD (thrombomodulin) mutations had the earliest onset and highest mortality. Membrane-cofactor protein (MCP) mutations were associated with the best prognosis. Plasma therapy induced remission in 55 to 80% of episodes in patients with CFH, C3, or THBD mutations or autoantibodies, whereas patients with CFI (factor I) mutations were poor responders. aHUS recurred frequently after kidney transplantation except for patients with MCP mutations. Results underline the need of genetic screening for all susceptibility factors as part of clinical management of aHUS and for identification of patients who could safely benefit from kidney transplant.

Genetics and complement in atypical HUS

Central to the pathogenesis of atypical hemolytic uremic syndrome (aHUS) is over-activation of the alternative pathway of complement. Following the initial discovery of mutations in the complement regulatory protein, factor H, mutations have been described in factor I, membrane cofactor protein and thrombomodulin, which also result in decreased complement regulation. Autoantibodies to factor H have also been reported to impair complement regulation in aHUS. More recently, gain of function mutations in the complement components C3 and Factor B have been seen. This review focuses on the genetic causes of aHUS, their functional consequences, and clinical effect.