Screening for complement system abnormalities in patients with atypical hemolytic uremic syndrome

Atypical haemolytic uraemic syndrome: a case of rare genetic mutation

Complement-mediated kidney disease has been an evolving area in the field of nephrology. Atypical haemolytic uraemic syndrome (aHUS) is a rare thrombotic microangiopathy that affects multiple organs, particularly kidneys. The disease is characterised by a triad of haemolytic anaemia, thrombocytopenia and acute kidney injury (AKI). aHUS is most commonly caused by dysregulation of alternative complement pathway. In contrast to shiga toxin-associated haemolytic uraemic syndrome, diarrheal prodrome is usually absent in children with aHUS. We report a 2-year, 9-month-old boy who presented with acute dysentery and AKI. He had an unusual prolonged course of illness with hypocomplementaemia; hence, genetic testing was performed. He had a storming course in the hospital and succumbed to complications of the disease. Genetic study revealed digenic mutation in Complement Factor I and C3 Therefore, it is important to differentiate aHUS from other thrombotic microangiopathies to improve the outcome.

Inherited Kidney Complement Diseases

In the past 20 years, we have witnessed tremendous advances in our ability to diagnose and treat genetic diseases of the kidney caused by complement dysregulation. Staggering progress was realized toward a better understanding of the genetic underpinnings and pathophysiology of many forms of atypical hemolytic uremic syndrome (aHUS) and C3-dominant glomerulopathies that are driven by complement system abnormalities. Many of these seminal discoveries paved the way for the design and characterization of several innovative therapies, some of which have already radically improved patients' outcomes. This review offers a broad overview of the exciting developments that have occurred in the recent past, with a particular focus on single-gene (or Mendelian), complement-driven aHUS and C3-dominant glomerulopathies that should be of interest to both nephrologists and kidney researchers. The discussion is restricted to genes with robust associations with both aHUS and C3-dominant glomerulopathies (complement factor H, complement component 3, complement factor H-related proteins) or only aHUS (complement factor B, complement factor I, and membrane cofactor protein). Key questions and challenges are highlighted, along with potential avenues for future directions.

The role of complement in kidney disease

While the complement cascade is an important component of the innate immune system, uncontrolled activation can cause severe disease. This concept is illustrated by the prototypical complement-mediated renal disease atypical haemolytic uraemic syndrome (aHUS), which causes renal failure if untreated but when managed with the complement inhibitor eculizumab leaves the patient vulnerable to infection with encapsulated organisms. Complement activation is also implicated in the pathogenesis of many other renal and non-renal diseases, necessitating an understanding of complement biology and diagnostics. We review renal diseases in which complement over-activation is known to cause tissue injury; aHUS and C3 glomerulopathy. We also discuss the contribution of complement more widely to the pathophysiology of renal disease, and highlight the significance and side effects of anti-complement therapy relevant to the general physician.

Peri- and Post-operative Evaluation and Management of Atypical Hemolytic Uremic Syndrome (aHUS) in Kidney Transplantation

Atypical hemolytic uremic syndrome (aHUS) is a severe thrombotic microangiopathy characterized by over-activation of the alternative complement pathway. The etiology of the dysregulated complement system is commonly a genetic variant in one or more complement proteins as identified in ∼ 60%-70% patients. The risk of recurrence after a kidney transplantation is high and depends on the underlying complement abnormality. For a long time, kidney transplantation was contraindicated in these patients because of the high rate of recurrence and subsequent allograft loss. Over the past decade, advancements in the understanding of etiopathogenesis of aHUS and approval of the anti-complement drug, eculizumab, have allowed for successful kidney transplantation in these patients. All patients with ESRD due to aHUS should undergo screening for complement genetic variants. Patients in whom a genetic variant is not identified or in whom a genetic variant of uncertain significance is identified should undergo further testing to determine etiology of disease. This review aims to shed light on the diagnostic and therapeutic considerations in patients with aHUS preceding and following kidney transplantation.

Opposite Profiles of Complement in Antiphospholipid Syndrome (APS) and Systemic Lupus Erythematosus (SLE) Among Patients With Antiphospholipid Antibodies (aPL)

APS is the association of antiphospholipid antibodies (aPL) with thromboses and/or recurrent pregnancy loss (RPL). Among patients with SLE, one-third have aPL and 10–15% have a manifestation of secondary APS. Animal studies suggested that complement activation plays an important role in the pathogenesis of thrombosis and pregnancy loss in APS. We performed a cross-sectional study on complement proteins and genes in 525 patients with aPL. Among them, 237 experienced thromboses and 293 had SLE; 111 had both SLE and thromboses, and 106 had neither SLE nor thrombosis. Complement protein levels were determined by radial immunodiffusion for C4, C3 and factor H; and by functional ELISA for mannan binding lectin (MBL). Total C4, C4A and C4B gene copy numbers (GCN) were measured by TaqMan-based realtime PCR. Two to six copies of C4 genes are frequently present in a diploid genome, and each copy may code for an acidic C4A or a basic C4B protein. We observed significantly (a) higher protein levels of total C4, C4A, C4B, C3, and anticardiolipin (ACLA) IgG, (b) increased frequencies of lupus anticoagulant and males, and (c) decreased levels of complement factor H, MBL and ACLA-IgM among patients with thrombosis than those without thrombosis (N = 288). We also observed significantly lower GCNs of total C4 and C4A among aPL-positive patients with both SLE and thrombosis than others. By contrast, aPL-positive subjects with SLE had significantly reduced protein levels of C3, total C4, C4A, C4B and ACLA-IgG, and higher frequency of females than those without SLE. Patients with thrombosis but without SLE (N = 126), and patients with SLE but without thrombosis (N = 182) had the greatest differences in mean protein levels of C3 (p = 2.6 × 10⁻⁶), C4 (p = 2.2 × 10⁻⁹) and ACLA-IgG (p = 1.2 × 10⁻⁵). RPL occurred in 23.7% of female patients and thrombotic SLE patients had the highest frequency of RPL (41.0%; p = 3.8 × 10⁻¹⁰). Compared with non-RPL females, RPL had significantly higher frequency of thrombosis and elevated C4 protein levels. Female patients with homozygous C4A deficiency all experienced RPL (p = 0.0001) but the opposite was true for patients with homozygous C4B deficiency (p = 0.017). These results provide new insights and biomarkers for diagnosis and management of APS and SLE.

Rare Functional Variants in Complement Genes and Anti-FH Autoantibodies-Associated aHUS

Atypical hemolytic uremic syndrome (aHUS) is a rare disease characterized by microangiopathic hemolytic anemia, thrombocytopenia and renal failure. It is caused by genetic or acquired defects of the complement alternative pathway. Factor H autoantibodies (anti-FHs) have been reported in 10% of aHUS patients and are associated with the deficiency of factor H-related 1 (FHR1). However, FHR1 deficiency is not enough to cause aHUS, since it is also present in about 5% of Caucasian healthy subjects. In this study we evaluated the prevalence of genetic variants in CFH, CD46, CFI, CFB, C3, and THBD in aHUS patients with anti-FHs, using healthy subjects with FHR1 deficiency, here defined “supercontrols,” as a reference group. “Supercontrols” are more informative than general population because they share at least one risk factor (FHR1 deficiency) with aHUS patients. We analyzed anti-FHs in 305 patients and 30 were positive. The large majority were children (median age: 7.7 [IQR, 6.6–9.9] years) and 83% lacked FHR1 (n = 25, cases) due to the homozygous CFHR3-CFHR1 deletion (n = 20), or the compound heterozygous CFHR3-CFHR1 and CFHR1-CFHR4 deletions (n = 4), or the heterozygous CFHR3-CFHR1 deletion combined with a frameshift mutation in CFHR1 that generates a premature stop codon (n = 1). Of the 960 healthy adult subjects 48 had the FHR1 deficiency (“supercontrols”). Rare likely pathogenetic variants in CFH, THBD, and C3 were found in 24% of cases (n = 6) compared to 2.1% of the “supercontrols” (P-value = 0.005). We also found that the CFH H3 and the CD46_GGAAC haplotypes are not associated with anti-FHs aHUS, whereas these haplotypes are enriched in aHUS patients without anti-FHs, which highlights the differences in the genetic basis of the two forms of the disease. Finally, we confirm that common infections are environmental factors that contribute to the development of anti-FHs aHUS in genetically predisposed individuals, which fits with the sharp peak of incidence during scholar-age. Further studies are needed to fully elucidate the complex genetic and environmental factors underlying anti-FHs aHUS and to establish whether the combination of anti-FHs with likely pathogenetic variants or other risk factors influences disease outcome and response to therapies.

An adult case of atypical hemolytic uremic syndrome presented with posterior reversible encephalopathy syndrome: Successful response to late-onset eculizumab treatment

Atypical hemolytic uremic syndrome is a rare and progressive disease caused by uncontrolled alternative complement activation. Dysregulatıon of the complement activation results in thrombotic microangiopathy and multiorgan damage. A 29-yearold woman who was admitted with complaints of vomiting and headache was detected to have acute renal failure with microangiopathic hemolytic anemia (MAHA). After the diagnosis of atypical hemolytic uremic syndrome (aHUS), she was treated with plasma exchange (PE) and hemodialysis (HD). She has experienced hypertensionrelated posterior reversible encephalopathy syndrome (PRES) at the second plasma exchange. She was initiated on eculizumab therapy because of no response to PE on the 34^th days. Her renal functions progressively improved with eculizumab treatment. Dependence on dialysis was over by the 4^th month. Dialysis free-serum Creatinine level was 2.2 mg/dL [glomerular filtration rate (e-GFR): 30 mL/min/1.73 m²] after 24 months.

Neurological involvement (PRES, etc.) is the most common extrarenal complication and a major cause of mortality and morbidity from aHUS. More importantly, we showed that renal recovery may be obtained following late-onset eculizumab treatment in patient with aHUS after a long dependence on hemodialysis.

Be on Target: Strategies of Targeting Alternative and Lectin Pathway Components in Complement-Mediated Diseases

The complement system has moved into the focus of drug development efforts in the last decade, since its inappropriate or uncontrolled activation has been recognized in many diseases. Some of them are primarily complement-mediated rare diseases, such as paroxysmal nocturnal hemoglobinuria, C3 glomerulonephritis, and atypical hemolytic uremic syndrome. Complement also plays a role in various multifactorial diseases that affect millions of people worldwide, such as ischemia reperfusion injury (myocardial infarction, stroke), age-related macular degeneration, and several neurodegenerative disorders. In this review, we summarize the potential advantages of targeting various complement proteins with special emphasis on the components of the lectin (LP) and the alternative pathways (AP). The serine proteases (MASP-1/2/3, factor D, factor B), which are responsible for the activation of the cascade, are straightforward targets of inhibition, but the pattern recognition molecules (mannose-binding lectin, other collectins, and ficolins), the regulatory components (factor H, factor I, properdin), and C3 are also subjects of drug development. Recent discoveries about cross-talks between the LP and AP offer new approaches for clinical intervention. Mannan-binding lectin-associated serine proteases (MASPs) are not just responsible for LP activation, but they are also indispensable for efficient AP activation. Activated MASP-3 has recently been shown to be the enzyme that continuously supplies factor D (FD) for the AP by cleaving pro-factor D (pro-FD). In this aspect, MASP-3 emerges as a novel feasible target for the regulation of AP activity. MASP-1 was shown to be required for AP activity on various surfaces, first of all on LPS of Gram-negative bacteria.

Atypical Hemolytic Uremic Syndrome: A Brief Review

Atypical hemolytic uremic syndrome (aHUS) is a disease characterized by the triad of microangiopathic hemolytic anemia, thrombocytopenia and acute kidney injury. The histopathologic lesions of aHUS include thrombotic microangiopathy involving the glomerular capillaries and thrombosis involving arterioles or interlobar arteries. Extra-renal manifestations occur in up to 20% of patients. The majority of aHUS is caused by complement system defects impairing ordinary regulatory mechanisms. Activating events therefore lead to unbridled, ongoing complement activity producing widespread endothelial injury. Pathologic mutations include those resulting in loss-of-function in a complement regulatory gene (CFH, CFI, CD46 or THBD) or gain-of-function in an effector gene (CFB or C3). Treatment with the late complement inhibitor, eculizumab – a monoclonal antibody directed against C5 – is effective.

Pregnancy-induced atypical haemolytic uremic syndrome: A new era with eculizumab

Pregnancy is a well-recognised trigger of atypical haemolytic syndrome (P-aHUS) and often occurs in the post-partum period. Similar to atypical haemolytic uremic syndrome, it carries a poor prognosis with high morbidity particularly in the form of renal failure. Early recognition and intervention is crucial in its management particularly with the recent availability of eculizumab, a humanized monoclonal antibody to complement component C5, which has demonstrated drastic improvement in prognosis. The issue, however, is arriving at a timely diagnosis given the considerable amount of overlap in the clinical and biochemical manifestation of P-aHUS, HELLP syndrome (haemolysis, elevated liver enzyme and low platelet count) and other hypertensive disorders of pregnancy. We present a case report and literature review that highlights the clinical conundrum of arriving at the diagnosis. We also highlight the importance of early management of P-aHUS with eculizumab and its impact on improving morbidity.

Efficacy of rituximab and plasmapharesis in an adult patient with antifactor H autoantibody-associated hemolytic uremic syndrome: A case report and literature review

Antifactor H antibody (anti-CFHAb) is found in 6% to 25% cases of atypical hemolytic uremic syndrome (aHUS) in children, but has been only exceptionally reported in adults. There is no consensus about the best treatment for this type of aHUS. We report the case of an adult patient treated successfully with plasma exchange (PE), steroids, and rituximab.A 27-year-old Caucasian male presented to hospital with anemia, thrombocytopenia, and acute renal failure. One week earlier, he had digestive problems with diarrhea. The diagnosis of anti-CFHAb-associated aHUS (82,000 AU/mL) without CFHR gene mutations was established.He received Rituximab 375 mg/m (4 pulses) with PE and steroids. This treatment achieved renal and hematological remission at day (D) 31 and negative anti-CFHAb at D45 (<100 AU/mL). At D76, a fifth rituximab pulse was performed while CD19 was higher than 10/mm. Steroids were stopped at month (M) 9. The patient has not relapsed during long-term follow-up (M39).Rituximab therapy can be considered for anti-CFHAb-associated aHUS. Monitoring of anti-CFHAb titer may help to guide maintenance therapeutic strategies including Rituximab infusion.

Maintenance eculizumab dose adjustment in the treatment of atypical hemolytic uremic syndrome: a case report and review of the literature

Atypical hemolytic uremic syndrome (aHUS) patients treated with eculizumab may require higher doses to achieve and maintain optimal clinical response. Further studies are warranted to elucidate optimal dosing regimens of eculizumab in aHUS patients, and whether dosing regimens can be predicted based on mutational status, eculizumab levels, or other testing.

Characterization of a New DGKE Intronic Mutation in Genetically Unsolved Cases of Familial Atypical Hemolytic Uremic Syndrome

BACKGROUND AND OBJECTIVES

Genetic and acquired abnormalities causing dysregulation of the complement alternative pathway contribute to atypical hemolytic uremic syndrome (aHUS), a rare disorder characterized by thrombocytopenia, nonimmune microangiopathic hemolytic anemia, and acute kidney failure. However, in a substantial proportion of patients the disease-associated alterations are still unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Whole-exome and whole-genome sequencing were performed in two unrelated families with infantile recessive aHUS. Sequencing of cDNA from affected individuals was used to test for the presence of aberrant mRNA species. Expression of mutant diacylglycerol kinase epsilon (DGKE) protein was evaluated with western blotting.

RESULTS

Whole-exome sequencing analysis with conventional variant filtering parameters did not reveal any obvious candidate mutation in the first family. The report of aHUS-associated mutations in DGKE, encoding DGKE, led to re-examination of the noncoding DGKE variants obtained from next-generation sequencing, allowing identification of a novel intronic DGKE mutation (c.888+40A>G) that segregated with disease. Sequencing of cDNA from affected individuals revealed aberrant forms of DGKE mRNA predicted to cause profound abnormalities in the protein catalytic site. By whole-genome sequencing, the same mutation was found in compound heterozygosity with a second nonsense DGKE mutation in all affected siblings of another unrelated family. Homozygous and compound heterozygous patients presented similar clinical features, including aHUS presentation in the first year of life, multiple relapsing episodes, and proteinuria, which are prototypical of DGKE-associated aHUS.

CONCLUSIONS

This is the first report of a mutation located beyond the exon-intron boundaries in aHUS. Intronic mutations such as these are underreported because conventional filtering parameters used to process next-generation sequencing data routinely exclude these regions from downstream analyses in both research and clinical settings. The results suggest that analysis of noncoding regions of aHUS-associated genes coupled with mRNA sequencing might provide a tool to explain genetically unsolved aHUS cases.

Complement regulators in human disease: lessons from modern genetics

First identified in human serum in the late 19th century as a 'complement' to antibodies in mediating bacterial lysis, the complement system emerged more than a billion years ago probably as the first humoral immune system. The contemporary complement system consists of nearly 60 proteins in three activation pathways (classical, alternative and lectin) and a terminal cytolytic pathway common to all. Modern molecular biology and genetics have not only led to further elucidation of the structure of complement system components, but have also revealed function-altering rare variants and common polymorphisms, particularly in regulators of the alternative pathway, that predispose to human disease by creating 'hyperinflammatory complement phenotypes'. To treat these 'complementopathies', a monoclonal antibody against the initiator of the membrane attack complex, C5, has received approval for use. Additional therapeutic reagents are on the horizon.

Thrombotic microangiopathy and indications for therapeutic plasma exchange

Thrombotic microangiopathy (TMA) is a clinicopathological condition associated with a wide variety of medical conditions. TMA is classically characterized by microangiopathic hemolytic anemia, thrombocytopenia, and microvascular thrombi that cause end-organ damage. The most prominent diagnoses associated with TMA are thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS). Although TTP and HUS can have similar clinical and laboratory features and are often lumped together as a combined entity referred to as “TTP/HUS,” the pathologic processes causing TMA and optimal therapies for these conditions are different. Empiric use of therapeutic plasma exchange (TPE) in the setting of TMA is common. The high risk of morbidity and mortality associated with some causes of TMA justify rapid institution of this relatively low-risk procedure. However, many causes of TMA do not respond to TPE and prolonged courses of exchange in the absence of an underlying diagnosis may cause a detrimental delay in appropriate medical therapy. The American Society of Apheresis has published guidelines for the use of TPE for several distinct conditions associated with TMA. This list is not comprehensive and the use of TPE for other causes of TMA may be considered if the mechanism of the underlying disease process provides a clear rationale for this intervention.

Management of hemolytic uremic syndrome

Hemolytic uremic syndrome (HUS) is a disease characterized by hemolysis, thrombocytopenia, and acute kidney injury, although other organs may be involved. Most cases are due to infection with Shiga toxin-producing Escherichia coli (STEC). Early identification and initiation of best supportive care, with microbiological input to identify the pathogen, result in a favorable outcome in most patients. The remaining 10% of HUS cases are classed together as atypical HUS and have a diverse etiology. The majority are due to inherited or acquired abnormalities that lead to a failure to control complement activation. Atypical HUS occurring in other situations (for example, related to pregnancy or kidney transplantation) may also involve excessive complement activation. Plasma therapies can reverse defective complement control, and it is now possible to specifically target complement activation. This has led to improved outcomes in patients with atypical forms of HUS. We will review our current understanding of the pathogenesis of HUS and how this has led to advances in patient care.

Atypical hemolytic uremic syndrome

Hemolytic uremic syndrome (HUS) is a triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure. The atypical form of HUS is a disease characterized by complement overactivation. Inherited defects in complement genes and acquired autoantibodies against complement regulatory proteins have been described. Incomplete penetrance of mutations in all predisposing genes is reported, suggesting that a precipitating event or trigger is required to unmask the complement regulatory deficiency. The underlying genetic defect predicts the prognosis both in native kidneys and after renal transplantation. The successful trials of the complement inhibitor eculizumab in the treatment of atypical HUS will revolutionize disease management.

Hemolytic uremic syndrome

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

Hemolytic uremic syndrome

The thrombotic microangiopathies include both hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP). Although debate exists as to whether these are separate entities or a spectrum of disease, both result in the clinical picture of thrombocytopenia, hemolytic anemia, and varying degrees of renal and neurologic involvement. Etiology of HUS includes diarrheal infection due to Shiga toxin-producing bacteria, complement deficiency, pneumococcal infection, and cobalamin deficiency. In disease ascribed to TTP, the main etiologic factor is deficiency of an enzyme known as a disintegrin-like and metalloprotease with thrombospondin type 1 repeats, number 13 (ADAMTS-13). The clinical manifestations may vary, but neurologic involvement can be significant, with reports of hypertensive encephalopathy, seizures, thrombosis and infarct. In nondiarrheal forms of disease, recurrence may occur and clinical diagnosis is essential in order to provide a targeted therapy for the suspected etiology. Therapies include supportive care, cobalamin supplementation, as well as plasma infusion and exchange. End stage renal disease may result and transplantation is curative for some forms of the disease. More recent research focuses on targeted immunotherapy to prevent autoantibody prevention. As of yet, there is no one cure for these potentially devastating diseases, and diagnosis and treatment selection presents a challenge to the clinician.

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.

Combination of everolimus with calcineurin inhibitor medication resulted in post-transplant haemolytic uraemic syndrome in lung transplant recipients--a case series

BACKGROUND

Post-transplant haemolytic uraemic syndrome (HUS) is a rare but serious disease with a high mortality rate, when left untreated. Immunosuppressive drugs like calcineurin inhibitors as well as mammalian target of rapamycin inhibitors have been reported as causative agents for post-transplant HUS.

METHODS

A retrospective observational study was performed in lung transplant recipients, who took part in an interventional study, in two centres. Haemoglobin, platelets, creatinine and lactate dehydrogenase levels were monitored during routine follow-up and patients with deteriorating kidney function were screened for post-transplant HUS. All cases of post-transplant HUS were identified by clinical and laboratory findings. Outcome was recorded until 6 months after diagnosis.

RESULTS

A total of 2188 visits in 512 lung transplant recipients (outpatients) were analysed. Out of those, 126 patients took part in an interventional study. In this study, 67 were switched to everolimus in combination with calcineurin inhibitors 4 weeks after transplantation, 59 patients remained on standard immunosuppression (calcineurin inhibitors, mycophenolate mofetil and prednisolone). Five cases of post-transplant HUS were identified in the everolimus group. None of the patients had evidence of gastrointestinal infection or preexisting renal disease. Post-transplant HUS was treated with therapeutic plasma exchange and methylprednisolone pulse therapy. Everolimus was discontinued in all five patients. This treatment regimen led to normalization of haemoglobin, platelets and improved renal function. Two patients developed end-stage renal failure and were maintained on haemodialysis. One patient died due to multiorgan failure. Improvement of renal function was seen in two patients. No further cases were recorded in patients without everolimus during the study period.

CONCLUSIONS

Our data should raise the awareness of post-transplant HUS in lung transplant recipients. Post-transplant HUS is a rare disease, but it is a serious cause of acute renal failure in lung transplant recipients treated with a combination of everolimus and calcineurin inhibitors.

Age-related macular degeneration: genetic and clinical findings

Age-related macular degeneration (AMD) is a sight threatening eye disease that affects millions of humans over the age of 65 years. It is considered to be the major cause of irreversible blindness in the elderly population in the developed world. The disease is prevalent in Europe and the United States, which has a large number of individuals of European descent. AMD is characterized by a progressive loss of central vision attributable to degenerative and neovascular changes that occur in the interface between the neural retina and the underlying choroid. This location contains the retinal photoreceptors, the retinal pigmented epithelium, a basement membrane complex known as Bruch's membrane and a network of choroidal capillaries. AMD is increasingly recognized as a complex genetic disorder where one or more genes contribute to an individual's susceptibility to development of the condition, while the prevailing view is that the disease stems from the interaction of multiple genetic and environmental factors. Although it has been proposed that a threshold event occurs during normal aging, the sequelae of biochemical, cellular, and molecular events leading to AMD are not fully understood. Here, we review the clinical aspects of AMD and summarize the genes which have been reported to have a positive association with the disease.

Atypical hemolytic uremic syndrome in the Tunisian population

BACKGROUND

Hemolytic uremic syndrome consists of a triad of acquired hemolytic anemia, thrombocytopenia and renal failure.

AIM

Our objectives were to determine epidemiology, clinical and laboratory characteristics of patients with atypical hemolytic uremic syndrome (aHUS) to determine the relationship between the complement protein deficit and aHUS in the Tunisian population.

METHODS

We studied retrospectively four cases of atypical HUS in adults admitted in the Nephrology Department of Fattouma Bourguiba Universitary Hospital in Monastir between 2000 and 2008.

RESULTS

Three patients had renal failure that required dialysis. One of them received kidney transplantation with no further recurrence of aHUS. Three patients had normal C3, C4, CFH, and FB levels, and in all patients anti-FH autoantibodies were absent. The kidney biopsy of one patient showed in addition to lupus glomerulonephritis histological findings consistent with TMA. A decrease in C3, C4 and CFH levels in this patient was found both before and after the cure.

CONCLUSION

Nephrologists should be aware of autoimmune conditions and genetic abnormalities of the complement regulatory genes as possible pathogenic mechanisms in atypical HUS patients.

Complement, age-related macular degeneration and a vision of the future

Age-related macular degeneration (AMD) is one of the most well-characterized late-onset, complex trait diseases. Remarkable advances in our understanding of the genetic and biological foundations of this disease were derived from a recent convergence of scientific and clinical data. Importantly, the more recent identification of AMD-associated variations in a number of complement pathway genes has provided strong support for earlier, paradigm-shifting studies that suggested that aberrant function of the complement system plays a key role in disease etiology. Collectively, this wealth of information has provided an impetus for the development of powerful tools to accurately diagnose disease risk and progression and complement-based therapeutics that will ultimately delay or prevent AMD. Indeed, we are poised to witness a new era of a personalized approach toward the assessment, management, and treatment of this debilitating, chronic disease.

Liver-kidney transplantation to cure atypical hemolytic uremic syndrome

Atypical hemolytic uremic syndrome is often associated with mutations in genes encoding complement regulatory proteins and secondary disorders of complement regulation. Progression to kidney failure and recurrence with graft loss after kidney transplantation are frequent. The most common mutation is in the gene encoding complement factor H. Combined liver-kidney transplantation may correct this complement abnormality and prevent recurrence when the defect involves genes encoding circulating proteins that are synthesized in the liver, such as factor H or I. Good outcomes have been reported when surgery is associated with intensified plasma therapy. A consensus conference to establish treatment guidelines for atypical hemolytic uremic syndrome was held in Bergamo in December 2007. The recommendations in this article are the result of combined clinical experience, shared research expertise, and a review of the literature and registry information. This statement defines groups in which isolated kidney transplantation is extremely unlikely to be successful and a combined liver-kidney transplant is recommended and also defines those for whom kidney transplant remains a viable option. Although combined liver-kidney or isolated liver transplantation is the preferred therapeutic option in many cases, the gravity of risk associated with the procedure has not been eliminated completely, and assessment of risk and benefit requires careful and individual attention.

Recent developments related to the laboratory diagnosis of primary immunodeficiency diseases

PURPOSE OF REVIEW

The rapid increases in newly recognized primary immunodeficiency diseases (PIDs), including their clinical, genetic and laboratory-associated abnormalities, make staying abreast of the latest developments a challenge. This review provides an overview of current information directly and indirectly related to the laboratory diagnosis of PIDs.

RECENT FINDINGS

The latest classification and several prevalence studies provide the framework for understanding the breadth, categories and incidence rates of over 120 recognized disease entities. The latter is followed by reviews of new information related to specific PIDs including new tests, new genetic associations and newly discovered laboratory-based abnormalities. The final section presents new PIDs and a discussion of the future potential of array-based technologies in the diagnosis of PIDs.

SUMMARY

The information provided in this review will allow a new appreciation of previously underestimated PIDs' prevalence rates and the delay in their diagnosis. Understanding the molecular causes of PIDs will lead to earlier diagnoses and new targets for improved therapeutic intervention. The presentation of new diagnostic tests should encourage other laboratories to assess their potential in their own laboratories. Ultimately, this information will lead to an increase in the understanding of novel laboratory parameters associated with specific PID and should improve the time required to attain an accurate diagnosis.

CD46-induced immunomodulatory CD4+ T cells express the adhesion molecule and chemokine receptor pattern of intestinal T cells

Tissue homing of activated T cells is typically mediated through their specific integrin and chemokine receptor repertoire. Activation of human primary CD4(+) T cells in the presence of CD46 cross-linking induces the development of a distinct immunomodulatory T cell population characterized by high IL-10/granzyme B production. How these regulatory T cells (Tregs) migrate/home to specific tissue sites is not understood. In this study, we determined the adhesion protein and chemokine receptor expression pattern on human CD3/CD46-activated peripheral blood CD4(+) T cells. CD3/CD46-activated, but not CD3/CD28-activated, T cells up-regulate the integrin alpha(4)beta(7). The interaction of alpha(4)beta(7) with its ligand mucosal addressin cell adhesion molecule 1 (MAdCAM-1) mediates homing or retention of T cells to the intestine. CD3/CD46-activated Tregs adhere to/roll on MAdCAM-1-expressing HeLa cells, similar to T cells isolated from the human lamina propria (LP). This interaction is inhibited by silencing MAdCAM-1 expression in HeLa cells or by the addition of blocking Abs to beta(7). CD46 activation of T cells also induced the expression of the surface-bound cytokine LIGHT and the chemokine receptor CCR9, both marker constitutively expressed by gut LP-resident T cells. In addition, we found that approximately 10% of the CD4(+) T lymphocytes isolated from the LP of patients undergoing bariatric surgery contain T cells that spontaneously secrete a cytokine pattern consistent with that from CD46-activated T cells. These data suggest that CD46-induced Tregs might play a role in intestinal immune homeostasis where they could dampen unwanted effector T cell responses through local IL-10/granzyme B production.

Recurrent atypical hemolytic uremic syndrome associated with factor I mutation in a living related renal transplant recipient

Atypical hemolytic uremic syndrome, or the nondiarrheal form of hemolytic uremic syndrome, is a rare disorder typically classified as familial or sporadic. Recent literature has suggested that approximately 50% of patients have mutations in factor H (CFH), factor I (CFI), or membrane cofactor protein (encoded by CD46). Importantly, results of renal transplantation in patients with mutations in either CFH or CFI are dismal, with recurrent disease leading to graft loss in the majority of cases. We describe an adult renal transplant recipient who developed recurrent hemolytic uremic syndrome 1 month after transplantation. Bidirectional sequencing of CFH, CFI, and CD46 confirmed that the patient was heterozygous for a novel missense mutation, a substitution of a serine reside for a tyrosine residue at amino acid 369, in CFI. This report reemphasizes the importance of screening patients with atypical hemolytic uremic syndrome for mutations in these genes before renal transplantation and shows the challenges in the management of these patients.

[Haemolytic uremic syndrome and thrombotic thrombocytopenic purpura: classification based on molecular etiology and review of recent developments in diagnostics]

Haemolytic uremic syndrome and thrombotic thrombocytopenic purpura are overlapping clinical entities based on historical classification. Recent developments in the unfolding of the pathomechanisms of these diseases resulted in the creation of a molecular etiology-based classification. Understanding of some causative relationships yielded detailed diagnostic approaches, novel therapeutic options and thorough prognostic assortment of the patients. Although haemolytic uremic syndrome and thrombotic thrombocytopenic purpura are rare diseases with poor prognosis, the precise molecular etiology-based diagnosis might properly direct the therapy of the affected patients. The current review focuses on the theoretical background and detailed description of the available diagnostic possibilities, and some practical information necessary for the interpretation of their results.

What's new in haemolytic uraemic syndrome?

Recent advances in understanding the aetiology of the disorders that make up the haemolytic uraemic syndrome (HUS) permit a revised classification of the syndrome. With appropriate laboratory support, an aetiologically-based subgroup diagnosis can be made in all but a few cases. HUS caused by enterohaemorrhagic Escherichia coli remains by far the most prevalent subgroup, and new insights into this zoonosis are discussed. The most rapidly expanding area of interest is the subgroup of inherited and acquired abnormalities of complement regulation. Details of the pathogenesis are incomplete but it is reasonable to conclude that local activation of the alternative pathway of complement in the glomerulus is a central event. There is no evidence-based treatment for this diagnostic subgroup. However, in circumstances where there is a mutated plasma factor such as complement factor H, strategies to replace the abnormal protein by plasmapheresis or more radically by liver transplantation are logical, and anecdotal successes are reported. In summary, the clinical presentation of HUS gives a strong indication as to the underlying cause. Patients without evidence of EHEC infection should be fully investigated to determine the aetiology. Where complement abnormalities are suspected there is a strong argument for empirical and early plasma exchange, although rapid advances in this field may provide more specific treatments in the near future.

Complement regulatory genes and hemolytic uremic syndromes

Hemolytic uremic syndrome is a triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure. It is one of a group of conditions termed the thrombotic microangiopathies, which are characterized by prominent endothelial cell injury. It may be diarrheal-associated or atypical (aHUS). Evidence for a pathogenic role of the alternative pathway of complement was first suggested in 1974. Mutations in the complement regulatory proteins factor H, membrane cofactor protein (CD46), and factor I predispose to aHUS development. Mutations of the activating components factor B and complement C3 have also been reported. Penetrance is approximately 50%, suggesting other genetic and environmental modifiers are needed for disease expression. Identification of mutations is important owing to differences in mortality, renal survival, and outcome of renal transplantation. Current treatment is plasma infusion/exchange, but complement inhibitor therapy provides hope for the future.

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.

Complement and the atypical hemolytic uremic syndrome in children

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

Characterization of mutations in complement factor I (CFI) associated with hemolytic uremic syndrome

Recent studies have identified mutations in the complement regulatory gene factor I (CFI) that predispose to atypical hemolytic uremic syndrome (aHUS). CFI is a two-chain serine protease in which the light chain carries the catalytic domain while the heavy chain's function is unclear. It downregulates the alternative and classical complement pathways by cleaving the alpha' chains of C3b and C4b in the presence of cofactor proteins (known as cofactor activity). Many CFI mutations in aHUS result in low CFI levels with a consequent quantitative defect in complement regulation. In others, the mutant protein is present in normal amounts but the presumed functional deficiency has not yet been defined. In this report we examine the nature of the functional defect in aHUS-associated CFI mutations. The I322T, D501N and D506V mutations reside in the serine protease domain of CFI and result in secreted proteins that lack C3b and C4b cofactor activity. The delTTCAC (1446-1450) mutant leads to a protein that is not secreted. The R299W mutant lies in a region of the CFI heavy chain of no known function. Our assessments demonstrate decreased C3b and C4b cofactor activity, providing evidence that this region is important for cofactor activity. In two other heavy chain mutants and one probable polymorphic variant, no functional deficiency was identified. These defective mutant proteins will result in an inability to appropriately control the complement cascade at sites of endothelial cell injury. The excessive complement activation for a given degree of damage may result in generation of a procoagulant state and aHUS.

Inherited complement regulatory protein deficiency predisposes to human disease in acute injury and chronic inflammatory statesthe examples of vascular damage in atypical hemolytic uremic syndrome and debris accumulation in age-related macular degeneration

In this chapter, we examine the role of complement regulatory activity in atypical hemolytic uremic syndrome (aHUS) and age-related macular degeneration (AMD). These diseases are representative of two distinct types of complement-mediated injury, one being acute and self-limited, the other reflecting accumulation of chronic damage. Neither condition was previously thought to have a pathologic relationship to the immune system. However, alterations in complement regulatory protein genes have now been identified as major predisposing factors for the development of both diseases. In aHUS, heterozygous mutations leading to haploinsufficiency and function-altering polymorphisms in complement regulators have been identified, while in AMD, polymorphic haplotypes in complement genes are associated with development of disease. The basic premise is that a loss of function in a plasma or membrane inhibitor of the alternative complement pathway allows for excessive activation of complement on the endothelium of the kidney in aHUS and on retinal debris in AMD. These associations have much to teach us about the host's innate immune response to acute injury and to chronic debris deposition. We all experience cellular injury and, if we live long enough, will deposit debris in blood vessel walls (atherosclerosis leading to heart attacks and strokes), the brain (amyloid proteins leading to Alzheimer's disease), and retina (lipofuscin pigments leading to AMD). These are three common causes of morbidity and mortality in the developed world. The clinical, genetic, and immunopathologic understandings derived from the two examples of aHUS and AMD may illustrate what to anticipate in related conditions. They highlight how a powerful recognition and effector system, the alternative complement pathway, reacts to altered self. A response to acute injury or chronic debris accumulation must be appropriately balanced. In either case, too much activation or too little regulation promotes undesirable tissue damage and human disease.