Atypical Hemolytic Uremic Syndrome (aHUS) and Adenosine Deaminase (ADA)-Deficient Severe Combined Immunodeficiency (SCID)-Two Diseases That Exacerbate Each Other: Case Report.

Hemolytic uremic syndrome (HUS) is defined by the triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury (AKI). Atypical HUS (aHUS), distinguished by its etiology, is caused by uncontrolled overactivation of the alternative complement pathway. The correct diagnosis of aHUS is complex and involves various gene mutations. Severe combined immunodeficiency (SCID), characterized by severe T-cell lymphocytopenia and a lack of antigen-specific T-cell and B-cell immune responses, is of seldom occurrence. In 10-15% of pediatric patients, SCID is caused by adenosine deaminase (ADA) deficiency. The authors describe the case of a boy who suffered from both aHUS and ADA-deficient SCID. At the age of 9 months, the patient presented acute kidney injury with anuria and coagulopathy. The diagnosis of aHUS was established on the basis of alternative complement pathway deregulation and disease-associated gene mutations. Further examination revealed immune system failure and, at the age of 13 months, the ADA deficiency was confirmed by genetic tests and the boy was diagnosed with ADA-SCID. ADA SCID has recently been described as a possible triggering factor of aHUS development and progression. However, more research is required in this field. Nevertheless, it is crucial in clinical practice to be aware of these two co-existing life-threatening diseases.

Thrombotic microangiopathy during pregnancy.

Pregnancy is a high-risk time for the development of different kinds of thrombotic microangiopathy (TMA). Three major syndromes including TTP (thrombotic thrombocytopenic purpura), PE/HELLP (preeclampsia/hemolysis, elevated liver function tests, low platelets), and aHUS (atypical hemolytic- uremic syndrome) should be sought in pregnancy-TMA. These severe disorders share multiple clinical features and overlaps and even the coexistence of more than one pathologic mechanism. Each of these disorders finally ends in endothelial damage and fibrin thrombi formation within the microcirculation that fragments RBCs (schystocytes), aggregates platelets, and creates ischemic injury in the targeted organs i.e.; kidney and brain. Although the mechanisms of these severe disorders have been revealed, pregnancy-related TMA still interfaces with diagnostic and therapeutic challenges. Here, we highlight the current knowledge of diagnosis and management of these complications during pregnancy.

Improved Renal Recovery with Eculizumab Therapy among Children with High Prevalence of Mutation-Associated Atypical Hemolytic Uremic Syndrome: A Retrospective Cohort Study.

INTRODUCTION: Genetic defects that determine uncontrolled activation of the alternative complement pathway have been well documented, which account for approximately 40-60% of atypical hemolytic uremic syndrome (aHUS) cases worldwide. In Saudi Arabia, nearly half of the marriages are consanguineous, resulting in a high prevalence of such genetic diseases. Recent studies have demonstrated the effectiveness of eculizumab against aHUS. OBJECTIVE: We report our experience of using plasma therapy or/and eculizumab to treat children with aHUS in a tertiary care center in Saudi Arabia and to compare their clinical characteristics, genetic mutations, and treatment outcomes. METHODS: A retrospective cohort study was conducted between January 2010 and May 2017. Data, including demographic parameters, clinical presentation, hospital stay duration, need for dialysis, renal recovery, genetic mutations, and outcomes, were obtained from electronic medical records of all eligible patients. RESULTS: Overall, 21 children with aHUS were included, of which 12 (57.1%) received eculizumab therapy and 9 (42.9%) received only plasma therapy. End-stage renal disease occurred in 7 children (33.3%), of which 4 (57.1%) received only plasma therapy and 3 (42.9%) received eculizumab therapy whose genetic mutations were not related to the complement dysregulation system. No child who received eculizumab therapy showed recurrence; however, 3 children (33.3%) who received plasma therapy alone showed recurrence. Genetic mutations were detected in 12/20 (60%) of those who underwent genetic screening. CONCLUSIONS: Children who received eculizumab therapy showed good renal recovery and maintained remission compared with children who received plasma therapy alone. Genetic mutations were detected in 60% of the patients, which was associated with a high prevalence of consanguineous marriages.

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

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

Ockham's razor defeated: about two atypical cases of hemolytic uremic syndrome.

BACKGROUND: Medical investigation is a favorite application of Ockham's razor, in virtue of which when presented with competing hypotheses, the solution with the fewest assumptions should be privileged. Hemolytic uremic syndrome (HUS) encompasses diseases with distinct pathological mechanisms, such as HUS due to shiga-like toxin-producing bacteria (STEC-HUS) and atypical HUS, linked to defects in the alternate complement pathway. Other etiologies such as Parvovirus B19 infection are exceptional. All these causes are rare to such extent that we usually consider them mutually exclusive. We report here two cases of HUS that could be traced to multiple causes. CASES PRESENTATION: Case 1 presented as vomiting and diarrhea. All biological characteristics of HUS were present. STEC was found in stool (by PCR and culture). After initial remission, a recurrence occurred and patient was started on Eculizumab. Genetic analysis revealed the heterozygous presence of a CFHR1/CFH hybrid gene. The issue was favorable under treatment. In case 2, HUS presented as fever, vomiting and purpura of the lower limbs. Skin lesions and erythroblastopenia led to suspect Parvovirus B19 primo-infection, which was confirmed by peripheral blood and medullar PCR. Concurrently, stool culture and PCR revealed the presence of STEC. Evolution showed spontaneous recovery. CONCLUSIONS: Both cases defy Ockham's razor in the sense that multiple causes could be traced to a single outcome; furthermore, they invite us to reflect on the physiopathology of HUS as they question the classical distinction between STEC-HUS and atypical HUS. We propose a two-hit mechanism model leading to HUS. Indeed, in case 1, HUS unfolded as a result of the synergistic interaction between an infectious trigger and a genetic predisposition. In case 2 however, it is the simultaneous occurrence of two infectious triggers that led to HUS. In dissent from Ockham's razor, an exceptional disease such as HUS may stem from the sequential occurrence or co-occurrence of several rare conditions.

Genetic and Protein Structural Evaluation of Atypical Hemolytic Uremic Syndrome and C3 Glomerulopathy.

Atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy (C3G) are associated with loss of regulation of the alternative pathway of complement and its resulting overactivation. As rare diseases, genetic variants leading to aHUS and C3G were previously analysed in relatively low patient numbers. To improve this analysis, data were pooled from six centres. Totals of 610 rare variants for aHUS and 82 for C3G were presented in an interactive database for 13 genes. Using allele frequency comparisons with the Exome Aggregation Consortium as a reference genome, the patients with aHUS showed significantly more protein-altering ultrarare variants (allele frequency <0.01%) in five genes CFH, CFI, CD46, C3, and DGKE. In patients with C3G, the corresponding association was only found for C3 and CFH. Protein structure analyses of these five proteins showed distinct differences in the positioning of these variants in C3 and FH. For aHUS, variants were clustered at the C-terminus of FH and implicated changes in the binding of FH to host cell surfaces. For C3G, variants were clustered at the N-terminal C3b binding site of FH and implicated changes in the fluid-phase regulation of C3b. We discuss the utility of the Web database as a patient resource for clinicians.

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.

Baseline characteristics of patients with atypical haemolytic uraemic syndrome (aHUS): The Australian cohort in a global aHUS registry.

AIMS: To describe the baseline characteristics and treatment of Australian patients diagnosed with atypical haemolytic uraemic syndrome (aHUS) reported to the Global aHUS Registry. METHODS: Descriptive analysis of the Australian cohort with aHUS (n = 106) was undertaken for demographics, disease characteristics and prior treatment with eculizumab; comparing with the global cohort (n = 1688) for certain pre-specified disease characteristics. RESULTS: In Australia, almost two-thirds of patients diagnosed with aHUS were female and over 80% of patients were Caucasians, with similar proportions reported in the global cohort. Less than 6% of patients in the Australia and global cohorts were reported to have a history of autoimmune disease (4% vs 2%, respectively; P = .21) or cancer (5% vs 5%, respectively; P = .93), conditions that have been associated with secondary HUS. In the Australian cohort, 26% had received a kidney transplant and 68% of patients had received eculizumab. Kidneys were the most common organ involvement, followed by gastrointestinal tract (26%) and cardiovascular system (19%), with 35% of patients reported to have had at least two organs involved within 6 months prior to baseline visit or entry into the registry. Complement factor H was the most common pathogenic complement gene variant in the Australian patients. CONCLUSION: Data from the aHUS registry confirms and defines region-specific disease characteristics among a selected group of Australian children and adults with aHUS reported to the registry. Ongoing and more inclusive data will provide further information about temporal trends and treatment outcomes, representing a unique opportunity for clinicians and researchers to further develop knowledge surrounding this rare disease.

Renal Biopsy Prognostic Findings in Children With Atypical Hemolytic Uremic Syndrome.

BACKGROUND: The aim of this study was to investigate the histopathological findings in kidney biopsies in children with atypical hemolytic uremic syndrome (aHUS) and to determine whether specific pathological findings in aHUS have a prognostic value. METHODS: Renal biopsy specimens of 29 patients who were recorded in the national Turkish aHUS registry database were available for review. Histopathological findings were compared with the clinical and laboratory features at the presentation and the final outcome. RESULTS: The mean age at presentation and follow-up period was 4.9 ± 3.9 and 3.9 ± 3.0 years, respectively. The median time interval from the first symptom to biopsy was 10 days. Vascular thrombosis and interstitial fibrosis were significantly related to chronic kidney disease (CKD) requiring dialysis or kidney transplantation during follow-up (5.6-fold, for both). Glomerular necrosis, cortical necrosis, and glomerular sclerosis were markedly associated with CKD without dialysis (6.2-fold, 13.3-fold, and 8.8-fold, respectively). However, presence of endothelial swelling, subendothelial widening, and fragmented erythrocytes was found to be correlated with a favorable final outcome. CONCLUSIONS: Presence of vascular thrombosis, cortical necrosis, and glomerular sclerosis in histopathological evaluation correlated with developing CKD. Chronic changes in the interstitial compartment were also related to poor prognosis, a finding that has been shown for the first time in pediatric aHUS cases.

Isolated thrombotic microangiopathy of the small intestine in a patient with atypical hemolytic uremic syndrome - a case report.

BACKGROUND: Atypical hemolytic uremic syndrome (aHUS) is a rare disease characterized by systemic thrombotic microangiopathy (TMA) reflected by hemolysis, anemia, thrombocytopenia and systemic organ injury. The optimal management of aHUS-patients when undergoing kidney transplantation to prevent recurrence in the allograft is eculizumab, an approved recombinant antibody targeting human complement component C5. CASE PRESENTATION: A 39 year-old woman presented with severe abdominal pain, diarrhea and emesis for 3 days. In her past medical history she had experienced an episode of aHUS leading to end stage renal disease (ESRD) in 2007 and a genetic workup revealed a heterozygous mutation in the membrane cofactor protein gene. In 2014 she underwent cadaveric kidney transplantation. Four years later she had to go back on hemodialysis due to allograft failure following a severe systemic cytomegalovirus infection resulting in transplant failure. At presentation she still received calcineurin-inhibitor therapy and reported subfebrile temperatures and pain projecting over the transplant prior to the current symptoms. A contrast enhanced CT-scan of the abdomen revealed inflammatory wall thickening of the small intestine. Diagnostic endoscopy discovered fresh blood in the small intestine without a clear source of bleeding. Histopathology of the small intestine biopsies showed severe thrombotic microangiopathy. Of note, the patient persistently had no signs of systemic hemolysis. Since the TMA of the small intestine was most likely due to aHUS, eculizumab treatment was initiated which abolished the symptoms. CONCLUSION: Here we report a patient with thrombotic microangiopathy with predominant manifestation in a single organ, the small intestine, due to aHUS with absence of systemic signs and symptoms. aHUS patients usually require a secondary trigger for the disease to manifest. In this case, the trigger may be attributed to the dysfunctional renal transplant, which was subsequently explanted. Histology of the explanted kidney showed severe inflammation due to purulent nephritis and signs of cellular rejection. After nephrectomy, we continued eculizumab therapy until the patient completely recovered. No signs of TMA recurred after discontinuation of eculizumab, further supporting the concept of the renal transplant as the main trigger of TMA of the small intestine in our patient.

Cocaine-associated atypical haemolytic uraemic syndrome in a genetically susceptible individual.

Atypical haemolytic uraemic syndrome (aHUS) is a severe, life-threatening condition that requires early recognition and urgent treatment. In aHUS rare genetic variants in CFH, CFI, CD46, C3 and CFB predispose to complement over activation. This case describes a case of aHUS in which there was a strong temporal association between disease onset and the use of smoked cocaine. The patient was found to have a rare genetic variant in the CFI gene which may have been unmasked by first-time exposure to cocaine. The patient stabilized and improved with early administration of eculizumab, supporting the notion of an underlying immunological pathogenesis and the importance of early intervention.

Complement and Coagulation: Cross Talk Through Time.

Two complex protein defense systems-complement and coagulation-are based on amplifying enzyme cascades triggered by specific local stimuli. Excess systemic activation of either system is pathologic and is normally prevented by a family of regulatory proteins. The 2 systems are ancient biological processes which share a common origin that predates vertebrate evolution. Recent research has uncovered multiple opportunities for cross talk between complement and coagulation including proteins traditionally viewed as coagulation factors that activate and regulate complement, and proteins traditionally seen as part of the complement system that participate in coagulation. Ten examples of cross talk between the 2 systems are described. The mutual engagement of both systems is increasingly recognized to occur in human diseases. Three conditions-paroxysmal nocturnal hemoglobinuria, atypical hemolytic uremic syndrome, and the antiphospholipid syndrome-provide examples of the importance of interactions between complement and coagulation in human biology. A better understanding of the mutual engagement of these 2 ancient defense systems is expected to result in improved diagnostics and new treatments for systemic diseases.

Atypical Hemolytic Uremic Syndrome Presenting as Acute Heart Failure-A Rare Presentation: Diagnosis Supported by Skin Biopsy.

Atypical hemolytic uremic syndrome (aHUS) is a rare disorder of uncontrolled complement activation that manifests classically as anemia, thrombocytopenia, and renal failure, although extrarenal manifestations are observed in 20% of the patient most of which involving central nervous system, with relatively rare involvement of the heart. In this article, we report the case of a 24-year-old male with no history of heart disease presenting with acute systolic heart failure along with microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. Given his presentation of thrombotic microangiopathy (TMA), along with laboratory results significant for low haptoglobin, platelets, hemoglobin, C3, C4, CH50, and normal ADAMTS13 levels, with no diarrhea and negative STEC polymerase chain reaction in stool, aHUS diagnosis was established with strong clinical suspicion, and immediate initiation of treatment was advised. Kidney biopsy to confirm diagnosis of aHUS was inadvisable because of thrombocytopenia, so the skin biopsy of a rash on his arm was done, which came to be consistent with thrombotic microangiopathy. Our case highlights a relatively rare association between aHUS and cardiac involvement, and the use of skin biopsy to support diagnosis of aHUS in patients who cannot undergo renal biopsy because of thrombocytopenia.

Atypical Hemolytic-Uremic Syndrome: An Update on Pathophysiology, Diagnosis, and Treatment.

Atypical hemolytic uremic syndrome (aHUS), a rare variant of thrombotic microangiopathy, is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and renal impairment. The condition is associated with poor clinical outcomes with high morbidity and mortality. Atypical HUS predominantly affects the kidneys but has the potential to cause multi-organ system dysfunction. This uncommon disorder is caused by a genetic abnormality in the complement alternative pathway resulting in over-activation of the complement system and formation of microvascular thrombi. Abnormalities of the complement pathway may be in the form of mutations in key complement genes or autoantibodies against specific complement factors. We discuss the pathophysiology, clinical manifestations, diagnosis, complications, and management of aHUS. We also review the efficacy and safety of the novel therapeutic agent, eculizumab, in aHUS, pregnancy-associated aHUS, and aHUS in renal transplant patients.

Genotype-phenotype correlations of low-frequency variants in the complement system in renal disease and age-related macular degeneration.

Genetic alterations in the complement system have been linked to a variety of diseases, including atypical hemolytic uremic syndrome (aHUS), C3 glomerulopathy (C3G), and age-related macular degeneration (AMD). We performed sequence analysis of the complement genes complement factor H (CFH), complement factor I (CFI), and complement C3 (C3) in 866 aHUS/C3G and 697 AMD patients. In total, we identified 505 low-frequency alleles, representing 121 unique variants, of which 51 are novel. CFH contained the largest number of unique low-frequency variants (n = 64; 53%), followed by C3 (n = 32; 26%) and CFI (n = 25; 21%). A substantial number of variants were found in both patients groups (n = 48; 40%), while 41 (34%) variants were found only in aHUS/C3G and 32 (26%) variants were AMD specific. Genotype-phenotype correlations between the disease groups identified a higher frequency of protein altering alleles in short consensus repeat 20 (SCR20) of factor H (FH), and in the serine protease domain of factor I (FI) in aHUS/C3G patients. In AMD, a higher frequency of protein-altering alleles was observed in SCR3, SCR5, and SCR7 of FH, the SRCR domain of FI, and in the MG3 domain of C3. In conclusion, we observed a substantial overlap of variants between aHUS/C3G and AMD; however, there is a distinct clustering of variants within specific domains.

Thrombomodulin and Endothelial Dysfunction: A Disease-Modifier Shared between Malignant Hypertension and Atypical Hemolytic Uremic Syndrome.

Thrombomodulin (TM) is an endothelial glycoprotein that is present in all blood vessels. Five percent of all patients with atypical hemolytic uremic syndrome (aHUS) have mutations in the gene coding for TM, with a peak presentation in young children. Mutations often translate into quantitative and qualitative abnormalities of this endothelial glycoprotein. Outcome of the TM-associated aHUS is relatively poor with frequent relapses after transplantation despite its membrane-bound character. We observed a woman presenting with malignant hypertension (MHT) and associated kidney, brain, cardiac, and hematological involvement with thrombotic microangiopathy on kidney biopsy. She had a documented mutation of the gene coding for TM, which was associated with both aHUS and an increased risk for venous and arterial thrombosis. As TM has anti-coagulant, anti-inflammatory, and cytoprotective properties and also attenuates alternative complement activation, this glycoprotein could play an active role in other diseases with endothelial involvement apart from aHUS. We discuss the potential role of TM in the pathophysiology of various endotheliopathies including MHT. We also provide a framework for future therapeutic options.

Complement activation in atypical hemolytic uremic syndrome and scleroderma renal crisis: a critical analysis of pathophysiology.

Scleroderma is an autoimmune disease that affects multiple systems. While pathophysiologic mechanisms governing the development of scleroderma are relatively poorly understood, advances in our understanding of the complement system are clarifying the role of complement pathways in the development of atypical hemolytic uremic syndrome and scleroderma renal crisis. The abundant similarities in their presentation as well as the clinical course are raising the possibility of a common underlying pathogenesis. Recent reports are emphasizing that complement pathways appear to be the unifying link. This article reviews the role of complement system in the development of atypical hemolytic uremic syndrome and scleroderma renal crisis, and calls for heightened awareness to the development of thrombotic angiopathy in patients with scleroderma.

Complement activation in atypical hemolytic uremic syndrome and scleroderma renal crisis: a critical analysis of pathophysiology / Ativação de complemento em síndrome urêmica hemolítica atípica e crise renal por esclerodermia: uma análise crítica da fisiopatologia

ABSTRACT Scleroderma is an autoimmune disease that affects multiple systems. While pathophysiologic mechanisms governing the development of scleroderma are relatively poorly understood, advances in our understanding of the complement system are clarifying the role of complement pathways in the development of atypical hemolytic uremic syndrome and scleroderma renal crisis. The abundant similarities in their presentation as well as the clinical course are raising the possibility of a common underlying pathogenesis. Recent reports are emphasizing that complement pathways appear to be the unifying link. This article reviews the role of complement system in the development of atypical hemolytic uremic syndrome and scleroderma renal crisis, and calls for heightened awareness to the development of thrombotic angiopathy in patients with scleroderma.

RESUMO A esclerodermia é uma doença autoimune que afeta múltiplos sistemas. Embora os mecanismos fisiopatológicos que regem o desenvolvimento da esclerodermia sejam relativamente pouco compreendidos, os avanços em nossa compreensão do sistema do complemento estão esclarecendo o papel das vias do complemento no desenvolvimento da síndrome urêmica hemolítica atípica e da crise renal da esclerodermia. As abundantes semelhanças em sua apresentação, bem como o curso clínico, estão aumentando a possibilidade de uma patogênese subjacente comum. Relatórios recentes estão enfatizando que as vias de complemento parecem ser o link unificador. Este artigo analisa o papel do sistema do complemento no desenvolvimento da síndrome urêmica hemolítica atípica e da crise renal na esclerodermia, e exige maior conscientização para com o desenvolvimento da angiopatia trombótica em pacientes com esclerodermia.

Treatment and management of children with haemolytic uraemic syndrome.

Haemolytic uraemic syndrome (HUS), comprising microangiopathic haemolytic anaemia, thrombocytopaenia and acute kidney injury, remains the leading cause of paediatric intrinsic acute kidney injury, with peak incidence in children aged under 5 years. HUS most commonly occurs following infection with Shiga toxin-producing Escherichia coli (STEC-HUS). Additionally, HUS can occur as a result of inherited or acquired dysregulation of the alternative complement cascade (atypical HUS or aHUS) and in the setting of invasive pneumococcal infection. The field of HUS has been transformed by the discovery of the central role of complement in aHUS and the dawn of therapeutic complement inhibition. Herein, we address these three major forms of HUS in children, review the latest evidence for their treatment and discuss the management of STEC infection from presentation with bloody diarrhoea, through to development of fulminant HUS.