Pathogenesis of Atypical Hemolytic Uremic Syndrome

Atypical Hemolytic Uremic Syndrome: A Review of Complement Dysregulation, Genetic Susceptibility and Multiorgan Involvement

Atypical hemolytic uremic syndrome (aHUS) is a rare, life-threatening thrombotic microangiopathy (TMA) characterized by complement dysregulation, leading to microvascular thrombosis and multi-organ injury. TMAs are defined by thrombocytopenia, microangiopathic hemolytic anemia and organ dysfunction caused by small-vessel thrombosis. Unlike thrombotic thrombocytopenic purpura, which results from severe ADAMTS13 deficiency, aHUS is driven by uncontrolled activation of the alternative complement pathway. While the kidneys are most frequently affected, other vital organs can also be involved. Genetic susceptibility contributes significantly to disease risk, but a trigger such as infection, pregnancy or autoimmune disease is usually required. Diagnosis is challenging due to overlapping features with other TMAs and relies on exclusion and complement testing. C5 inhibitors, such as eculizumab and ravulizumab, have revolutionized treatment but necessitate prophylactic vaccination and ongoing clinical surveillance. While these therapies provide effective disease control, discontinuing treatment remains complex, especially in patients with complement gene mutations. New therapies targeting various points in the complement cascade are under investigation and may offer safer, more cost-effective options. Progress in genetic profiling and biomarker discovery is essential for earlier diagnosis, individualized therapy and relapse prevention. This review highlights recent advances in the understanding of aHUS pathophysiology, clinical features and evolving therapeutic strategies aimed at improving patient outcomes.

Atypical presentation of H1N1-induced thrombotic microangiopathy with CD46 gene mutation

INTRODUCTION

Thrombotic microangiopathy (TMA) is a pathological description which clinically presents with thrombocytopenia, microangiopathic hemolytic anemia (MAHA), and organ dysfunction. The etiology of TMA is broadly classified into four categories: primary hereditary, primary acquired, secondary, and infection associated. H1N1 influenza is a rare etiology of complement-mediated TMA (CM-TMA) with there being under 30 cases reported to date, and its odd presentation with hemoptysis making it a challenge to diagnose.

CASE PRESENTATION

We present a case of a Caucasian female in her 20s presenting to the hospital with a viral prodrome in setting of a new acute kidney injury (creatinine 8.2 mg/dL), thrombocytopenia (platelet count 14,000/mm3), and H1N1 influenza positive. She developed hemoptysis the next day, with no respiratory distress. Rheumatology work-up for antineutrophilic cytoplasmic antibodies (ANCA), anti-glomerular basement membrane (anti-GBM), and antiphospholipid syndrome (APS) antibodies was negative. CT chest was also negative for pulmonary hemorrhage. Plasma exchange was started empirically until ADAMTS13 activity returned normal (120%), and she was further commenced on eculizumab after an atypical hemolytic uremic syndrome (aHUS)/TMA/Complement 3 Glomerulopathy (C3G) gene panel was sent. Molecular studies revealed a splice site variant of MCP/CD46 gene, which was reiterated on a renal biopsy. The patient was counselled on the genetic results, including predisposition to future events and the importance of long-term eculizumab treatment.

DISCUSSION

CM-TMA is a consequence of alternative pathway dysregulation, commonly associated with genetic mutations which could phenotypically be unmasked by infections, such as influenza virus.

CONCLUSION

Our case highlights the importance of keeping a broad differential beyond classic pulmonary-renal syndromes in patients presenting with hemoptysis and TMA, while understanding the pathophysiology of infections unmasking genetic mutations in CM-TMA.
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A Case of Atypical Hemolytic Uremic Syndrome With a Complement Factor I Mutation Triggered by a Femoral Neck Fracture

Atypical hemolytic uremic syndrome is a thrombotic microangiopathy caused by the abnormal activation of the alternative complement pathway. Mutations in complement-related genes and autoantibodies against complement regulators are involved in the pathogenesis of this condition; the frequency of, and prognosis of patients harbouring, each genetic mutation varies based on the region and race. Complement factor I (CFI) mutations have been observed in 4%-8% of cases in Europe; however, they have not yet been reported in Japan. We present the first Japanese case of atypical hemolytic uremic syndrome in a patient harbouring a CFI mutation. An 83-year-old female patient presented with severe acute kidney injury, thrombocytopenia, and hemolytic anaemia following a femoral neck fracture. Plasma exchange and haemodialysis were initiated, resulting in improved kidney function and platelet count. However, the platelet count decreased when plasma exchange was discontinued. Therefore, we administered ravulizumab, an anti-complement 5 monoclonal antibody, which led to the maintenance of stable kidney function and platelet count. Genetic analysis revealed a CFI mutation, and the patient was treated with ravulizumab for 2 years without relapse. Individuals diagnosed with atypical hemolytic uremic syndrome harbouring CFI mutations experience poor outcomes, including low rates of remission, high rates of mortality, and progression to end-stage kidney disease. Our case serves as a crucial example demonstrating how prompt identification and appropriate management can lead to better patient outcomes.

The Path to Accessible Care: Development and Impact of Eculizumab Biosimilars for Paroxysmal Nocturnal Hemoglobinuria and Atypical Hemolytic Uremic Syndrome

Eculizumab, a humanized monoclonal antibody targeting complement C5, is the first approved drug for complement-mediated diseases and indicated to treat paroxysmal nocturnal hemoglobinuria, atypical hemolytic uremic syndrome, myasthenia gravis, and neuromyelitis optica spectrum disorder. The introduction of eculizumab has improved the prognosis of paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome to near-normal life expectancy and quality of life. Administration of eculizumab resulted in a rapid and sustained reduction in hemolytic activity and a consequent risk of thrombosis in paroxysmal nocturnal hemoglobinuria, and thrombotic microangiopathy in atypical hemolytic uremic syndrome, respectively. Nevertheless, many patients still have difficulty accessing eculizumab treatment because of its high costs. Biosimilars to reference eculizumab may increase patient access to treatment by creating market competition and eventually decreasing treatment costs. Clinical use of biosimilars in Europe in the last 15 years has demonstrated that they are as safe and effective as their reference products, and can also drive cost reductions and increase patients' access to treatment. This review aims to increase awareness about the importance of biosimilars of reference eculizumab and their entry for use in patients with paroxysmal nocturnal hemoglobinuria or atypical hemolytic uremic syndrome based on the accumulated experience of other previously approved biosimilars, and to provide an overview of the stringent biosimilar development pathway in general and the concept of extrapolation in particular.

Severe pregnancy-associated atypical hemolytic uremia syndrome in the context of the COVID-19 pandemic: a novel survival case report

BACKGROUND

Pregnancy-associated atypical hemolytic uremic syndrome (aHUS) is a form of thrombotic microangiopathy (TMA) caused by uncontrolled activation of the complement system during pregnancy or the postpartum period. In the intensive care unit, aHUS must be differentiated from sepsis-related multiple organ dysfunction, thrombotic thrombocytopenic purpura (TTP), hemolysis, elevated liver enzymes, and low platelet (HELLP) syndrome. Early recognition of aHUS is critical for effective treatment and improved prognosis. Although tests such as the ADAMTS13 level, peripheral blood smears, complement testing, and blood cultures are useful for diagnosing aHUS, these tests are time-consuming and may not be widely available. This report describes a case of severe aHUS in a pregnant woman during the coronavirus disease 2019 (COVID-19) pandemic.

CASE PRESENTATION

A 26-year-old patient with a history of four pregnancies and one delivery (P4G1) presented at 30 weeks and 2 days of gestation with vaginal fluid leakage and fetal growth restriction detected by ultrasound at a different hospital. During labor induction, the patient developed a high fever and coagulopathy, followed by heart failure, acute kidney injury, anemia, and severe thrombocytopenia. The patient remained alert and coherent, with no evidence of neurological dysfunction. She was transferred to our department and was given invasive respiratory support, blood transfusion, continuous renal replacement therapy, capacity management, and other comprehensive treatments. Due to the ongoing COVID-19 pandemic, ADAMTS13 testing and complement inhibitor therapy were unavailable. A diagnosis of pregnancy-associated aHUS was made based on the patient's history, clinical presentation, and standard laboratory results. The patient was prescribed 13 sessions of hemodialysis. Post-treatment evaluation showed normalized complement C3 and C4 levels, stabilized platelet and hemoglobin levels, and gradual normalization of liver function. Renal function improved gradually, and a bone marrow biopsy revealed no fragmented red blood cells. The patient was transferred to the Department of Nephrology on day 40 and back to the local hospital on day 42. The patient was followed up for 3 years, during which her renal function returned to normal, with no recurrence of thrombocytopenia or microangiopathic hemolytic anemia.

CONCLUSIONS

This case highlights the challenges and importance of diagnosing and managing pregnancy-associated aHUS and multiple organ failure in a low-resource setting.

Development and validation of a prediction model for estimating patency rates after treatment of haemodialysis access dysfunction

OBJECTIVE

This study aims to develop a risk assessment model for predicting haemodialysis access dysfunction and to construct a nomogram.

METHOD

The clinical data of patients with haemodialysis access dysfunction treated at our hospital from October 2020 to January 2024 were retrospectively analysed. The least absolute shrinkage and selection operator regression method was used to filter variables and select predictors, while Cox regression was applied to filter variables and construct a nomogram. The discriminatory ability of the model was determined by calculating the area under the curve (AUC). Calibration was evaluated using bootstrap internal validation and the Hosmer-Lemeshow test. The clinical utility and applicability of the model were assessed through decision curve analysis (DCA) and the clinical impact curve (CIC). Subgroup analysis of risk factors for haemodialysis access dysfunction was performed using Kaplan-Meier survival curves.

RESULT

The study included 423 patients, and seven variables were used to construct the risk prediction model and nomogram for haemodialysis access dysfunction. The C-index of the prediction model was 0.783, and the time-dependent AUC (>0.8) at 6, 12, 18 and 24 months post-surgery indicated strong discriminatory ability. The calibration curve and Hosmer-Lemeshow test demonstrated good agreement between the prediction of the nomogram and the observed values. The DCA and CIC curves further confirmed the clinical practicability of the model.

CONCLUSION

A risk assessment model and nomogram for haemodialysis access dysfunction based on seven variables were successfully constructed. This model demonstrates good discrimination and calibration, offering valuable guidance for clinical decision-making and significant clinical utility.

Atypical hemolytic uremic syndrome with a C3 variant following COVID-19: a case report

Atypical hemolytic uremic syndrome (aHUS) is a form of thrombotic microangiopathy (TMA) characterized by the triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury, and is caused by overactivation of the alternative complement pathway. A 13-year-old Japanese boy with an unremarkable medical history developed symptoms of TMA following coronavirus disease 2019 (COVID-19) infection with mild respiratory symptoms. He was eventually diagnosed with aHUS with a gain-of-function C3 variant. He improved with supportive therapy and plasma exchange, and did not require anti-C5 antibody therapy. In the literature, more than 20 cases of de novo or relapsed aHUS have been described following COVID-19. It has been shown that the complement lectin pathway can be activated by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike and N proteins, and the alternative pathway can be activated by the SARS-CoV-2 spike protein. The current case highlights the possibility that COVID-19, even when respiratory symptoms are not severe, can trigger aHUS.

Diacylglycerol Kinases and Its Role in Lipid Metabolism and Related Diseases

Lipids are essential components of eukaryotic membranes, playing crucial roles in membrane structure, energy storage, and signaling. They are predominantly synthesized in the endoplasmic reticulum (ER) and subsequently transported to other organelles. Diacylglycerol kinases (DGKs) are a conserved enzyme family that phosphorylate diacylglycerol (DAG) to produce phosphatidic acid (PA), both of which are key intermediates in lipid metabolism and second messengers involved in numerous cellular processes. Dysregulation of DGK activity is associated with several diseases, including cancer and metabolic disorders. In this review, we provide a comprehensive overview of DGK types, functions, cellular localization, and their potential as therapeutic targets. We also discuss DGKs' roles in lipid metabolism and their physiological functions and related diseases.

Protein-losing enteropathy as a new phenotype in atypical hemolytic uremic syndrome caused by CD46 gene mutation

BACKGROUND

Atypical hemolytic uremic syndrome (aHUS) is a life-threatening thrombotic microangiopathy. Genetic defects in the alternative complement (AP) pathway have been identified in 60-70% of individuals. Eculizumab is recommended as a first-line therapy.

METHODS

We collected the clinical data of a pediatric patient with aHUS accompanied by protein-losing enteropathy (PLE). Genetic testing was performed. Related literature on aHUS combined with PLE was reviewed.

RESULTS

A 15-year-old Chinese girl was diagnosed with aHUS at 3.7 years of age and experienced five episodes; her symptoms completely resolved with plasma treatment. Severe gastrointestinal symptoms and hypoalbuminemia presented after the first episode, and PLE was diagnosed. A novel homozygous CD46 variant was identified, and FACS revealed significantly decreased CD46 expression. She presented at a recent relapse with persistent GI symptoms and headache and progressed to chronic kidney failure; peritoneal dialysis was initiated. Eculizumab was given 8 months after the last recurrence. Surprisingly, PLE was cured. Afterward, dialysis was discontinued, and eGFR recovered to 44.8 ml/min/1.73 m2. A review of the literature indicated that PLE with thrombosis was caused by CD55 variants via hyperactivation of the AP system. We report an aHUS patient with PLE caused by CD46 variants. Symptoms of both PLE and aHUS were significantly alleviated in our patient and patients with CD55 variants treated with eculizumab, indicating that PLE was a new symptom of aHUS in our patient with a CD46 variant.

CONCLUSIONS

Our case expands the phenotype of aHUS caused by a CD46 mutation and provides evidence of the efficacy of eculizumab after a long phase of chronic kidney failure.

The Inhibitory Effects of a Factor B-Binding DNA Aptamer Family Supersede the Gain of Function of Factor B Variants Associated with Atypical Hemolytic Uremic Syndrome

Aptamers are short, single-stranded oligonucleotides that selectively bind to target biomolecules. Although they generally exhibit good binding specificity, their affinities are often limited because of the relative lack of hydrophobic groups in nucleic acids. Chemically modified nucleotides incorporating hydrophobic structures into uracil have been synthesized to address this obstacle. Modified DNA aptamers containing such nonstandard nucleotides have been developed for >20 different complement proteins. These modified aptamers show increased affinity and enhanced serum stability and have potential value as therapeutic agents. We recently conducted a structure/function study on a family of modified DNA aptamers that bind specifically to complement Factor B (FB). This work revealed that these aptamers selectively inhibit the complement alternative pathway (AP) by preventing the formation of the AP complement component C3 (C3) proconvertase complex, C3bB. Certain patients with atypical hemolytic uremic syndrome express gain-of-function variants of FB that enhance the formation of the proconvertase complex and/or decrease the efficacy of endogenous regulators against the C3 convertases they form. To investigate whether these FB-binding aptamers could override the effects of disease-causing mutations in FB, we examined how they interacted with several FB variants, including D279G, F286L, K323E, and K350N, in various assays of complement function. We found that the inhibitory effect of the FB-binding aptamers superseded the gain-of-function mutations in FB, although the aptamers could not dissociate preformed C3 convertases. These findings suggest that FB-binding aptamers could be further developed as a potential treatment for certain atypical hemolytic uremic syndrome patients or those with other diseases characterized by excessive complement activity.

Eculizumab for adult patients with atypical haemolytic-uraemic syndrome: full dataset analysis of Japanese post-marketing surveillance

BACKGROUND

Eculizumab has been approved for atypical haemolytic-uraemic syndrome (aHUS) in Japan since 2013. Post-marketing surveillance enrolled patients with aHUS who received ≥ 1 dose of eculizumab to assess eculizumab safety and effectiveness.

METHODS

We evaluated serious adverse events and effectiveness endpoints, i.e., haematologic normalization, a decrease of ≥ 25% in serum creatinine (sCr) levels, and complete thrombotic microangiopathy (TMA) response in adult patients with aHUS without other underlying diseases. In addition, the difference of baseline characteristics between patients who did and did not meet effectiveness endpoints was examined.

RESULTS

In this safety and effectiveness analysis, 79 adult patients were included; median age was 54.0 years, median treatment duration was 30 weeks. Total exposure time of eculizumab was 75.51 patient-years, and 94 serious adverse events were reported in 39 patients. No unexpected safety signals were identified in this population. Mean platelet count, lactate dehydrogenase and estimated glomerular filtration rate significantly improved after 7 days of treatment. Complete TMA response, haematologic normalization and the improvement of sCr levels were met by 35.3%, 40.4% and 51.3% of patients, respectively. Median treatment duration was shorter in patients who did not achieve complete TMA response (6 weeks) than in patients who did (114 weeks). Multivariate analysis suggested that the time from the most recent TMA episode to start of eculizumab treatment was negatively associated with kidney function improvement.

CONCLUSIONS

No unexpected safety signals of eculizumab were identified in Japanese patients with aHUS in a real-world setting. Renal outcomes were negatively associated with the time from the most recent TMA episode to the initiation of eculizumab treatment.

The utility of the normal thin section skin biopsy in the assessment of systemic/extracutaneous disease and small fiber neuropathy

Diseases reflective of multiorgan vascular injury of diverse etiology, peripheral nerve disease, dysautonomia syndromes, and intravascular lymphoma may exhibit abnormalities on a normal skin biopsy that may be instrumental in establishing a diagnosis. A retrospective review of our database was conducted to uncover cases where a normal skin biopsy was performed to rule in or out such systemic diseases as complement-driven thrombotic microvascular disease (including atypical hemolytic uremic syndrome, posttransplant thrombotic microangiopathy, and severe or critical COVID-19), systemic capillary leak syndrome, cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) intravascular B cell lymphoma, small fiber neuropathy, dysautonomia syndromes, and mast cell activation syndrome. Among the special studies were immunohistochemical staining to detect C5b-9, CD56, and myxovirus resistance protein A, as well as mast cell, B and T cell markers. Characteristic patterns were critical in establishing diagnoses such as : increased C5b-9 microvascular deposition in the deltoid area (atypical hemolytic uremic syndrome, posttransplant thrombotic microangiopathy, catastrophic antiphospholipid antibody syndrome, and severe or critical COVID-19); enhanced type I interferon signaling (systemic capillary leak syndrome); ultrastructural arteriopathic changes (CADASIL); reduced cutaneous autonomic innervation in the lower extremities (small fiber neuropathy and postural orthostatic tachycardia syndrome); presence of intravascular lymphocytes on biopsy of abdominal, thigh, and buttock skin (intravascular B cell lymphoma); and a higher than normal density of mast cells in the absence of other inflammatory cell types (mast cell activation syndrome). The skin is clearly a critical window for understanding extracutaneous disease, a concept well exemplified by the myriad of diseases suggested by the microscopic and/or ultrastructural examination of clinically normal skin and therefore establishing the normal skin biopsy as an important tool for understanding certain extracutaneous reactive, neoplastic and paraneoplastic syndromes as well as small fiber neuropathy.

Systemic lupus erythematosus presenting with atypical hemolytic uremic syndrome: a case report and review of the literature

Systemic lupus erythematosus (SLE) can present with a diverse array of hematologic manifestations, among which atypical hemolytic uremic syndrome (aHUS) is a rare entity. SLE-triggered aHUS has significant morbidity and mortality without timely intervention, yet its frequency remains uncertain and optimal strategies for complement-directed therapies are largely expert-driven. We performed a comprehensive literature review and present a case of a 23-year-old female newly diagnosed with SLE/class IV lupus nephritis who developed aHUS that rapidly responded to the C5 antagonist, eculizumab. Review of the current literature identified forty-nine published cases of SLE with concurrent aHUS and revealed a predilection for aHUS in younger SLE patients, concurrent presentation with lupus nephritis, anti-dsDNA positivity, and complement system abnormalities. Over seventy percent of cases used eculizumab as complement-directed therapy with a trend towards faster time to improvement in laboratory parameters, though reported outcomes were highly variable. Early recognition of aHUS in SLE is pivotal in guiding appropriate therapeutic interventions, and prompt initiation of eculizumab may reduce the potential morbidity associated with plasmapheresis and additional immunosuppression. While eculizumab showcases promising results, its optimal timing and duration remain elusive. An understanding of a patients' complement genetics could aid management strategies, and ongoing research into complement-targeted therapies offers promising avenues for both SLE and aHUS treatment.

Anti-C5 monoclonal antibody treatment showing pathological resolution of complement-mediated atypical hemolytic uremic syndrome: a case report

BACKGROUND

No reports have shown histological changes before and after anti-C5 monoclonal antibody treatment in patients with atypical hemolytic uremic syndrome (aHUS). Here, we report a rare case of complement-mediated aHUS with a complement factor H (CFH) mutation and anti-CFH antibodies who underwent multiple kidney biopsies.

CASE PRESENTATION

A 53-year-old woman developed aHUS with CFH gene mutation [c.3572C > T (p. Ser1191 Leu)] and anti-CFH antibodies. Her father had succumbed to acute kidney injury (AKI) in his 30 s. She exhibited AKI, thrombocytopenia, and hemolytic anemia with schistocytes. After improving the platelet count with one session of plasma exchange, a kidney biopsy was performed one month after the onset of symptoms. Blood vessel thrombosis, obvious endothelial swelling, endocapillary hypercellularity, and subendothelial exudative lesions in the glomeruli and arterioles were detected. Anti-C5 monoclonal antibody treatment with eculizumab immediately improved disease activity. A second biopsy 3 months later revealed marked improvement of endothelial injuries with residual membrane double contours and exudative lesions. A third biopsy at 17 months after gradual improvement of kidney function showed a further decrease of double contours along with alterations of the exudative lesions to fibrous intimal thickening.

CONCLUSIONS

This is the first report showing the pathophysiology of aHUS in the kidneys and the efficacy of anti-C5 monoclonal antibody treatment by presenting serial kidney pathological features before and after anti-C5 monoclonal antibody treatment. Since her CFH mutation was considered the most important pathological condition, treatment centered on eculizumab was administered, resulting in a good long-term prognosis. In addition, kidney pathological resolution in aHUS occurred over 1 year after anti-C5 monoclonal antibody treatment.

[The complement cascade in renal pathology]

The complement cascade comprises a variety of soluble and cell surface proteins and is an important component of the innate immune system. When the cascade is triggered by any of the three activation pathways, the complement system rapidly produces large amounts of protein fragments that are potent mediators of inflammatory, vasoactive, and metabolic responses. All activation pathways lead to the terminal complement cascade with the formation of the membrane attack complex, which lyses cells by forming membrane pores. Although the complement system is essential for pathogen defense and homeostasis, excessive or uncontrolled activation can lead to tissue damage. Recent research shows that the complement system is activated in almost all kidney diseases, even those not traditionally considered immune-mediated. In directly complement-mediated kidney diseases, complement factors or regulators are defective, afunctional or inactivated by antibodies. In many other renal diseases, the complement system is activated secondarily as a result of renal damage and is therefore involved in the pathogenesis of the disease, but is not the trigger. The detection of complement deposits is also used to diagnose kidney disease. This review describes the structure of the complement system and the effects of its dysregulation as a cause and modulator of renal disease.

Clinical presentation and management of atypical hemolytic uremic syndrome in Latin America: a narrative review of the literature

INTRODUCTION

Comprehensive information about atypical hemolytic uremic syndrome (aHUS) is relatively scarce outside of Europe and North America. This narrative review assembles available published data about the clinical presentation and management of aHUS in Latin America.

AREAS COVERED

A search conducted in February 2023 of the MEDLINE (from inception), Embase (from inception), and LILACS/IBECS (1950 to 2023) databases using search terms 'atypical hemolytic uremic syndrome' and 'Latin America' and their variations retrieved 51 records (full papers and conference abstracts) published in English, Spanish, or Portuguese. After de-duplication, manual screening of titles/abstracts and addition of author-known articles, 25 articles were included of which 17 (68%) are full papers. All articles were published during the years 2013-2022. Articles include cohort studies, a registry analysis, and case reports from Argentina, Brazil, Chile and Columbia. Overall, Latin American patients with aHUS present the classic epidemiological, clinical, and genetic characteristics associated with this condition as described in other world regions. Depending on the country and time of reporting, aHUS in Latin America was treated mainly with plasma therapy and/or eculizumab. Where reported, eculizumab substantially improved aHUS-related outcomes in almost all adult and pediatric patients.

EXPERT OPINION

Eculizumab has dramatically altered the natural course of aHUS, improving prognosis and patient outcomes. Addressing economic challenges and investing in healthcare infrastructure will be essential to implement strategies for timely detection and early treatment of aHUS in Latin America.

Overlapping Atypical Hemolytic Uremic Syndrome and C3 Glomerulopathy with Mutation in CFI in a Japanese Patient: A Case Report

A 34-year-old Japanese man presented with blurred vision, headache, nausea, anemia, thrombocytopenia, and severe renal dysfunction. Thrombotic microangiopathy was initially suspected to have been caused by malignant hypertension. Antihypertensive medications did not improve his thrombocytopenia or renal dysfunction, and other diseases causing thrombotic microangiopathy were ruled out. Therefore, the patient was diagnosed with atypical hemolytic uremic syndrome. A renal biopsy revealed an overlap of thrombotic microangiopathy and C3 glomerulopathy. Genetic testing revealed c.848A>G (p.Asp283Gly), a missense heterozygous variant in the gene encoding complement factor I. Overlapping atypical hemolytic uremic syndrome and C3 glomerulopathy with complement factor I mutation is very rare, especially in Japan.

Pregnancy-Associated Atypical Hemolytic Uremic Syndrome: A Case Report with MCP Gene Mutation and Successful Eculizumab Treatment

Pregnancy-associated atypical hemolytic uremic syndrome (P-aHUS) is a rare condition characterized by microangiopathic hemolytic anemia and kidney injury from thrombotic microangiopathy. P-aHUS occurs in approximately 1 in 25,000 pregnancies and is strongly related to complement dysregulation and pregnancy-related disorders, such as preeclampsia, eclampsia, and hemolysis, elevated liver enzymes, low platelet (HELLP) syndrome, resulting in adverse perinatal and fetal outcomes. Complement dysregulation in P-aHUS is commonly attributed to genetic mutations or autoantibodies affecting complement factors, including CFH , CFI , and MCP. We present a case of a 25-year-old primigravida who experienced severe preeclampsia and HELLP syndrome followed by the development of complicated P-aHUS during the early postpartum period. The patient exhibited severe clinical manifestations, including hypertensive emergency, central nervous system involvement, renal impairment, and microangiopathic hemolytic anemia. Timely initiation of eculizumab therapy resulted in successful disease remission. Further genetic analysis revealed a likely rare pathogenic MCP gene variant.

TMA in Kidney Transplantation

Thrombotic microangiopathy (TMA) is a rare and devastating complication of kidney transplantation, which often leads to graft failure. Posttransplant TMA (PT-TMA) may occur either de novo or as a recurrence of the disease. De novo TMA can be triggered by immunosuppressant drugs, antibody-mediated rejection, viral infections, and ischemia/reperfusion injury in patients with no evidence of the disease before transplantation. Recurrent TMA may occur in the kidney grafts of patients with a history of atypical hemolytic uremic syndrome (aHUS) in the native kidneys. Studies have shown that some patients with aHUS carry genetic abnormalities that affect genes that code for complement regulators (CFH, MCP, CFI) and components (C3 and CFB), whereas in 10% of patients (mostly children), anti-FH autoantibodies have been reported. The incidence of aHUS recurrence is determined by the underlying genetic or acquired complement abnormality. Although treatment of the causative agents is usually the first line of treatment for de novo PT-TMA, this approach might be insufficient. Plasma exchange typically resolves hematologic abnormalities but does not improve kidney function. Targeted complement inhibition is an effective treatment for recurrent TMA and may be effective in de novo PT-TMA as well, but it is necessary to establish which patients can benefit from different therapeutic options and when and how these can be applied.

X-linked C1GALT1C1 mutation causes atypical hemolytic uremic syndrome

Hemolytic-uremic syndrome (HUS), mostly secondary to infectious diseases, is a common cause of acute kidney injury in children. It is characterized by progressive acute kidney failure due to severe thrombotic microangiopathy, associated with nonimmune, Coombs-negative hemolytic anemia and thrombocytopenia. HUS is caused mostly by Shiga toxin-producing E. Coli, and to a lesser extent by Streptococcus pneumonia. In Streptococcus pneumonia HUS (pHUS), bacterial neuraminidase A exposes masked O-glycan sugar residues on erythrocytes, known as the T antigen, triggering a complement cascade causing thrombotic microangiopathy. Atypical HUS (aHUS) is a life-threatening genetic form of the disease, whose molecular mechanism is only partly understood. Through genetic studies, we demonstrate a novel X-linked form of aHUS that is caused by a de-novo missense mutation in C1GALT1C1:c.266 C > T,p.(T89I), encoding a T-synthase chaperone essential for the proper formation and incorporation of the T antigen on erythrocytes. We demonstrate the presence of exposed T antigen on the surface of mutant erythrocytes, causing aHUS in a mechanism similar to that suggested in pHUS. Our findings suggest that both aHUS caused by mutated C1GALT1C1 and pHUS are mediated by the lectin-complement-pathway, not comprehensively studied in aHUS. We thus delineate a shared molecular basis of aHUS and pHUS, highlighting possible therapeutic opportunities.

Complement in immune thrombocytopenia (ITP): The role of complement in refractory ITP

Immune thrombocytopenia (ITP) is a disorder characterized by low platelets due to increased clearance and decreased platelet production. While ITP has been characterized as an acquired disorder of the adaptive immune system, the resulting platelet autoantibodies provide ancillary links to the innate immune system via antibody interaction with the complement system. Most autoantibodies in patients with ITP are of the IgG1 subclass, which can be potent activators of the classical complement pathway. Antibody-coated platelets can initiate complement activation via the classical pathway leading to both direct platelet destruction and enhanced clearance of C3b-coated platelets by complement receptors. Similar autoantibody interactions with bone marrow megakaryocytes can also result in complement injury and ineffective thrombopoiesis. The development of novel therapeutic complement inhibitors has revived interest in the role of complement in autoantibody-mediated disorders, such as ITP. A recent early-phase clinical trial of a classical complement pathway inhibitor has demonstrated efficacy in a subset of ITP patients refractory to conventional immune modulation. In this review, we will analyse the role of complement in refractory ITP.

Eculizumab Versus Ravulizumab for the Treatment of Atypical Hemolytic Uremic Syndrome: A Systematic Review

Atypical hemolytic uremic syndrome (aHUS) is a type of thrombotic microangiopathy and is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney failure. The complement cascade plays an integral role in aHUS. Mutations in the complement cascade, especially in the alternative pathway (AP) lead to an unregulated and continuous activation of the cascade. Eculizumab and ravulizumab are humanized monoclonal antibodies that inhibit the complement cascade. This systematic analysis reviews the evidence for both antibodies to compare them in terms of safety and efficacy. This review will also assess the evidence for biomarker associations with interventions, the role of genetic mutations in the prognosis of disease, and the financial burden of both treatment options. An in-depth search was conducted across PubMed, Science Direct, and Cochrane Library following the PRISMA 2020 guidelines. Both eculizumab and ravulizumab were comparable in safety and efficacy but ravulizumab was preferred by patients and their caregivers as it posed a lower financial burden and had less frequent dosing. Soluble complement 5b-9 (sC5b), especially in urine, has the potential to be used as a biomarker to assess response to treatment. Genetic mutations, especially mutations in complement factor I (CFI), membrane cofactor protein (MCP), and complement factor H (CFH), were associated with a higher risk of recurrence, and therefore care should be taken when attempting to discontinue treatment in this subset of patients. Treatment with a monoclonal antibody should be initiated as soon as a genetic mutation is identified. Blinded, double-arm, clinical trials preferably with larger sample sizes are needed to effectively compare both the monoclonal antibodies.

Clinical features and management of atypical hemolytic uremic syndrome patient with DGKE gene variants: a case report

Background

Atypical hemolytic uremic syndrome (aHUS) with diacylglycerol kinase epsilon (DGKE) gene variant is a rare variant of thrombotic microangiopathy (TMA). The information on the clinical features, management and long-term outcomes of DGKE-aHUS patients have not yet been fully elucidated. The aim of this study was to report a novel variant of the DGKE gene in a Chinese population with aHUS.

Case presentation

The present work reports a 7-month-old boy with aHUS, possibly triggered by gastrointestinal infection, without complement activation, with little response to plasma therapy and nephroprotective measures. The patient died during the 8th week of his hospital stay. The causes of death were intracranial hemorrhage and multiorgan dysfunction. Comprehensive WES of peripheral blood-derived DNA revealed two heterozygous variations in the DGKE exon region: NM_003647.2, c.610dup, p.Thr204Asnfs*4 and deletion of exons 4-6.

Conclusions

This case suggest that atypical HUS with DGKE gene variant has a poor prognosis with a high mortality rate, which typically manifests in the first year of life and presents as a systemic disease with early-onset HUS with rapidly worsening renal function and chronic proteinuria. There is no specific treatment for DGKE-aHUS. There have an uncertain benefit of plasma therapy for DGKE-aHUS patients. The literature demonstrated that anti-complement therapy showed benefits for DGKE-aHUS with complement activation and autoantibodies during the overt TMA presentation but did not prevent TMA relapses. Early diagnosis and treatment may prevent complications and improve prognosis.

A bispecific inhibitor of complement and coagulation blocks activation in complementopathy models via a novel mechanism

Inhibitors of complement and coagulation are present in the saliva of a variety of blood-feeding arthropods that transmit parasitic and viral pathogens. Here, we describe the structure and mechanism of action of the sand fly salivary protein lufaxin, which inhibits the formation of the central alternative C3 convertase (C3bBb) and inhibits coagulation factor Xa (fXa). Surface plasmon resonance experiments show that lufaxin stabilizes the binding of serine protease factor B (FB) to C3b but does not detectably bind either C3b or FB alone. The crystal structure of the inhibitor reveals a novel all β-sheet fold containing 2 domains. A structure of the lufaxin-C3bB complex obtained via cryo-electron microscopy (EM) shows that lufaxin binds via its N-terminal domain at an interface containing elements of both C3b and FB. By occupying this spot, the inhibitor locks FB into a closed conformation in which proteolytic activation of FB by FD cannot occur. C3bB-bound lufaxin binds fXa at a separate site in its C-terminal domain. In the cryo-EM structure of a C3bB-lufaxin-fXa complex, the inhibitor binds to both targets simultaneously, and lufaxin inhibits fXa through substrate-like binding of a C-terminal peptide at the active site as well as other interactions in this region. Lufaxin inhibits complement activation in ex vivo models of atypical hemolytic uremic syndrome (aHUS) and paroxysmal nocturnal hemoglobinuria (PNH) as well as thrombin generation in plasma, providing a rationale for the development of a bispecific inhibitor to treat complement-related diseases in which thrombosis is a prominent manifestation.

The Prevalence and Incidence of Hemolytic Uremic Syndrome: A Systematic Review

A hemolytic uremic syndrome is an uncommon but severe condition brought on by an overactive alternative complement system, typically involving a hereditary component. It will be crucial to comprehend the epidemiology of hemolytic uremic syndrome as research advances toward bettering its diagnosis and treatment. A systematic review was conducted to evaluate the incidence and prevalence estimates of hemolytic uremic syndrome (HUS) internationally. A thorough literature search was conducted using PubMed, Springer, Cochrane Library for Systematic Reviews, and Embase databases between 2012 and 2023 in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 recommendations. A further source of data was the PubMed Central search engine. To make sure that the evaluation included just the studies that were the most pertinent, a population, interventions, comparators, and outcomes (PICO) eligibility criterion was also used. Eight articles were included in this review. HUS had an annual crude incidence of 0.66 per 100,000 people and a standard annual incidence of 0.57 per 100,000 people. Females were more likely than males to develop HUS, but only marginally more frequently. Patients under 20 years old were the age group where HUS was most common. HUS had an average cost of $21,500 per patient, which was more expensive than the country's overall inpatient average cost for the same period. This is due to patients requiring supportive care, antibiotics, plasma exchange, plasma infusion, and renal replacement therapy, and it could take multiple courses of treatment before they improve. It was concluded that several variables, including the region, the age group affected, and the frequency of the underlying bacterial infection, determine the prevalence and incidence of HUS. HUS is often more common in children than adults and is more common in some nations. Overall, HUS is an uncommon disorder that can have significant repercussions for people who have it. For better results and fewer consequences, HUS must be diagnosed and treated as soon as possible.

A case report of an atypical haemolytic uremic syndrome in pregnancy: something wicked this way comes

BACKGROUND

Atypical Haemolytic Uremic Syndrome is an acute life-threatening condition, characterized by the clinical triad of microangiopathic hemolytic anaemia, thrombocytopenia, kidney injury. Management of pregnants affected by Atypical Haemolytic Uremic Syndrome can be a serious concern for obstetric anesthesiologist in the delivery room and in the intensive care unit.

CASE PRESENTATION

A 35-year-old primigravida with a monochorionic diamniotic twin pregnancy, presented with an acute haemorrhage due to retained placenta after elective caesarean section and underwent surgical exploration. In the postoperative period, the patient progressively developed hypoxemic respiratory failure and, later on, anaemia, severe thrombocytopenia, and acute kidney injury. A timely diagnosis of Atypical Haemolytic Uremic Syndrome was made. Non-invasive ventilation and high-flow nasal cannula oxygen therapy sessions were initially required. Hypertensive crisis and fluid overload were aggressively treated with a combination of beta and alpha adrenergic blockers (labetalol 0,3 mg/kg/h by continuous intravenous infusion for the first 24 hours, bisoprolol 2,5 mg twice daily for the first 48 hours, doxazosin 2 mg twice daily), central sympatholytics (methyldopa 250 mg twice daily for the first 72 hours, transdermal clonidine 5 mg by the third day), diuretics (furosemide 20 mg three times daily), calcium antagonists (amlodipine 5 mg twice daily). Eculizumab 900 mg was administered via intravenous infusion once per week, attaining hematological and renal remissions. The patient also received several blood transfusion units and anti- meningococcal B, anti-pneumococcal, anti-haemophilus influenzae type B vaccination. Her clinical condition progressively improved, and she was finally discharged from intensive care unit 5 days after admission.

CONCLUSIONS

The clinical course of this report underlines how crucial it is for the obstetric anaesthesiologist to promptly identify Atypical Haemolytic Uremic Syndrome, since early initiation of eculizumab, together with supportive therapy, has a direct effect on patient outcome.

Atypical Hemolytic Uremic Syndrome Secondary to Pancreatitis: A Case Report

This is a report of an extremely rare case of an atypical hemolytic uremic syndrome (aHUS) that appears to have been triggered by acute pancreatitis. A 68-year-old man was examined at a medical institution because of sudden lower abdominal pain. The patient was diagnosed with acute pancreatitis on computed tomography. Hemoglobinuria and laboratory findings indicative of intravascular hemolysis were noted. Biochemical analysis revealed normal results for von Willebrand factor activity, antiplatelet antibodies, and ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13), and stool culture was negative for Shiga-toxin-producing Escherichia coli, leading to the diagnosis of aHUS. Treatment for acute pancreatitis resulted in improvement in the laboratory findings, and the patient's progress was monitored without treatment intervention for aHUS. On day 2 of hospitalization, the abdominal symptoms and hemoglobinuria resolved without any subsequent recurrence. In the absence of any complications, the patient was transferred back to the initial hospital on day 26 of hospitalization. When hemolytic anemia or thrombocytopenia of unknown etiology is observed, aHUS should be suspected, and clinicians should be aware that acute pancreatitis may be a potential cause of aHUS.

Endotoxemic Shock: A Molecular Phenotype in Sepsis

BACKGROUND

Marked heterogeneity exists among patients with sepsis, both in terms of distribution of organ dysfunction and its severity. Such heterogeneity could be explained by the presence of multiple subtypes of sepsis that may have important implications for treatment.

METHODS

Narrative review of published literature involving endotoxin from 1970 to 2022.

RESULTS

In humans, endotoxemia is most consistently associated with a specific pattern of organ failure including shock, endothelial dysfunction, acute kidney injury, and hepatic dysfunction. This pattern is consistent with complement activation and uncontrolled inflammation, two features of endotoxemia. Unbiased discovery using artificial intelligence also identifies a subtype of sepsis which features these same organ failures.

CONCLUSION

Endotoxin appears to represent an important molecular phenotype of sepsis with unique clinical features and high mortality.

The level of serotonin and its metabolite in hemolytic-uremic syndrome in children

Hemolytic-uremic syndrome includes a triad of symptoms: microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. Given the progressive course of hemolytic-uremic syndrome, up to the terminal stage of renal failure, it is necessary to search for early markers of renal tissue damage as prognostically significant factors in the development of nephrosclerosis, which is of particular importance in childhood to optimize the management of such patients. The analysis of the literature data demonstrates the actual role of serotonin and platelet-mediated effect of serotonin on fibroinflammatory processes in kidney vessels. Thus, changes in the serotonergic system in patients already at the onset of hemolytic-uremic syndrome are of great interest in order to develop new diagnostic approaches that allow optimizing early diagnosis and slowing down the progression of renal damage in this category of patients. These studies will expand knowledge about the role of the serotonergic system in the formation of chronic kidney disease in children with hemolytic-uremic syndrome. 

A Multicenter Study Evaluating the Discontinuation of Eculizumab Therapy in Children with Atypical Hemolytic Uremic Syndrome

Background: Atypical hemolytic uremic syndrome (aHUS) is a rare, life-threatening thrombotic microangiopathy (TMA), which has been treated successfully with eculizumab. The optimal duration of eculizumab in treating patients with aHUS remains poorly defined. Methods: We conducted a multicenter retrospective study in the Arabian Gulf region for children of less than 18 years of age who were diagnosed with aHUS and who discontinued eculizumab between June 2013 and June 2021 to assess the rate and risk factors of aHUS recurrence. Results: We analyzed 28 patients with a clinical diagnosis of aHUS who had discontinued eculizumab. The most common reason for the discontinuation of eculizumab was renal and hematological remission (71.4%), followed by negative genetic testing (28.6%). During a median follow-up period of 24 months after discontinuation, 8 patients (28.5%) experienced HUS relapse. The risk factors of recurrence were positive genetic mutations (p = 0.020). On the other hand, there was no significant relationship between the relapse and age of presentation, the need for acute dialysis, the duration of eculizumab therapy before discontinuation, or the timing of eculizumab after the presentation. Regarding the renal outcomes after discontinuation, 23 patients were in remission with normal renal function, while 4 patients had chronic kidney disease (CKD) (three of them had pre-existing chronic kidney disease (CKD) before discontinuation, and one case developed a new CKD after discontinuation) and one patient underwent transplantation. Conclusions: The discontinuation of eculizumab in patients with aHUS is not without risk; it can result in HUS recurrence. Eculizumab discontinuation can be performed with close monitoring of the patients. It is essential to assess risk the factors for relapse before eculizumab discontinuation, in particular in children with a positive complement variant and any degree of residual CKD, as HUS relapse may lead to additional loss of kidney function. Resuming eculizumab promptly after relapse is effective in most patients.

The role of the complement system in kidney glomerular capillary thrombosis

The complement system is part of the innate immune system. The crucial step in activating the complement system is the generation and regulation of C3 convertase complexes, which are needed to generate opsonins that promote phagocytosis, to generate C3a that regulates inflammation, and to initiate the lytic terminal pathway through the generation and activity of C5 convertases. A growing body of evidence has highlighted the interplay between the complement system, coagulation system, platelets, neutrophils, and endothelial cells. The kidneys are highly susceptible to complement-mediated injury in several genetic, infectious, and autoimmune diseases. Atypical hemolytic uremic syndrome (aHUS) and lupus nephritis (LN) are both characterized by thrombosis in the glomerular capillaries of the kidneys. In aHUS, congenital or acquired defects in complement regulators may trigger platelet aggregation and activation, resulting in the formation of platelet-rich thrombi in the kidneys. Because glomerular vasculopathy is usually noted with immunoglobulin and complement accumulation in LN, complement-mediated activation of tissue factors could partly explain the autoimmune mechanism of thrombosis. Thus, kidney glomerular capillary thrombosis is mediated by complement dysregulation and may also be associated with complement overactivation. Further investigation is required to clarify the interaction between these vascular components and develop specific therapeutic approaches.

Overview on the role of complement-specific autoantibodies in diseases

The complement system is recognized as a major pathogenic or contributing factor in an ever-growing number of diseases. In addition to inherited factors, autoantibodies to complement proteins have been detected in various systemic and organ-specific disorders. These include antibodies directed against complement components, regulators and receptors, but also protein complexes such as autoantibodies against complement convertases. In some cases, the autoantibodies are relatively well characterized and a pathogenic role is incurred and their detection has diagnostic value. In other cases, the relevance of the autoantibodies is rather unclear. This review summarizes what we know of complement specific autoantibodies in diseases and identifies unresolved questions regarding their functional effect and relevance.

Atypical hemolytic uremic syndrome after myomectomy: A case report

Atypical hemolytic uremic syndrome (aHUS) is a rare form of thrombotic microangiopathy due to inability to regulate the complement cascade, resulting in thrombocytopenia, intravascular hemolysis, and end-organ damage. Over 70% of cases are associated with mutations in complement or complement regulatory proteins, and some two-thirds have recognized complement-activating conditions triggering an aHUS event. We describe a case of aHUS after abdominal myomectomy in a 42-year-old woman that was managed with plasma exchange and eculizumab (an anti-C5 monoclonal antibody). The diagnosis was confirmed by biopsy of normal-appearing deltoid skin that demonstrated microvascular C5b-9 deposition, diagnostic of systemic complement pathway activation. Although extremely uncommon following gynecologic surgery, aHUS should be considered in the setting of postoperative oliguric acute kidney injury, as prompt diagnosis is necessary to prevent significant morbidity and mortality.

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Thrombotic microangiopathy is a potentially lethal complication of myomectomy.

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Atypical hemolytic uremic syndrome following surgery has been rarely reported.

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Eculizumab is a life-saving treatment for atypical hemolytic uremic syndrome.

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Normal deltoid skin biopsy may support the diagnosis of complement deposition.

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This is a case of atypical hemolytic uremic syndrome after abdominal myomectomy.

Systematic review of atypical hemolytic uremic syndrome biomarkers

BACKGROUND AND OBJECTIVES

Observing biomarkers that affect alternative pathway dysregulation components may be effective in obtaining a new and more rapid diagnostic portrayal of atypical hemolytic uremic syndrome. We have conducted a systematic review on the aHUS biomarkers: C3, C5a, C5b-9, factor B, complement factor B, H, and I, CH50, AH50, D-dimer, as well as anti-CFH antibodies.

METHODS

An exhaustive literature search was conducted for aHUS patient population plasma/serum, collected/reported at the onset of diagnosis. A total of 60 studies were included with the data on 837 aHUS subjects, with at least one biomarker reported.

RESULTS

The biomarkers C3 [mean (SD): 72.1 (35.0), median: 70.5 vs. reference range: 75-175 mg/dl, n = 752]; CH50 [28.3 (32.1), 24.3 vs. 30-75 U/ml, n = 63]; AH50 [27.6% (30.2%), 10% vs. ≥ 46%, n = 23]; and CFB [13.1 (6.6), 12.4, vs. 15.2-42.3 mg/dl, n = 19] were lower among aHUS subjects as compared with the reference range. The biomarkers including C4 [mean (SD): 20.4 (9.5), median: 20.5 vs. reference range: 14-40 mg/dl, n = 343]; C4d [7.2 (6.5), 4.8 vs. ≤ 9.8 μg/ml, n = 108]; CFH [40.2 (132.3), 24.5 vs. 23.6-43.1 mg/dl, n = 123 subjects]; and CFI [8.05 (5.01), 6.55 mg/dl vs. 4.4-18.1 mg/dl, n = 38] were all observed to be within the reference range among aHUS subjects. The biomarkers C5a [mean (SD): 54.9 (32.9), median: 48.8 vs. reference range: 10.6-26.3 mg/dl, n = 117]; C5b-9 [466.0 (401.4), 317 (186-569.7) vs. ≤ 250 ng/ml, n = 174]; Bb [2.6 (2.1), 1.9 vs. ≤ 1.6 μg/ml, n = 77] and D-dimer [246 (65.05), 246 vs. < 2.2 ng/ml, 2, n = 2 subjects] were higher among patients with aHUS compared with the reference range.

CONCLUSION

If a comprehensive complement profile were built using our data, aHUS would be identified by low levels of C3, CH50, AH50, and CFB along with increased levels of C5a, C5b-9, Bb, anti-CFH autoantibodies, and D-dimer. A higher resolution version of the Graphical abstract is available as Supplementary information.

Life-Threatening Microangiopathy or Vitamin Deficiency: A Case Report of the Clinical Manifestations of Pseudo-Thrombotic Microangiopathic Anemia

Hemolytic anemia with thrombocytopenia and organ damage raises suspicion for thrombotic microangiopathy (TMA), a pathology that results in thrombosis within the small vessels secondary to endothelial injury. While usually attributed to atypical hemolytic uremic syndrome (aHUS) or thrombotic thrombocytopenic purpura (TTP), an increasingly recognized and treatable entity is pseudo-thrombotic microangiopathic anemia (pseudo-TMA) secondary to severe vitamin B-12 deficiency.

While TMA often requires expensive diagnostic testing and can lead to invasive treatment options such as plasma exchange, immunosuppression, and/or complement cascade blocking, pseudo-TMA requires only vitamin supplementation. Therefore, the prompt and accurate diagnosis of this entity is important for the clinician to recognize in order to avoid unnecessary health costs and institute appropriate treatment.

We present the case of a 51-year-old male without any past medical history, who presented with generalized weakness, dyspnea on exertion, and decreased exercise tolerance for several months and was found to have severe microangiopathic anemia with work-up concerning for TTP. After stabilization, he was found to have severe B-12 deficiency secondary to newly diagnosed pernicious anemia and was treated with subcutaneous B-12 injections with improvement in clinical symptoms and laboratory parameters. This presentation highlights the need for prompt diagnosis and high clinical suspicion for vitamin deficiencies as a source of pseudo-microangiopathy.

Anti-Factor H Antibodies in Egyptian Children with Hemolytic Uremic Syndrome

Background

Atypical hemolytic uremic syndrome (aHUS) is an important cause of acute kidney injury in children. It is primarily caused by dysregulation of the complement alternative pathway due to genetic mutations, mainly in complement factor H genes, or due to anti-factor H autoantibodies (anti-FH), leading to uncontrolled overactivation of the complement system. Early diagnosis and treatment of autoimmune HUS (AI-HUS) is essential and leads to a favorable outcome.

Methods

Fifty pediatric HUS patients and 50 age- and sex-matched controls were included in the study. Patients were subjected to full history taking, clinical examination, and laboratory testing. All candidates were subjected to an assessment of anti-FH in serum by a homemade enzyme-linked immunosorbent assay technique.

Results

A high frequency of serum anti-FH was detected in our aHUS patients. The disease onset of AI-HUS was mainly observed in March and April, with significantly higher rates in school-aged males. All patients who started immunosuppressives early together with plasmapheresis upon detection of their anti-FH had complete renal function recovery.

Conclusion

The high frequency of AI-HUS revealed in Egyptian HUS children in our study highlights the importance of implementing anti-FH testing in Egypt to provide early recognition for immediate proper management, including early immunosuppressive therapy, and hence improving patient outcomes.

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.

A Novel Homozygous In-Frame Deletion in Complement Factor 3 Underlies Early-Onset Autosomal Recessive Atypical Hemolytic Uremic Syndrome - Case Report

Background and Objectives

Atypical hemolytic uremic syndrome (aHUS) is mostly attributed to dysregulation of the alternative complement pathway (ACP) secondary to disease-causing variants in complement components or regulatory proteins. Hereditary aHUS due to C3 disruption is rare, usually caused by heterozygous activating mutations in the C3 gene, and transmitted as autosomal dominant traits. We studied the molecular basis of early-onset aHUS, associated with an unusual finding of a novel homozygous activating deletion in C3.

Design, Setting, Participants, & Measurements

A male neonate with eculizumab-responsive fulminant aHUS and C3 hypocomplementemia, and six of his healthy close relatives were investigated. Genetic analysis on genomic DNA was performed by exome sequencing of the patient, followed by targeted Sanger sequencing for variant detection in his close relatives. Complement components analysis using specific immunoassays was performed on frozen plasma samples from the patient and mother.

Results

Exome sequencing revealed a novel homozygous variant in exon 26 of C3 (c.3322_3333del, p.Ile1108_Lys1111del), within the highly conserved thioester-containing domain (TED), fully segregating with the familial disease phenotype, as compatible with autosomal recessive inheritance. Complement profiling of the patient showed decreased C3 and FB levels, with elevated levels of the terminal membrane attack complex, while his healthy heterozygous mother showed intermediate levels of C3 consumption.

Conclusions

Our findings represent the first description of aHUS secondary to a novel homozygous deletion in C3 with ensuing unbalanced C3 over-activation, highlighting a critical role for the disrupted C3-TED domain in the disease mechanism.

Thrombotic microangiopathies: First report of 294 cases from a single institution experience in Argentina

Introduction

Introduction: Thrombotic microangiopathies (TMAs) are rare disorders associated with fatal outcomes if left uncared for. However, healthcare problems in developing countries tend to limit medical assistance to patients.

Methods

Methods: We prospectively studied an Argentine cohort of 294 consecutive patients from 2013 to 2016. Patients’ subcategory classification relied on clinical symptoms and presence or absence of trigger events associated with TMA.

Results

Main suspected disorders were the primary TMAs known as thrombotic thrombocytopenic purpura (TTP) (n = 72/294, 24%) and atypical haemolytic uraemic syndrome (aHUS) (n = 94/294, 32%). In acute phase, demographic parameters for acquired TTP (aTTP) (n = 28) and aHUS (n = 47) showed that both groups were characterised by a young median age (37 and 25 years, respectively) and female predominance (60% and 86%). Median of a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 activity was significantly lower in aTTP than in aHUS group (1.4% vs 83%) and was associated with a more severe thrombocytopenia (15 × 10⁹ vs 53 × 10⁹/L). Creatinine (Cr) and urea (Ur) were significantly increased in aHUS compared to aTTP subjects (Cr: 3.7 vs 0.7 mg/dL, Ur: 118 vs 33 mg/dL). Gastrointestinal and neurological symptoms were more frequent in aHUS and aTTP, respectively.

Conclusion

The first description of a TMA cohort in Argentina revealed similar clinical presentations to those of other countries.

Investigation of the Initial Host Response of Naïve Atlantic Salmon (Salmo salar) Inoculated with Paramoeba perurans

Amoebic Gill Disease (AGD), caused by the ectoparasite Paramoeba perurans is characterised by hyperplasia of the gill epithelium and lamellar fusion. In this study, the initial host response of naïve Atlantic salmon (Salmo salar) inoculated with P. perurans was investigated. Using gel-free proteomic techniques and mass spectrometry gill and serum samples were analysed at 7 timepoints (2, 3, 4, 7, 9, 11 and 14 days) post-inoculation with P. perurans. Differential expression of immune related proteins was assessed by comparison of protein expression from each time point against naïve controls. Few host immune molecules associated with innate immunity showed increased expression in response to gill colonisation by amoebae. Furthermore, many proteins with roles in immune signalling, phagocytosis and T-cell proliferation were found to be inhibited upon disease progression. Initially, various immune factors demonstrated the anticipated increase in expression in response to infection in the serum while some immune inhibition became apparent at the later stages of disease progression. Taken together, the pro-immune trend observed in serum, the lack of a robust early immune response in the gill and the diversity of those proteins in the gill whose altered expression negatively impact the immune response, support the concept of a pathogen-derived suppression of the host response.

Thrombotic microangiopathies assessment: mind the complement

When faced with microangiopathic haemolytic anaemia, thrombocytopenia and organ dysfunction, clinicians should suspect thrombotic microangiopathy (TMA). The endothelial damage that leads to this histological lesion can be triggered by several conditions or diseases, hindering an early diagnosis and aetiological treatment. However, due to systemic involvement in TMA and its low incidence, an accurate early diagnosis is often troublesome. In the last few decades, major improvements have been made in the pathophysiological knowledge of TMAs such as thrombotic thrombocytopenic purpura [TTP, caused by ADAMTS-13 (a disintegrin and metalloproteinase with a thrombospondin Type 1 motif, member 13) deficiency] and atypical haemolytic uraemic syndrome (aHUS, associated with dysregulation of the alternative complement pathway), together with enhancements in patient management due to new diagnostic tools and treatments. However, diagnosis of aHUS requires the exclusion of all the other entities that can cause TMA, delaying the introduction of terminal complement blockers, which have shown high efficacy in haemolysis control and especially in avoiding organ damage if used early. Importantly, there is increasing evidence that other forms of TMA could present overactivation of the complement system, worsening their clinical progression. This review addresses the diagnostic and therapeutic approach when there is clinical suspicion of TMA, emphasizing complement evaluation as a potential tool for the inclusive diagnosis of aHUS, as well as for the improvement of current knowledge of its pathophysiological involvement in other TMAs. The development of both new complement activation biomarkers and inhibitory treatments will probably improve the management of TMA patients in the near future, reducing response times and improving patient outcomes.

Case Report: Severe Complement-Mediated Thrombotic Microangiopathy in IgG4-Related Disease Secondary to Anti-Factor H IgG4 Autoantibodies

Objective

To first describe and estimate the potential pathogenic role of Ig4 autoantibodies in complement-mediated thrombotic microangiopathy (TMA) in a patient with IgG4-related disease (IgG4-RD).

Methods

This study is a case report presenting a retrospective review of the patient’s medical chart. Plasma complement C3 and C4 levels, immunoglobulin isotypes and subclasses were determined by nephelometry, the complement pathways’ activity (CH50, AP50, MBL) using WIESLAB^® Complement System assays. Human complement factor H levels, anti-complement factor H auto-antibodies were analyzed by ELISA, using HRP-labeled secondary antibodies specific for human IgG, IgG4, and IgA, respectively. Genetic analyses were performed by exome sequencing of 14 gens implicated in complement disorders, as well as multiplex ligation-dependent probe amplification looking specifically for CFH, CFHR1-2-3, and 5.

Results

Our brief report presents the first case of IgG4-RD with complement-mediated TMA originating from both pathogenic CFHR 1 and CFHR 4 genes deletions, and inhibitory anti-complement factor H autoantibodies of the IgG4 subclass. Remission was achieved with plasmaphereses, corticosteroids, and cyclophosphamide. Following remission, the patient was diagnosed with lymphocytic meningitis and SARS-CoV-2 pneumonia with an uneventful recovery.

Conclusion

IgG4-RD can be associated with pathogenic IgG4 autoantibodies. Genetic predisposition such as CFHR1 and CFHR4 gene deletions enhance the susceptibility to the formation of inhibitory anti-Factor H IgG4 antibodies.

Treatment of Rare Inflammatory Kidney Diseases: Drugs Targeting the Terminal Complement Pathway

The complement system comprises the frontline of the innate immune system. Triggered by pathogenic surface patterns in different pathways, the cascade concludes with the formation of a membrane attack complex (MAC; complement components C5b to C9) and C5a, a potent anaphylatoxin that elicits various inflammatory signals through binding to C5a receptor 1 (C5aR1). Despite its important role in pathogen elimination, priming and recruitment of myeloid cells from the immune system, as well as crosstalk with other physiological systems, inadvertent activation of the complement system can result in self-attack and overreaction in autoinflammatory diseases. Consequently, it constitutes an interesting target for specialized therapies. The paradigm of safe and efficacious terminal complement pathway inhibition has been demonstrated by the approval of eculizumab in paroxysmal nocturnal hematuria. In addition, complement contribution in rare kidney diseases, such as lupus nephritis, IgA nephropathy, atypical hemolytic uremic syndrome, C3 glomerulopathy, or antineutrophil cytoplasmic antibody-associated vasculitis has been demonstrated. This review summarizes the involvement of the terminal effector agents of the complement system in these diseases and provides an overview of inhibitors for complement components C5, C5a, C5aR1, and MAC that are currently in clinical development. Furthermore, a link between increased complement activity and lung damage in severe COVID-19 patients is discussed and the potential for use of complement inhibitors in COVID-19 is presented.

Complement-Related Proteins and Their Measurements: The Current Status of Clinical Investigation

Complement has been considered to be a factor that protects the host against invading microorganisms during infection. However, in recent years, complement-related protein deficiency has been found to be involved in the onset of various diseases, such as autoimmune and inflammatory diseases. In Japan, C3, C4, and CH50 tests were generally performed only when a complement system examination was necessary and there were not enough examinations for other complement factors. Since the complement system has a very complicated activation pathway, at present, it is not well known which molecule must be measured to understand the pathological condition or pathogenesis in complement-related diseases. Furthermore, since the frequency of complement factor gene alleles also differs depending on race, data from foreign countries cannot be directly applied to Japanese populations. Under these circumstances, the Japanese Association for Complement Research (JACR) has prepared approximately 20 items for complement-related examinations, including the 5 categories of functional analysis, complement factors, complement regulators, activation products, and autoantibodies.

Distinct genetic profile with recurrent population-specific missense variants in Korean adult atypical hemolytic uremic syndrome

INTRODUCTION

Atypical hemolytic uremic syndrome (aHUS) is a rare thrombotic microangiopathy (TMA), characterized by micro-angiopathic hemolytic anemia, thrombocytopenia, and renal failure. In more than half of cases, genetic defects leading to overactivation of the alternative complement system have been identified. In this study, we investigated genetic defects in Korean adult patients with aHUS.

MATERIALS AND METHODS

Sixty-six Korean adult patients with aHUS were ascertained from the Korean TMA Registry. Genetic variants of 15 aHUS-related genes (eight core genes [CFH, CFB, CFI, CD46, C3, THBD, PLG, and DGKE] and seven candidate genes [CFP, C4BPA, and CHFR1-5]) were analyzed from exome sequencing data. Multiplex ligation-dependent probe amplification of CFH and related genes was performed to detect hybrid genes or large deletions.

RESULTS

Thirty patients (45%) had at least one aHUS-related variant (s) in eight core genes (total 40 variant alleles). The most frequently affected gene was CFH (13/40, 32%), followed by THBD (8/40, 20%) and CD46 (7/40, 18%). The two most common variants were Asp486Tyr of THBD (N = 7) and Tyr1058His-Val1060Leu of CFH (N = 5, linked on the same allele), accounting for 30% (12/40). In seven candidate genes, 19 variants were detected. When combined, 40 patients (61%) had at least one variant in 15 core or candidate genes. No patients had anti-CFH Ab or hybrid gene/CFHR1 homozygous deletions.

CONCLUSIONS

The genetic profile of Korean adult aHUS was unique with recurrent missense variants, demonstrating ethnicity- and age-dependent differences in the genetic background of aHUS.

Plasma exchange and thrombotic microangiopathies: From pathophysiology to clinical practice

Thrombotic microangiopathy (TMA) brings together many diseases that have a commonality in the apparition of mechanical hemolysis with consuming thrombopenia. In all cases, these diseases can be life threatening, thereby justifying the implementation of treatment as an emergency. First-line treatment represents plasma exchange. This treatment has proven efficiency in improving the vital patient's and functional prognosis. However, the administration methods of plasma exchange can be redefined in light of the understanding of the pathophysiology of TMA. The aim of this review is to try to define, from pathophysiology, the place of plasma exchanges in the modern therapeutic arsenal of TMA.