Atypical Hemolytic-Uremic Syndrome: Genetic Basis, Clinical Manifestations, and a Multidisciplinary Approach to Management

Multidisciplinary consensus on the diagnosis and management of patients with atypical Hemolytic Uremic Syndrome (complement-mediated TMA): Recommendations from Italian scientific societies, patient associations and regulators

Atypical Hemolytic Uremic Syndrome (aHUS) is a severe, systemic, rare disease (RD) that can occur in people of all ages, and is associated with high rates of morbidity and mortality. Because the management of patients with aHUS can be difficult, more effective strategies should be implemented. Faculty members from several Italian Scientific Societies, Patient Associations and Regional Institutional Experts on RDs met to discuss aHUS management within a multidisciplinary team (MDT), using a Delphi process to develop consensus recommendations. Consensus (≥70 % agreement by faculty members) was reached on 51 statements with the aim of improving patient management and outcomes. These statements provide a unified framework for the differential diagnosis of aHUS, prompt recognition of the pathology, referral to RD reference centers, selecting between treatment relapse prevention measures options, patient management by a MDT and improving the overall awareness of aHUS. Despite the broad scope of the consensus statements, several unmet needs in the management of patients with aHUS were identified, including diagnostic suspicion, rapid genetic investigations, regular review of the centers of expertise (considering the number of treated patients), permanent clinical referral in treatment centers and widespread expertise among adult and pediatric specialists. We hope that this standardized framework will form the basis of the "digital ecosystem" concept and development of possible information technology solutions to assist the MDT involved in the management of patients with aHUS.

Catastrophic Thrombosis: A Narrative Review

Catastrophic thrombosis is a severe condition characterized by a hypercoagulable tendency, leading to multiple thromboembolic events in different blood vessels, usually within a short timeframe. Several conditions have been associated with the development of catastrophic thrombosis, including the catastrophic antiphospholipid syndrome, thrombotic anti-platelet factor 4 immune disorders, thrombotic microangiopathies, cancers, the hyper-eosinophilic syndrome, pregnancy, infections, trauma, and drugs. Thrombotic storm represents a medical emergency whose management represents a serious challenge for physicians. Besides the prompt start of anticoagulation, a patient's prognosis depends on early recognition and possible treatment of the underlying condition. In this narrative review, we summarize the main characteristics of catastrophic thrombosis, analyzing the various conditions triggering such life-threatening complication. Finally, an algorithm with the diagnostic workup and the initial management of patients with catastrophic thrombosis is presented.

Hematologic Complications of Pregnancy

Hematologic complications are common in pregnancy and can significantly impact both maternal and fetal health. Recognizing and treating these complications can be challenging due to the limited evidence available to guide clinical consultants. Iron deficiency anemia is the most prevalent hematologic issue in pregnancy and often occurs due to increased maternal blood volume and the nutritional demands of the growing fetus. Thrombocytopenia is the second most commonly occurring hematologic issue in pregnancy and can be associated with increased blood loss and complications during childbirth. However, the most common type of thrombocytopenia in pregnancy is gestational thrombocytopenia, which does not typically require clinical management. Thus, it is important to distinguish gestational thrombocytopenia from other etiologies of thrombocytopenia in pregnancy that require immediate treatment, including immune thrombocytopenia, thrombotic thrombocytopenic purpura, preeclampsia, and HELLP (hemolysis, elevated liver enzyme levels, and low platelet levels) syndrome. Other important hematologic conditions in pregnancy include non-inherited anemias, such as autoimmune hemolytic anemia and aplastic anemia, as well as inherited anemias, such as sickle cell disease and thalassemia, which may require specialized management to optimize maternal and fetal outcomes. Additionally, bleeding disorders, such as von Willebrand disease and hemophilia, pose unique challenges in pregnancy, especially around the time of delivery, due to the risk of excessive bleeding. Lastly, thromboembolic disorders, such as venous thromboembolism (VTE), remain the leading cause of mortality in pregnancy in developed countries. Pregnancy-related hormonal changes, venous stasis, and hypercoagulability contribute to an increased thromboembolic risk, further exacerbated by additional risk factors such as obesity or a prior personal or family history of VTE. This review aims to summarize current guidelines and management of the most common hematologic disorders in pregnancy.

Atheroembolic Kidney Disease and Atypical Hemolytic Uremic Syndrome: Two Sides of the Same Coin?

INTRODUCTION

Atheroembolic kidney disease (AEKD) is an under-recognized cause of kidney failure, secondary to the obstruction of the renal artery and/or its branches due to the rupture of an unstable atherosclerotic plaque in patients treated with surgical and invasive cardiovascular procedures. The embolization of cholesterol crystals in the renal artery activates the complement and triggers an inflammatory reaction. Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy caused by the hyperactivation of the alternative complement pathway, leading to a prothrombotic and proinflammatory state on the endothelial surface. AEKD and aHUS could share the involvement of the complement in their pathophysiological mechanism and the former could lead to the latter.

CASE PRESENTATION

A 72-year-old man was referred to our clinic because of a rapid worsening of renal function after 9 months from an endovascular aortic repair (EVAR). After 4 months from the intervention, his renal function worsened, he developed hypereosinophilia and skin lesions; the renal ultrasound showed increased resistance indexes, strongly suggestive of atheroembolic kidney disease. Successively, we observed thrombocytopenia, anemia, increased LDH, low plasmatic haptoglobin, schistocytes in blood smear, and normal ADAMTS13. We promptly diagnosed an atypical hemolytic uremic syndrome and started ravulizumab.

CONCLUSION

To our knowledge, this is the first case of aHUS secondary to a subacute AEKD. Further studies are necessary to fill the gap in the knowledge of the precise mechanism leading to aHUS secondary to AEKD and to confirm that they are two sides of the same coin.

[Thrombopenia and hemolytic anemia in acute and emergency medicine : Detailed view at thrombotic microangiopathies]

Recognizing anemia and thrombpenia in acute and emergency medicine is easy. Acute (microangiopathic hemolytic) anemia and thrombopenia can be a sign of thrombotic microangiopathy (TMA). TMA syndromes are potentially life-threatening diseases. Diagnosing a TMA syndrome, causal differentiation and treatment require specialist knowledge that is not always available in acute and emergency medicine. Many differential diagnoses and examinations are usually necessary to make a correct diagnosis. Therefore, a standardized diagnostic algorithm is helpful for early diagnosis and treatment initiation.

Effect of Oxidative Stress on Mitochondrial Damage and Repair in Heart Disease and Ischemic Events

The literature analysis conducted in this review discusses the latest achievements in the identification of cardiovascular damage induced by oxidative stress with secondary platelet mitochondrial dysfunction. Damage to the platelets of mitochondria as a result of their interactions with reactive oxygen species (ROS) and reactive nitrogen species (RNS) can lead to their numerous ischemic events associated with hypoxia or hyperoxia processes in the cell. Disturbances in redox reactions in the platelet mitochondrial membrane lead to the direct oxidation of cellular macromolecules, including nucleic acids (DNA base oxidation), membrane lipids (lipid peroxidation process) and cellular proteins (formation of reducing groups in repair proteins and amino acid peroxides). Oxidative changes in biomolecules inducing tissue damage leads to inflammation, initiating pathogenic processes associated with faster cell aging or their apoptosis. The consequence of damage to platelet mitochondria and their excessive activation is the induction of cardiovascular and neurodegenerative diseases (Parkinson's and Alzheimer's), as well as carbohydrate metabolism disorders (diabetes). The oxidation of mitochondrial DNA can lead to modifications in its bases, inducing the formation of exocyclic adducts of the ethano and propano type. As a consequence, it disrupts DNA repair processes and conduces to premature neoplastic transformation in critical genes such as the p53 suppressor gene, which leads to the development of various types of tumors. The topic of new innovative methods and techniques for the analysis of oxidative stress in platelet mitochondria based on methods such as a nicking assay, oxygen consumption assay, Total Thrombus formation Analysis System (T-Tas), and continuous-flow left ventricular assist devices (CF-LVADs) was also discussed. They were put together into one scientific and research platform. This will enable the facilitation of faster diagnostics and the identification of platelet mitochondrial damage by clinicians and scientists in order to implement adequate therapeutic procedures and minimize the risk of the induction of cardiovascular diseases, including ischemic events correlated with them. A quantitative analysis of the processes of thrombus formation in cardiovascular diseases will provide an opportunity to select specific anticoagulant and thrombolytic drugs under conditions of preserved hemostasis.

Hemostasis and complement in allogeneic hematopoietic stem cell transplantation: clinical significance of two interactive systems

Hematopoietic stem cell transplantation (HCT) represents a curative treatment option for certain malignant and nonmalignant hematological diseases. Conditioning regimens before HCT, the development of graft-versus-host disease (GVHD) in the allogeneic setting, and delayed immune reconstitution contribute to early and late complications by inducing tissue damage or humoral alterations. Hemostasis and/or the complement system are biological regulatory defense systems involving humoral and cellular reactions and are variably involved in these complications after allogeneic HCT. The hemostasis and complement systems have multiple interactions, which have been described both under physiological and pathological conditions. They share common tissue targets, such as the endothelium, which suggests interactions in the pathogenesis of several serious complications in the early or late phase after HCT. Complications in which both systems interfere with each other and thus contribute to disease pathogenesis include transplant-associated thrombotic microangiopathy (HSCT-TMA), sinusoidal obstruction syndrome/veno-occlusive disease (SOS/VOD), and GVHD. Here, we review the current knowledge on changes in hemostasis and complement after allogeneic HCT and how these changes may define clinical impact.

A Rare Case of Atypical Hemolytic Uremic Syndrome Presenting as Chronic Interstitial Nephritis

Atypical hemolytic uremic syndrome commonly presents as rapidly progressive renal failure and is histologically characterized by thrombotic microangiopathy (TMA). TMA presenting with acute renal failure requires aggressive medical management. Here, we present a case of a 30-year-old man who presented with a history of accelerated hypertension and a strong family history of end-stage renal disease, in September 2023. Upon evaluation, he was found to have a creatinine level of 2 mg/dl, bland urine and normal-sized kidneys; a renal biopsy revealed chronic interstitial nephritis. Genetic analysis for autosomal dominant tubulointerstitial kidney disease and nephronophthisis yielded negative results. The patient was managed with antihypertensive medications. In January 2024, he was admitted with a history of confusion, headache, and alcohol binge. He had a blood pressure of 200/100 mmHg and had grade 3 hypertensive retinopathy. Laboratory tests revealed anemia with thrombocytopenia, bland urine, normal coagulation parameters, indirect hyperbilirubinemia, normal-sized kidneys on ultrasound, and elevated lactate dehydrogenase levels. MRI of the brain revealed symmetrical hyperintensities in bilateral cerebellum and the dorsal brainstem. Complement levels revealed low C3 levels and genetic analysis revealed a homozygous deletion in the complement factor H-related 3 (CFHR3) gene. The autoantibody for complement factor H was negative. The patient was managed conservatively with adequate blood pressure control. This case highlights the effects of complement dysregulation on the renal tubulointerstitium.

Successful Management of Atypical Hemolytic-Uremic Syndrome in Pregnancy Using Eculizumab: A Case Review

Hemolytic-uremic syndrome (HUS) is a rare thrombotic microangiopathy characterized by the triad of microangiopathic hemolytic anemia (MAHA), thrombocytopenia, and acute kidney injury. The disease is pathologically marked by fibrinoid necrosis within renal arterioles and glomerular capillaries. HUS can be categorized into typical variants, often linked to Shiga toxin-producing Escherichia coli (STEC) infection, and atypical variants that stem from dysregulation in the alternative complement pathway. Pregnancy is a recognized predisposing condition for HUS due to the potential reduction in complement regulatory proteins and the possibility of heightened maternal immune response. This report illustrates the case of a 36-year-old woman who, at 36 weeks of gestation, faced a breech presentation and was diagnosed with atypical HUS (aHUS) after placental abruption. Following a cesarean section, she developed complications, including a pelvic hematoma and bilateral hydronephrosis. Despite initial suboptimal response to plasmapheresis, the patient exhibited marked clinical improvement with eculizumab treatment, with no evidence of disease relapse.

Cutting-Edge Techniques and Drugs for the Treatment of Pulmonary Embolism: Current Knowledge and Future Perspectives

Pulmonary embolism (PE) is a potentially life-threatening condition requiring prompt diagnosis and treatment. Recent advances have led to the development of newer techniques and drugs aimed at improving PE management, reducing its associated morbidity and mortality and the complications related to anticoagulation. This review provides an overview of the current knowledge and future perspectives on PE treatment. Anticoagulation represents the first-line treatment of hemodynamically stable PE, direct oral anticoagulants being a safe and effective alternative to traditional anticoagulation: these drugs have a rapid onset of action, predictable pharmacokinetics, and low bleeding risk. Systemic fibrinolysis is suggested in patients with cardiac arrest, refractory hypotension, or shock due to PE. With this narrative review, we aim to assess the state of the art of newer techniques and drugs that could radically improve PE management in the near future: (i) mechanical thrombectomy and pulmonary embolectomy are promising techniques reserved to patients with massive PE and contraindications or failure to systemic thrombolysis; (ii) catheter-directed thrombolysis is a minimally invasive approach that can be suggested for the treatment of massive or submassive PE, but the lack of large, randomized controlled trials represents a limitation to widespread use; (iii) novel pharmacological approaches, by agents inhibiting thrombin-activatable fibrinolysis inhibitor, factor Xia, and the complement cascade, are currently under investigation to improve PE-related outcomes in specific settings.

Thrombotic microangiopathy after kidney transplantation: Expanding etiologic and pathogenetic spectra

Thrombotic microangiopathy (TMA) is an uncommon but serious complication that not only affects native kidneys but also transplanted kidneys. This review is specifically focused on post-transplant TMA (PT-TMA) involving kidney transplant recipients. Its reported prevalence in the latter population varies from 0.8% to 14% with adverse impacts on both graft and patient survival. It has many causes and associations, and the list of etiologic agents and associations is growing constantly. The pathogenesis is equally varied and a variety of patho genetic pathways lead to the development of microvascular injury as the final common pathway. PT-TMA is categorized in many ways in order to facilitate its management. Ironically, more than one causes are contributory in PT-TMA and it is often difficult to pinpoint one particular cause in an individual case. Pathologically, the hallmark lesions are endothelial cell injury and intravascular thrombi affecting the microvasculature. Early diagnosis and classification of PT-TMA are imperative for optimal outcomes but are challenging for both clinicians and pathologists. The Banff classification has addressed this issue and has developed minimum diagnostic criteria for pathologic diagnosis of PT-TMA in the first phase. Management of the condition is also challenging and still largely empirical. It varies from simple maneuvers, such as plasmapheresis, drug withdrawal or modification, or dose reduction, to lifelong complement blockade, which is very expensive. A thorough understanding of the condition is imperative for an early diagnosis and quick treatment when the treatment is potentially effective. This review aims to increase the awareness of relevant stakeholders regarding this important, potentially treatable but under-recognized cause of kidney allograft dysfunction.

Bacterial Virus Forcing of Bacterial O-Antigen Shields: Lessons from Coliphages

In most Gram-negative bacteria, outer membrane (OM) lipopolysaccharide (LPS) molecules carry long polysaccharide chains known as the O antigens or O polysaccharides (OPS). The OPS structure varies highly from strain to strain, with more than 188 O serotypes described in E. coli. Although many bacteriophages recognize OPS as their primary receptors, these molecules can also screen OM proteins and other OM surface receptors from direct interaction with phage receptor-binding proteins (RBP). In this review, I analyze the body of evidence indicating that most of the E. coli OPS types robustly shield cells completely, preventing phage access to the OM surface. This shield not only blocks virulent phages but also restricts the acquisition of prophages. The available data suggest that OPS-mediated OM shielding is not merely one of many mechanisms of bacterial resistance to phages. Rather, it is an omnipresent factor significantly affecting the ecology, phage-host co-evolution and other related processes in E. coli and probably in many other species of Gram-negative bacteria. The phages, in turn, evolved multiple mechanisms to break through the OPS layer. These mechanisms rely on the phage RBPs recognizing the OPS or on using alternative receptors exposed above the OPS layer. The data allow one to forward the interpretation that, regardless of the type of receptors used, primary receptor recognition is always followed by the generation of a mechanical force driving the phage tail through the OPS layer. This force may be created by molecular motors of enzymatically active tail spikes or by virion structural re-arrangements at the moment of infection.