C3 glomerulopathies: dense deposit disease and C3 glomerulonephritis.

Dense deposit disease (DDD) and C3 glomerulonephritis (C3GN) are types of membranoproliferative glomerulonephritis classified as C3 glomerulopathies. These conditions are characterized by an increased number of intraglomerular cells and diffuse thickening of the glomerular capillary walls, along with the deposition of C3 and minimal or absent immunoglobulin deposits. The underlying cause of both DDD and C3Gn is an abnormal activation of the alternative complement pathway, which can result from acquired or genetic alteration. In acquired forms of DDD and C3GN, the dysregulation of the alternative pathway is commonly induced by the presence of C3 nephritic factors (C3NeFs), which are autoantibodies that stabilize C3 convertase. Both DDD and C3GN can affect individuals of any age, but DDD is primarily diagnosed in children, whereas C3GN tends to be diagnosed at a significantly higher age. The presenting features of these diseases are variable and may include proteinuria, hematuria, hypertension, or kidney failure. A common finding in these diseases is low serum C3 levels with normal serum C4 levels. Chronic deterioration of renal function is commonly observed in DDD and C3GN, often leading to end-stage renal disease (ESRD), especially in DDD. Kidney transplantation outcomes in patients with these conditions are characterized by histological recurrence, which may contribute to higher rates of allograft failure.

Glomerulopatía por C3: algoritmo diagnóstico en gestantes

La enfermedad glomerular comprende un grupo heterogéneo de entidades que se caracterizan por la pérdida de la arquitectura o función del glomérulo secundario a proceso inflamatorio del mismo de etiología autoinmune, infecciosa, paraneoplásica, que puede ser identificada con estudios de histopatología. Su reconocimiento durante la gestación representa un reto diagnóstico por la sobreposición de cambios fisiológicos, el debut de enfermedades autoinmunitarias o de enfermedades genéticas, entre otros. La presentación clínica suele encajar en grupos sindromáticos específicos, sin embargo, es frecuente que sean clínicamente indistinguibles o sobrepuestos. El debut de la enfermedad renal con curso clínico de rápida instauración y de evolución desfavorable con respecto a la función renal, hace mandatorio un estudio completo desde el abordaje clínico hasta la interpretación de los hallazgos histopatológicos, encaminado en la distinción de causas primarias y secundarias. Si bien las glomerulonefritis primarias no son las más frecuentes en la gestación, la identificación certera del diagnóstico y su adecuada clasificación permite el manejo dirigido y óptimo de las mismas. Se presentan los casos clínicos de dos gestantes con enfermedad glomerular primaria, con discrepancia en su diagnóstico, enfatizando en sus manifestaciones durante el curso de la gestación, el algoritmo diagnóstico utilizado, el tratamiento inicial y de mantenimiento utilizado. Se resalta la utilidad de la biopsia renal, específicamente la inmunofluorencia para aclarar el mismo.

Glomerular disease involves a heterogeneous group of entities that are characterized by loss of the architecture and function of the glomerulus and this can be caused by immunity, infectious and paraneoplastic etiologies. The aforementioned can be identified in histopathological studies. The recognition of this entity during pregnancy represents a diagnostic challenge due to the superposition of physiological changes, the development of autoimmune diseases and / or genetic disease, among others. Clinical manifestations can be into specific syndromic groups; however we can find indistinguishable manifestations and overlapping of this. When the disease is present its common to find rapidly establishment and unfavorable evolution about renal function. With this it's necessary to complete studies involving the initial clinical approach until histopathological findings with the goal to find primary and secondary causes. As it's known primary glomerulonephritis is not the most frequent in pregnancy, the accuracy in the diagnosis and the proper classification allows the direct and soon management. In this case report we describe 2 pregnant women with primary glomerular disease with discrepancy in their diagnosis. We talk about manifestations during pregnancy, the algorithm used in the diagnosis and finally the initial treatment and the maintenance used in these patients.

Modeling C3 glomerulopathies: C3 convertase regulation on an extracellular matrix surface.

Introduction: C3 glomerulopathies (C3G) are ultra-rare complement-mediated diseases that lead to end-stage renal disease (ESRD) within 10 years of diagnosis in ~50% of patients. Overactivation of the alternative pathway (AP) of complement in the fluid phase and on the surface of the glomerular endothelial glycomatrix is the underlying cause of C3G. Although there are animal models for C3G that focus on genetic drivers of disease, in vivo studies of the impact of acquired drivers are not yet possible. Methods: Here we present an in vitro model of AP activation and regulation on a glycomatrix surface. We use an extracellular matrix substitute (MaxGel) as a base upon which we reconstitute AP C3 convertase. We validated this method using properdin and Factor H (FH) and then assessed the effects of genetic and acquired drivers of C3G on C3 convertase. Results: We show that C3 convertase readily forms on MaxGel and that this formation was positively regulated by properdin and negatively regulated by FH. Additionally, Factor B (FB) and FH mutants impaired complement regulation when compared to wild type counterparts. We also show the effects of C3 nephritic factors (C3Nefs) on convertase stability over time and provide evidence for a novel mechanism of C3Nef-mediated C3G pathogenesis. Discussion: We conclude that this ECM-based model of C3G offers a replicable method by which to evaluate the variable activity of the complement system in C3G, thereby offering an improved understanding of the different factors driving this disease process.

Substitutions at position 263 within the von Willebrand factor type A domain determine the functionality of complement C2 protein.

The complement system is one of the first defense lines protecting from invading pathogens. However, it may turn offensive to the body's own cells and tissues when deregulated by the presence of rare genetic variants that impair physiological regulation and/or provoke abnormal activity of key enzymatic components. Factor B and complement C2 are examples of paralogs engaged in the alternative and classical/lectin complement pathway, respectively. Pathogenic mutations in the von Willebrand factor A domain (vWA) of FB have been known for years. Despite substantial homology between two proteins and the demonstration that certain substitutions in FB translated to C2 result in analogous phenotype, there was a limited number of reports on pathogenic C2 variants in patients. Recently, we studied a cohort of patients suffering from rare kidney diseases and confirmed the existence of two gain-of-function and three loss-of-function mutations within the C2 gene sequences coding for the vWA domain (amino acids 254-452) or nearly located unstructured region (243-253) of C2 protein. Herein, we report the functional consequences of amino acid substitution of glutamine at position 263. The p.Q263G variant resulted in the gain-of-function phenotype, similarly to a homologous mutation p.D279G in FB. Conversely, the p.Q263P variant found in a patient with C3 glomerulopathy resulted in the loss of C2 function. Our results confirm that the N-terminal part of the vWA domain is a hot spot crucial for the complement C2 function.

Thrombotic Microangiopathy, an Unusual Form of Monoclonal Gammopathy of Renal Significance: Report of 3 Cases and Literature Review.

Monoclonal gammopathies result from neoplastic clones of the B-cell lineage and may cause kidney disease by various mechanisms. When the underlying clone does not meet criteria for a malignancy requiring treatment, the paraprotein is called a monoclonal gammopathy of renal significance (MGRS). One rarely reported kidney lesion associated with benign paraproteins is thrombotic microangiopathy (TMA), provisionally considered as a combination signifying MGRS. Such cases may lack systemic features of TMA, such as a microangiopathic hemolytic anemia, and the disease may be kidney limited. There is no direct deposition of the paraprotein in the kidney, and the presumed mechanism is disordered complement regulation. We report three cases of kidney limited TMA associated with benign paraproteins that had no other detectable cause for the TMA, representing cases of MGRS. Two of the cases are receiving clone directed therapy, and none are receiving eculizumab. We discuss in detail the pathophysiological basis for this possible association. Our approach to therapy involves first ruling out other causes of TMA as well as an underlying B-cell malignancy that would necessitate direct treatment. Otherwise, clone directed therapy should be considered. If refractory to such therapy or the disease is severe and multisystemic, C5 inhibition (eculizumab or ravulizumab) may be indicated as well.

Recurrent Glomerular Diseases in Renal Transplantation with Focus on Role of Electron Microscopy.

Background: The common causes of renal transplant complications include active or chronic rejection process, infections, and toxicity but also recurrent or de novo diseases, which play an important role in affecting long-term graft function or graft loss. Summary: Recurrent disease in renal transplantation is defined as recurrence of the original kidney disease leading to end-stage kidney disease. They comprise a heterogeneous group of predominantly glomerular and some tubulointerstitial and vascular lesions, which include primary kidney diseases (e.g., focal segmental glomerulosclerosis, membranous glomerulonephritis, and IgA nephropathy) or those secondary to systemic autoimmune, metabolic, and infectious processes that can range from subclinical to clinically overt acute, subacute, or chronic clinical presentations. In addition to the knowledge of prior renal disease and routine/periodic serum and urine testing for kidney function, a complete transplant renal biopsy examination is essential in the identification and differentiation of these diseases. The time of onset and severity of these diseases depend on the underlying etiopathogenetic mechanisms and the varied rates of recurrence in the early or late posttransplant period, often being modified by the current immunosuppressive protocols and other donor and recipient predisposing characteristics. Key Messages: Transplant kidney biopsy findings provide diagnostic accuracy and prognostic information regarding the potential for reversibility along with detection of unsuspected or clinically symptomatic recurrent diseases, with any concomitant rejection process or toxicity, for appropriate therapeutic decision-making. Routine electron microscopy in transplant kidney biopsies is a valuable tool in recognizing fully developed or early/subtle features of evolving recurrent diseases, often during the subclinical phases, in for cause or surveillance allograft biopsies.

Factor B and C4b2a Autoantibodies in C3 Glomerulopathy.

C3 Glomerulopathy (C3G) is a renal disease mediated primarily by dysregulation of the alternative pathway of complement. Complement is the cornerstone of innate immunity. It targets infectious microbes for destruction, clears immune complexes, and apoptotic cells from the circulation, and augments the humoral response. In C3G, this process becomes dysregulated, which leads to the deposition of complement proteins-including complement component C3-in the glomerular basement membrane of the kidney. Events that trigger complement are typically environmental insults like infections. Once triggered, in patients who develop C3G, complement activity is sustained by a variety of factors, including rare or novel genetic variants in complement genes and autoantibodies that alter normal complement protein function and/or regulation. Herein, we review two such autoantibodies, one to Factor B and the other to C4b2a, the C3 convertase of the classical, and lectin pathways. These two types of autoantibodies are identified in a small fraction of C3G patients and contribute marginally to the C3G phenotype.

Both Monoclonal and Polyclonal Immunoglobulin Contingents Mediate Complement Activation in Monoclonal Gammopathy Associated-C3 Glomerulopathy.

C3 glomerulopathy (C3G) results from acquired or genetic abnormalities in the complement alternative pathway (AP). C3G with monoclonal immunoglobulin (MIg-C3G) was recently included in the spectrum of "monoclonal gammopathy of renal significance." However, mechanisms of complement dysregulation in MIg-C3G are not described and the pathogenic effect of the monoclonal immunoglobulin is not understood. The purpose of this study was to investigate the mechanisms of complement dysregulation in a cohort of 41 patients with MIg-C3G. Low C3 level and elevated sC5b-9, both biomarkers of C3 and C5 convertase activation, were present in 44 and 78% of patients, respectively. Rare pathogenic variants were identified in 2/28 (7%) tested patients suggesting that the disease is acquired in a large majority of patients. Anti-complement auto-antibodies were found in 20/41 (49%) patients, including anti-FH (17%), anti-CR1 (27%), anti-FI (5%) auto-antibodies, and C3 Nephritic Factor (7%) and were polyclonal in 77% of patients. Using cofactor assay, the regulation of the AP was altered in presence of purified IgG from 3/9 and 4/7 patients with anti-FH or anti-CR1 antibodies respectively. By using fluid and solid phase AP activation, we showed that total purified IgG of 22/34 (65%) MIg-C3G patients were able to enhance C3 convertase activity. In five documented cases, we showed that the C3 convertase enhancement was mostly due to the monoclonal immunoglobulin, thus paving the way for a new mechanism of complement dysregulation in C3G. All together the results highlight the contribution of both polyclonal and monoclonal Ig in MIg-C3G. They provide direct insights to treatment approaches and opened up a potential way to a personalized therapeutic strategy based on chemotherapy adapted to the B cell clone or immunosuppressive therapy.

Eculizumab reversed severe distal ischemic syndrome and glomerulonephritis with isolated C3 deposits associated with anti-factor H autoantibodies: a case report.

B-cell clones can produce a monoclonal immunoglobulin, which may be responsible for visceral involvements. Kidney involvement is frequent, affecting 20 to 50% of patients with multiple myeloma. One mechanism underlying this involvement is a dysregulation of the complement alternative pathway, leading to C3 glomerulopathies. We report a patient who had a multiple myeloma, C3 glomerulopathy related to factor H autoantibody, and digital ischemia, who was treated successfully with eculizumab, an anti-complement therapy, without any relapse in 2 years of follow-up.

Complement Dysregulation and Disease: Insights from Contemporary Genetics.

The vertebrate complement system consists of sequentially interacting proteins that provide for a rapid and powerful host defense. Nearly 60 proteins comprise three activation pathways (classical, alternative, and lectin) and a terminal cytolytic pathway common to all. Attesting to its potency, nearly half of the system's components are engaged in its regulation. An emerging theme over the past decade is that variations in these inhibitors predispose to two scourges of modern humans. One, occurring most often in childhood, is a rare but deadly thrombomicroangiopathy called atypical hemolytic uremic syndrome. The other, age-related macular degeneration, is the most common form of blindness in the elderly. Their seemingly unrelated clinical presentations and pathologies share the common theme of overactivity of the complement system's alternative pathway. This review summarizes insights gained from contemporary genetics for understanding how dysregulation of this powerful innate immune system leads to these human diseases.

Overview of Laboratory Testing and Clinical Presentations of Complement Deficiencies and Dysregulation.

Historically, complement disorders have been attributed to immunodeficiency associated with severe or frequent infection. More recently, however, complement has been recognized for its role in inflammation, autoimmune disorders, and vision loss. This paradigm shift requires a fundamental change in how complement testing is performed and interpreted. Here, we provide an overview of the complement pathways and summarize recent literature related to hereditary and acquired angioedema, infectious diseases, autoimmunity, and age-related macular degeneration. The impact of complement dysregulation in atypical hemolytic uremic syndrome, paroxysmal nocturnal hemoglobinuria, and C3 glomerulopathies is also described. The advent of therapeutics such as eculizumab and other complement inhibitors has driven the need to more fully understand complement to facilitate diagnosis and monitoring. In this report, we review analytical methods and discuss challenges for the clinical laboratory in measuring this complex biochemical system.

Reclassification of membranoproliferative glomerulonephritis: Identification of a new GN: C3GN.

This review revises the reclassification of the membranoproliferative glomerulonephritis (MPGN) after the consensus conference that by 2015 reclassified all the glomerulonephritis basing on etiology and pathogenesis, instead of the histomorphological aspects. After reclassification, two types of MPGN are to date recognized: The immunocomplexes mediated MPGN and the complement mediated MPGN. The latter type is more extensively described in the review either because several of these entities are completely new or because the improved knowledge of the complement cascade allowed for new diagnostic and therapeutic approaches. Overall the complement mediated MPGN are related to acquired or genetic cause. The presence of circulating auto antibodies is the principal acquired cause. Genetic wide association studies and family studies allowed to recognize genetic mutations of different types as causes of the complement dysregulation. The complement cascade is a complex phenomenon and activating factors and regulating factors should be distinguished. Genetic mutations causing abnormalities either in activating or in regulating factors have been described. The diagnosis of the complement mediated MPGN requires a complete study of all these different complement factors. As a consequence, new therapeutic approaches are becoming available. Indeed, in addition to a nonspecific treatment and to the immunosuppression that has the aim to block the auto antibodies production, the specific inhibition of complement activation is relatively new and may act either blocking the C5 convertase or the C3 convertase. The drugs acting on C3 convertase are still in different phases of clinical development and might represent drugs for the future. Overall the authors consider that one of the principal problems in finding new types of drugs are both the rarity of the disease and the consequent poor interest in the marketing and the lack of large international cooperative studies.

Understanding the complement-mediated glomerular diseases: focus on membranoproliferative glomerulonephritis and C3 glomerulopathies.

An enhanced understanding of the role of complement in the pathogenesis of membranoproliferative glomerulonephritis has led to reclassification of the latter into immunoglobulin-mediated and non-immunoglobulin-mediated disease. The new classification schema resulted in improved diagnostic clinical algorithms, while it brought into light again the diseases, which are characterized by the presence of glomerular deposits, composed predominantly by C3, in the absence of significant amounts of immunoglobulins in renal biopsy, namely, C3 glomerulopathies (dense deposit disease and C3 glomerulonephritis). Despite the lack of randomized controlled trials following the advances in the understanding of the pathogenetic pathways involved in membranoproliferative glomerulonephritis, it is important that the new mechanistic approach has opened new roads for the exploration and discovery of targeted therapies.

Overview of C3 Glomerulopathy.

C3 glomerulopathy is an umbrella term, which includes several rare forms of glomerulonephritis (GN) with underlying defects in the alternate complement cascade. A common histological feature noted in all these GN is dominant C3 deposition in the glomerulus. In this review, we will provide an overview of the complement system as well as mediators, with an introduction to pharmaceutical agents that can alter the pathway.

Complement related kidney diseases: Recurrence after transplantation.

The recurrence of renal disease after renal transplantation is becoming one of the main causes of graft loss after kidney transplantation. This principally concerns some of the original diseases as the atypical hemolytic uremic syndrome (HUS), the membranoproliferative glomerulonephritis (MPGN), in particular the MPGN now called C3 glomerulopathy. Both this groups of renal diseases are characterized by congenital (genetic) or acquired (auto-antibodies) modifications of the alternative pathway of complement. These abnormalities often remain after transplantation because they are constitutional and poorly influenced by the immunosuppression. This fact justifies the high recurrence rate of these diseases. Early diagnosis of recurrence is essential for an optimal therapeutically approach, whenever possible. Patients affected by end stage renal disease due to C3 glomerulopathies or to atypical HUS, may be transplanted with extreme caution. Living donor donation from relatives is not recommended because members of the same family may be affected by the same gene mutation. Different therapeutically approaches have been attempted either for recurrence prevention and treatment. The most promising approach is represented by complement inhibitors. Eculizumab, a monoclonal antibody against C5 convertase is the most promising drug, even if to date is not known how long the therapy should be continued and which are the best dosing. These facts face the high costs of the treatment. Eculizumab resistant patients have been described. They could benefit by a C3 convertase inhibitor, but this class of drugs is by now the object of randomized controlled trials.

Anti-complement therapy for glomerular diseases.

A major shift in our understanding of glomerular diseases is the focus on which components of the complement pathway are involved in mediating kidney injury. For example, the membranoproliferative glomerulonephritis lesion is no longer classified solely by ultrastructural findings on biopsy and is now divided into immune-complex-mediated lesions vs complement-mediated lesions. In turn, this emphasis on complement leads to interest in therapies that target complement as potential disease-modifying agents. Eculizumab, the first available anti-complement therapy, blocks at the level of C5 and has revolutionized the treatment of atypical hemolytic uremic syndrome. Whether this agent will work equally well for the far more heterogeneous entities of C3 glomerulonephritis and dense deposit disease remains unclear. Instead, newer agents that target C3 may turn out to be the most effective and specific therapy for these C3 glomerulopathies.

Diagnostic tests and treatment options in glomerular disease: 2014 update.

Glomerular diseases historically have been challenging disorders to comprehend and treat for patients and physicians alike. Kidney biopsy is the gold standard of diagnosis, but the link between pathophysiology and the histologic representation of kidney injury has remained elusive in many of these diseases. As a result, treatment of glomerular disease usually involves therapies that are not specific to disease pathogenesis, such as blockade of the renin-angiotensin-aldosterone system and various immunosuppression regimens. Recent research has resulted in greater insight into some glomerular diseases, leading to the hope that new diagnostic tests and treatments targeting disease-specific mechanisms are on the horizon. We review recent progress on the understanding, diagnosis, and treatment of 4 glomerular diseases: immunoglobulin A nephropathy, focal segmental glomerulosclerosis, the C3 glomerulopathies, and idiopathic membranous nephropathy.