Longitudinal change in proteinuria and kidney outcomes in C3 glomerulopathy.

INTRODUCTION: The association between a change in proteinuria over time and its impact on kidney prognosis has not been analysed in complement component 3 (C3) glomerulopathy. This study aims to investigate the association between the longitudinal change in proteinuria and the risk of kidney failure. METHODS: This was a retrospective, multicentre observational cohort study in 35 nephrology departments belonging to the Spanish Group for the Study of Glomerular Diseases. Patients diagnosed with C3 glomerulopathy between 1995 and 2020 were enrolled. A joint modelling of linear mixed-effects models was applied to assess the underlying trajectory of a repeatedly measured proteinuria, and a Cox model to evaluate the association of this trajectory with the risk of kidney failure. RESULTS: The study group consisted of 85 patients, 70 C3 glomerulonephritis and 15 dense deposit disease, with a median age of 26 years (range 13-41). During a median follow-up of 42 months, 25 patients reached kidney failure. The longitudinal change in proteinuria showed a strong association with the risk of this outcome, with a doubling of proteinuria levels resulting in a 2.5-fold increase of the risk. A second model showed that a ≥50% proteinuria reduction over time was significantly associated with a lower risk of kidney failure (hazard ratio 0.79; 95% confidence interval 0.56-0.97; P < 0.001). This association was also found when the ≥50% proteinuria reduction was observed within the first 6 and 12 months of follow-up. CONCLUSIONS: The longitudinal change in proteinuria is strongly associated with the risk of kidney failure. The change in proteinuria over time can provide clinicians a dynamic prediction of kidney outcomes.

Validation of a Histologic Scoring Index for C3 Glomerulopathy.

RATIONALE & OBJECTIVE: A previous study that evaluated associations of kidney biopsy findings with disease progression in patients with C3 glomerulopathy (C3G) proposed a prognostic histologic index (C3G-HI) that has not yet been validated. Our objective was to validate the performance of the C3G-HI in a new patient population. STUDY DESIGN: Multicenter, retrospective cohort study. SETTING & PARTICIPANTS: 111 patients fulfilling diagnostic criteria of C3G between January 1995 and December 2019, from 33 nephrology departments belonging to the Spanish Group for the Study of Glomerular Diseases (GLOSEN). PREDICTORS: Demographic, clinical parameters, C3G-HI total activity score, and the C3G-HI total chronicity score. OUTCOME: Time to kidney failure. ANALYTICAL APPROACH: Intraclass correlation coefficients and κ statistic were used to summarize inter-rater reproducibility for assessment of histopathology in kidney biopsies. The nonlinear relationships of risk of kidney failure with the total activity score and total chronicity score were modeled using Cox proportional hazards analysis that incorporated cubic splines. RESULTS: The study group included 93 patients with C3 glomerulonephritis and 18 with dense-deposit disease. Participants had an overall meanage of 35±22 (SD) years. Forty-eight patients (43%) developed kidney failure after a mean follow-up of 65±27 months. The overall inter-rater reproducibility was very good for the total activity score (intraclass correlation coefficient [ICC]=0.63) and excellent for total chronicity score (ICC=0.89). Baseline estimated glomerular filtration rate (eGFR), 24-hour proteinuria, and treatment with immunosuppression were the main determinants of kidney failure in a model with only clinical variables. Only tubular atrophy and interstitial fibrosis were identified as predictors in a model with histological variables. When the total activity score and total chronicity score were added to the model, only the latter was identified as an independent predictor of kidney failure. LIMITATIONS: Only a subset of the kidney biopsies was centrally reviewed. Residual confounding. CONCLUSIONS: We validated the performance of C3G-HI as a predictor of kidney failure in patients with C3G. The total chronicity score was the principal histologic correlate of kidney failure.

Clinical outcome of SARS-CoV-2 infection in immunosuppressed children in Spain.

Limited information is available regarding SARS-CoV-2 infections in children with underlying diseases. A retrospective study of children less than 15 years old with primary or secondary immunosuppression infected with SARS-CoV-2 during March 2020 was performed. In this series, 8 immunocompromised patients with COVID-19 disease are reported, accounting for 15% of the positive cases detected in children in a reference hospital. The severity of the symptoms was mild-moderate in the majority with a predominance of febrile syndrome, with mild radiological involvement and in some cases with mild respiratory distress that required oxygen therapy. The rational and prudent management of these patients is discussed, evaluating possible treatments and options for hospitalization or outpatient follow-up.Conclusion: In our experience, monitoring of children with immunosuppression and COVID-19 disease can be performed as outpatients if close monitoring is possible. Hospitalization should be assessed when high fever, radiological involvement, and/or respiratory distress are present. What is Known: • SARS-CoV-2 infection is usually mild in children. What is New: • Outcome of immunosuppressed children with COVID-19 is generally good, with a mild-moderate course.

Development and validation of a nomogram to predict kidney survival at baseline in patients with C3 glomerulopathy.

Background: C3 glomerulopathy is a rare and heterogeneous complement-driven disease. It is often challenging to accurately predict in clinical practice the individual kidney prognosis at baseline. We herein sought to develop and validate a prognostic nomogram to predict long-term kidney survival. Methods: We conducted a retrospective, multicenter observational cohort study in 35 nephrology departments belonging to the Spanish Group for the Study of Glomerular Diseases. The dataset was randomly divided into a training group (n = 87) and a validation group (n = 28). The least absolute shrinkage and selection operator (LASSO) regression was used to screen the main predictors of kidney outcome and to build the nomogram. The accuracy of the nomogram was assessed by discrimination and risk calibration in the training and validation sets. Results: The study group comprised 115 patients, of whom 46 (40%) reached kidney failure in a median follow-up of 49 months (range 24-112). No significant differences were observed in baseline estimated glomerular filtration rate (eGFR), proteinuria or total chronicity score of kidney biopsies, between patients in the training versus those in the validation set. The selected variables by LASSO were eGFR, proteinuria and total chronicity score. Based on a Cox model, a nomogram was developed for the prediction of kidney survival at 1, 2, 5 and 10 years from diagnosis. The C-index of the nomogram was 0.860 (95% confidence interval 0.834-0.887) and calibration plots showed optimal agreement between predicted and observed outcomes. Conclusions: We constructed and validated a practical nomogram with good discrimination and calibration to predict the risk of kidney failure in C3 glomerulopathy patients at 1, 2, 5 and 10 years.

Complement Genetic Variants and FH Desialylation in S. pneumoniae-Haemolytic Uraemic Syndrome.

Haemolytic Uraemic Syndrome associated with Streptococcus pneumoniae infections (SP-HUS) is a clinically well-known entity that generally affects infants, and could have a worse prognosis than HUS associated to E. coli infections. It has been assumed that complement genetic variants associated with primary atypical HUS cases (aHUS) do not contribute to SP-HUS, which is solely attributed to the action of the pneumococcal neuraminidase on the host cellular surfaces. We previously identified complement pathogenic variants and risk polymorphisms in a few Hungarian SP-HUS patients, and have now extended these studies to a cohort of 13 Spanish SP-HUS patients. Five patients presented rare complement variants of unknown significance, but the frequency of the risk haplotypes in the CFH-CFHR3-CFHR1 region was similar to the observed in aHUS. Moreover, we observed desialylation of Factor H (FH) and the FH-Related proteins in plasma samples from 2 Spanish and 4 Hungarian SP-HUS patients. To analyze the functional relevance of this finding, we compared the ability of native and "in vitro" desialylated FH in: (a) binding to C3b-coated microtiter plates; (b) proteolysis of fluid-phase and surface-bound C3b by Factor I; (c) dissociation of surface bound-C3bBb convertase; (d) haemolytic assays on sheep erythrocytes. We found that desialylated FH had reduced capacity to control complement activation on sheep erythrocytes, suggesting a role for FH sialic acids on binding to cellular surfaces. We conclude that aHUS-risk variants in the CFH-CFHR3-CFHR1 region could also contribute to disease-predisposition to SP-HUS, and that transient desialylation of complement FH by the pneumococcal neuraminidase may have a role in disease pathogenesis.

Advances in understanding the aetiology of atypical Haemolytic Uraemic Syndrome.

Atypical Haemolytic Uraemic Syndrome (aHUS) is a thrombotic microangiopathy that often provokes irreversible renal damage and post-transplantation recurrence. Studies performed during the last decade have shown that 50-60% of aHUS patients present genetic or acquired defects in the complement system that enhance the initial endothelial damage and favour disease development. This review analyses the complement proteins and processes that are disturbed in aHUS patients, and outlines the relevance of a prompt genetic/molecular diagnosis for improving clinical management and prognosis.

COVID-19 in children treated with immunosuppressive medication for kidney diseases.

BACKGROUND: Children are recognised as at lower risk of severe COVID-19 compared with adults, but the impact of immunosuppression is yet to be determined. This study aims to describe the clinical course of COVID-19 in children with kidney disease taking immunosuppressive medication and to assess disease severity. METHODS: Cross-sectional study hosted by the European Rare Kidney Disease Reference Network and supported by the European, Asian and International paediatric nephrology societies. Anonymised data were submitted online for any child (age <20 years) with COVID-19 taking immunosuppressive medication for a kidney condition. Study recruited for 16 weeks from 15 March 2020 to 05 July 2020. The primary outcome was severity of COVID-19. RESULTS: 113 children were reported in this study from 30 different countries. Median age: 13 years (49% male). Main underlying reasons for immunosuppressive therapy: kidney transplant (47%), nephrotic syndrome (27%), systemic lupus erythematosus (10%). Immunosuppressive medications used include: glucocorticoids (76%), mycophenolate mofetil (MMF) (54%), tacrolimus/ciclosporine A (58%), rituximab/ofatumumab (11%). 78% required no respiratory support during COVID-19 illness, 5% required bi-level positive airway pressure or ventilation. Four children died; all deaths reported were from low-income countries with associated comorbidities. There was no significant difference in severity of COVID-19 based on gender, dialysis status, underlying kidney condition, and type or number of immunosuppressive medications. CONCLUSIONS: This global study shows most children with a kidney disease taking immunosuppressive medication have mild disease with SARS-CoV-2 infection. We therefore suggest that children on immunosuppressive therapy should not be more strictly isolated than children who are not on immunosuppressive therapy.

Mycophenolate Mofetil in C3 Glomerulopathy and Pathogenic Drivers of the Disease.

BACKGROUND AND OBJECTIVES: C3 glomerulopathy is a complement-mediated disease arising from abnormalities in complement genes and/or antibodies against complement components. Previous studies showed that treatment with corticosteroids plus mycophenolate mofetil (MMF) was associated with improved outcomes, although the genetic profile of these patients was not systematically analyzed. This study aims to analyze the main determinants of disease progression and response to this therapeutic regimen. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We conducted a retrospective, multicenter, observational cohort study in 35 nephrology departments belonging to the Spanish Group for the Study of Glomerular Diseases. Patients diagnosed with C3 glomerulopathy (n=81) or dense deposit disease (n=16) between January 1995 and March 2018 were enrolled. Multivariable and propensity score matching analyses were used to evaluate the association of clinical and genetic factors with response to treatment with corticosteroids and MMF as measured by proportion of patients with disease remission and kidney survival (status free of kidney failure). RESULTS: The study group comprised 97 patients (84% C3 glomerulopathy, 16% dense deposit disease). Forty-two patients were treated with corticosteroids plus MMF, and this treatment was associated with a higher rate of remission and lower probability of kidney failure (79% and 14%, respectively) compared with patients treated with other immunosuppressives (24% and 59%, respectively), or ecluzimab (33% and 67%, respectively), or conservative management (18% and 65%, respectively). The therapeutic superiority of corticosteroids plus MMF was observed both in patients with complement abnormalities and with autoantibodies. However, patients with pathogenic variants in complement genes only achieved partial remission, whereas complete remissions were common among patients with autoantibody-mediated forms. The main determinant of no remission was baseline proteinuria. Relapses occurred after treatment discontinuation in 33% of the patients who had achieved remission with corticosteroids plus MMF, and a longer treatment length of MMF was associated with a lower risk of relapse. CONCLUSIONS: The beneficial response to corticosteroids plus MMF treatment in C3 glomerulopathy appears independent of the pathogenic drivers analyzed in this study.

TRPC6 mutational analysis in a large cohort of patients with focal segmental glomerulosclerosis.

BACKGROUND: Mutations in the TRPC6 gene have been reported in six families with adult-onset (17-57 years) autosomal dominant focal segmental glomerulosclerosis (FSGS). Electrophysiology studies confirmed augmented calcium influx only in three of these six TRPC6 mutations. To date, the role of TRPC6 in childhood and adulthood non-familial forms is unknown. METHODS: TRPC6 mutation analysis was performed by direct sequencing in 130 Spanish patients from 115 unrelated families with FSGS. An in silico scoring matrix was developed to evaluate the pathogenicity of amino acid substitutions, by using the bio-physical and bio-chemical differences between wild-type and mutant amino acid, the evolutionary conservation of the amino acid residue in orthologues, homologues and defined domains, with the addition of contextual information. RESULTS: Three new missense substitutions were identified in two clinically non-familial cases and in one familial case. The analysis by means of this scoring system allowed us to classify these variants as likely pathogenic mutations. One of them was detected in a female patient with unusual clinical features: mesangial proliferative FSGS in childhood (7 years) and partial response to immunosupressive therapy (CsA + MMF). Asymptomatic carriers of this likely mutation were found within her family. CONCLUSIONS: We describe for the first time TRPC6 mutations in children and adults with non-familial FSGS. It seems that TRPC6 is a gene with a very variable penetrance that may contribute to glomerular diseases in a multi-hit setting.

Nephritic Factors: An Overview of Classification, Diagnostic Tools and Clinical Associations.

Nephritic factors comprise a heterogeneous group of autoantibodies against neoepitopes generated in the C3 and C5 convertases of the complement system, causing its dysregulation. Classification of these autoantibodies can be clustered according to their stabilization of different convertases either from the classical or alternative pathway. The first nephritic factor described with the capacity to stabilize C3 convertase of the alternative pathway was C3 nephritic factor (C3NeF). Another nephritic factor has been characterized by the ability to stabilize C5 convertase of the alternative pathway (C5NeF). In addition, there are autoantibodies against assembled C3/C5 convertase of the classical and lectin pathways (C4NeF). These autoantibodies have been mainly associated with kidney diseases, like C3 glomerulopathy and immune complex-associated-membranoproliferative glomerulonephritis. Other clinical situations where these autoantibodies have been observed include infections and autoimmune disorders such as systemic lupus erythematosus and acquired partial lipodystrophy. C3 hypocomplementemia is a common finding in all patients with nephritic factors. The methods to measure nephritic factors are not standardized, technically complex, and lack of an appropriate quality control. This review will be focused in the description of the mechanism of action of the three known nephritic factors (C3NeF, C4NeF, and C5NeF), and their association with human diseases. Moreover, we present an overview regarding the diagnostic tools for its detection, and the main therapeutic approach for the patients with nephritic factors.

Mutations in proteins of the alternative pathway of complement and the pathogenesis of atypical hemolytic uremic syndrome.

Atypical hemolytic uremic syndrome is associated with mutations in the complement proteins factor H, factor I, factor B, C3, or membrane cofactor protein in about 50% of patients. The evolution and prognosis of the disease in patients carrying mutations in factor H is particularly poor, and renal transplantation most often fails because of recurrence of the disease in the graft. The risk of rapid loss of renal function in patients with functional mutations in factor H requires that effective treatment be initiated as soon as possible, but identification of these patients relies on genetic studies that are time consuming. We describe a case in which an in vitro hemolytic assay proved useful for rapidly assessing factor H dysfunction and for testing whether this dysfunction could be corrected with fresh frozen plasma. In the context of this case, we summarize recent advances in understanding the molecular mechanisms contributing to atypical hemolytic uremic syndrome, including descriptions of DNA- and protein-based analysis. We conclude that functional analysis of factor H should help rationalize the plasma treatment of patients with atypical hemolytic uremic syndrome.

Steroid-resistant nephrotic syndrome: long-term evolution after sequential therapy.

We present a retrospective study of 30 children of mean age 3.02 +/- 1.81 years with steroid-resistant nephrotic syndrome (SRNS) treated with intravenous injection of methylprednisolone plus orally administered prednisone; 24 children also received cyclophosphamide (CP). Sixteen were resistant to steroids from the beginning, and 14 after a mean of 11.26 +/- 16.61 months. The initial histological diagnosis was: 18 minimal change disease (MCD), 11 focal segmental glomerulosclerosis (FSGS) and one diffuse mesangial proliferative glomerulonephritis (DMPG). Total remission was achieved in 22 patients (73.3%), partial response in three (10%) and no response in five (16.6%), two of whom were brothers carrying an NPHS2 gene double mutation. There was no difference in response between the MCD and FSGS patients; the only patient with DMPG did not respond. Only initial resistance was a sign of bad prognosis. At follow-up (6.4 +/- 3.6 years from last pulse), 21/22 were still in remission, 14/21 were without treatment. Six patients required cyclosporine or mycophenolate mofetil because of steroid dependence. Two non-responders developed end-stage renal failure (ESRF); the remaining patients maintained normal glomerular filtration. The treatment was well tolerated. In conclusion, most of the patients treated with sequential therapy consisting of methylprednisolone (MP) (100%) and CP (80%) showed remission and preserved renal function, but 20% developed steroid dependence.