A case-based narrative review of pregnancy-associated atypical hemolytic uremic syndrome/complement-mediated thrombotic microangiopathy.

Atypical hemolytic uremic syndrome is a complement-mediated thrombotic microangiopathy caused by uncontrolled activation of the alternative complement pathway in the setting of autoantibodies to or rare pathogenic genetic variants in complement proteins. Pregnancy may serve as a trigger and unmask atypical hemolytic uremic syndrome/complement-mediated thrombotic microangiopathy (aHUS/CM-TMA), which has severe, life-threatening consequences. It can be difficult to diagnose aHUS/CM-TMA in pregnancy due to overlapping clinical features with other thrombotic microangiopathy syndromes including hypertensive disorders of pregnancy. However, the distinction among thrombotic microangiopathy etiologies in pregnancy is important because each syndrome has specific disease management and treatment. In this narrative review, we discuss 2 cases to illustrate the diagnostic challenges and evolving approach in the management of pregnancy-associated aHUS/CM-TMA. The first case involves a 30-year-old woman presenting in the first trimester who was diagnosed with aHUS/CM-TMA and treated with eculizumab from 19 weeks' gestation. Genetic testing revealed a likely pathogenic variant in CFI. She successfully delivered a healthy infant at 30 weeks' gestation. In the second case, a 22-year-old woman developed severe postpartum HELLP syndrome, requiring hemodialysis. Her condition improved with supportive management, yet investigations assessing for aHUS/CM-TMA remained abnormal 6 months postpartum consistent with persistent complement activation but negative genetic testing. Through detailed case discussion describing tests assessing for placental health, fetal anatomy, complement activation, autoantibodies to complement regulatory proteins, and genetic testing for aHUS/CM-TMA, we describe how these results aided in the clinical diagnosis of pregnancy-associated aHUS/CM-TMA and assisted in guiding patient management, including the use of anticomplement therapy.

Corrigendum: Delphi: A Democratic and Cost-Effective Method of Consensus Generation in Transplantation.

[This corrects the article DOI: 10.3389/ti.2023.11589.].

Corrigendum: Thrombotic Microangiopathy in the Renal Allograft: Results of the TMA Banff Working Group Consensus on Pathologic Diagnostic Criteria.

[This corrects the article DOI: 10.3389/ti.2023.11590.].

Delphi: A Democratic and Cost-Effective Method of Consensus Generation in Transplantation.

The Thrombotic Microangiopathy Banff Working Group (TMA-BWG) was formed in 2015 to survey current practices and develop minimum diagnostic criteria (MDC) for renal transplant TMA (Tx-TMA). To generate consensus among pathologists and nephrologists, the TMA BWG designed a 3-Phase study. Phase I of the study is presented here. Using the Delphi methodology, 23 panelists with >3 years of diagnostic experience with Tx-TMA pathology listed their MDC suggesting light, immunofluorescence, and electron microscopy lesions, clinical and laboratory information, and differential diagnoses. Nine rounds (R) of consensus resulted in MDC validated during two Rs using online evaluation of whole slide digital images of 37 biopsies (28 TMA, 9 non-TMA). Starting with 338 criteria the process resulted in 24 criteria and 8 differential diagnoses including 18 pathologic, 2 clinical, and 4 laboratory criteria. Results show that 3/4 of the panelists agreed on the diagnosis of 3/4 of cases. The process also allowed definition refinement for 4 light and 4 electron microscopy lesions. For the first time in Banff classification, the Delphi methodology was used to generate consensus. The study shows that Delphi is a democratic and cost-effective method allowing rapid consensus generation among numerous physicians dealing with large number of criteria in transplantation.

Thrombotic Microangiopathy in the Renal Allograft: Results of the TMA Banff Working Group Consensus on Pathologic Diagnostic Criteria.

The Banff community summoned the TMA Banff Working Group to develop minimum diagnostic criteria (MDC) and recommendations for renal transplant TMA (Tx-TMA) diagnosis, which currently lacks standardized criteria. Using the Delphi method for consensus generation, 23 nephropathologists (panelists) with >3 years of diagnostic experience with Tx-TMA were asked to list light, immunofluorescence, and electron microscopic, clinical and laboratory criteria and differential diagnoses for Tx-TMA. Delphi was modified to include 2 validations rounds with histological evaluation of whole slide images of 37 transplant biopsies (28 TMA and 9 non-TMA). Starting with 338 criteria in R1, MDC were narrowed down to 24 in R8 generating 18 pathological, 2 clinical, 4 laboratory criteria, and 8 differential diagnoses. The panelists reached a good level of agreement (70%) on 76% of the validated cases. For the first time in Banff classification, Delphi was used to reach consensus on MDC for Tx-TMA. Phase I of the study (pathology phase) will be used as a model for Phase II (nephrology phase) for consensus regarding clinical and laboratory criteria. Eventually in Phase III (consensus of the consensus groups) and the final MDC for Tx-TMA will be reported to the transplantation community.

Molecular Characterization of Membranous Nephropathy.

BACKGROUND: Molecular characterization of nephropathies may facilitate pathophysiologic insight, development of targeted therapeutics, and transcriptome-based disease classification. Although membranous nephropathy (MN) is a common cause of adult-onset nephrotic syndrome, the molecular pathways of kidney damage in MN require further definition. METHODS: We applied a machine-learning framework to predict diagnosis on the basis of gene expression from the microdissected kidney tissue of participants in the Nephrotic Syndrome Study Network (NEPTUNE) cohort. We sought to identify differentially expressed genes between participants with MN versus those of other glomerulonephropathies across the NEPTUNE and European Renal cDNA Bank (ERCB) cohorts, to find MN-specific gene modules in a kidney-specific functional network, and to identify cell-type specificity of MN-specific genes using single-cell sequencing data from reference nephrectomy tissue. RESULTS: Glomerular gene expression alone accurately separated participants with MN from those with other nephrotic syndrome etiologies. The top predictive classifier genes from NEPTUNE participants were also differentially expressed in the ERCB participants with MN. We identified a signature of 158 genes that are significantly differentially expressed in MN across both cohorts, finding 120 of these in a validation cohort. This signature is enriched in targets of transcription factor NF-κB. Clustering these MN-specific genes in a kidney-specific functional network uncovered modules with functional enrichments, including in ion transport, cell projection morphogenesis, regulation of adhesion, and wounding response. Expression data from reference nephrectomy tissue indicated 43% of these genes are most highly expressed by podocytes. CONCLUSIONS: These results suggest that, relative to other glomerulonephropathies, MN has a distinctive molecular signature that includes upregulation of many podocyte-expressed genes, provides a molecular snapshot of MN, and facilitates insight into MN's underlying pathophysiology.

Rituximab or Cyclosporine in the Treatment of Membranous Nephropathy.

BACKGROUND: B-cell anomalies play a role in the pathogenesis of membranous nephropathy. B-cell depletion with rituximab may therefore be noninferior to treatment with cyclosporine for inducing and maintaining a complete or partial remission of proteinuria in patients with this condition. METHODS: We randomly assigned patients who had membranous nephropathy, proteinuria of at least 5 g per 24 hours, and a quantified creatinine clearance of at least 40 ml per minute per 1.73 m2 of body-surface area and had been receiving angiotensin-system blockade for at least 3 months to receive intravenous rituximab (two infusions, 1000 mg each, administered 14 days apart; repeated at 6 months in case of partial response) or oral cyclosporine (starting at a dose of 3.5 mg per kilogram of body weight per day for 12 months). Patients were followed for 24 months. The primary outcome was a composite of complete or partial remission of proteinuria at 24 months. Laboratory variables and safety were also assessed. RESULTS: A total of 130 patients underwent randomization. At 12 months, 39 of 65 patients (60%) in the rituximab group and 34 of 65 (52%) in the cyclosporine group had a complete or partial remission (risk difference, 8 percentage points; 95% confidence interval [CI], -9 to 25; P = 0.004 for noninferiority). At 24 months, 39 patients (60%) in the rituximab group and 13 (20%) in the cyclosporine group had a complete or partial remission (risk difference, 40 percentage points; 95% CI, 25 to 55; P<0.001 for both noninferiority and superiority). Among patients in remission who tested positive for anti-phospholipase A2 receptor (PLA2R) antibodies, the decline in autoantibodies to anti-PLA2R was faster and of greater magnitude and duration in the rituximab group than in the cyclosporine group. Serious adverse events occurred in 11 patients (17%) in the rituximab group and in 20 (31%) in the cyclosporine group (P = 0.06). CONCLUSIONS: Rituximab was noninferior to cyclosporine in inducing complete or partial remission of proteinuria at 12 months and was superior in maintaining proteinuria remission up to 24 months. (Funded by Genentech and the Fulk Family Foundation; MENTOR ClinicalTrials.gov number, NCT01180036.).

Acute kidney injury after Pfizer COVID-19 vaccine due to crescentic fibrillary glomerulonephritis.

Fibrillary glomerulonephritis (FGN) is a rare glomerular disease manifesting with proteinuria, renal impairment, hematuria, hypertension, and in a very small proportion can be associated with rapidly progressive glomerulonephritis and, rarely, crescent formation. The main modality for diagnosis is kidney biopsy, which ultrastructurally demonstrates randomly arranged non-branching mesangial and glomerular basement membrane (GBM) fibrils and positive staining for the biomarker DNAJB9. The pathogenesis is largely unknown. It was previously hypothesized to represent an immune-complex-type glomerulonephritis, as most cases show IgG4 restriction. We present the first case of crescentic FGN after mRNA Pfizer vaccine for COVID-19. A strong temporal association between vaccination, elevated creatinine, and diffuse crescentic fibrillary process was found. Immunological, neoplastic, and infectious causes were ruled out. We hypothesized that the vaccine stimulated an immune response that triggered crescentic FGN, however, further investigations will be needed to elucidate the direct role of COVID-19 vaccination in crescentic glomerular disease.

IgA Nephropathy: Core Curriculum 2021.

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerular disease worldwide. The diagnostic histologic hallmark is dominant or codominant IgA staining on kidney biopsy; however, patients may present with various clinical syndromes ranging from asymptomatic abnormalities noted on urinalysis to rapidly progressive glomerulonephritis. Given substantial heterogeneity in the clinical course of disease, online risk calculators are available that may assist in prognostication and inform discussions with patients. Comprehensive supportive treatment is central in the initial therapy of IgAN; the additive benefit of currently available immunosuppressive agents remains an area of controversy. Although proteinuria is attenuated by the use of corticosteroids, the long-term benefits have been questioned, and the use of corticosteroids is associated with severe adverse effects, notably infection. Recent advances in our understanding of mucosal immunity and the role of the complement system in IgAN pathogenesis are leading to development of novel therapeutic options, which are being evaluated in ongoing clinical trials. In this installment of the AJKD Core Curriculum in Nephrology, IgAN pathogenesis, clinical manifestations, histology, prediction tools, and treatment are reviewed, and case examples are presented to illustrate the approach to the management of patients with IgAN.

Ultrastructural Characterization of Proteinuric Patients Predicts Clinical Outcomes.

BACKGROUND: The analysis and reporting of glomerular features ascertained by electron microscopy are limited to few parameters with minimal predictive value, despite some contributions to disease diagnoses. METHODS: We investigated the prognostic value of 12 electron microscopy histologic and ultrastructural changes (descriptors) from the Nephrotic Syndrome Study Network (NEPTUNE) Digital Pathology Scoring System. Study pathologists scored 12 descriptors in NEPTUNE renal biopsies from 242 patients with minimal change disease or FSGS, with duplicate readings to evaluate reproducibility. We performed consensus clustering of patients to identify unique electron microscopy profiles. For both individual descriptors and clusters, we used Cox regression models to assess associations with time from biopsy to proteinuria remission and time to a composite progression outcome (≥40% decline in eGFR, with eGFR<60 ml/min per 1.73 m2, or ESKD), and linear mixed models for longitudinal eGFR measures. RESULTS: Intrarater and interrater reproducibility was >0.60 for 12 out of 12 and seven out of 12 descriptors, respectively. Individual podocyte descriptors such as effacement and microvillous transformation were associated with complete remission, whereas endothelial cell and glomerular basement membrane abnormalities were associated with progression. We identified six descriptor-based clusters with distinct electron microscopy profiles and clinical outcomes. Patients in a cluster with more prominent foot process effacement and microvillous transformation had the highest rates of complete proteinuria remission, whereas patients in clusters with extensive loss of primary processes and endothelial cell damage had the highest rates of the composite progression outcome. CONCLUSIONS: Systematic analysis of electron microscopic findings reveals clusters of findings associated with either proteinuria remission or disease progression.

Secretion of the epithelial sodium channel chaperone PCSK9 from the cortical collecting duct links sodium retention with hypercholesterolemia in nephrotic syndrome.

The proprotein PCSK9 functions as a chaperone for the epithelial sodium channel in the cortical collecting duct (CCD), is highly expressed in the liver, and plays a significant role in the pathogenesis of hypercholesterolemia. Lower levels of PCSK9 expression also occur in the normal kidney and intestine. Here, we found increased PCSK9 expression in the CCD of biopsies of patients with primary glomerular disease and explored a possible relationship with hypercholesterolemia of nephrotic syndrome. Significantly elevated serum PCSK9 and cholesterol levels were noted in two models of focal and segmental glomerulosclerosis, the Rrm2b-/- mouse and the Buffalo/Mna rat. Increased expression of PCSK9 in the kidney occurred when liver expression was reduced in both models. The impact of reduced or increased PCSK9 in the CCD on hypercholesterolemia in nephrotic syndrome was next studied. Mice with selective deficiency of PCSK9 expression in the collecting duct failed to develop hypercholesterolemia after injection of nephrotoxic serum. Blocking epithelial sodium channel activity with Amiloride in Rrm2b-/- mice resulted in increased expression of its chaperone PCSK9 in the CCD, followed by elevated plasma levels and worsening hypercholesterolemia. Thus, our data suggest that PCSK9 in the kidney plays a role in the initiation of hypercholesterolemia in nephrotic syndrome and make a case for depletion of PCSK9 early in patients with nephrotic syndrome to prevent the development of hypercholesterolemia.

The zinc fingers and homeoboxes 2 protein ZHX2 and its interacting proteins regulate upstream pathways in podocyte diseases.

Zinc fingers and homeoboxes (ZHX) proteins are heterodimeric transcriptional factors largely expressed at the cell membrane in podocytes in vivo. We found ZHX2-based heterodimers in podocytes, with ZHX2-ZHX1 predominantly at the cell membrane of the podocyte cell body, and ZHX2-ZHX3 at the slit diaphragm. In addition to changes in overall ZHX2 expression, there was increased podocyte nuclear ZHX3 and ZHX2 in patients with focal segmental glomerulosclerosis, and increased podocyte nuclear ZHX1 in patients with minimal change disease. Zhx2 deficient mice had increased podocyte ZHX1 and ZHX3 expression. Zhx2 deficient mice and podocyte specific Zhx2 overexpressing transgenic rats develop worse experimental focal segmental glomerulosclerosis than controls, with increased nuclear ZHX3 and ZHX2, respectively. By contrast, podocyte specific Zhx2 overexpressing transgenic rats develop lesser proteinuria during experimental minimal change disease due to peripheral sequestration of ZHX1 by ZHX2. Using co-immunoprecipitation, the interaction of ZHX2 with aminopeptidase A in the podocyte body cell membrane, and EPHRIN B1 in the slit diaphragm were noted to be central to upstream events in animal models of minimal change disease and focal segmental glomerulosclerosis, respectively. Mice deficient in Enpep, the gene for aminopeptidase A, and Efnb1, the gene for ephrin B1 developed worse albuminuria in glomerular disease models. Targeting aminopeptidase A in Zhx2 deficient mice with monoclonal antibodies induced albuminuria and upregulation of the minimal change disease mediator angiopoietin-like 4 through nuclear entry of ZHX1. Thus, podocyte ZHX2 imbalance is a critical factor in human glomerular disease, with minimal change disease disparities mediated mostly through ZHX1, and focal segmental glomerulosclerosis deviations through ZHX3 and ZHX2.

Performance of the 2016 ACR/EULAR SS classification criteria in patients with secondary Sjögren's syndrome.

OBJECTIVES: To evaluate the performance of the 2016 ACR-EULAR classification Sjögren's syndrome (SS) criteria for classifying patients with secondary SS. METHODS: We randomly selected 300 patients with systemic lupus erythematosus, rheumatoid arthritis and scleroderma, as well as 50 with primary SS. SS diagnosis was established by two independent rheumatologists and was based on the combination of symptoms, signs, diagnostic tests and medical chart review. We evaluated the fulfillment of the 2002 AECG, 2012 ACR and 2016 ACR/EULAR criteria, and their performance using as the gold standard the clinical diagnosis. RESULTS: We identified 154 patients with a clinical (definitive/probable) SS diagnosis, 95 patients (61.7%) fulfilled the AECG, 96 patients (62.3%) the ACR and 90 (58.4%) the 2016 ACR/EULAR criteria. Among the subset with definitive SS clinical diagnosis (n=99), 83 patients (83.8%) fulfilled the AECG, 77 (77.7%) the ACR and 79 (79.7%) the 2016 ACR/EULAR criteria. The concordance rate between the clinical diagnosis (definitive/probable) and the AECG, ACR and 2016 ACR/ EULAR criteria was κ=0.58, κ=0.55 and κ=0.60, respectively. The 2016 ACR/EULAR criteria showed the best AUCs results (0.87 definitive/probable diagnosis, 0.90 definitive diagnosis), followed by the AECG (0.82 definitive/probable diagnosis, 0.85 definitive diagnosis) and ACR (0.80 definitive/probable diagnosis, 0.79 definitive diagnosis) criteria. As a sensitivity analysis, the results were similar when excluding patients with primary SS. CONCLUSIONS: Our study provides further evidence that the 2016 ACR/EULAR criteria are applicable in the setting of secondary SS.

Nephrotic Syndrome With Cancer Immunotherapies: A Report of 2 Cases.

Oncologic immunotherapies use a patient's immune response to eliminate tumor cells by modulation of immune checkpoints, including programmed cell death 1 (PD-1) and cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) proteins. Immune-mediated sequelae, including interstitial nephritis, have been reported; however, glomerular disease appears rare. We describe 2 cases of nephrotic syndrome in patients treated with these agents. Patient 1 received the anti-PD-1 antibody pembrolizumab for Hodgkin lymphoma. Following his second dose, he developed nephrotic syndrome and acute kidney injury. Biopsy showed diffuse foot-process effacement consistent with minimal change disease and findings of acute tubular injury. Pembrolizumab therapy cessation and corticosteroid treatment yielded improvement in proteinuria and acute kidney injury. Patient 2 received the CTLA-4 antibody ipilimumab for melanoma. He developed nephrotic syndrome with biopsy changes consistent with minimal change disease. Ipilimumab therapy was stopped and proteinuria resolved following corticosteroid treatment. Ipilimumab rechallenge caused relapse of nephrotic-range proteinuria. These cases suggest an association between therapeutic immune activation and the development of nephrotic syndrome. Given the increasing prevalence of oncologic immunotherapies, monitoring patients for renal sequelae is warranted.

Reproducibility of the NEPTUNE descriptor-based scoring system on whole-slide images and histologic and ultrastructural digital images.

The multicenter Nephrotic Syndrome Study Network (NEPTUNE) digital pathology scoring system employs a novel and comprehensive methodology to document pathologic features from whole-slide images, immunofluorescence and ultrastructural digital images. To estimate inter- and intra-reader concordance of this descriptor-based approach, data from 12 pathologists (eight NEPTUNE and four non-NEPTUNE) with experience from training to 30 years were collected. A descriptor reference manual was generated and a webinar-based protocol for consensus/cross-training implemented. Intra-reader concordance for 51 glomerular descriptors was evaluated on jpeg images by seven NEPTUNE pathologists scoring 131 glomeruli three times (Tests I, II, and III), each test following a consensus webinar review. Inter-reader concordance of glomerular descriptors was evaluated in 315 glomeruli by all pathologists; interstitial fibrosis and tubular atrophy (244 cases, whole-slide images) and four ultrastructural podocyte descriptors (178 cases, jpeg images) were evaluated once by six and five pathologists, respectively. Cohen's kappa for inter-reader concordance for 48/51 glomerular descriptors with sufficient observations was moderate (0.40

Utility of the American-European Consensus Group and American College of Rheumatology Classification Criteria for Sjögren's syndrome in patients with systemic autoimmune diseases in the clinical setting.

OBJECTIVE: The aim of this study was to evaluate the feasibility and performance of the American-European Consensus Group (AECG) and ACR Classification Criteria for SS in patients with systemic autoimmune diseases. METHODS: Three hundred and fifty patients with primary SS, SLE, RA or scleroderma were randomly selected from our patient registry. Each patient was clinically diagnosed as probable/definitive SS or non-SS following a standardized evaluation including clinical symptoms and manifestations, confirmatory tests, fluorescein staining test, autoantibodies, lip biopsy and medical chart review. Using the clinical diagnosis as the gold standard, the degree of agreement with each criteria set and between the criteria sets was estimated. RESULTS: One hundred fifty-four (44%) patients were diagnosed with SS. The AECG criteria were incomplete in 36 patients (10.3%) and the ACR criteria in 96 (27.4%; P < 0.001). Nevertheless, their ability to classify patients was almost identical, with a sensitivity of 61.6 vs 62.3 and a specificity of 94.3 vs 91.3, respectively. Either set of criteria was met by 123 patients (80%); 95 (61.7%) met the AECG criteria and 96 (62.3%) met the ACR criteria, but only 68 (44.2%) patients met both sets. The concordance rate between clinical diagnosis and AECG or ACR criteria was moderate (k statistic 0.58 and 0.55, respectively). Among 99 patients with definitive SS sensitivity was 83.3 vs 77.7 and specificity was 90.8 vs 85.6, respectively. A discrepancy between clinical diagnosis and criteria was seen in 59 patients (17%). CONCLUSION: The feasibility of the SS AECG criteria is superior to that of the ACR criteria, however, their performance was similar among patients with systemic autoimmune diseases. A subset of SS patients is still missed by both criteria sets.

TRPC6 is a glomerular slit diaphragm-associated channel required for normal renal function.

Progressive kidney failure is a genetically and clinically heterogeneous group of disorders. Podocyte foot processes and the interposed glomerular slit diaphragm are essential components of the permeability barrier in the kidney. Mutations in genes encoding structural proteins of the podocyte lead to the development of proteinuria, resulting in progressive kidney failure and focal segmental glomerulosclerosis. Here, we show that the canonical transient receptor potential 6 (TRPC6) ion channel is expressed in podocytes and is a component of the glomerular slit diaphragm. We identified five families with autosomal dominant focal segmental glomerulosclerosis in which disease segregated with mutations in the gene TRPC6 on chromosome 11q. Two of the TRPC6 mutants had increased current amplitudes. These data show that TRPC6 channel activity at the slit diaphragm is essential for proper regulation of podocyte structure and function.

Predicting Sjögren's syndrome in patients with recent-onset SLE.

OBJECTIVE: To determine the prevalence of SS in a cohort of recent-onset SLE patients and evaluate the clinical and immunological variables that may identify SLE patients prone to develop SS. METHODS: A total of 103 patients participating in a prospective cohort of recent-onset SLE were assessed for fulfilment of the American European Consensus Group criteria for SS using a three-phase approach: screening (European questionnaire, Schirmer-I test and wafer test), confirmation (fluorescein staining test, non-stimulated whole-salivary flow and anti-Ro/La antibodies) and lip biopsy. Anti-Ro/SSA and anti-La/SSB antibodies and RF were measured at entry into the cohort and at SS assessment. RESULTS: Ninety-three females and 10 males were included. Mean age at lupus diagnosis was 25.9 ± 8.9 years, and lupus duration at SS assessment was 30.9 ± 9.1 years. SS was diagnosed in 19 (18.5%) patients, all female, and the patients were older at SLE diagnosis than patients without SS (30.8 ± 9.3 vs 24 ± 8.8 years, P = 0.004). Anti-Ro/SSA antibody was more common in SLE-SS patients (84% vs 55%, P = 0.02, LR + 1.53, 95% CI 1.14, 2.04). In the multivariate analysis, age ≥25 years and anti-Ro/SSA antibodies at SLE diagnosis were identified as predictors of SLE-SS, while the absence of anti-Ro/SSA, anti-La/SSB and RF seems to be protective (LR- 0.14, 95% CI 0.02, 0.95). CONCLUSION: The overlap of SLE and SS occurs in almost one-fifth of SLE patients and presents early during its evolution. SLE onset at age ≥25 years plus the presence of anti-Ro/SSA antibody at diagnosis are useful predictors, while the absence of anti-Ro/SSA, anti-La/SSB and RF identifies patients at lowest risk.