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American Journal of Kidney Diseases

The Evolving Role of Novel Biomarkers in Glomerular Disease: A Review

Published:October 16, 2020DOI:https://doi.org/10.1053/j.ajkd.2020.06.016
      Recent advances in glomerular biology have expanded our understanding of glomerular diseases, leading to more precise therapeutic options. Since the discovery of the autoantigen phospholipase A2 receptor in primary membranous nephropathy 10 years ago, the serologic evaluation of glomerular diseases has become more detailed and nuanced for nephrologists. In addition to phospholipase A2 receptor antibodies, circulating autoantibodies now include thrombospondin type 1 domain–containing 7A and most recently, neural epidermal growth factor–like 1 protein for membranous nephropathy. Additionally, discoveries in C3 glomerulopathy and fibrillary glomerulonephritis are poised to improve the diagnostic approach to these disorders by using novel biomarkers to complement traditional histologic patterns on kidney biopsy. Although kidney biopsies are considered the gold standard in profiling glomerular diseases, validated novel glomerular biomarkers contribute substantially to the diagnostic and therapeutic approaches through their ability to improve sensitivity, permit dynamic longitudinal monitoring of disease activity, and capture genetic heterogeneity. We describe the value of specific biomarkers in selected glomerular diseases, with the major focus on their clinical applicability.

      Index Words

      Introduction

      Guidance on the management of patients with glomerular diseases necessitates an accurate diagnosis together with the ability to predict the clinical course and responsiveness to therapy. For glomerular diseases, kidney biopsy remains the gold standard that for decades has provided diagnostic and prognostic information that forms the basis of current therapies. There are certain limitations to biopsies. Biopsies are processed for light (LM), immunofluorescence (IF), and electron microscopy (EM) and provide a “snapshot” in time of the disease. They do not necessarily reflect on the dynamic nature of disease activity and course governed by a complex pathogenesis. Biopsies do not always differentiate between primary or secondary disease and do not provide an association between appearance and prognosis or responsiveness to treatment. Moreover, biopsies are invasive.
      Traditional biomarkers, including serum creatinine, estimated glomerular filtration rate (eGFR), albuminuria, and proteinuria, lack sensitivity and specificity. Thus, the search for specific and sensitive serologic and or tissue biomarkers is an active area of investigation in glomerular diseases. There are a large number of glomerular biomarkers under investigation. We have chosen to review a select few, for which considerable research advances have been made that offer clinical applicability and or lend insight to pathogenesis.

      Membranous Nephropathy

      Overview

      Membranous nephropathy (MN), the most common nondiabetic cause of nephrotic syndrome in adults, is caused by antibodies targeting autoantigens at the podocyte cell membrane–basement membrane interface, resulting in immune complex formation (Table 1).
      • Glassock R.J.
      Diagnosis and natural course of membranous nephropathy.
      Traditionally the diagnosis was based on the histologic pattern resulting from immune complex formation as seen on kidney biopsy. LM demonstrates thickened glomerular basement membrane with “spikes” and “holes” on silver stain, granular capillary wall staining of polyclonal immunoglobulin G (IgG) with variable C3 staining on IF, and podocyte effacement with subepithelial deposits on EM.
      • Fogo A.B.
      • Lusco M.A.
      • Najafian B.
      • Alpers C.E.
      AJKD Atlas of Renal Pathology: membranous nephropathy.
      Various biopsy findings differentiate primary from secondary MN (mesangial deposits, full house staining [ie, all 5 major immunofluorescent stains on a kidney biopsy—IgM, IgG, IgA, C3, and C1q—are all positive]) in the presence of associated conditions such as systemic lupus erythematosus, Sjögren syndrome, malignancy, and nonsteroidal anti-inflammatory drug use.
      Table 1Biomarkers of Membranous Nephropathy in Adults
      BiomarkerDiseaseMethod of DetectionMalignancy Screening and RateIncidenceComments
      Phospholipase A2 receptor 1 (PLA2R)Primary MNSerum: ELISA,
      Commercially available.
      IIF,
      Commercially available.
      WB

      Tissue: IHC, IF
      Age-appropriate screening; rate of malignancy: ~9%
      • Timmermans S.A.
      • Ayalon R.
      • van Paassen P.
      • et al.
      Anti-phospholipase A2 receptor antibodies and malignancy in membranous nephropathy.
      ~70%-80% of idiopathic MN
      • Most common antigen in primary MN
      • Biopsy not necessary if eGFR > 60 without evidence of secondary/superimposed cause
      • IgG4 dominant
      Neural epidermal growth factor-like 1 protein (NELL-1)Primary MNSerum: WB

      Tissue: IF, IHC
      Search for malignancy; rate of malignancy: 11.7-33%
      • Sethi S.
      • Debiec H.
      • Madden B.
      • et al.
      Neural epidermal growth factor-like 1 protein (NELL-1) associated membranous nephropathy.
      • Caza Tiffany
      • Hassen Samar
      • Zeljko Dvanajscak
      • et al.
      NELL1 is a target antigen in malignancy-associated membranous nephropathy.
      ∼3.8%-16% of PLA2R, THD7A-negative idiopathic MN
      • 2nd most common antigen in MN
      • IgG1 dominant
      Thrombospondin type 1 domain containing 7A (THSd7A)Primary MNSerum: ELISA, IIF,
      Commercially available.
      WB

      Tissue: IHC, IF
      Aggressive screening including urogenital and gastrointestinal/colorectal: rate of malignancy: 6%-20%
      • Hoxha E.
      • Beck Jr., L.H.
      • Wiech T.
      • et al.
      An indirect immunofluorescence method facilitates detection of thrombospondin type 1 domain-containing 7A-specific antibodies in membranous nephropathy.
      ,
      • Hoxha E.
      • Wiech T.
      • Stahl P.R.
      • et al.
      A mechanism for cancer-associated membranous nephropathy.
      ,
      • Sharma S.G.
      • Larsen C.P.
      Tissue staining for THSD7A in glomeruli correlates with serum antibodies in primary membranous nephropathy: a clinicopathological study.
      1%-5% of idiopathic MN (~10% of PLA2R negative)
      • 3rd most common antigen in MN
      • ELISA not commercially available
      • IgG4 dominant
      Exostosin 1/exostosin 2 (EXT1/EXT2)Secondary MNTissue: IHC, IFLimited data to recommend screening; rate of malignancy: 7.6%
      • Sethi S.
      • Madden B.J.
      • Debiec H.
      • et al.
      Exostosin 1/exostosin 2-associated membranous nephropathy.
      11.6% of PLA2R-negative MN
      • Tissue marker of class V lupus ~1/3 of cases & autoimmune disease, typically young, female
      • IgG1 dominant
      Abbreviations: eGFR, estimated glomerular filtration rate (in mL/min/1.73 m2); ELISA, enzyme-linked immunosorbent assay; IF, immunofluorescence; IgG4, immunoglobulin G4; IHC, immunohistochemical; IIF, indirect immunofluorescence; MN, membranous nephropathy; PLA2R, phospholipase A2 receptor; WB, Western blot.
      a Commercially available.
      However, the discovery of circulating antibodies to the phospholipase A2 receptor (PLA2R) autoantigen as a specific marker for primary MN has created a new schema of categorizing and treating primary MN. Most autoantigens in primary MN have been discovered; PLA2R and thrombospondin type 1 domain–containing 7 (THSD7A) are found in 70% and 1% to 5% of patients with primary MN, respectively. Neural epidermal growth factor-like 1 protein (NELL-1) identifies 16% of PLA2R-negative MN cases, making it the second most common autoantigen in primary MN.
      • Beck Jr., L.H.
      • Bonegio R.G.
      • Lambeau G.
      • et al.
      M-Type phospholipase A2 receptor as target antigen in idiopathic membranous nephropathy.
      • Tomas N.M.
      • Beck Jr., L.H.
      • Meyer-Schwesinger C.
      • et al.
      Thrombospondin type-1 domain-containing 7A in idiopathic membranous nephropathy.
      • Sethi S.
      • Debiec H.
      • Madden B.
      • et al.
      Neural epidermal growth factor-like 1 protein (NELL-1) associated membranous nephropathy.
      Exostosin 1 and 2 (EXT1/EXT2)-related MN in PLA2R-negative THSD7A-negative cases has expanded the diagnostic spectrum in secondary MN.
      • Sethi S.
      • Madden B.J.
      • Debiec H.
      • et al.
      Exostosin 1/exostosin 2-associated membranous nephropathy.
      These serologic-based approaches to identify subtypes of MN are transforming our molecular understanding of MN.
      • De Vriese A.S.
      • Glassock R.J.
      • Nath K.A.
      • Sethi S.
      • Fervenza F.C.
      A proposal for a serology-based approach to membranous nephropathy.

      PLA2R MN

      Serology-Based Diagnosis of PLA2R MN

      Observational and retrospective studies have shown modest sensitivity but high specificity for serologic diagnosis of PLA2R MN.
      • Francis J.M.
      • Beck Jr., L.H.
      • Salant D.J.
      Membranous nephropathy: a journey from bench to bedside.
      • Debiec H.
      • Ronco P.
      PLA2R autoantibodies and PLA2R glomerular deposits in membranous nephropathy.
      • Qin W.
      • Beck Jr., L.H.
      • Zeng C.
      • et al.
      Anti-phospholipase A2 receptor antibody in membranous nephropathy.
      • Hoxha E.
      • Kneissler U.
      • Stege G.
      • et al.
      Enhanced expression of the M-type phospholipase A2 receptor in glomeruli correlates with serum receptor antibodies in primary membranous nephropathy.
      • Du Y.
      • Li J.
      • He F.
      • et al.
      The diagnosis accuracy of PLA2R-AB in the diagnosis of idiopathic membranous nephropathy: a meta-analysis.
      In a recent meta-analysis, the pooled sensitivity of serum anti-PLA2R antibody was 65% (range, 63%-67%),
      • Li W.
      • Zhao Y.
      • Fu P.
      Diagnostic test accuracy of serum anti-PLA2R autoantibodies and glomerular PLA2R antigen for diagnosing idiopathic membranous nephropathy: an updated meta-analysis.
      depending on the assay (IF or enzyme-linked immunosorbent assay [ELISA]), stage, and ethnicity. A widely used commercially available autoantibody test for PLA2R is highly sensitive (96.5%) and specific (~100%) and correlates with proteinuria, relapse, chronic kidney disease outcomes, and response to therapy, with faster and more sensitive assays on the horizon.
      • De Vriese A.S.
      • Glassock R.J.
      • Nath K.A.
      • Sethi S.
      • Fervenza F.C.
      A proposal for a serology-based approach to membranous nephropathy.
      ,
      • Qin W.
      • Beck Jr., L.H.
      • Zeng C.
      • et al.
      Anti-phospholipase A2 receptor antibody in membranous nephropathy.
      ,
      • Dahnrich C.
      • Saschenbrecker S.
      • Gunnarsson I.
      • Schlumberger W.
      • Ronco P.
      • Debiec H.
      Development of a standardized chemiluminescence immunoassay for the detection of autoantibodies against human M-type phospholipase A2 receptor in primary membranous nephropathy.
      • Hofstra J.M.
      • Debiec H.
      • Short C.D.
      • et al.
      Antiphospholipase A2 receptor antibody titer and subclass in idiopathic membranous nephropathy.
      • Timmermans S.A.
      • Abdul Hamid M.A.
      • Cohen Tervaert J.W.
      • Damoiseaux J.G.
      • van Paassen P.
      Anti-PLA2R antibodies as a prognostic factor in PLA2R-related membranous nephropathy.
      • Pourcine F.
      • Dahan K.
      • Mihout F.
      • et al.
      Prognostic value of PLA2R autoimmunity detected by measurement of anti-PLA2R antibodies combined with detection of PLA2R antigen in membranous nephropathy: a single-centre study over 14 years.
      • Beck Jr., L.H.
      • Fervenza F.C.
      • Beck D.M.
      • et al.
      Rituximab-induced depletion of anti-PLA2R autoantibodies predicts response in membranous nephropathy.
      • Dahnrich C.
      • Komorowski L.
      • Probst C.
      • et al.
      Development of a standardized ELISA for the determination of autoantibodies against human M-type phospholipase A2 receptor in primary membranous nephropathy.
      These studies prove that the serum anti-PLA2R antibody is a true biomarker and is a primary target of disease control. Monitoring of antibodies to PLA2R is the current standard of care for PLA2R MN.

      Anti-PLA2R Antibody Titer

      High anti-PLA2R antibody titer is associated with lower odds of remission and higher rate of kidney failure and nephrotic syndrome, although a high titer by ELISA is not well defined.
      • Hoxha E.
      • Thiele I.
      • Zahner G.
      • Panzer U.
      • Harendza S.
      • Stahl R.A.
      Phospholipase A2 receptor autoantibodies and clinical outcome in patients with primary membranous nephropathy.
      • Hoxha E.
      • Harendza S.
      • Pinnschmidt H.
      • Panzer U.
      • Stahl R.A.
      PLA2R antibody levels and clinical outcome in patients with membranous nephropathy and non-nephrotic range proteinuria under treatment with inhibitors of the renin-angiotensin system.
      • Kim Y.G.
      • Choi Y.W.
      • Kim S.Y.
      • et al.
      Anti-phospholipase A2 receptor antibody as prognostic indicator in idiopathic membranous nephropathy.
      • Dahan K.
      • Debiec H.
      • Plaisier E.
      • et al.
      Rituximab for severe membranous nephropathy: a 6-month trial with extended follow-up.
      Some studies considered a high titer to be >97.6 RU/mL, whereas others consider it to be >1,034 RU/mL.
      • Pourcine F.
      • Dahan K.
      • Mihout F.
      • et al.
      Prognostic value of PLA2R autoimmunity detected by measurement of anti-PLA2R antibodies combined with detection of PLA2R antigen in membranous nephropathy: a single-centre study over 14 years.
      ,
      • Jullien P.
      • Seitz Polski B.
      • Maillard N.
      • et al.
      Anti-phospholipase A2 receptor antibody levels at diagnosis predicts spontaneous remission of idiopathic membranous nephropathy.
      The variability of assays drives this difference because both in-house and commercially available ELISAs are in use. Therefore, it is important to interpret an ELISA titer value with respect to the assay and the studies using the assay. It is not advised to use assays interchangeably and it is not clear whether one assay is superior to another.
      “Epitope spreading” in PLA2R MN is thought to represent resistant disease.
      • Seitz-Polski B.
      • Debiec H.
      • Rousseau A.
      • et al.
      Phospholipase A2 receptor 1 epitope spreading at baseline predicts reduced likelihood of remission of membranous nephropathy.
      PLA2R is a transmembrane protein of 180 kDa that has an extensive extracellular region consisting of 10 globular domains of 7 to 17 kDa; these comprise a cysteine-rich domain, a fibronectin type II domain, and 8 C-type lectin domains (CTLD1-8)
      • Seitz-Polski B.
      • Debiec H.
      • Rousseau A.
      • et al.
      Phospholipase A2 receptor 1 epitope spreading at baseline predicts reduced likelihood of remission of membranous nephropathy.
      • Seitz-Polski B.
      • Dahan K.
      • Debiec H.
      • et al.
      High-dose rituximab and early remission in PLA2R1-related membranous nephropathy.
      • Seitz-Polski B.
      • Dolla G.
      • Payre C.
      • et al.
      Epitope spreading of autoantibody response to PLA2R associates with poor prognosis in membranous nephropathy.
      • Fresquet M.
      • Jowitt T.A.
      • Gummadova J.
      • et al.
      Identification of a major epitope recognized by PLA2R autoantibodies in primary membranous nephropathy.
      (Fig 1). The cysteine-rich domain is the dominant primary epitope; CTLD1 and CTLD7 are the 2 other independent epitopes targeted by antibodies in PLA2R MN. Theoretically, epitope spreading beyond the original cysteine-rich domain allows for diversification of the immunologic response to the antigen.
      • Seitz-Polski B.
      • Debiec H.
      • Rousseau A.
      • et al.
      Phospholipase A2 receptor 1 epitope spreading at baseline predicts reduced likelihood of remission of membranous nephropathy.
      • Seitz-Polski B.
      • Dahan K.
      • Debiec H.
      • et al.
      High-dose rituximab and early remission in PLA2R1-related membranous nephropathy.
      • Seitz-Polski B.
      • Dolla G.
      • Payre C.
      • et al.
      Epitope spreading of autoantibody response to PLA2R associates with poor prognosis in membranous nephropathy.
      ,
      • Cornaby C.
      • Gibbons L.
      • Mayhew V.
      • Sloan C.S.
      • Welling A.
      • Poole B.D.
      B Cell epitope spreading: mechanisms and contribution to autoimmune diseases.
      A high titer (>369 RU/mL) has been found to be consistently associated with epitope spreading, and “spreaders” have more resistant disease, more proteinuria, and lower eGFR. High titers are considered a poor prognostic indicator (Fig 1).
      • Seitz-Polski B.
      • Debiec H.
      • Rousseau A.
      • et al.
      Phospholipase A2 receptor 1 epitope spreading at baseline predicts reduced likelihood of remission of membranous nephropathy.
      ,
      • Seitz-Polski B.
      • Dahan K.
      • Debiec H.
      • et al.
      High-dose rituximab and early remission in PLA2R1-related membranous nephropathy.
      Figure thumbnail gr1
      Figure 1Intramolecular epitope spreading of the anti–phospholipase A2 receptor antibody (anti-PLA2R) versus baseline multidomain recognition. The reactivity of anti-PLA2R antibodies to a ubiquitous epitope in the cysteine-rich (CysR) domain (left) “spreads” to include subdominant epitopes of the first (center, C-type lectin domain [CTLD1]) and seventh and eighth CTLDs (right, CTLD7 and CTLD8) distinct from the CysR epitope. Disease progression is positively correlated with greater urinary protein excretion and patient age and inversely correlated with the likelihood of remission. An alternative hypothesis is that antibodies to multiple domains are present at the time of diagnosis, and progression of disease is correlated with total anti-PLA2R antibody levels. Abbreviation: FNII, fibronectin type II domain.
      In a large prospective cohort, CTLD8 was identified as a fourth epitope
      • Reinhard L.
      • Zahner G.
      • Menzel S.
      • Koch-Nolte F.
      • Stahl R.A.K.
      • Hoxha E.
      Clinical relevance of domain-specific phospholipase A2 receptor 1 antibody levels in patients with membranous nephropathy.
      ; all patients had baseline epitope spreading, recognizing at least 2 epitopes (cysteine-rich domain–fibronectin type II domain–CTLD1 and CTLD7 to CTLD8). Furthermore, when 150 patients were followed up for a median of 54 months, anti-PLA2R antibody titer and not epitope-specific titers predicted outcomes. The discrepancy between the 2 findings may be attributed to variabilities in assay detection (Western blot [WB} or ELISA), serum dilution, cross-reactivity, construct design, and threshold for positivity.
      • Beck Jr., L.H.
      • Salant D.J.
      Refining our understanding of the PLA2R-antibody response in primary membranous nephropathy: looking forward, looking back.
      The same challenges in defining clinically relevant titer thresholds also apply to defining epitope-specific subtypes in PLA2R MN. Thus, further studies are needed to clarify the importance of epitope spreading.

      PLA2R MN with GFR > 60 mL/min/1.73 m2

      In patients in whom primary MN is suspected, accurate diagnosis by ELISA can be obtained while simultaneously screening for secondary causes, including viral hepatitis, antinuclear antibodies, IgG4, sarcoidosis, age-appropriate malignancy screening, and medication and nonsteroidal anti-inflammatory drug use.
      • De Vriese A.S.
      • Glassock R.J.
      • Nath K.A.
      • Sethi S.
      • Fervenza F.C.
      A proposal for a serology-based approach to membranous nephropathy.
      ,
      • Timmermans S.A.
      • Ayalon R.
      • van Paassen P.
      • et al.
      Anti-phospholipase A2 receptor antibodies and malignancy in membranous nephropathy.
      This noninvasive serologic-based approach is reasonable, especially if risk of biopsy is high or if the patient refuses. This serologic-based approach to the diagnosis of PLA2R MN is supported by a recent retrospective study in which 838 patients were tested for anti-PLA2R antibody; 97 were positive by ELISA (>2 RU/mL) confirmed with indirect IF (IIF), a kidney biopsy, and a negative workup for secondary causes. They were then analyzed in groups according to eGFR (> 60 vs <60 mL/min/1.73 m2). The rate of superimposed disease was higher in those with eGFR < 60 mL/min/1.73 m2 (13.5% [5/37]), which included diabetic nephropathy, acute tubular necrosis, and 2 patients with focal segmental glomerulosclerosis. Notably, 2 patients with superimposed disease (crescentic and diabetic nephropathy) had eGFR ≤ 12 mL/min/1.73 m2 and high total renal chronicity score on biopsy, limiting the benefit of immunosuppressive therapy.
      • Bobart S.A.
      • De Vriese A.S.
      • Pawar A.S.
      • et al.
      Noninvasive diagnosis of primary membranous nephropathy using phospholipase A2 receptor antibodies.
      Of 97 patients, only 2 would have required more extensive workup or change in immunosuppression (allergic interstitial nephritis and crescentic disease). Thus, for patients with suspected MN and eGFR > 60 mL/min/1.73 m2 with no evidence of secondary causes, a biopsy to prove serologic-positive PLA2R MN is not necessary (Fig 2).
      Figure thumbnail gr2
      Figure 2Proposed approach to serologic diagnosis of phospholipase A2 receptor (PLA2R) membranous nephropathy (MN). Sensitivity of the serologic assays is not uniform and depends on ethnicity. This algorithm is based on the study by Bobart et al
      • Bobart S.A.
      • De Vriese A.S.
      • Pawar A.S.
      • et al.
      Noninvasive diagnosis of primary membranous nephropathy using phospholipase A2 receptor antibodies.
      (predominantly White North American cohort). aIn general it should include a search for autoimmune disease (lupus), medications (nonsteroidal anti-inflammatory drugs), malignancy, and infections (viral hepatitis). Abbreviations: eGFR, estimated glomerular filtration rate; ELISA, enzyme-linked immunosorbent assay; IFT, immunofluorescence testing.
      As ELISA becomes more widely used, the utility of a kidney biopsy in this situation is likely to be diminished; however, more false-positives are likely to be found. In one study, although investigators confirmed anti-PLA2R antibody with both ELISA and IIF, there was only 1 patient with an ELISA result > 20 RU/mL and negative IF results.
      • Bobart S.A.
      • De Vriese A.S.
      • Pawar A.S.
      • et al.
      Noninvasive diagnosis of primary membranous nephropathy using phospholipase A2 receptor antibodies.
      Additionally, there was only 1 patient with negative ELISA (<2 RU/mL) and positive IIF results. In both cases, MN was diagnosed on biopsy. Therefore, although it is common practice to confirm the diagnosis of PLA2R MN serologically with both ELISA and the more sensitive IIF, the use of combined testing may not significantly improve sensitivity and specificity substantially for routine cases, however this will require further study.

      PLA2R MN With GFR < 60 mL/min/1.73 m2

      The severity of tubulointerstitial scarring is a prognostic indicator in glomerular disease. However, it is not clear if this is superior to clinical data in MN.
      • Nath K.A.
      Tubulointerstitial changes as a major determinant in the progression of renal damage.
      • D’Amico G.
      Influence of clinical and histological features on actuarial renal survival in adult patients with idiopathic IgA nephropathy, membranous nephropathy, and membranoproliferative glomerulonephritis: survey of the recent literature.
      • Troyanov S.
      • Roasio L.
      • Pandes M.
      • Herzenberg A.M.
      • Cattran D.C.
      Renal pathology in idiopathic membranous nephropathy: a new perspective.
      • Bohle A.
      • Wehrmann M.
      • Bogenschutz O.
      • et al.
      The long-term prognosis of the primary glomerulonephritides. A morphological and clinical analysis of 1747 cases.
      • Sprangers B.
      • Bomback A.S.
      • Cohen S.D.
      • et al.
      Idiopathic membranous nephropathy: clinical and histologic prognostic features and treatment patterns over time at a tertiary referral center.
      In a prospective observational study, 243 patients who had MN, circulating antibody to PLA2R, and biopsy-proven PLA2R tissue antigen positivity were followed up for a median of 48 months.
      • Mahmud M.
      • Pinnschmidt H.O.
      • Reinhard L.
      • et al.
      Role of phospholipase A2 receptor 1 antibody level at diagnosis for long-term renal outcome in membranous nephropathy.
      Patients were stratified according to ELISA PLA2R antibody tertiles, and 36 patients reached the study end point of doubling of serum creatinine level or kidney failure. Baseline independent predictors of the primary outcome were anti-PLA2R antibody level by ELISA (hazard ratio [HR], 1.36; 95% CI, 1.11-1.66; P = 0.01) and interstitial fibrosis and tubular atrophy (HR, 1.32; 95% CI, 1.03-1.68; P = 0.03). This study did not control for immunosuppressive therapy, which was most often cyclosporine (81/243). Therefore, conclusions about optimal therapy as it relates to baseline characteristics of glomerulosclerosis, fibrosis, or anti-PLA2R antibody level cannot be made. Patients with higher anti-PLA2R antibody levels tended to be older, with lower eGFR and higher proteinuria. These data suggest that little prognostic information is gained by obtaining a biopsy when clinical data including anti-PLA2R antibody level are available and a secondary cause clinically is excluded. However, advanced chronic kidney disease was not well represented in this study, and the point at which immunosuppression becomes futile and progression to kidney failure becomes inevitable is not well defined.
      Although detection of circulating antibody and tissue staining for PLA2R antigen is highly specific, its presence does not exclude the possibility of superimposed disease. Hypertensive damage has been seen in cases of higher anti-PLA2R antibody titer and is associated with progressive decline in kidney function in MN and poor response to immunosuppression in diabetic patients.
      • Glassock R.J.
      Diagnosis and natural course of membranous nephropathy.
      ,
      • Hoxha E.
      • Harendza S.
      • Pinnschmidt H.
      • Panzer U.
      • Stahl R.A.
      M-Type phospholipase A2 receptor autoantibodies and renal function in patients with primary membranous nephropathy.
      ,
      • Bhadauria D.
      • Chellappan A.
      • Kaul A.
      • et al.
      Idiopathic membranous nephropathy in patients with diabetes mellitus: a diagnostic and therapeutic quandary!.
      IIF to detect PLA2R antigen in kidney biopsies was performed in 85 cases of primary and 80 cases of secondary MN.
      • Larsen C.P.
      • Messias N.C.
      • Silva F.G.
      • Messias E.
      • Walker P.D.
      Determination of primary versus secondary membranous glomerulopathy utilizing phospholipase A2 receptor staining in renal biopsies.
      PLA2R antigen staining showed specificity of 83% (95% CI, 72%-90%), with hepatitis C virus infection, sarcoidosis, and neoplasm making up most cases of secondary MN with PLA2R tissue positivity. However, when samples were stained for IgG subtype, IgG4 was dominant, suggesting the possibility that these diseases were superimposed on primary PLA2R MN and not causative.
      Few clinical scenarios reduce the utility of PLA2R serologic testing and necessitate a kidney biopsy for diagnosis. As mentioned, crescentic disease in MN is a rare (<1% of MN) but well-described entity. It is often associated with antineutrophil cytoplasmic antibody, anti–glomerular basement membrane positivity, or very rarely monoclonal gammopathy of unknown significance. However, some are serologically negative.
      • Rodriguez E.F.
      • Nasr S.H.
      • Larsen C.P.
      • Sethi S.
      • Fidler M.E.
      • Cornell L.D.
      Membranous nephropathy with crescents: a series of 19 cases.
      • Nasr S.H.
      • Said S.M.
      • Valeri A.M.
      • et al.
      Membranous glomerulonephritis with ANCA-associated necrotizing and crescentic glomerulonephritis.
      • Jia X.Y.
      • Hu S.Y.
      • Chen J.L.
      • et al.
      The clinical and immunological features of patients with combined anti-glomerular basement membrane disease and membranous nephropathy.
      • James S.H.
      • Lien Y.H.
      • Ruffenach S.J.
      • Wilcox G.E.
      Acute renal failure in membranous glomerulonephropathy: a result of superimposed crescentic glomerulonephritis.
      • Tse W.Y.
      • Howie A.J.
      • Adu D.
      • et al.
      Association of vasculitic glomerulonephritis with membranous nephropathy: a report of 10 cases.
      • Dwyer K.M.
      • Agar J.W.
      • Hill P.A.
      • Murphy B.F.
      Membranous nephropathy and anti-neutrophil cytoplasmic antibody-associated glomerulonephritis: a report of 2 cases.
      • Sethi S.
      Membranous glomerulonephritis with monoclonal immune deposits and crescents.
      Often patients present with heavy proteinuria, hematuria, and acute kidney injury. In a case series of MN with crescents, 38% (6/16) stained for PLA2R on biopsy.
      • Rodriguez E.F.
      • Nasr S.H.
      • Larsen C.P.
      • Sethi S.
      • Fidler M.E.
      • Cornell L.D.
      Membranous nephropathy with crescents: a series of 19 cases.
      In a recent case series of MN with necrotizing and crescent glomerulonephritis, 2 of 15 were positive for both serum anti-PLA2R antibody and tissue antigen while being negative for antineutrophil cytoplasmic antibody and anti–glomerular basement membrane.
      • Nikolopoulou A.
      • Huang-Doran I.
      • McAdoo S.P.
      • Griffith M.E.
      • Cook H.T.
      • Pusey C.D.
      Membranous glomerulonephritis with crescents.
      Both had MN diagnosed initially and transformed into crescentic disease; 40% with dual crescentic and MN reached kidney failure in a 72-month median follow-up. PLA2R MN has also been reported post–hematopoietic stem cell transplantation with crescent formation and as a manifestation of graft-versus-host disease that responded to corticosteroid therapy.
      • Kitamura M.
      • Hisano S.
      • Kurobe Y.
      • et al.
      Membranous nephropathy with crescent after hematopoietic cell transplantation.
      • Huang X.
      • Qin W.
      • Zhang M.
      • Zheng C.
      • Zeng C.
      • Liu Z.
      Detection of anti-PLA2R autoantibodies and IgG subclasses in post-allogeneic hematopoietic stem cell transplantation membranous nephropathy.
      • Byrne-Dugan C.J.
      • Collins A.B.
      • Lam A.Q.
      • Batal I.
      Membranous nephropathy as a manifestation of graft-versus-host disease: association with HLA antigen typing, phospholipase A2 receptor, and C4d.
      Therefore, isolated positive PLA2R serologic results do not obviate the search for secondary causes or always permit eliminating kidney biopsies (and potentially missing a crescentic lesion) and should always be interpreted with clinical context. Although MN with crescents is extremely rare, a rapid decline in kidney function with hematuria should alert the nephrologist to the possibility of crescentic disease, even in the presence of PLA2R positivity.

      THSD7A MN

      THSD7A is a glycosylated 250-kDa type 1 transmembrane protein highly expressed on podocytes and is a specific biomarker for primary MN.
      • Tomas N.M.
      • Beck Jr., L.H.
      • Meyer-Schwesinger C.
      • et al.
      Thrombospondin type-1 domain-containing 7A in idiopathic membranous nephropathy.
      ,
      • Tomas N.M.
      • Hoxha E.
      • Reinicke A.T.
      • et al.
      Autoantibodies against thrombospondin type 1 domain-containing 7A induce membranous nephropathy.
      In a recent meta-analysis of more than 4,000 patients with MN, 3% (95% CI, 3%-4%) had autoantibodies directed against THSD7A, and prevalence was 10% (95% CI, 6%-15%) in PLA2R-negative patients.
      • Ren S.
      • Wu C.
      • Zhang Y.
      • et al.
      An update on clinical significance of use of THSD7A in diagnosing idiopathic membranous nephropathy: a systematic review and meta-analysis of THSD7A in IMN.
      Similarly, in a study of 1,276 patients with MN in German and North American cohorts, the combined prevalence was 3.1%.
      • Hoxha E.
      • Beck Jr., L.H.
      • Wiech T.
      • et al.
      An indirect immunofluorescence method facilitates detection of thrombospondin type 1 domain-containing 7A-specific antibodies in membranous nephropathy.
      One of 130 patients with MN enrolled in the MENTOR trial had THSD7A MN.
      • Fervenza F.C.
      • Appel G.B.
      • Barbour S.J.
      • et al.
      Rituximab or cyclosporine in the treatment of membranous nephropathy.
      Taken together, THSD7A prevalence is low, and providing detailed clinicopathologic characteristics is challenging.
      THDSD7A MN may be associated with malignancy. In a cohort of 1,276 patients with MN, 40 had THSD7A MN by IIF; 8 (20%) developed malignancy within 3 months of diagnosis.
      • Hoxha E.
      • Beck Jr., L.H.
      • Wiech T.
      • et al.
      An indirect immunofluorescence method facilitates detection of thrombospondin type 1 domain-containing 7A-specific antibodies in membranous nephropathy.
      THSD7A is expressed in human tumors, including gall bladder, colorectal, endometrial, and breast.
      • Xian L.
      • Dong D.
      • Luo J.
      • et al.
      Expression of THSD7A in neoplasm tissues and its relationship with proteinuria.
      • Hoxha E.
      • Wiech T.
      • Stahl P.R.
      • et al.
      A mechanism for cancer-associated membranous nephropathy.
      • Sharma S.G.
      • Larsen C.P.
      Tissue staining for THSD7A in glomeruli correlates with serum antibodies in primary membranous nephropathy: a clinicopathological study.
      Reduction in THSD7A antibodies and/or proteinuria has been seen following treatment of the tumor, thus potentially linking malignancy and MN.
      • Xian L.
      • Dong D.
      • Luo J.
      • et al.
      Expression of THSD7A in neoplasm tissues and its relationship with proteinuria.
      ,
      • Sharma S.G.
      • Larsen C.P.
      Tissue staining for THSD7A in glomeruli correlates with serum antibodies in primary membranous nephropathy: a clinicopathological study.
      ,
      • Wang T.
      • Zhang Y.
      • Liu M.
      • Kang X.
      • Kang L.
      • Zhang H.
      THSD7A as a marker for paraneoplastic membranous nephropathy.
      However, malignancy in MN was found to be less common in other studies (6%-16%).
      • Hoxha E.
      • Beck Jr., L.H.
      • Wiech T.
      • et al.
      An indirect immunofluorescence method facilitates detection of thrombospondin type 1 domain-containing 7A-specific antibodies in membranous nephropathy.
      ,
      • Hoxha E.
      • Wiech T.
      • Stahl P.R.
      • et al.
      A mechanism for cancer-associated membranous nephropathy.
      ,
      • Sharma S.G.
      • Larsen C.P.
      Tissue staining for THSD7A in glomeruli correlates with serum antibodies in primary membranous nephropathy: a clinicopathological study.
      These discrepancies may be due to differences in study protocol, local practice of cancer screening, and selection bias. Given the association between THSD7A and MN, an in-depth search for malignancy is warranted when THS7A positivity is encountered.
      THSD7A antibodies are thought to be pathogenic. A THSD7A MN–positive patient with kidney failure with a titer of 1:1,000 at the time of transplantation was reported to have recurrence in less than 1 year, with the allograft staining positive for THSD7A.
      • Tomas N.M.
      • Hoxha E.
      • Reinicke A.T.
      • et al.
      Autoantibodies against thrombospondin type 1 domain-containing 7A induce membranous nephropathy.
      Moreover, sera from 2 patients with THSD7A MN bound to mouse THSD7A antigen on podocytes, colocalizing with nephrin at the slit diaphragm 2 hours after intravenous injection, and induced histologic features of MN with proteinuria.
      • Tomas N.M.
      • Hoxha E.
      • Reinicke A.T.
      • et al.
      Autoantibodies against thrombospondin type 1 domain-containing 7A induce membranous nephropathy.
      THSD7A localizes to the slit diaphragm of podocyte foot processes and is associated with enhanced stabilization of the slit diaphragm in cultured podocytes, supporting a pathogenic role.
      • Herwig J.
      • Skuza S.
      • Sachs W.
      • et al.
      Thrombospondin type 1 domain-containing 7A localizes to the slit diaphragm and stabilizes membrane dynamics of fully differentiated podocytes.
      The positivity rate of antibody in serum and tissue is highly correlated.
      • Ren S.
      • Wu C.
      • Zhang Y.
      • et al.
      An update on clinical significance of use of THSD7A in diagnosing idiopathic membranous nephropathy: a systematic review and meta-analysis of THSD7A in IMN.
      Serum IIF has 92% diagnostic sensitivity and 100% specificity.
      • Hoxha E.
      • Beck Jr., L.H.
      • Wiech T.
      • et al.
      An indirect immunofluorescence method facilitates detection of thrombospondin type 1 domain-containing 7A-specific antibodies in membranous nephropathy.
      In a small study, 24 patients with serologic positivity to THSD7A also had positivity on tissue by IIF.
      • Sharma S.G.
      • Larsen C.P.
      Tissue staining for THSD7A in glomeruli correlates with serum antibodies in primary membranous nephropathy: a clinicopathological study.
      ELISA detected anti-THSD7A autoantibodies with sensitivity comparable to IIF and WB in 45 of 49 patients with THSD7A MN.
      • Zaghrini C.
      • Seitz-Polski B.
      • Justino J.
      • et al.
      Novel ELISA for thrombospondin type 1 domain-containing 7A autoantibodies in membranous nephropathy.
      Only 3 were negative for circulating antibody (WB, ELISA, and IIF) but positive on biopsy. At baseline, patients in the lowest anti-THSD7A antibody level tertile (23-122 RU/mL) saw the highest rate of remission (92%), whereas patients in combined middle (134–566 RU/mL) and high (606-13,920 RU/mL) tertiles saw statistically significant less remission (P = 0.006).
      • Zaghrini C.
      • Seitz-Polski B.
      • Justino J.
      • et al.
      Novel ELISA for thrombospondin type 1 domain-containing 7A autoantibodies in membranous nephropathy.
      Although ELISA titers for anti-THSD7A antibody appear to correlate with disease activity similar to PLA2R, ELISA is not yet commercially available. IIF testing is commercially available to clinicians and can be acquired from other specialized laboratories, thus allowing for differentiating primary from secondary MN in PLA2R-negative cases. However, IIF is not suited for longitudinal monitoring.

      Summary

      The discovery of circulating antibodies to autoantigens in MN has led to an exponential growth in our understanding of MN. Testing for these antibodies is likely to continue to expand in clinical practice. However, as with any test, there are important clinical caveats, such as superimposed glomerular disease, progressed chronic kidney disease, and the association of malignancy, that need to be taken into account when interpreting these tests. As testing for autoantibodies increases and potentially fewer biopsies are performed, we must remain informed and judicious in their clinical application.

      C3 Glomerulopathy

      Overview

      C3 glomerulopathy (C3G) is a spectrum of diseases with the common mechanism of dysregulation of alternative complement in the fluid phase. C3G is a remarkably heterogeneous and an ultrarare disease (about 2-3 cases per million) and often results from trigger events such as infection, autoimmunity, or monoclonal gammopathy.
      • Ravindran A.
      • Fervenza F.C.
      • Smith R.J.H.
      • De Vriese A.S.
      • Sethi S.
      C3 glomerulopathy: ten years’ experience at Mayo Clinic.
      Underlying abnormalities in the alternative complement pathway are manifest as acquired drivers (the autoantibodies C3 nephritic factor [C3Nef], C4Nef, C5Nef, monoclonal gammopathy, and anti-factor H) or genetic drivers (mutations of C3 or the complement factor genes CFB, CFH, CFI, and CFHR1-CHR5).
      • Smith R.J.H.
      • Appel G.B.
      • Blom A.M.
      • et al.
      C3 glomerulopathy - understanding a rare complement-driven renal disease.
      Although mutations in complement genes are common (13%-37%), a fraction of these are known to be or likely be pathogenic (12.9% in a large Mayo Clinic case series).
      • Ravindran A.
      • Fervenza F.C.
      • Smith R.J.H.
      • De Vriese A.S.
      • Sethi S.
      C3 glomerulopathy: ten years’ experience at Mayo Clinic.
      ,
      • Servais A.
      • Noel L.H.
      • Roumenina L.T.
      • et al.
      Acquired and genetic complement abnormalities play a critical role in dense deposit disease and other C3 glomerulopathies.
      ,
      • Rabasco C.
      • Cavero T.
      • Roman E.
      • et al.
      Effectiveness of mycophenolate mofetil in C3 glomerulonephritis.
      Our understanding of the genetics and genotype-phenotype correlation of C3G is incomplete. A KDIGO (Kidney Disease: Improving Global Outcomes) controversies report of 2017 concluded that there is no clear benefit of performing genetic analysis in every case of C3G. However, genetic results may assist in treatment decisions.
      • Goodship T.H.
      • Cook H.T.
      • Fakhouri F.
      • et al.
      Atypical hemolytic uremic syndrome and C3 glomerulopathy: conclusions from a “Kidney Disease: Improving Global Outcomes” (KDIGO) Controversies Conference.
      Additionally, genetic testing should be undertaken when familial causes are suspected (ie, CFHR5 nephropathy).
      Outcomes of C3G are varied, some with rapid progression of kidney disease compared with other reports showing kidney failure in 36.5% of patients at 10 years.
      • Servais A.
      • Noel L.H.
      • Roumenina L.T.
      • et al.
      Acquired and genetic complement abnormalities play a critical role in dense deposit disease and other C3 glomerulopathies.
      The decision to treat with immunosuppression is largely dependent on non–disease-specific factors, including severity of proteinuria, kidney function, and degree of tubular atrophy/interstitial fibrosis.
      • Bomback A.S.
      • Santoriello D.
      • Avasare R.S.
      • et al.
      C3 glomerulonephritis and dense deposit disease share a similar disease course in a large United States cohort of patients with C3 glomerulopathy.
      Although no specific therapy for C3G is currently available, retrospective studies suggest that immunosuppressive treatment with mycophenolate mofetil and corticosteroids is beneficial compared with conservative treatment.
      • Ravindran A.
      • Fervenza F.C.
      • Smith R.J.H.
      • De Vriese A.S.
      • Sethi S.
      C3 glomerulopathy: ten years’ experience at Mayo Clinic.
      ,
      • Rabasco C.
      • Cavero T.
      • Roman E.
      • et al.
      Effectiveness of mycophenolate mofetil in C3 glomerulonephritis.
      ,
      • Avasare R.S.
      • Canetta P.A.
      • Bomback A.S.
      • et al.
      mycophenolate mofetil in combination with steroids for treatment of C3 glomerulopathy: a case series.
      Given the remarkable heterogeneity of presentation, associated disease, and pathogenesis, with poor outcomes, the discovery of a viable biomarker is critical.

      Tissue Biomarkers in C3G

      C3G causes significant glomerular deposition of complement C3, C5, C6, C7, C8, and C9, with C3 being most abundant.
      • Sethi S.
      • Vrana J.A.
      • Fervenza F.C.
      • et al.
      Characterization of C3 in C3 glomerulopathy.
      A study by Sethi et al
      • Sethi S.
      • Vrana J.A.
      • Fervenza F.C.
      • et al.
      Characterization of C3 in C3 glomerulopathy.
      • Sethi S.
      • Gamez J.D.
      • Vrana J.A.
      • et al.
      Glomeruli of dense deposit disease contain components of the alternative and terminal complement pathway.
      • Sethi S.
      • Fervenza F.C.
      • Zhang Y.
      • et al.
      C3 glomerulonephritis: clinicopathological findings, complement abnormalities, glomerular proteomic profile, treatment, and follow-up.
      using laser microdissection and mass spectrometry to analyze the composition of complement deposits in 6 cases of C3G and dense deposit disease found that C3dg, which is cleaved from surface bound C3b, was the most abundant C3 protein detected (Fig 3). Importantly, the degradation products of C3 (iC3c and C3dg) do not form new convertases, but are opsonins and participate in adaptive immune stimulation. This is important because routine evaluation for C3 by IF detects C3c, which does not include C3dg. Therefore, routine IF studies cannot accurately reflect complement activation as a disease biomarker.
      • Sethi S.
      • Vrana J.A.
      • Fervenza F.C.
      • et al.
      Characterization of C3 in C3 glomerulopathy.
      • Sethi S.
      • Gamez J.D.
      • Vrana J.A.
      • et al.
      Glomeruli of dense deposit disease contain components of the alternative and terminal complement pathway.
      • Sethi S.
      • Fervenza F.C.
      • Zhang Y.
      • et al.
      C3 glomerulonephritis: clinicopathological findings, complement abnormalities, glomerular proteomic profile, treatment, and follow-up.
      Figure thumbnail gr3
      Figure 3Alternative complement cascade and hypothesized role of complement factor H (CFH)-related protein 5 (CFHR5). Formation of C3 convertases leads to cleavage of C3 and formation of C5 convertase, creating potent anaphylatoxins (C3a and C5a) that mediate the inflammatory response. C3b is degraded into iC3b and C3dg, which mediate phagocytosis and an adaptive immune response. CFH is a strong inhibitor of C3 convertase, whereas CFHR5 preserves C3 convertase activity by inhibiting CFH. C5b causes terminal complement activation membrane attack complexes.
      A recent small retrospective study of patients with C3G further explored the characterization of complement proteins by analyzing an array of proteins (including factor H-related protein 5 [FHR5], FHR1, FH, C3b/iC3b/C3c, C3dg, C5b-9, properdin, C4d, and C1q) through targeted antibodies on formalin-fixed paraffin-embedded kidney biopsy samples. They found similar results to those found by mass spectrometry by Sethi et al, with a notable addition that FHR5 was the most prevalent protein, was more prevalent than FHR1, and was detected in 96% of native samples and 100% of transplant samples with at least 1+ intensity. The staining intensity of FHR5 correlated with the intensities of C3b/iC3b/C3c, C3dg, and C5b9, yet only the staining intensity of FHR5 and C5b-9 negatively correlated with eGFR. Serial biopsies obtained in recurrent crescentic C3G showed that FHR5 correlated with disease activity but was unaltered by C5 inhibition with eculizumab.
      • Medjeral-Thomas N.R.
      • Moffitt H.
      • Lomax-Browne H.J.
      • et al.
      Glomerular complement factor H-related protein 5 (FHR5) is highly prevalent in C3 glomerulopathy and associated with renal impairment.
      This suggests that clinical improvement with eculizumab may result from reduced production of C5a, a potent anaphylatoxin, and inflammatory cell recruitment and not inhibition of terminal complement. Further analysis of FHR5 as a biomarker will require larger cohorts to capture a difference in disease courses, non–complement-mediated comparators, and correlations with serial biopsies to understand the evolution of FHR5 staining with respect to treatment, progression, proteinuria, and changes in morphology.
      • D’Agati V.D.
      • Bomback A.S.
      In search of C3G tissue biomarkers.
      The diagnosis of C3G remains challenging and often relies on both a structural and functional assessment, which poses significant challenges in interpretation for many nephrologists given that they do not routinely use these assays. These studies represent intriguing concepts in the pathogenesis of C3G and potential emerging biomarkers, which are desperately needed not only to guide diagnosis but also treatment.

      Fibrillary Glomerulonephritis

      Fibrillary glomerulonephritis (FGN) is a rare proliferative glomerulopathy defined ultrastructurally by haphazardly arranged fibrils that are 10 to 30 nm in diameter and a lack of Congo red staining for amyloid. Determining the fibril size is both challenging and crucial due to overlaps in size with amyloid fibrils (8-12 nm) and immunotactoid glomerulopathy fibrils (>35 nm).
      • Rosenstock J.L.
      • Markowitz G.S.
      Fibrillary glomerulonephritis: an update.
      FGN occurs mainly in adults around 50 years of age, with hematuria (82%), proteinuria (average protein excretion of 5.7 g/d), or full nephrotic syndrome (~33%).
      • Nasr S.H.
      • Valeri A.M.
      • Cornell L.D.
      • et al.
      Fibrillary glomerulonephritis: a report of 66 cases from a single institution.
      It has been associated with dysproteinemia in 4% to 42% of cases depending on the population, with 5% to 11% and 7% to 27% also having an autoimmune disease or hepatitis C virus infection, respectively.
      • Rosenstock J.L.
      • Markowitz G.S.
      Fibrillary glomerulonephritis: an update.
      • Nasr S.H.
      • Valeri A.M.
      • Cornell L.D.
      • et al.
      Fibrillary glomerulonephritis: a report of 66 cases from a single institution.
      • Nasr S.H.
      • Dasari S.
      • Lieske J.C.
      • et al.
      Serum levels of DNAJB9 are elevated in fibrillary glomerulonephritis patients.
      • Iskandar S.S.
      • Falk R.J.
      • Jennette J.C.
      Clinical and pathologic features of fibrillary glomerulonephritis.
      • Fogo A.
      • Qureshi N.
      • Horn R.G.
      Morphologic and clinical features of fibrillary glomerulonephritis versus immunotactoid glomerulopathy.
      • Alpers C.E.
      • Kowalewska J.
      Fibrillary glomerulonephritis and immunotactoid glomerulopathy.
      • Hsu H.C.
      • Churg J.
      Glomerular microfibrils in renal disease: a comparative electron microscopic study.
      Prognosis is abysmal, with 44% of patients reaching kidney failure at a mean follow-up of 52.3 months according to the large case series from the Mayo Clinic, and there remains no established treatment.
      • Nasr S.H.
      • Valeri A.M.
      • Cornell L.D.
      • et al.
      Fibrillary glomerulonephritis: a report of 66 cases from a single institution.
      Clinicians are dependent on biopsy for diagnosis, and histologic features can vary significantly. The patterns by LM are diverse, including membranoproliferative glomerulonephritis, mesangial proliferative, diffuse proliferative glomerulonephritis, and membranous and diffuse sclerosing. Patients with diffuse sclerosing and diffuse proliferative glomerulonephritis experience the worst outcomes, reaching kidney failure in 7 and 20 months, respectively.
      • Rosenstock J.L.
      • Markowitz G.S.
      Fibrillary glomerulonephritis: an update.
      ,
      • Alpers C.E.
      • Kowalewska J.
      Fibrillary glomerulonephritis and immunotactoid glomerulopathy.
      ,
      • Rosenstock J.L.
      • Markowitz G.S.
      • Valeri A.M.
      • Sacchi G.
      • Appel G.B.
      • D’Agati V.D.
      Fibrillary and immunotactoid glomerulonephritis: Distinct entities with different clinical and pathologic features.
      The presence of fibrils, described in diabetic nephropathy, obesity-related glomerulopathy, focal segmental glomerulosclerosis, malignant hypertension, and hemolytic uremic syndrome, is relatively nonspecific.
      • Hsu H.C.
      • Churg J.
      Glomerular microfibrils in renal disease: a comparative electron microscopic study.
      ,
      • Gong W.
      • Liu Z.H.
      • Zeng C.H.
      • et al.
      Amylin deposition in the kidney of patients with diabetic nephropathy.
      Cryoglobulinemia can have a similar appearance and must be excluded.
      • Markowitz G.S.
      • Cheng J.T.
      • Colvin R.B.
      • Trebbin W.M.
      • D’Agati V.D.
      Hepatitis C viral infection is associated with fibrillary glomerulonephritis and immunotactoid glomerulopathy.
      Despite its diagnostic advantages, EM is not widely available and takes much longer than LM and IF. A specific biomarker to properly classify the disease is needed. Recently, DNAJ homolog subfamily B member 9 (DNAJB9) was identified as an abundant protein in FGN by laser-capture microdissection and mass spectrometry.
      • Nasr S.H.
      • Vrana J.A.
      • Dasari S.
      • et al.
      DNAJB9 is a specific immunohistochemical marker for fibrillary glomerulonephritis.
      DNAJB9 is a molecular chaperone and functions by binding to immunoglobulins that assist in folding and degrading misfolded proteins to protect cells from stress apoptosis.
      • Rosenstock J.L.
      • Markowitz G.S.
      Fibrillary glomerulonephritis: an update.
      ,
      • Lee H.J.
      • Kim J.M.
      • Kim K.H.
      • Heo J.I.
      • Kwak S.J.
      • Han J.A.
      Genotoxic stress/p53-induced DNAJB9 inhibits the pro-apoptotic function of p53.
      ,
      • Dong M.
      • Bridges J.P.
      • Apsley K.
      • Xu Y.
      • Weaver T.E.
      ERdj4 and ERdj5 are required for endoplasmic reticulum-associated protein degradation of misfolded surfactant protein C.
      DNAJB9 is present in podocytes as well as mesangial and endothelial cells in the glomerulus.
      • Rosenstock J.L.
      • Markowitz G.S.
      Fibrillary glomerulonephritis: an update.
      DNAJB9 was detected in serum using an immunoprecipitation-linked multiple reaction monitoring assay with sensitivity of 67% and specificity of 98% for FGN when compared with amyloidosis, myeloma, non-FGN glomerular disease, and healthy individuals and was negatively associated with eGFR.
      • Nasr S.H.
      • Dasari S.
      • Lieske J.C.
      • et al.
      Serum levels of DNAJB9 are elevated in fibrillary glomerulonephritis patients.
      These results suggest that serum detection could prove useful as a biomarker for diagnosis and potentially longitudinal monitoring, pending an effective therapy. Of course, additional studies will need to replicate these findings. The sensitivity (98%) and specificity (99%) of DNAJB9 for FGN by immunohistochemistry is impressive when FGN is compared with amyloidosis, other glomerular diseases (n = 98), and healthy individuals. DNAJB9 localizes to FGN fibrils and colocalizes with IgG, giving credence to FGN autoimmune association.
      However, the mechanism by which DNAJB9 contributes to pathogenicity is far from being fully understood.
      • Nasr S.H.
      • Vrana J.A.
      • Dasari S.
      • et al.
      DNAJB9 is a specific immunohistochemical marker for fibrillary glomerulonephritis.
      Congo red staining, although routinely performed and widely available, is imperfect in differentiating amyloid and nonamyloid diseases. In 18 patients with rare congophilic FGN, DNAJB9 was found to be specific for FGN and excluded amyloid that was confirmed by laser microdissection and mass spectrometry, currently the gold standard in the diagnosis of amyloid.
      • Alexander M.P.
      • Dasari S.
      • Vrana J.A.
      • et al.
      Congophilic fibrillary glomerulonephritis: a case series.
      In the largest retrospective study from multiple North American sites (1997-2017) analyzing 296 biopsies, clinicopathologic features, and outcomes of FGN, DNAJB9 staining confirmed the diagnosis in 100% of patients with FGN. DNAJB9 further established the diagnosis in 79% (23/29) of cases labeled as possible FGN due to atypical features that would raise the possibility of paraprotein-mediated disease (including Congo red positivity, IgG monotypic light chain staining on IF, and fibril size outside the norm).
      • Andeen N.K.
      • Troxell M.L.
      • Riazy M.
      • et al.
      Fibrillary glomerulonephritis: clinicopathologic features and atypical cases from a multi-institutional cohort.
      Taken together, DNAJB9 is highly specific and testing should be performed when FGN is suspected.
      It is truly remarkable that for a disease as rare as FGN, a highly sensitive and specific biomarker has been discovered in the form of DNAJB9. Although much remains to be understood concerning DNAJB9 and its role in the pathogenesis of FGN, we agree with Nasr and Fogo
      • Nasr S.H.
      • Fogo A.B.
      New developments in the diagnosis of fibrillary glomerulonephritis.
      that the diagnostic strength of DNAJB9 should result in altering the disease name to “DNAJB9-associated FGN” from FGN. It will be exciting to see how DNAJB9 will lend to our understanding of pathogenesis and treatment of this unique disease.

      Conclusions

      Novel glomerular biomarkers have provided clinicians with insight into glomerular disease pathogenesis and have advanced care by enabling tailored therapy. The clinical applicability of the various biomarkers presented here varies greatly. Although some are highly relevant clinically, widely accessible, and scalable, others are currently more exploratory and should remain complementary to the kidney biopsy. Despite inherent limitations, kidney biopsy still remains the gold standard for the diagnosis of glomerular disease when used in its current form to understand pathogenesis. Whereas exciting progress has been made in certain kidney diseases, the field is only beginning to appreciate the power of identifying biomarkers aided by molecular profiling and large-scale data generation and integration, along with prospectively collected clinical data. With new molecular techniques such as proteomics and transcriptomics currently being studied and applied to kidney tissue, a much deeper level of understanding of glomerular disease will soon be realized. As new glomerular biomarkers of glomerular disease continue to be discovered and validated, it is imperative to have a clear understanding of their use and limitations in relation to the role of kidney biopsies. Overcoming these challenges in the future, the nephrologist has the opportunity to affect the care of patients through personalized treatment regimens leading to improved outcomes.

      Article Information

      Authors’ Full Names and Academic Degrees

      Corey Cavanaugh, DO, and Mark D. Okusa, MD.

      Support

      None.

      Financial Disclosure

      Dr Okusa reports being a prior holder of equity in Adenosine Therapeutics, LLC; receipt of royalty payments from UptoDate; travel and/or honoria not related to the subject of this review (from Yale O’Brien External Advisory Committee, Yale University, UAB O’Brien Center, Mount Sinai, Northwestern University, CRRT Taipei and India, Hong Kong Society of Nephrology, Japanese Society of Nephrology, Johns Hopkins University, University of Florida, Tokyo University, University of Maryland, FASEB, and Keystone Symposia); and receipt of research grants not related to this review (from Am Pharma, Pfizer, John Bower Foundation).

      Peer Review

      Received March 2, 2020, in response to an invitation from the journal. Evaluated by 3 external peer reviewers, with direct editorial input from an Associate Editor and a Deputy Editor. Accepted in revised form June 6, 2020.

      References

        • Glassock R.J.
        Diagnosis and natural course of membranous nephropathy.
        Semin Nephrol. 2003; 23: 324-332
        • Fogo A.B.
        • Lusco M.A.
        • Najafian B.
        • Alpers C.E.
        AJKD Atlas of Renal Pathology: membranous nephropathy.
        Am J Kidney Dis. 2015; 66: e15-e17
        • Beck Jr., L.H.
        • Bonegio R.G.
        • Lambeau G.
        • et al.
        M-Type phospholipase A2 receptor as target antigen in idiopathic membranous nephropathy.
        N Engl J Med. 2009; 361: 11-21
        • Tomas N.M.
        • Beck Jr., L.H.
        • Meyer-Schwesinger C.
        • et al.
        Thrombospondin type-1 domain-containing 7A in idiopathic membranous nephropathy.
        N Engl J Med. 2014; 371: 2277-2287
        • Sethi S.
        • Debiec H.
        • Madden B.
        • et al.
        Neural epidermal growth factor-like 1 protein (NELL-1) associated membranous nephropathy.
        Kidney Int. 2020; 97: 163-174
        • Sethi S.
        • Madden B.J.
        • Debiec H.
        • et al.
        Exostosin 1/exostosin 2-associated membranous nephropathy.
        J Am Soc Nephrol. 2019; 30: 1123-1136
        • De Vriese A.S.
        • Glassock R.J.
        • Nath K.A.
        • Sethi S.
        • Fervenza F.C.
        A proposal for a serology-based approach to membranous nephropathy.
        J Am Soc Nephrol. 2017; 28: 421-430
        • Francis J.M.
        • Beck Jr., L.H.
        • Salant D.J.
        Membranous nephropathy: a journey from bench to bedside.
        Am J Kidney Dis. 2016; 68: 138-147
        • Debiec H.
        • Ronco P.
        PLA2R autoantibodies and PLA2R glomerular deposits in membranous nephropathy.
        N Engl J Med. 2011; 364: 689-690
        • Qin W.
        • Beck Jr., L.H.
        • Zeng C.
        • et al.
        Anti-phospholipase A2 receptor antibody in membranous nephropathy.
        J Am Soc Nephrol. 2011; 22: 1137-1143
        • Hoxha E.
        • Kneissler U.
        • Stege G.
        • et al.
        Enhanced expression of the M-type phospholipase A2 receptor in glomeruli correlates with serum receptor antibodies in primary membranous nephropathy.
        Kidney Int. 2012; 82: 797-804
        • Du Y.
        • Li J.
        • He F.
        • et al.
        The diagnosis accuracy of PLA2R-AB in the diagnosis of idiopathic membranous nephropathy: a meta-analysis.
        PLoS One. 2014; 9e104936
        • Li W.
        • Zhao Y.
        • Fu P.
        Diagnostic test accuracy of serum anti-PLA2R autoantibodies and glomerular PLA2R antigen for diagnosing idiopathic membranous nephropathy: an updated meta-analysis.
        Front Med (Lausanne). 2018; 5: 101
        • Dahnrich C.
        • Saschenbrecker S.
        • Gunnarsson I.
        • Schlumberger W.
        • Ronco P.
        • Debiec H.
        Development of a standardized chemiluminescence immunoassay for the detection of autoantibodies against human M-type phospholipase A2 receptor in primary membranous nephropathy.
        Kidney Int Rep. 2020; 5: 182-188
        • Hofstra J.M.
        • Debiec H.
        • Short C.D.
        • et al.
        Antiphospholipase A2 receptor antibody titer and subclass in idiopathic membranous nephropathy.
        J Am Soc Nephrol. 2012; 23: 1735-1743
        • Timmermans S.A.
        • Abdul Hamid M.A.
        • Cohen Tervaert J.W.
        • Damoiseaux J.G.
        • van Paassen P.
        Anti-PLA2R antibodies as a prognostic factor in PLA2R-related membranous nephropathy.
        Am J Nephrol. 2015; 42: 70-77
        • Pourcine F.
        • Dahan K.
        • Mihout F.
        • et al.
        Prognostic value of PLA2R autoimmunity detected by measurement of anti-PLA2R antibodies combined with detection of PLA2R antigen in membranous nephropathy: a single-centre study over 14 years.
        PLoS One. 2017; 12e0173201
        • Beck Jr., L.H.
        • Fervenza F.C.
        • Beck D.M.
        • et al.
        Rituximab-induced depletion of anti-PLA2R autoantibodies predicts response in membranous nephropathy.
        J Am Soc Nephrol. 2011; 22: 1543-1550
        • Dahnrich C.
        • Komorowski L.
        • Probst C.
        • et al.
        Development of a standardized ELISA for the determination of autoantibodies against human M-type phospholipase A2 receptor in primary membranous nephropathy.
        Clin Chim Acta. 2013; 421: 213-218
        • Hoxha E.
        • Thiele I.
        • Zahner G.
        • Panzer U.
        • Harendza S.
        • Stahl R.A.
        Phospholipase A2 receptor autoantibodies and clinical outcome in patients with primary membranous nephropathy.
        J Am Soc Nephrol. 2014; 25: 1357-1366
        • Hoxha E.
        • Harendza S.
        • Pinnschmidt H.
        • Panzer U.
        • Stahl R.A.
        PLA2R antibody levels and clinical outcome in patients with membranous nephropathy and non-nephrotic range proteinuria under treatment with inhibitors of the renin-angiotensin system.
        PLoS One. 2014; 9e110681
        • Kim Y.G.
        • Choi Y.W.
        • Kim S.Y.
        • et al.
        Anti-phospholipase A2 receptor antibody as prognostic indicator in idiopathic membranous nephropathy.
        Am J Nephrol. 2015; 42: 250-257
        • Dahan K.
        • Debiec H.
        • Plaisier E.
        • et al.
        Rituximab for severe membranous nephropathy: a 6-month trial with extended follow-up.
        J Am Soc Nephrol. 2017; 28: 348-358
        • Jullien P.
        • Seitz Polski B.
        • Maillard N.
        • et al.
        Anti-phospholipase A2 receptor antibody levels at diagnosis predicts spontaneous remission of idiopathic membranous nephropathy.
        Clin Kidney J. 2017; 10: 209-214
        • Seitz-Polski B.
        • Debiec H.
        • Rousseau A.
        • et al.
        Phospholipase A2 receptor 1 epitope spreading at baseline predicts reduced likelihood of remission of membranous nephropathy.
        J Am Soc Nephrol. 2018; 29: 401-408
        • Seitz-Polski B.
        • Dahan K.
        • Debiec H.
        • et al.
        High-dose rituximab and early remission in PLA2R1-related membranous nephropathy.
        Clin J Am Soc Nephrol. 2019; 14: 1173-1182
        • Seitz-Polski B.
        • Dolla G.
        • Payre C.
        • et al.
        Epitope spreading of autoantibody response to PLA2R associates with poor prognosis in membranous nephropathy.
        J Am Soc Nephrol. 2016; 27: 1517-1533
        • Fresquet M.
        • Jowitt T.A.
        • Gummadova J.
        • et al.
        Identification of a major epitope recognized by PLA2R autoantibodies in primary membranous nephropathy.
        J Am Soc Nephrol. 2015; 26: 302-313
        • Cornaby C.
        • Gibbons L.
        • Mayhew V.
        • Sloan C.S.
        • Welling A.
        • Poole B.D.
        B Cell epitope spreading: mechanisms and contribution to autoimmune diseases.
        Immunol Lett. 2015; 163: 56-68
        • Reinhard L.
        • Zahner G.
        • Menzel S.
        • Koch-Nolte F.
        • Stahl R.A.K.
        • Hoxha E.
        Clinical relevance of domain-specific phospholipase A2 receptor 1 antibody levels in patients with membranous nephropathy.
        J Am Soc Nephrol. 2020; 31: 197-207
        • Beck Jr., L.H.
        • Salant D.J.
        Refining our understanding of the PLA2R-antibody response in primary membranous nephropathy: looking forward, looking back.
        J Am Soc Nephrol. 2020; 31: 8-11
        • Timmermans S.A.
        • Ayalon R.
        • van Paassen P.
        • et al.
        Anti-phospholipase A2 receptor antibodies and malignancy in membranous nephropathy.
        Am J Kidney Dis. 2013; 62: 1223-1225
        • Bobart S.A.
        • De Vriese A.S.
        • Pawar A.S.
        • et al.
        Noninvasive diagnosis of primary membranous nephropathy using phospholipase A2 receptor antibodies.
        Kidney Int. 2019; 95: 429-438
        • Nath K.A.
        Tubulointerstitial changes as a major determinant in the progression of renal damage.
        Am J Kidney Dis. 1992; 20: 1-17
        • D’Amico G.
        Influence of clinical and histological features on actuarial renal survival in adult patients with idiopathic IgA nephropathy, membranous nephropathy, and membranoproliferative glomerulonephritis: survey of the recent literature.
        Am J Kidney Dis. 1992; 20: 315-323
        • Troyanov S.
        • Roasio L.
        • Pandes M.
        • Herzenberg A.M.
        • Cattran D.C.
        Renal pathology in idiopathic membranous nephropathy: a new perspective.
        Kidney Int. 2006; 69: 1641-1648
        • Bohle A.
        • Wehrmann M.
        • Bogenschutz O.
        • et al.
        The long-term prognosis of the primary glomerulonephritides. A morphological and clinical analysis of 1747 cases.
        Pathol Res Pract. 1992; 188: 908-924
        • Sprangers B.
        • Bomback A.S.
        • Cohen S.D.
        • et al.
        Idiopathic membranous nephropathy: clinical and histologic prognostic features and treatment patterns over time at a tertiary referral center.
        Am J Nephrol. 2012; 36: 78-89
        • Mahmud M.
        • Pinnschmidt H.O.
        • Reinhard L.
        • et al.
        Role of phospholipase A2 receptor 1 antibody level at diagnosis for long-term renal outcome in membranous nephropathy.
        PLoS One. 2019; 14e0221293
        • Hoxha E.
        • Harendza S.
        • Pinnschmidt H.
        • Panzer U.
        • Stahl R.A.
        M-Type phospholipase A2 receptor autoantibodies and renal function in patients with primary membranous nephropathy.
        Clin J Am Soc Nephrol. 2014; 9: 1883-1890
        • Bhadauria D.
        • Chellappan A.
        • Kaul A.
        • et al.
        Idiopathic membranous nephropathy in patients with diabetes mellitus: a diagnostic and therapeutic quandary!.
        Clin Kidney J. 2018; 11: 46-50
        • Larsen C.P.
        • Messias N.C.
        • Silva F.G.
        • Messias E.
        • Walker P.D.
        Determination of primary versus secondary membranous glomerulopathy utilizing phospholipase A2 receptor staining in renal biopsies.
        Mod Pathol. 2013; 26: 709-715
        • Rodriguez E.F.
        • Nasr S.H.
        • Larsen C.P.
        • Sethi S.
        • Fidler M.E.
        • Cornell L.D.
        Membranous nephropathy with crescents: a series of 19 cases.
        Am J Kidney Dis. 2014; 64: 66-73
        • Nasr S.H.
        • Said S.M.
        • Valeri A.M.
        • et al.
        Membranous glomerulonephritis with ANCA-associated necrotizing and crescentic glomerulonephritis.
        Clin J Am Soc Nephrol. 2009; 4: 299-308
        • Jia X.Y.
        • Hu S.Y.
        • Chen J.L.
        • et al.
        The clinical and immunological features of patients with combined anti-glomerular basement membrane disease and membranous nephropathy.
        Kidney Int. 2014; 85: 945-952
        • James S.H.
        • Lien Y.H.
        • Ruffenach S.J.
        • Wilcox G.E.
        Acute renal failure in membranous glomerulonephropathy: a result of superimposed crescentic glomerulonephritis.
        J Am Soc Nephrol. 1995; 6: 1541-1546
        • Tse W.Y.
        • Howie A.J.
        • Adu D.
        • et al.
        Association of vasculitic glomerulonephritis with membranous nephropathy: a report of 10 cases.
        Nephrol Dial Transplant. 1997; 12: 1017-1027
        • Dwyer K.M.
        • Agar J.W.
        • Hill P.A.
        • Murphy B.F.
        Membranous nephropathy and anti-neutrophil cytoplasmic antibody-associated glomerulonephritis: a report of 2 cases.
        Clin Nephrol. 2001; 56: 394-397
        • Sethi S.
        Membranous glomerulonephritis with monoclonal immune deposits and crescents.
        Nephrol Dial Transplant. 2005; 20: 1768-1769
        • Nikolopoulou A.
        • Huang-Doran I.
        • McAdoo S.P.
        • Griffith M.E.
        • Cook H.T.
        • Pusey C.D.
        Membranous glomerulonephritis with crescents.
        Kidney Int Rep. 2019; 4: 1577-1584
        • Kitamura M.
        • Hisano S.
        • Kurobe Y.
        • et al.
        Membranous nephropathy with crescent after hematopoietic cell transplantation.
        Intern Med. 2019; 58: 91-96
        • Huang X.
        • Qin W.
        • Zhang M.
        • Zheng C.
        • Zeng C.
        • Liu Z.
        Detection of anti-PLA2R autoantibodies and IgG subclasses in post-allogeneic hematopoietic stem cell transplantation membranous nephropathy.
        Am J Med Sci. 2013; 346: 32-37
        • Byrne-Dugan C.J.
        • Collins A.B.
        • Lam A.Q.
        • Batal I.
        Membranous nephropathy as a manifestation of graft-versus-host disease: association with HLA antigen typing, phospholipase A2 receptor, and C4d.
        Am J Kidney Dis. 2014; 64: 987-993
        • Tomas N.M.
        • Hoxha E.
        • Reinicke A.T.
        • et al.
        Autoantibodies against thrombospondin type 1 domain-containing 7A induce membranous nephropathy.
        J Clin Invest. 2016; 126: 2519-2532
        • Ren S.
        • Wu C.
        • Zhang Y.
        • et al.
        An update on clinical significance of use of THSD7A in diagnosing idiopathic membranous nephropathy: a systematic review and meta-analysis of THSD7A in IMN.
        Ren Fail. 2018; 40: 306-313
        • Hoxha E.
        • Beck Jr., L.H.
        • Wiech T.
        • et al.
        An indirect immunofluorescence method facilitates detection of thrombospondin type 1 domain-containing 7A-specific antibodies in membranous nephropathy.
        J Am Soc Nephrol. 2017; 28: 520-531
        • Fervenza F.C.
        • Appel G.B.
        • Barbour S.J.
        • et al.
        Rituximab or cyclosporine in the treatment of membranous nephropathy.
        N Engl J Med. 2019; 381: 36-46
        • Xian L.
        • Dong D.
        • Luo J.
        • et al.
        Expression of THSD7A in neoplasm tissues and its relationship with proteinuria.
        BMC Nephrol. 2019; 20: 332
        • Hoxha E.
        • Wiech T.
        • Stahl P.R.
        • et al.
        A mechanism for cancer-associated membranous nephropathy.
        N Engl J Med. 2016; 374: 1995-1996
        • Sharma S.G.
        • Larsen C.P.
        Tissue staining for THSD7A in glomeruli correlates with serum antibodies in primary membranous nephropathy: a clinicopathological study.
        Mod Pathol. 2018; 31: 616-622
        • Wang T.
        • Zhang Y.
        • Liu M.
        • Kang X.
        • Kang L.
        • Zhang H.
        THSD7A as a marker for paraneoplastic membranous nephropathy.
        Int Urol Nephrol. 2019; 51: 371-373
        • Herwig J.
        • Skuza S.
        • Sachs W.
        • et al.
        Thrombospondin type 1 domain-containing 7A localizes to the slit diaphragm and stabilizes membrane dynamics of fully differentiated podocytes.
        J Am Soc Nephrol. 2019; 30: 824-839
        • Zaghrini C.
        • Seitz-Polski B.
        • Justino J.
        • et al.
        Novel ELISA for thrombospondin type 1 domain-containing 7A autoantibodies in membranous nephropathy.
        Kidney Int. 2019; 95: 666-679
        • Ravindran A.
        • Fervenza F.C.
        • Smith R.J.H.
        • De Vriese A.S.
        • Sethi S.
        C3 glomerulopathy: ten years’ experience at Mayo Clinic.
        Mayo Clin Proc. 2018; 93: 991-1008
        • Smith R.J.H.
        • Appel G.B.
        • Blom A.M.
        • et al.
        C3 glomerulopathy - understanding a rare complement-driven renal disease.
        Nat Rev Nephrol. 2019; 15: 129-143
        • Servais A.
        • Noel L.H.
        • Roumenina L.T.
        • et al.
        Acquired and genetic complement abnormalities play a critical role in dense deposit disease and other C3 glomerulopathies.
        Kidney Int. 2012; 82: 454-464
        • Rabasco C.
        • Cavero T.
        • Roman E.
        • et al.
        Effectiveness of mycophenolate mofetil in C3 glomerulonephritis.
        Kidney Int. 2015; 88: 1153-1160
        • Goodship T.H.
        • Cook H.T.
        • Fakhouri F.
        • et al.
        Atypical hemolytic uremic syndrome and C3 glomerulopathy: conclusions from a “Kidney Disease: Improving Global Outcomes” (KDIGO) Controversies Conference.
        Kidney Int. 2017; 91: 539-551
        • Bomback A.S.
        • Santoriello D.
        • Avasare R.S.
        • et al.
        C3 glomerulonephritis and dense deposit disease share a similar disease course in a large United States cohort of patients with C3 glomerulopathy.
        Kidney Int. 2018; 93: 977-985
        • Avasare R.S.
        • Canetta P.A.
        • Bomback A.S.
        • et al.
        mycophenolate mofetil in combination with steroids for treatment of C3 glomerulopathy: a case series.
        Clin J Am Soc Nephrol. 2018; 13: 406-413
        • Sethi S.
        • Vrana J.A.
        • Fervenza F.C.
        • et al.
        Characterization of C3 in C3 glomerulopathy.
        Nephrol Dial Transplant. 2017; 32: 459-465
        • Sethi S.
        • Gamez J.D.
        • Vrana J.A.
        • et al.
        Glomeruli of dense deposit disease contain components of the alternative and terminal complement pathway.
        Kidney Int. 2009; 75: 952-960
        • Sethi S.
        • Fervenza F.C.
        • Zhang Y.
        • et al.
        C3 glomerulonephritis: clinicopathological findings, complement abnormalities, glomerular proteomic profile, treatment, and follow-up.
        Kidney Int. 2012; 82: 465-473
        • Medjeral-Thomas N.R.
        • Moffitt H.
        • Lomax-Browne H.J.
        • et al.
        Glomerular complement factor H-related protein 5 (FHR5) is highly prevalent in C3 glomerulopathy and associated with renal impairment.
        Kidney Int Rep. 2019; 4: 1387-1400
        • D’Agati V.D.
        • Bomback A.S.
        In search of C3G tissue biomarkers.
        Kidney Int Rep. 2019; 4: 1359-1361
        • Rosenstock J.L.
        • Markowitz G.S.
        Fibrillary glomerulonephritis: an update.
        Kidney Int Rep. 2019; 4: 917-922
        • Nasr S.H.
        • Valeri A.M.
        • Cornell L.D.
        • et al.
        Fibrillary glomerulonephritis: a report of 66 cases from a single institution.
        Clin J Am Soc Nephrol. 2011; 6: 775-784
        • Nasr S.H.
        • Dasari S.
        • Lieske J.C.
        • et al.
        Serum levels of DNAJB9 are elevated in fibrillary glomerulonephritis patients.
        Kidney Int. 2019; 95: 1269-1272
        • Iskandar S.S.
        • Falk R.J.
        • Jennette J.C.
        Clinical and pathologic features of fibrillary glomerulonephritis.
        Kidney Int. 1992; 42: 1401-1407
        • Fogo A.
        • Qureshi N.
        • Horn R.G.
        Morphologic and clinical features of fibrillary glomerulonephritis versus immunotactoid glomerulopathy.
        Am J Kidney Dis. 1993; 22: 367-377
        • Alpers C.E.
        • Kowalewska J.
        Fibrillary glomerulonephritis and immunotactoid glomerulopathy.
        J Am Soc Nephrol. 2008; 19: 34-37
        • Hsu H.C.
        • Churg J.
        Glomerular microfibrils in renal disease: a comparative electron microscopic study.
        Kidney Int. 1979; 16: 497-504
        • Rosenstock J.L.
        • Markowitz G.S.
        • Valeri A.M.
        • Sacchi G.
        • Appel G.B.
        • D’Agati V.D.
        Fibrillary and immunotactoid glomerulonephritis: Distinct entities with different clinical and pathologic features.
        Kidney Int. 2003; 63: 1450-1461
        • Gong W.
        • Liu Z.H.
        • Zeng C.H.
        • et al.
        Amylin deposition in the kidney of patients with diabetic nephropathy.
        Kidney Int. 2007; 72: 213-218
        • Markowitz G.S.
        • Cheng J.T.
        • Colvin R.B.
        • Trebbin W.M.
        • D’Agati V.D.
        Hepatitis C viral infection is associated with fibrillary glomerulonephritis and immunotactoid glomerulopathy.
        J Am Soc Nephrol. 1998; 9: 2244-2252
        • Nasr S.H.
        • Vrana J.A.
        • Dasari S.
        • et al.
        DNAJB9 is a specific immunohistochemical marker for fibrillary glomerulonephritis.
        Kidney Int Rep. 2018; 3: 56-64
        • Lee H.J.
        • Kim J.M.
        • Kim K.H.
        • Heo J.I.
        • Kwak S.J.
        • Han J.A.
        Genotoxic stress/p53-induced DNAJB9 inhibits the pro-apoptotic function of p53.
        Cell Death Differ. 2015; 22: 86-95
        • Dong M.
        • Bridges J.P.
        • Apsley K.
        • Xu Y.
        • Weaver T.E.
        ERdj4 and ERdj5 are required for endoplasmic reticulum-associated protein degradation of misfolded surfactant protein C.
        Mol Biol Cell. 2008; 19: 2620-2630
        • Alexander M.P.
        • Dasari S.
        • Vrana J.A.
        • et al.
        Congophilic fibrillary glomerulonephritis: a case series.
        Am J Kidney Dis. 2018; 72: 325-336
        • Andeen N.K.
        • Troxell M.L.
        • Riazy M.
        • et al.
        Fibrillary glomerulonephritis: clinicopathologic features and atypical cases from a multi-institutional cohort.
        Clin J Am Soc Nephrol. 2019; 14: 1741-1750
        • Nasr S.H.
        • Fogo A.B.
        New developments in the diagnosis of fibrillary glomerulonephritis.
        Kidney Int. 2019; 96: 581-592
        • Caza Tiffany
        • Hassen Samar
        • Zeljko Dvanajscak
        • et al.
        NELL1 is a target antigen in malignancy-associated membranous nephropathy.
        Kidney Int. 2020; https://doi.org/10.1016/j.kint.2020.07.039