Results of a nation-wide cohort study suggest favorable long-term outcomes of clone-targeted chemotherapy in immunotactoid glomerulopathy

Successful Treatment of Monoclonal Immunotactoid Glomerulopathy Associated with Chronic Lymphocytic Leukemia Using Ibrutinib

A 71-year-old woman developed nephrotic syndrome during 10-year follow-up for chronic lymphocytic leukemia. A renal biopsy sample analysis revealed IgG1-lambda-positive monoclonal immunotactoid glomerulopathy (mITG). The patient was treated with ibrutinib, a Bruton tyrosine kinase inhibitor, and complete renal remission was achieved after 24 months. ITG is a rare disease that is characterized by glomerular deposition. In particular, mITG, which presents immune deposits that exhibit light-chain restriction, is often associated with hematologic disorders. Most patients with mITG receive immunosuppressive therapy and/or chemotherapy; however, to our knowledge, there have been no reports of treatment with ibrutinib.

Insights into proliferative glomerulonephritis with monoclonal immunoglobulin deposits - is it really monoclonal or not?

PURPOSE OF REVIEW

Proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID), is a disease defined by the presence of glomerulonephritis with nonorganized mono-isotypic immunoglobulin (Ig) deposits. This review will discuss the pathogenesis of PGNMID and address novel techniques for detection of monoclonal Ig and pathologic B-cell clones and for distinguishing monoclonal from oligoclonal Ig deposits.

RECENT FINDINGS

Because of low detection rate of circulating monoclonal Ig and nephritogenic B-cell clones and emerging reports of PGNMID-IgG in children, it has been recently argued that many PGNMID-IgG3 cases may not be monoclonal lesions. A mass spectrometry-based method, serum matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry, has been shown to have superior sensitivity than immunofixation for detection of monoclonal Ig in PGNMID and other monoclonal gammopathy of renal significance (MGRS) lesions. Two novel sequencing techniques, RNA-based immunoglobulin repertoire sequencing and single-molecule real-time sequencing of monoclonal immunoglobulin, enable identification of the full-length variable sequence of monoclonal Ig, even in MGRS patients with low tumor burden and undetectable monoclonal Ig by conventional methods. Finally, staining of kidney biopsy for Ig light chain variable domain subgroups may allow for separation of true monoclonal from oligoclonal PGNMID.

SUMMARY

Novel sequencing, mass spectrometry, and immunofluorescence techniques have the potential to increase the detection rate of nephritogenic monoclonal Ig/B-cell clone and distinguish monoclonal from oligoclonal deposits in PGNMID.

Renal Pathology Society/International Kidney and Monoclonal Gammopathy Research Group consensus on pathologic definitions and terminology of monoclonal gammopathy-associated kidney lesions

The spectrum of kidney lesions associated with monoclonal gammopathy has significantly expanded over the past 2 decades, with description of new entities and variants of old entities. Pathologic diagnosis is challenging because of lesional complexity, heterogeneity, and reliance on electron microscopy and ancillary techniques. A lack of precise pathologic definitions and uniform terminology has hampered diagnostic accuracy. To address these challenges, the Renal Pathology Society and International Kidney and Monoclonal Gammopathy Research Group jointly tasked a working group of nephropathologists and nephrologists to establish consensus-based terminology and definitions for monoclonal gammopathy-associated kidney lesions. Participants included experts in the field with international representation. This report presents their recommendations. For each lesion, prerequisite (mandatory) diagnostic criteria and supportive (nonmandatory) features are proposed. New terminology is provided for some lesions. Application of standardized terminology and definitions should help harmonize kidney biopsy diagnosis with precision therapy in the monoclonal gammopathy-associated kidney disorders.

Kidney disease in multiple myeloma

Renal disease is a frequent complication of symptomatic multiple myeloma, that increases morbidity and reduces quality of life and overall survival. It may result from various lesions, the most frequent being light chain cast nephropathy (LCCN), related to precipitation of monoclonal free light chains (FLC) with uromodulin in distal tubules. Rapid identification of the type of kidney disease with appropriate management is key. LCCN typically reveals the underlying myeloma and manifests with severe acute kidney injury, high serum FLC level (>500 mg/l) and predominant light chain proteinuria (urine albumin/creatinine ratio <10 %). Urgent therapy is required, based on vigorous fluid expansion, correction of precipitating factors and introduction of efficient anti-myeloma therapy which choice should consider renal elimination of each agent and patient frailty. Early and deep reduction in serum FLC level conditions renal recovery, warranting assessment of efficacy by serial serum FLC level monitoring. In newly diagnosed patients, the combination of bortezomib, high-dose dexamethasone and an anti-CD38 monoclonal antibody is commonly used. The benefit to risk balance of quadruplets incorporating cyclophosphamide or an immunodulatory agent requires to be evaluated in prospective studies. In patients with severe acute kidney injury, reinforcing chemotherapy with FLC removal through plasma exchange or high-cutoff hemodialysis may increase the probability of renal response, despite controversial data from randomized trials. Histological assessment of the extent of cast formation and interstitial fibrosis/tubular atrophy may help evaluating renal prognosis and refining therapy. Thanks to improved overall survival, renal transplantation may be considered in selected candidates with end-stage kidney disease.

Ultrastructural overlap between immunotactoid and cryoglobulin glomerulopathy: A case report

Immunotactoid glomerulopathy (ITG), a condition characterised by highly organised microtubules on electron microscopy, and cryoglobulin glomerulopathy (CG) are rare forms of kidney injury that may be encountered in patients with cryoglobulinaemia. It has been proposed these two entities are part of the same disease process following observed clinical and histological similarities.

Renal manifestations of MGUS

Kidney disease is a common complication of monoclonal immunoglobulin (MIg)-secreting B-cell disorders and predominantly occurs in patients who do not meet the criteria for an overt hematological disease. To distinguish this situation from monoclonal gammopathy of undetermined significance, which lacks organ damage, the term monoclonal gammopathy of renal significance (MGRS) was introduced to depict the association of a small, otherwise indolent B-cell clone, with renal disease induced by the secreted MIg. The spectrum of renal disorders in MGRS is wide, encompassing both tubular and glomerular disorders, classified according to the composition of deposits and their ultrastructural pattern of organization. Renal lesions, independent of the tumor burden, are mostly governed by the molecular characteristics of the MIg variable domain and involve either direct (deposition or precipitation) or indirect (autoantibody activity, complement activation) mechanisms. The diagnosis, often suggested by careful analysis of renal and extrarenal symptoms, almost always requires histological confirmation by a kidney biopsy with light, immunofluorescence, and electron microscopy studies. Most patients do not have a known monoclonal gammopathy at presentation. Hematologic investigations should include serum and urine protein electrophoresis and immunofixation, serum-free light chain measurements, and bone marrow studies with flow cytometry and cytogenetics to determine the nature of the pathogenic clone (most commonly plasmocytic). Early diagnosis before the development of severe chronic kidney disease and rapid achievement of deep hematological response through clone-targeted chemotherapy (currently based on proteasome inhibitor and monoclonal anti-CD38 antibody-based combinations for plasma cell clones) are the main factors influencing long-term renal and patient outcomes.

Immunotactoid Glomerulopathy

Immunotactoid glomerulopathy (ITG) is a rare glomerular disease that typically presents with proteinuria, hematuria, and kidney dysfunction. A kidney biopsy is essential to establish the diagnosis of ITG. ITG is characterized by glomerular electron-dense immunoglobulin deposits with hollow-cored microtubules. ITG is classified as either monoclonal or polyclonal based on immunofluorescence staining of the immunoglobulin deposits. Monoclonal ITG is associated with an underlying hematologic disorder in two-thirds of the cases, lymphoma and plasma cell dyscrasias being the most common. Polyclonal ITG is associated with autoimmune diseases but can be seen with hematologic disorders and chronic infections. Due to the preponderance of hematologic disorders in both monoclonal and polyclonal ITG, a thorough hematologic workup must be performed in all cases of ITG. In monoclonal ITG with a detectable clone, clone-directed therapy is administered to achieve hematologic remission, as the renal response is highly dependent on the hematologic response. In clone-negative monoclonal ITG, anti-B cell therapy is often used as a first-line therapy. Management of polyclonal ITG without an underlying hematologic disorder is poorly defined. Compared to monoclonal ITG, patients with polyclonal ITG have a higher risk of progression to end-stage kidney disease. Recurrence of ITG following kidney transplantation is common and is often associated with hematologic relapse.

Paraprotein-Mediated Glomerular Diseases

Paraproteinemias are a group of complex diseases associated with an overproduction of a monoclonal immunoglobulin that can cause a diversity of kidney disorders and end-organ damage. In this review, we focus on paraprotein-mediated glomerular diseases. Kidney biopsy plays a crucial role in diagnosing these disorders, enabling the identification of specific histological patterns. These lesions are categorized into organized (such as amyloidosis, immunotactoid glomerulopathy, fibrillary glomerulonephritis, cryoglobulinemic glomerulonephritis, and monoclonal crystalline glomerulopathies) and nonorganized deposits (such as monoclonal Ig deposition disease and proliferative glomerulonephritis with monoclonal Ig deposits) based on the characteristics of immunofluorescence findings and the ultrastructural appearance of deposits on electron microscopy. This review aims to provide an update, highlight, and discuss clinicopathological aspects such as definition, epidemiology, clinical manifestations, mechanisms of kidney injury, histological features, and diagnostic procedures.

[Latest updates on immunotactoid glomerulopathy and fibrillary glomerulonephritis]

Various hematologic malignancies can lead to renal complications. The most common of these hemopathies to affect the kidney is multiple myeloma, however an increasing number of kidney diseases are associated with other monoclonal gammopathies. It is recognized that clones in small abundance can be responsible for severe organ damage, thus the concept of monoclonal gammopathy of renal significance (MGRS) has emerged. Although the hemopathy in these patients is more consistent with monoclonal gammopathy of undetermined significance (MGUS) than with multiple myeloma, the diagnosis of a renal complication changes the therapeutic management. Preservation and restoration of renal function is possible with treatment targeting the responsible clone. In this article, we take as an example immunotactoid and fibrillary glomerulopathies, two distinct entities with different etiologies and consequently different management. Immunotactoid glomerulopathy is most often associated with monoclonal gammopathy or chronic lymphocytic leukemia, the deposits on renal biopsy are monotypic, and treatment is therefore based on clone targeting. Fibrillary glomerulonephritis, on the other hand, is caused by autoimmune diseases or solid cancers. Deposits on renal biopsy are in the vast majority polyclonal. There is a specific immunohistochemical marker, DNAJB9, and treatment is less well established.

Pharmacovigilance for rare diseases: a bibliometrics and knowledge-map analysis based on web of science

OBJECTIVES

The aims of this paper is to search and explore publications in the field of pharmacovigilance for rare diseases and to visualize general information, research hotspots, frontiers and future trends in the field using the bibliometric tool CiteSpace to provide evidence-based evidence for scholars.

METHODS

We searched the Web of Science Core Collection (WoSCC) for studies related to pharmacovigilance for rare diseases, spanning January 1, 1997-October 25, 2022. CiteSpace software was utilized to discuss countries/regions, institutions, authors, journals, and keywords.

RESULTS

After screening, a total of 599 valid publications were included in this study, with a significant upward trend in the number of publications. These studies were from 68 countries/regions with the United States and the United Kingdom making the largest contributions to the field. 4,806 research scholars from 493 institutions conducted studies on pharmacovigilance for rare diseases. Harvard University and University of California were the top two productive institutions in the research field. He Dian of the Affiliated Hospital of Guizhou Medical University and Peter G.M. Mol of the University of Groningen, The Netherlands, were the two most prolific researchers. The Cochrane Database of Systematic Reviews and the New England Journal of Medicine were the journals with the highest number of articles and co-citation frequency respectively. Clinical trial, therapy and adverse event were the top three most cited keywords.

CONCLUSIONS

Based on keywords co-occurrence analysis, four research topics were identified: orphan drug clinical trials, postmarketing ADR surveillance for orphan drugs, rare diseases and orphan drug management, and diagnosis and treatment of rare diseases. Immune-related adverse reactions and benefit-risk assessment of enzyme replacement therapy were at the forefront of research in this field. Treatment outcomes, early diagnosis and natural history studies of rare diseases may become hotspots for future research.

Monoclonal gammopathy of renal significance: Multidisciplinary approach to diagnosis and treatment

Monoclonal gammopathy of renal significance (MGRS) is a hemato-nephrological term referring to a heterogeneous group of kidney disorders characterized by direct or indirect kidney injury caused by a monoclonal immunoglobulin (MIg) produced by a B cell or plasma cell clone that does not meet current hematologic criteria for therapy. MGRS-associated kidney diseases are diverse and can result in the development of end stage kidney disease (ESKD). The diagnosis is typically made by nephrologists through a kidney biopsy. Many distinct pathologies have been identified and they are classified based on the site or composition of the deposited Mig, or according to histological and ultrastructural findings. Therapy is directed towards the identified underlying clonal population and treatment decisions should be coordinated between hematologists and nephrologists in a multidisciplinary fashion, depend on the type of MGRS, the degree of kidney function impairment and the risk of progression to ESKD.

Kidney Transplantation in Patients With Monoclonal Gammopathy of Renal Significance

Monoclonal gammopathy of renal significance (MGRS) defines disorders characterized by direct or indirect kidney injury caused by a monoclonal immunoglobulin produced by a B-cell or plasma-cell clone that does not meet current hematologic criteria for therapy. MGRS-associated kidney diseases are diverse and can result in the development of end-stage kidney disease. The current paradigm states that the underlying hematologic condition should be treated and in deep remission before kidney transplantation can be performed because recurrence has been reported for all MGRS-associated kidney diseases. However, we suggest that decisions regarding kidney transplantation in MGRS patients should be individualized considering many factors such as the subtype of MGRS-associated kidney disease, patient age and comorbidity, presence and risk of extrarenal complications, estimated waiting time, the availability of a living kidney donor, and previous hematological treatment and response. Thus, kidney transplantation should be considered even in treatment-naive patients, with hematological treatment initiated after successful kidney transplantation.

Light Chain-Only Immunotactoid Glomerulopathy: A Case Report

The monotypic variant of immunotactoid glomerulopathy (ITG), strongly associated with low-grade lymphoproliferative disorders, is characterized histologically by glomerulonephritis and microtubular deposits of monoclonal immunoglobulin G (IgG). We report a patient with high-risk κ light chain multiple myeloma who presented with acute kidney injury, hematuria, proteinuria, and hypocomplementemia. Kidney biopsy revealed immunotactoid glomerulopathy concomitant with κ light chain myeloma cast nephropathy. The glomerular microtubular deposits stained for κ light chain and C3 only. Proteomic analysis of glomeruli and atypical casts detected κ light chain constant domain and a single VL variability subgroup (IGKV3) in both glomeruli and casts (without γ, α, or μ heavy chain or λ light chain). C3, C5, C6, C7, and C9 were detected in glomeruli. No autoantibodies against alternative pathway of complement proteins were detected. Despite clone-directed chemotherapy, the patient remained on dialysis treatment. For this light chain-only variant of immunotactoid glomerulopathy, pathogenesis potentially involves activation of the alternative pathway of complement by a nephrotoxic κ light chain.

The characteristics of seronegative and seropositive non-hepatitis-associated cryoglobulinemic glomerulonephritis

cryoglobulinemic glomerulonephritis (CryoGN) are not well-defined and cases with undetectable serum cryoglobulin (seronegative CryoGN) have not been investigated. Corresponding author: To resolve this, we retrospectively identified 81 patients with biopsy-proven non-hepatitis CryoGN, including 22 with seronegative CryoGN. The median age was 61 years and 76% presented with nephritic syndrome. A hematologic condition was found in 89% of patients, including monoclonal gammopathy of renal significance (65%) and symptomatic lymphoproliferative disorder (35%). In the seropositive group, 56% had type II, 29% type I, 8% type III cryoglobulin. Extrarenal manifestations, mostly of skin, were present in 64% and were significantly less common in seronegative CryoGN. Glomerular deposits by immunofluorescence were IgM dominant (84%) and polytypic (70%) in the seropositive group, whereas 52% of seronegative cases had monotypic deposits (i.e., type I cryoglobulin). Ultrastructurally, the deposits were organized in 77% of cases. Substructure appearance significantly differed according to the type of CryoGN, forming most commonly short cylindrical structures in type II and other organized substructures in type I CryoGN. Most patients were treated with clone-directed therapy. On follow up (median 33 months), 77% had partial or complete remission, 10% reached kidney failure and 14% died. Predictors of kidney failure on univariate analysis were AKIN stage 3, positive rheumatoid factor and biclonal gammopathy at diagnosis. We conclude that most CryoGN cases (types I and II) are due to hematologic condition and are associated with favorable outcome after clone-directed therapy. Seronegative CryoGN accounts for about a quarter of cases and is mostly a kidney-limited disease. Thus, further investigations are needed to unravel the pathophysiology of seronegative CryoGN.

Novel approaches beyond standard immunofluorescence for kidney biopsies

PURPOSE OF REVIEW

Immunofluorescence on frozen tissue (IF-F) utilizing antibodies against immunoglobulin (Ig) heavy and light chains (IgA, IgG and IgM, kappa and lambda) and components of classical and alternative complement pathways (C1q, C3c and C4) is the standard of renal pathology. However, conventional IF-F has limitations, particularly in nephropathies associated with organized and/or monoclonal Ig deposits. This review will discuss new applications of established methods beyond conventional IF-F and recent novel immunohistochemical methods.

RECENT FINDINGS

The combined application of paraffin immunofluorescence (IF-P) and IgG subtype staining excluded monotypic deposits in 62-66% of DNA J homolog subfamily B member 9-associated fibrillary glomerulonephritis (FGN) with apparent monotypic deposits by IF-F, whereas IF-P unmasks IgG deposits in a subset of cases of immunotactoid glomerulopathy. A novel IF technique targeting epitopes at the junction of the Ig heavy and light chains was introduced and unmasked polytypic deposits in a subset of glomerulonephritis with apparent monotypic deposits on IF-F. A recent study described the successful application of co-detection by indexing (CODEX) multiplexed IF to visualize more than a dozen target antigens within a single kidney tissue section. Finally, immunohistochemical protocols for detection of the novel antigens in membranous nephropathy have already entered the clinical practice of renal pathology.

SUMMARY

Novel ancillary techniques in renal pathology have the potential to significantly enhance our ability to evaluate renal biopsies.

Acute glomerulonephritis

Glomerulonephritis is a heterogeneous group of disorders that present with a combination of haematuria, proteinuria, hypertension, and reduction in kidney function to a variable degree. Acute presentation with full blown nephritic syndrome or rapidly progressive glomerulonephritis is uncommon and is mainly restricted to patients with post-infectious glomerulonephritis, anti-neutrophil cytoplasmic antibodies-associated vasculitis, and anti-glomerular basement membrane disease. Most frequently, patients present with asymptomatic haematuria and proteinuria with or without reduced kidney function. All glomerulonephritis disorders can show periods of exacerbation, but disease flairs characteristically occur in patients with IgA nephropathy or C3 glomerulopathy. The gold standard for the diagnosis of a glomerulonephritis is a kidney biopsy, with a hallmark glomerular inflammation that translates into various histopathological patterns depending on the location and severity of the glomerular injury. Traditionally, glomerulonephritis was classified on the basis of the different histopathological patterns of injury. In the last few years, substantial progress has been made in unravelling the underlying causes and pathogenetic mechanisms of glomerulonephritis and a causal approach to the classification of glomerulonephritis is now favoured over a pattern-based approach. As such, glomerulonephritis can be broadly classified as immune-complex glomerulonephritis (including infection-related glomerulonephritis, IgA nephropathy, lupus nephritis, and cryoglobulinaemic glomerulonephritis), anti-neutrophil cytoplasmic antibodies-associated (pauci-immune) glomerulonephritis, anti-glomerular basement membrane glomerulonephritis, C3 glomerulopathy, and monoclonal immunoglobulin-associated glomerulonephritis. We provide an overview of the clinical presentation, pathology, and the current therapeutic approach of the main representative disorders in the spectrum of glomerulonephritis.

Immunotactoid glomerulopathy - an enigmatic case in the setting of nodal marginal zone lymphoma and systemic sclerosis sine scleroderma

Background

Immunotactoid Glomerulopathy (ITG) is an exceedingly rare type of glomerulopathy characterised by distinctive electron microscopic features. ITG has been linked to lymphoproliferative or autoimmune disorders. The clinical manifestations are diverse including nephrotic syndrome (NS), haematuria, acute kidney injury and end stage renal failure (ESRD). We present a case with a stage 3 Nodal Marginal Zone Lymphoma (NMZL) and systemic sclerosis sine scleroderma (SSSS), where the evolution of ITG was documented in 2 renal biopsies 19 months apart. To the best of our knowledge, no cases have been reported linking ITG to NMZL. Furthermore, there is only one non-peer reviewed report linking ITG to scleroderma. We discuss the implications of our findings and highlight the satisfactory management of the case.

Case presentation

A 79-year-old female with history of systemic sclerosis sine scleroderma and stage 3 NMZL presented with acute kidney injury and NS on a background of chronic kidney disease. Her first kidney biopsy showed a diffuse proliferative glomerulonephritis and her serum protein electrophoresis showed no abnormalities. She was managed satisfactorily with conservative measures. She returned 19 months later with features of fluid overload, increasing proteinuria and rising serum creatinine. A repeat serum protein electrophoresis showed excess free kappa light chains and ITG was detected in the repeat kidney biopsy. Her kidney function and proteinuria showed a good and sustained response to rituximab administered after the second biopsy.

Conclusion

ITG is a rare type of glomerulopathy, associated with underlying haematological malignancies and autoimmune disorders that may result in ESRD.

Rituximab is one of the effective agents used in the management of ITG with haematological malignancies.

Paraneoplastic Glomerular Diseases

Paraneoplastic glomerular diseases (GNs) are rare manifestations in patients with underlying hematologic and solid organ malignancies and can occur before or after the detection of cancer. In the absence of established algorithms for investigation and reliable tests, they remain difficult to diagnose. Given the heterogeneity and infrequency of cases, the pathogenesis of most paraneoplastic GNs is poorly understood. Most of our recent understanding of paraneoplastic GNs has emerged from the discovery of target antigens in membranous nephropathy such as thrombospondin type-1 domain-containing protein 7A and neural epidermal growth factor-like 1 protein that appear to be promising in differentiating a primary vs paraneoplastic cause of membranous nephropathy. Treatment of paraneoplastic GNs is usually directed at the underlying malignancy. This review will focus on the epidemiology, pathogenesis, and diagnosis of paraneoplastic glomerular processes.

Monoclonal Gammopathy-Related Kidney Diseases

Monoclonal gammopathies occur secondary to a broad range of clonal B lymphocyte or plasma cell disorders, producing either whole or truncated monoclonal immunoglobulins. The kidneys are often affected by these monoclonal proteins, and, although not mutually exclusive, can involve the glomeruli, tubules, interstitium, and vasculature. The nephrotoxic potential of these monoclonal proteins is dependent on a variety of physicochemical characteristics that are responsible for the diverse clinicopathologic manifestations, including glomerular diseases with organized deposits, glomerular diseases with granular deposits, and other lesions, such as C3 glomerulopathy and thrombotic microangiopathy with unique pathophysiologic features. The diseases that involve primarily the tubulointerstitial and vascular compartments are light chain cast nephropathy, light chain proximal tubulopathy, crystal-storing histiocytosis, and crystalglobulin-induced nephropathy with distinct acute and chronic clinicopathologic features. The diagnosis of a monoclonal gammopathy-related kidney disease is established by identification of an underlying active or more commonly, low-grade hematologic malignancy, serologic evidence of a monoclonal gammopathy when detectable, and most importantly, monoclonal protein-induced pathologic lesions seen in a kidney biopsy, confirming the association with the monoclonal protein. Establishing a diagnosis may be challenging at times, particularly in the absence of an overt hematologic malignancy, with or without monoclonal gammopathy, such as proliferative glomerulonephritis with monoclonal immunoglobulin deposits. Overall, the treatment is directed against the underlying hematologic disorder and the potential source of the monoclonal protein.

RNA-based immunoglobulin repertoire sequencing is a new tool for the management of monoclonal gammopathy of renal (kidney) significance

The diagnostic approach of monoclonal gammopathy of renal significance is based on the detection of a monoclonal immunoglobulin in the blood and urine, and the identification of the underlying clone through bone marrow and/or peripheral blood cytologic and flow cytometry analysis. However, the monoclonal component and its corresponding clone may be undetectable using these routine techniques. Since clone identification is the cornerstone for guiding therapy and assessing disease response, more sensitive methods are required. We recently developed a high-throughput sequencing assay from bone marrow mRNA encoding immunoglobulins (RACE-RepSeq). This technique provides both full-length V(D)J region (variable, diversity and joining genes that generate unique receptors as antigen receptors) of the monoclonal immunoglobulin and the dominant immunoglobulin repertoire. This allows analysis of mutational patterns, immunoglobulin variable gene frequencies and diversity due to somatic hypermutation. Here, we evaluated the diagnostic performance of RACE-RepSeq in 16 patients with monoclonal-associated kidney lesions, and low serum monoclonal immunoglobulin and free light chain levels at diagnosis. Bone marrow immunohistochemical analysis was negative in all 11 patients so tested and 7 of 12 patients had no detectable clone matching the kidney deposits using flow cytometry analysis. By contrast, RACE-RepSeq detected a dominant clonal light chain sequence of matched isotype with respect to kidney deposits in all patients. Thus, high throughput mRNA sequencing appears highly sensitive to detect subtle clonal disorders in monoclonal gammopathy of renal significance and suggest this novel approach could help improve the management of this kidney disease.

The Clone Wars: Diagnosing and Treating Dysproteinemic Kidney Disease in the Modern Era

Dysproteinemic kidney diseases are disorders that occur as the result of lymphoproliferative (B cell or plasma cell) disorders that cause kidney damage via production of nephrotoxic monoclonal immunoglobulins or their components. These monoclonal immunoglobulins have individual physiochemical characteristics that confer specific nephrotoxic properties. There has been increased recognition and revised characterization of these disorders in the last decade, and in some cases, there have been substantial advances in disease understanding and treatments, which has translated to improved patient outcomes. These disorders still present challenges to nephrologists and patients, since they are rare, and the field of hematology is rapidly changing with the introduction of novel testing and treatment strategies. In this review, we will discuss the clinical presentation, kidney biopsy features, hematologic characteristics and treatment of dysproteinemic kidney diseases.

Untangling immunotactoid glomerulopathy in the MGRS era

Immunotactoid glomerulopathy (ITG) is a rare disease diagnosed by kidney biopsy showing characteristic microtubules, often in parallel arrays, in glomeruli on electron microscopy. Most cases are caused by lymphoproliferative disorders that produce monoclonal immunoglobulins that cause kidney damage, but these disorders do not meet criteria for overt malignancy. The published literature on ITG is limited. In this issue of Kidney International, 2 manuscripts provide significant insight into the clinical presentation, pathology, and treatment of ITG.

Diagnostic Approach to Glomerulonephritis With Fibrillar IgG Deposits and Light Chain Restriction

Introduction

The pathologic approach to glomerulonephritis (GN) with fibrillar IgG deposits and light chain restriction remains a diagnostic challenge.

Method

All GN with fibrillar deposits of IgG and apparent light chain restriction on standard immunofluorescence on frozen tissue (IF-F) accessioned at the Columbia Renal Pathology Laboratory from 2012 to 2019 were identified. Additional studies including staining for Congo red, DNAJB9, IgG subtypes, and immunofluorescence on pronase-digested paraffin sections (IF-P) were performed.

Result

Based on the results, biopsy samples were reclassified as polytypic DNAJB9-positive fibrillary glomerulonephritis (pFGN, n = 14), monotypic DNAJB9-positive FGN (mFGN, n = 7), GN with polytypic DNAJB9-negative fibrillar IgG deposits (n = 2), and GN with monotypic DNAJB9-negative fibrillar IgG deposits (n = 6). Among DNAJB9-positive FGN samples, IgG subtype staining was able to exclude monotypic deposits by demonstrating reactivity for ≥2 IgG subtypes (usually IgG1 and IgG4) in 67% (14 of 21), including 9 that would have been misclassified as monotypic by IF-F and IF-P alone. Monotypic DNAJB9-positive fibrillary glomerulonephritis (FGN) was not associated with monoclonal gammopathy in 5 of 6 patients. GN with monotypic DNAJB9-negative fibrillar IgG deposits exhibited focal parallel fibril alignment and frequent association with chronic lymphocytic leukemia, but lacked the diagnostic microtubules of immunotactoid GN.

Conclusion

A systematic diagnostic approach with ancillary techniques is essential for proper classification and assignment of monoclonal gammopathy of renal significance status in cases of GN with fibrillary IgG deposits and light chain restriction by IF-F.