Rationale and design of the Japanese Biomarkers in Nephrotic Syndrome (J-MARINE) study.

INTRODUCTION: Disease subtyping and monitoring are essential for the management of nephrotic syndrome (NS). Although various biomarkers for NS have been reported, their clinical efficacy has not been comprehensively validated in adult Japanese patients. METHODS: The Japanese Biomarkers in Nephrotic Syndrome (J-MARINE) study is a nationwide, multicenter, and prospective cohort study in Japan, enrolling adult (≥18 years) patients with minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS), membranous nephropathy (MN), membranoproliferative glomerulonephritis (MPGN), C3 glomerulopathy (C3G), and lupus nephritis (LN). Baseline clinical information and plasma and urine samples will be collected at the time of immunosuppressive therapy initiation or biopsy. Follow-up data and plasma and urine samples will be collected longitudinally based on the designated protocols. Candidate biomarkers will be measured: CD80, cytotoxic T-lymphocyte antigen 4, and soluble urokinase plasminogen activator receptor for MCD and FSGS; anti-phospholipase A2 receptor and thrombospondin type-1 domain-containing protein 7A antibodies for MN; fragment Ba, C3a, factor I, and properdin for MPGN/C3G; and CD11b, CD16b, and CD163 for LN. Outcomes include complete and partial remission, relapse of proteinuria, a 30% reduction in estimated glomerular filtration rate (eGFR), eGFR decline, and initiation of renal replacement therapy. The diagnostic accuracy and predictive ability for clinical outcomes will be assessed for each biomarker. RESULTS: From April 2019 to April 2023, 365 patients were enrolled: 145, 21, 138, 10, and 51 cases of MCD, FSGS, MN, MPGN/C3G, and LN, respectively. CONCLUSION: This study will provide valuable insights into biomarkers for NS and serve as a biorepository for future studies.

C3 Glomerulopathy and Related Disorders in Children: Etiology-Phenotype Correlation and Outcomes.

BACKGROUND AND OBJECTIVES: Membranoproliferative GN and C3 glomerulopathy are rare and overlapping disorders associated with dysregulation of the alternative complement pathway. Specific etiologic data for pediatric membranoproliferative GN/C3 glomerulopathy are lacking, and outcome data are based on retrospective studies without etiologic data. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: A total of 80 prevalent pediatric patients with membranoproliferative GN/C3 glomerulopathy underwent detailed phenotyping and long-term follow-up within the National Registry of Rare Kidney Diseases (RaDaR). Risk factors for kidney survival were determined using a Cox proportional hazards model. Kidney and transplant graft survival was determined using the Kaplan-Meier method. RESULTS: Central histology review determined 39 patients with C3 glomerulopathy, 31 with immune-complex membranoproliferative GN, and ten with immune-complex GN. Patients were aged 2-15 (median, 9; interquartile range, 7-11) years. Median complement C3 and C4 levels were 0.31 g/L and 0.14 g/L, respectively; acquired (anticomplement autoantibodies) or genetic alternative pathway abnormalities were detected in 46% and 9% of patients, respectively, across all groups, including those with immune-complex GN. Median follow-up was 5.18 (interquartile range, 2.13-8.08) years. Eleven patients (14%) progressed to kidney failure, with nine transplants performed in eight patients, two of which failed due to recurrent disease. Presence of >50% crescents on the initial biopsy specimen was the sole variable associated with kidney failure in multivariable analysis (hazard ratio, 6.2; 95% confidence interval, 1.05 to 36.6; P<0.05). Three distinct C3 glomerulopathy prognostic groups were identified according to presenting eGFR and >50% crescents on the initial biopsy specimen. CONCLUSIONS: Crescentic disease was a key risk factor associated with kidney failure in a national cohort of pediatric patients with membranoproliferative GN/C3 glomerulopathy and immune-complex GN. Presenting eGFR and crescentic disease help define prognostic groups in pediatric C3 glomerulopathy. Acquired abnormalities of the alternative pathway were commonly identified but not a risk factor for kidney failure.

Identification of plasma miR-106a-5p and miR-30a-5p as potential biomarkers for mesangial proliferative glomerulonephritis.

BACKGROUND: Although stable microRNAs (miRNAs) are present in human peripheral blood and have been considered as novel biomarkers for various diseases. But there is little research about miRNAs as biomarkers of mesangial proliferative glomerulonephritis (MsPGN). This study aimed to identify whether there exist disordered circulating miRNAs that can function as biomarkers for MsPGN disease activity. METHODS: The candidate miRNAs were validated in 70 MsPGN patients and 70 healthy controls by quantitative real-time PCR (RT-qPCR). The specificity and sensitivity of the miRNA panel was assessed by receiver operating characteristic (ROC) curves. In addition, the candidate miRNA levels were measured in the different MsPGN progression and in the membranous nephropathy (MN) patients and the hypothetical role of the candidate miRNA on mesangial cell proliferation was analysed. Situ hybridization was performed to examine the candidate miRNA levels in the glomerulus. RESULTS: These results showed that miR-106a-5p and miR-30a-5p were highly expressed in MsPGN patients compared with healthy controls and could discriminate MsPGN from healthy controls with an area under the ROC curve (AUC) of 0.93. In addition, the two miRNAs were not only higher in moderate and severe MsPGN patients, but could distinguish MsPGN from MN. We also observed a decreased expression in MsPGN regression group after treatment. Plasma miR-106a-5p level was positively correlated with estimated glomerular filtration rate (eGFR). Furthermore, the two miRNAs were highly expressed in MsPGN glomerulus and their overexpression could prompt mesangial cell proliferation. CONCLUSION: Plasma miR-30a-5p and miR-106a-5p can serve as novel and potential diagnostic biomarkers for MsPGN.

Parvovirus B19 infection and kidney injury: report of 4 cases and analysis of immunization and viremia in an adult cohort of 100 patients undergoing a kidney biopsy.

BACKGROUND: The seroprevalence of human Parvovirus B19 (PVB19) is 70-85% in adults worldwide. PVB19 is the etiologic agent of the fifth disease, is a cause of aplastic anemia, and can be associated with kidney injury. We aimed to describe the cases of 4 patients with kidney injury related to PVB19 primary infection, and to evaluate the seroprevalence of PVB19 and the incidence of PVB19 primary infection in patients undergoing a native kidney biopsy. METHODS: Cases of PVB19 infection with kidney injury were reviewed from the archives of the department of Nephrology. A systematic screening of anti-PVB19 IgG and IgM antibodies and viral DNA was performed in sera from 100 consecutive patients with a kidney biopsy in 2017-2018. RESULTS: The 4 patients with PVB19 infection-associated kidney disease displayed: one lupus-like glomerulonephritis (GN) without lupus auto-antibodies, one minimal change disease with tubular necrosis, one secondary hemolytic and uremic syndrome and one membrano-proliferative GN. In the 100 patients biopsied, 67 had elevated anti-PVB19 IgG, among whom 8 had elevated IgM, without circulating viral DNA, without any particular renal pathological pattern. One additional patient showed a seroconversion at the time of kidney biopsy, which revealed a class V lupus nephritis. CONCLUSION: PVB19 primary infection can be associated with different kidney diseases. The seroprevalence of PVB19 among patients with a kidney biopsy is similar to the overall population, and primary infection is rarely documented (1%) after systematic screening. Whether PV19 is nephrotoxic, or triggers renal endothelial injury and immune activation, remains to be elucidated.

Clinicopathological features of C3 glomerulopathy in children: a single-center experience.

BACKGROUND: C3 glomerulopathy (C3G) is defined by dominant glomerular deposition of C3 and minimal or no immunoglobulin, with two subtypes-dense deposit disease (DDD) and C3 glomerulonephritis (C3GN)-distinguished by features on electron microscopy (EM). Given that this rare disease has generally unfavorable yet highly variable outcomes, we sought out to review the histopathology, complement/genetic studies, and renal outcomes of pediatric patients with C3G at our institution. METHODS: All native kidney biopsies performed in a single pediatric hospital over a 10-year period were reviewed for features of C3G. Of 589 biopsy reports, we identified 9 patients fulfilling the diagnostic criteria for C3G and retrospectively reviewed their clinical chart and renal biopsy findings. RESULTS: We identified 4 patients with DDD, 4 with C3GN, and 1 indeterminate case, with features of both C3GN and DDD. Five patients were positive for one or more nephritic factors (C3NeF, C4NeF, C5NeF) with 1 patient additionally positive for complement factor H (CFH) autoantibody. Genetic testing done in 5 of the 9 patients failed to identify any causative mutations. Three patients showed progressive renal dysfunction over a mean follow-up period of 33 months. CONCLUSIONS: Complement and genetic studies are now routinely recommended for patients with a histopathological diagnosis of C3G. Careful interpretation of these studies and their prognostic and therapeutic implications in conjunction with biopsy findings is needed to further understand the pathophysiology of this rare disease in children.

A case report of recurrent membranoproliferative glomerulonephritis after kidney transplantation due to ventriculoatrial shunt infection.

BACKGROUND: Transplant failure requires the consideration of numerous potential causes including rejection, acute tubular necrosis, infection, and recurrence of the original kidney disease. Kidney biopsy is generally required to approach these differential diagnoses. However, the histopathological findings on their own do not always lead to a definite diagnosis. Consequently, it is crucial to integrate them with clinical findings and patient history when discussing histopathological patterns of injury. The histopathologic finding of a membranoproliferative glomerulonephritis (MPGN) is one of the most challenging constellations since it does not refer to a specific disease entity but rather reflects a pattern of injury that is the result of many different causes. Whilst MPGN is occasionally classified as immune complex mediated, careful evaluation usually reveals an underlying disorder such as chronic infection, plasma cell dyscrasia, complement disorders, and autoimmune disease. CASE PRESENTATION: We describe the case of a 43-year-old woman who was referred to us because of a slowly rising serum creatinine 4 years after kidney transplantation. As in the native kidney, the biopsy revealed an MPGN pattern of injury. The cause of this finding had not been established prior to transplantation leading to a classification as idiopathic MPGN in the past. Further workup at the time of presentation and allograft failure revealed chronic infection of a ventriculoatrial shunt as the most probable cause. CONCLUSION: This case underlines the fact that MPGN is not a disease but a histopathological description. Consequently, the causative disorder needs to be identified to avoid kidney failure and recurrence after transplantation.

Plasma exchange and rituximab treatments in primary membranous nephropathy combined with crescentic glomerulonephritis: A case report.

RATIONALE: Crescent formation is rare in primary membranous nephropathy (MN). Anti-phospholipase A2 receptor (PLA2R) antibodies are detectable in these patients. The mechanism and treatments are unknown. PATIENT CONCERNS: A 72-year-old female patient who presented with nephrotic syndrome, hematuria, and rapidly progressive kidney dysfunction. DIAGNOSES: Kidney biopsy was performed and the diagnosis was MN in combination with crescentic glomerulonephritis. Circulating anti-PLA2R IgG3 and IgG4 were detected of high level. INTERVENTIONS: The patient received plasma exchange and rituximab besides corticosteroids. OUTCOMES: The patient achieved complete remission of proteinuria and recovery of kidney function after the clearance of anti-PLA2R antibodies. LESSON: This case suggests a pathogenic role of anti-PLA2R antibodies in the mechanism of crescent formation in MN, which may need intensive therapy to eliminate the antibodies quickly.

Development of membranoproliferative glomerulonephritis-like glomerulopathy in a patient with neutrophilia resulting from endogenous granulocyte-colony stimulating factor overproduction: a case report.

BACKGROUND: The pathophysiologic role of exogenous granulocyte-colony stimulating factor (G-CSF) administration is reportedly linked to the progression of glomerulonephritis. However, the relationship between endogenous G-CSF overproduction and the progression of glomerulopathy has not been well investigated. CASE PRESENTATION: A 76-year-old woman presented with neutrophilia at a medical check-up and thorough examination revealed a high level of serum G-CSF. She subsequently developed mild renal dysfunction and proteinuria. Her renal biopsy showed lobulation of the glomeruli with mesangial proliferation and glomerular capillary walls with a double contour but no immune complex deposition, suggesting membranoproliferative glomerulonephritis-like glomerulopathy. Thereafter, her proteinuria levels fluctuated in parallel with the changes in her blood neutrophil count and finally reduced considerably in association with her decreased neutrophil count. CONCLUSIONS: The unique features of this case suggest that endogenous overproduction of G-CSF could play an important role in the pathogenesis of active glomerulonephritis.

Thrombotic microangiopathy with intraglomerular IgM pseudothrombi in Waldenström macroglobulinemia and IgM monoclonal gammopathy.

IgM secreting myelomas or lymphomas, including Waldenström macroglobulinemia, are associated with a varied spectrum of renal pathology, including intracapillary hyaline deposits, cryoglobulin, membranoproliferative glomerulonephritis, amyloid, monoclonal immunoglobulin deposition disease, cast nephropathy, and lymphoma infiltration. We report our single institution experience, and describe five cases with distinctive glomerular pathology: intracapillary IgM pseudothrombi and thrombotic microangiopathic change, with glomerular intracellular crystals in two biopsies. Two patients were hypocomplementemic at presentation. This series adds to the recent literature on paraprotein associated thrombotic microangiopathy.

A clone-directed approach may improve diagnosis and treatment of proliferative glomerulonephritis with monoclonal immunoglobulin deposits.

The optimal treatment for the monoclonal gammopathies of renal significance is not known, but there is consensus among experts that treatment should be specific for the underlying clone. The majority of patients with proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID) do not have an identifiable clone, and prior studies have found poor renal outcomes for patients with PGNMID treated with a variety of regimens. Here we present a retrospective case series of 19 patients with PGNMID with a more uniform, clone-directed approach. A circulating paraprotein was detected in 37% of patients, and the overall clone detection rate was 32%. Treatment was directed at the underlying clone or, for patients without a detectable clone, empirically prescribed to target the hypothesized underlying clone. Of the 16 patients who underwent treatment, the overall renal response rate was 88%, and 38% of patients experienced complete renal response (proteinuria reduction to under 0.5 gm/24 hours) with initial treatment. All patients were End Stage Renal Disease-free at last follow-up (median 693 days after diagnosis), and treatment was well tolerated. Thus, a clone-directed approach may lead to novel, targeted treatment strategies that could significantly improve outcomes for patients with PGNMID.

Favorable effect of bortezomib in dense deposit disease associated with monoclonal gammopathy: a case report.

BACKGROUND: Complement component 3 (C3) glomerulopathy, which includes dense deposit disease (DDD) and C3 glomerulonephritis, is caused by dysregulation of the alternative complement pathway. In most cases, C3 glomerulopathy manifests pathologically with membranoproliferative glomerulonephritis-like features. An association between C3 glomerulopathy and monoclonal gammopathy was recently reported in several cases, raising the possibility that C3 glomerulopathy is the underlying pathological process in monoclonal gammopathy of renal significance. CASE PRESENTATION: We herein report a case of monoclonal gammopathy-induced DDD that improved histologically and clinically with chemotherapy including bortezomib. Our case is the first in which treatment response can be linked to the histological response. Potential pathological insights are also discussed. CONCLUSIONS: Rapid and efficient chemotherapy has the potential to limit renal damage in monoclonal gammopathy-associated DDD.

C3 glomerulopathy associated with monoclonal Ig is a distinct subtype.

Monoclonal immunoglobulins (MIg) may play a causal role in C3 glomerulopathy (C3G) by impairing regulation of the alternative pathway of complement. Ninety-five patients with C3G were tested for MIg of which 36 were positive. Their mean age at diagnosis was 60 years and among patient 50 years and older, 65.1% had a MIg. At presentation, median serum creatinine and proteinuria were 1.9 mg/dL and 3.0 g/24 hours. Hematuria was present in 32 (88.9%) patients. Twelve (34.3%) patients had low C3 levels. C3 nephritic factor was detected in 45.8% patients; pathogenic variants in complement protein genes were rare. Hematologic evaluation revealed monoclonal gammopathy of renal significance in 26 patients, multiple myeloma in five, smoldering multiple myeloma in two, and chronic lymphocytic leukemia, lymphoma, or type I cryoglobulin each in one patient. After a median follow-up of 43.6 months, the median serum creatinine and proteinuria were 1.4 mg/dL and 0.8g/24 hours. Nine patients developed ESRD. Sixteen patients received MIg-targeted treatment, 17 patients received non-targeted treatment while three patients were managed conservatively. Of the 16 patients receiving MIg-targeted treatment, ten achieved complete/very good/partial hematologic response. Of these, seven achieved a complete/partial/stable renal response. Five patients receiving targeted treatment did not achieve hematologic response, none had a renal response. Patients receiving targeted treatment were more likely to have multiple myeloma/smoldering multiple myeloma. Patients receiving non-targeted treatment were more likely to have monoclonal gammopathy of renal significance. Thus, C3G with MIg is seen in older patients, C3 nephritic factor is the most common autoantibody detected, and MIg-targeted treatment may result in remission and stabilization of kidney function in a subset of these patients.

Patterns of Clinical Response to Eculizumab in Patients With C3 Glomerulopathy.

BACKGROUND: Cases reports and small series of patients with C3 glomerulopathy have reported variable efficacy of eculizumab. STUDY DESIGN: Case series of C3 glomerulopathy. SETTING & PARTICIPANTS: Pediatric and adult patients with C3 glomerulopathy treated with eculizumab between 2010 and 2016 were identified through the C3 glomerulopathy French registry database, and a questionnaire was sent to participating French pediatric and adult nephrology centers, as well as one pediatric referral center in Québec, Canada. OUTCOMES: Global or partial clinical renal response. MEASUREMENTS: Evolution of serum creatinine and proteinuria values. RESULTS: 26 patients (13 children/adolescents) were included. 22 (85%) patients had received steroids, plasma exchange, or immunosuppressive therapy before eculizumab, and 3 of them had rapid progression of their kidney disease despite treatment. At the initiation of eculizumab therapy, 11 (42%) patients had chronic kidney disease, 7 (27%) had rapidly progressive disease, and 3 (12%) required dialysis. After eculizumab treatment (median duration, 14 months), 6 (23%) patients had a global clinical response; 6 (23%), a partial clinical response; and 14 (54%), no response. Compared with those who had a partial clinical or no response, patients who had a global clinical response had lower estimated glomerular filtration rates, a more rapidly progressive course, and more extracapillary proliferation on kidney biopsy. Age, extent of renal fibrosis, frequency of nephrotic syndrome, low serum C3 and C3 nephritic factor and elevated soluble C5b-9 concentrations, or complement gene variants did not differ between responders and nonresponders. LIMITATIONS: Retrospective design without a control group, relatively small number of cases, inclusion of pediatric and adult cases. CONCLUSIONS: Eculizumab appears to be a potential treatment for patients with crescentic rapidly progressive C3 glomerulopathy. Its benefit in patients with non-rapidly progressing forms seems to be limited.

Diagnostic specificity of autoantibodies to M-type phospholipase A2 receptor (PLA2R) in differentiating idiopathic membranous nephropathy (IMN) from secondary forms and other glomerular diseases.

Autoantibody against phospholipase A2 receptor (anti-PLA2R) is a sensitive and specific biomarker of idiopathic membranous nephropathy (iMN), being found in approximately 70% of iMN patients and only occasionally in other glomerular diseases. However, whereas its diagnostic specificity vs. normal controls and other glomerulonephritides (GN) has been firmly established, its specificity vs. membranous nephropathy associated with various diseases (sMN) has given inconsistent results. The aim of our study was to evaluate the prevalence of anti-PLA2R antibodies in iMN in comparison with various control groups, including sMN. A total of 252 consecutive iMN patients, 184 pathological and 43 healthy controls were tested for anti-PLA2R antibody using indirect immunofluorescence (PLA2R IIFT, Euroimmun). Anti-PLA2R autoantibodies were detectable in 178/252 iMN patients, 1/80 primary GN, 0/72 secondary GN, 9/32 sMN and 0/43 healthy controls, with a diagnostic sensitivity of 70.6%. The diagnostic specificity of anti-PLA2R antibody vs. normal and pathological controls was 100 and 94.6% respectively. However, when the diagnostic specificity was calculated only vs. secondary forms of MN, it decreased considerably to 71.9%. Interestingly enough, 9 out of 10 anti-PLA2R positive patients in the disease control groups had membranous nephropathy associated with various diseases (7 cancer, 1 Crohn's disease, 1 scleroderma). In conclusion, anti-PLA2R positivity in a patient with MN, should not be considered sufficient to abstain from seeking a secondary cause, especially in patients with risk factors for neoplasia. The causal relationship between tumors and anti-PLA2R-induced MN remains to be established, as well as the possible mechanisms through which malignancies provoke autoimmunity.

Crescentic Glomerulonephritis With Immunoglobulin G4-Related Disease.

Immunoglobulin G4 (IgG4)-related disease is an uncommon autoimmune disease that affects multiple organ systems. Renal involvement typically presents as tubulointerstitial nephritis and less commonly as membranous glomerulonephritis. In this case report, we discuss a 68-year-old patient who presented with rapidly progressive glomerulonephritis. His renal biopsy revealed a membranoproliferative pattern of injury with fibrocellular crescents and extensive infiltration of the tubulointerstitium with IgG4-positive plasma cells. We treated the patient with both corticosteroids and rituximab because of the aggressive nature of crescentic glomerulonephritis. The patient demonstrated a partial improvement in kidney function after 2 cycles of rituximab with a decrease in serum creatinine levels from 6.9-4.7mg/dL after 6 months from presentation. This case illustrates the importance of considering IgG4-related disease in cases of rapidly progressive glomerulonephritis and the need for effective treatments for more aggressive forms of this recently recognized disease entity.

C3 glomerulonephritis with a severe crescentic phenotype.

BACKGROUND: C3 glomerulopathy (C3G) is rare type of glomerulonephritis resulting from the glomerular deposition of C3 due to dysregulation of the alternative pathway of complement. It is further subdivided into C3 glomerulonephritis (C3GN) and dense deposit disease (DDD), depending on the ultrastructural features. C3GN usually presents with a membranoproliferative pattern of injury. Crescents may or may not be present. However, we have noted a severe necrotizing and crescentic glomerulonephritis in a small subset of C3GN patients. CASE DIAGNOSIS/TREATMENT: We present the clinical features, kidney biopsy findings, complement evaluation, treatment, and follow-up of four C3GN patients. We also compare the findings with four DDD patients with a severe necrotizing and crescentic glomerulonephritis. The patients were young and presented with hematuria and proteinuria. The biopsy was remarkable for the large number of crescents, in association with bright glomerular staining for C3. The patients were treated with steroids/immunosuppressive drugs. Three of the 4 C3GN patients and 2 of the 4 DDD patients showed stable renal function at follow-up. We find remarkable similarities between our C3GN patients with crescents and the previously described entity of juvenile acute nonproliferative glomerulonephritis. CONCLUSIONS: To summarize, C3G with a severe crescentic phenotype is rare, affects children and young adults, and has a variable response to steroid and immunosuppressive treatment. It is important to recognize this rare cause of crescentic glomerulonephritis so that appropriate evaluation and treatment can be carried out.

Cryofibrinogen-Associated Glomerulonephritis.

Cryofibrinogen is an under-recognized cryoprotein. Cryofibrinogen is a cryoprecipitate that develops following plasma refrigeration, but does not occur in cold serum. People with cryofibrinogenemia may be asymptomatic, but this cryoprotein can be associated with thromboembolic disease, particularly affecting the skin. Kidney manifestations are relatively uncommon, but are likely underestimated. We describe clinical features and kidney biopsy results in 2 patients with cryofibrinogen-related kidney disease. Both patients presented with proteinuria and hematuria. One had significant cutaneous ulcers and palpable purpura. Kidney biopsy in both cases showed membranoproliferative glomerulonephritis with no immunoglobulin deposition. Weak segmental capillary wall fibrinogen staining was noted in glomeruli. Immunofluorescence studies following pronase digestion failed to reveal masked immunoglobulin deposits. Ultrastructural studies were distinctive and characterized by organized deposits of large-bore with multilayered tubular structures and fine fibrillary structures in a matrix. To confirm the composition of deposits, we extracted the cryoprecipitate from plasma of a patient and performed ultrastructural studies, which showed identical ultrastructural characteristics to those seen on the kidney biopsy. We also performed proteomic analysis of the cryoprecipitate that confirmed the presence of fibrinogen. Subsequent laboratory evaluation was positive for cryofibrinogen in both patients on multiple occasions. Appropriate therapy was instituted in both patients, which included prednisone, immunosuppressive therapy, and avoidance of cold exposure. In summary, we present clinical, kidney biopsy, and laboratory findings and the treatment and follow-up of cryofibrinogen-associated glomerulonephritis. Awareness of this entity will result in accurate diagnoses, appropriate investigation, and treatment.

C9orf72 ablation causes immune dysregulation characterized by leukocyte expansion, autoantibody production, and glomerulonephropathy in mice.

The expansion of a hexanucleotide (GGGGCC) repeat in C9ORF72 is the most common cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Both the function of C9ORF72 and the mechanism by which the repeat expansion drives neuropathology are unknown. To examine whether C9ORF72 haploinsufficiency induces neurological disease, we created a C9orf72-deficient mouse line. Null mice developed a robust immune phenotype characterized by myeloid expansion, T cell activation, and increased plasma cells. Mice also presented with elevated autoantibodies and evidence of immune-mediated glomerulonephropathy. Collectively, our data suggest that C9orf72 regulates immune homeostasis and an autoimmune response reminiscent of systemic lupus erythematosus (SLE) occurs in its absence. We further imply that haploinsufficiency is unlikely to be the causative factor in C9ALS/FTD pathology.