C1q nephropathy: a variant of focal segmental glomerulosclerosis

Nephrotic Syndrome Throughout Childhood: Diagnosing Podocytopathies From the Womb to the Dorm

The etiologies of podocyte dysfunction that lead to pediatric nephrotic syndrome (NS) are vast and vary with age at presentation. The discovery of numerous novel genetic podocytopathies and the evolution of diagnostic technologies has transformed the investigation of steroid-resistant NS while simultaneously promoting the replacement of traditional morphology-based disease classifications with a mechanistic approach. Podocytopathies associated with primary and secondary steroid-resistant NS manifest as diffuse mesangial sclerosis, minimal change disease, focal segmental glomerulosclerosis, and collapsing glomerulopathy. Molecular testing, once an ancillary option, has become a vital component of the clinical investigation and when paired with kidney biopsy findings, provides data that can optimize treatment and prognosis. This review focuses on the causes including selected monogenic defects, clinical phenotypes, histopathologic findings, and age-appropriate differential diagnoses of nephrotic syndrome in the pediatric population with an emphasis on podocytopathies.

An inactivating human TRPC6 channel mutation without focal segmental glomerulosclerosis

Transient receptor potential cation channel-6 (TRPC6) gene mutations cause familial focal segmental glomerulosclerosis (FSGS), which is inherited as an autosomal dominant disease. In patients with TRPC6-related FSGS, all mutations map to the N- or C-terminal TRPC6 protein domains. Thus far, the majority of TRPC6 mutations are missense resulting in increased or decreased calcium influx; however, the fundamental molecular mechanisms causing cell injury and kidney pathology are unclear. We report a novel heterozygous TRPC6 mutation (V691Kfs*) in a large kindred with no signs of FSGS despite a largely truncated TRPC6 protein. We studied the molecular effects of V691Kfs* TRPC6 mutant using the tridimensional cryo-EM structure of the tetrameric TRPC6 protein. The results indicated that V691 is localized at the pore-forming transmembrane region affecting the ion conduction pathway, and predicted that V691Kfs* causes closure of the ion-conducting pathway leading to channel inactivation. We assessed the impact of V691Kfs* and two previously reported TRPC6 disease mutants (P112Q and G757D) on calcium influx in cells. Our data show that the V691Kfs* fully inactivated the TRCP6 channel-specific calcium influx consistent with a complete loss-of-function phenotype. Furthermore, the V691Kfs* truncation exerted a dominant negative effect on the full-length TRPC6 proteins. In conclusion, the V691Kfs* non-functional truncated TRPC6 is not sufficient to cause FSGS. Our data corroborate recently characterized TRPC6 loss-of-function and gain-of-function mutants suggesting that one defective TRPC6 gene copy is not sufficient to cause FSGS. We underscore the importance of increased rather than reduced calcium influx through TRPC6 for podocyte cell death.

A clinicopathological and prognostic study of 18 children with C1q nephropathy and focal segmental glomerulosclerosis: an 18-year experience from a single center

BACKGROUND

C1q nephropathy is a relatively rare glomerulonephritis characterized by dominant mesangial deposition of C1q. Even though C1q nephropathy has been described for more than three decades, the clinicopathological features and renal outcomes remain unclear. C1q nephropathy may present diverse morphological patterns, including focal segmental glomerulosclerosis and, the notion of C1q nephropathy as a separate disease entity is still debated. This study aimed to describe the clinical and prognostic relevance of C1q nephropathy in children with primary focal segmental glomerulosclerosis.

METHODS

Three hundred eighty-nine children were diagnosed with primary focal segmental glomerulosclerosis in Jinling Hospital from 2003 to 2020. Among them, 18 cases fulfilled the criteria for C1q nephropathy. We then selected as a control group 18 children with primary focal segmental glomerulosclerosis without C1q nephropathy matched to those with C1q nephropathy for age, sex, and period of renal biopsy. Clinical and prognostic parameters were compared in children with and without C1q nephropathy. Renal end-point was defined as a ≥ 40% reduction in estimated glomerular filtration rate or end-stage renal disease.

RESULTS

Four point sixty-three percent (18/389) of primary focal segmental glomerulosclerosis cases were diagnosed with C1q nephropathy. The male-to-female ratio of patients diagnosed with C1q nephropathy was 1:1. The median age at biopsy and age at onset was 15.63 (13.00-16.50) years and 14.50 (9.00-16.00) years, respectively. The prevalence of nephrotic syndrome, hematuria, and hypertension was 38.90% (7/18), 72.20% (13/18), and 33.30% (5/18), respectively. Four (22.2%) patients were steroid-dependent, 13 (72.2%) patients were steroid-resistant, and 1 (5.6%) patient developed secondary steroid-resistance. During a follow-up of 52.24 (25.00-72.47) months, 10 (55.6%) patients achieved remission, and 5 (27.8%) progressed to the end-point [including 2 (11.11%) patients who developed end-stage kidney disease]. There was no significant difference in the estimated end-stage renal disease-free survival rates, the estimated end-point-free survival rates, and the long-term remission rate between patients with and without C1q nephropathy (Kaplan-Meier, Log-rank, all P > 0.05).

CONCLUSIONS

C1q nephropathy was rare in pediatric patients with focal segmental glomerulosclerosis. These patients usually had poor response to steroids. The long-term renal outcomes and remission of children with primary focal segmental glomerulosclerosis with C1q nephropathy were comparable to those without C1q nephropathy.

A possible role of classical complement pathway activation in the pathogenesis of immunoglobulin G nephropathy: a case report

Immunoglobulin G (IgG) nephropathy refers to a rare group of diseases characterized by deposits of IgG in the mesangial region. However, IgG nephropathy is controversial as a single disease entity, and its pathogenesis remains to be elucidated. In the present report, we discuss a case of IgG nephropathy in which we observed activation of the classical complement pathway.A 47-year-old woman was admitted to our hospital with nephrotic syndrome. Light-microscopic examination revealed neither proliferative nor sclerotic lesions in the glomeruli. However, unusual and large deposits were observed in the paramesangial area. An immunofluorescence study revealed predominant IgG and C1q and slight C3 deposits in the paramesangial area, suggesting immune-complex-type glomerular disease. An electron microscopic study also revealed different sizes of non-organized electron-dense deposits with a similar pattern of distribution, which were accompanied by foot process effacement. Clinically, there was no evidence of systemic diseases, such as infectious or autoimmune diseases (including systemic lupus erythematosus). Based on these findings, she was diagnosed with IgG nephropathy and treated with prednisolone. Steroid therapy was effective, and complete remission was maintained.Additional immunological examination revealed that IgG deposits were polyclonal and consisted mainly of the IgG1 and IgG3 subclasses. Furthermore, staining was positive for C4d and C5b-9. The present findings indicate that the pathogenesis of IgG nephropathy in our patient may have involved activation of the classical complement pathway.

C1q nephropathy in children with nephrotic syndrome: Treatment strategies and outcomes

Introduction:

There is a paucity of clinical data on C1q nephropathy (C1qN) in children in India and Southeast Asia. This is the first detailed analysis conducted to elucidate the prevalence, clinicopathological profile, and response to different immunosuppressives in children with C1qN in India.

Materials and Methods:

Detailed demographic profile, clinical features, urine and blood chemistries, kidney biopsy, and response to different immunosuppressives of the study participants were analyzed between August 2015 and October 2020 for steroid-dependent/-resistant nephrotic syndrome (NS).

Results:

C1qN was diagnosed in 16 (14.13%) of 113 children who underwent biopsy for steroid-dependent/-resistant NS. The mean age was 44 months (range 18–99 months) and male and female number was 12 (75%) and four (25%), respectively, and mean follow-up was 3.5 years. Eight (50%) had coexistent minimal-change nephrotic syndrome (MCNS) pattern, seven (43.7%) had focal segmental glomerulosclerosis (FSGS), and one (6.2%) had diffuse mesangial hypercellularity. Thirteen children had complete follow-up, of which eight (61.5%) and four (30.7%) cases presented as steroid-dependent and primary steroid-resistant NS, respectively, whereas one (7.6%) had joint pain with rashes. At presentation, seven (53.8%) had hypertension, 12 (92.3%) had nephrotic range proteinuria, and six cases (46.1%) had hematuria. Nine (75%) of 12 cases achieved complete remission with calcineurin inhibitor (CNI) therapy, and two were non responders, one was a partial responder, and one responded to mycophenolate. Of six FSGS cases, four had complete remission, one had partial remission, and one was in non-remission. Of six cases with MCNS, five had complete remission and one was in non-remission. Renal functions remained normal in all except one case who had progression to chronic kidney disease Stage 3.

Conclusion:

One out of seven children with difficult NS can have underlying C1qN. CNIs are most beneficial to attain and maintain remission. Renal functions remain normal in the majority. Along with C1q deposits, MCNS and FSGS patterns are seen equally and respond almost similarly to CNIs.

Epidemiology of 10-year paediatric renal biopsies in the region of southern Croatia

Background

Information about renal diseases in children is available from national registries of renal biopsies. Aim of the study was to compare the clinical presentation of glomerular diseases and tubulointerstitial space diseases with pathohistological diagnosis of indicated renal biopsies from pediatric population in the Croatian region of Dalmatia.

Methods

Out of 231 pediatric patients with suspected glomerular and tubulointerstitial diseases, 54 underwent ultrasound-guided renal biopsy at University Hospital of Split. Kidney allograft biopsy, and re-biopsy were excluded. The biopsy sections were examined under light microscopy, immunofluorescence and electron microscopy. The data was reviewed to determine the pathohistological spectrum and clinicopathologic correlations. We retrospectively analyzed kidney biopsy data from 2008 to 2017 and compared them to that between 1995 and 2005.

Results

The mean age of patients was 9.84 ± 5.4 years. Male:female ratio was 1.2:1. The main indications for biopsy were pure nephrotic syndrome without hematuria (25.9%), non-nephrotic proteinuria with haematuria (22.2%), nephritic syndrome with nephrotic proteinuria (18.5%), and isolated hematuria (16.7%). The most common pathohistological findings were IgA nephropathy (IgAN, 24.1%), minimal change disease (MCD, 16.7%), Henoch-Schönlein purpura glomerulonephritis (HSPN, 14.8%), Alport syndrome and focal segmental glomerulosclerosis (AS and FSGS, 11.1% each), tubulointerstitial nephritis and membranous glomerulopathy (TIN and MGN, 3.7% each), while other cases were diagnosed rarely.

Conclusions

Changes in epidemiology of renal diseases in children between the analyzed periods showed an increasing trend of IgAN, MCD, HSPN, AS and FSGS, while mesangioproliferative glomerulonephritis (MesPGN) and endoproliferative glomerulonephritis (EDGN) showed a decreasing trend that can be explained with the new pathohistological classification.

Therapeutic Response to Corticosteroids Remains a Valid Approach to Initial Management of Children With Idiopathic Nephrotic Syndrome

Complete remission of idiopathic nephrotic syndrome (INS) in response to corticosteroids has been widely adopted as an indicator of satisfactory long-term outcomes in pediatric patients. The approach was based on the results of studies conducted in the 1960s and 1970s. The studies found that corticosteroid-responsive minimal change disease (MCD) was the most frequent diagnosis in INS patients. In more recent years, studies have reported increased frequency of focal segmental glomerulosclerosis (FSGS) and primary corticosteroid resistance without a corresponding increase of FSGS. It became unclear whether withholding kidney biopsy before treatment with corticosteroids is still the best management practice. We performed a retrospective chart review at the UPMC Children's Hospital of Pittsburgh and identified patients who were referred for evaluation of edema or proteinuria between 2002 and 2014. We identified 114 pediatric patients with INS who were treated initially with a corticosteroid (prednisone or prednisolone) 2 mg/kg (max 60 mg)/day for 4-6 weeks followed by 2 mg/kg (max 60 mg) every other day for 4-6 weeks and had not received a corticosteroid-sparing agent before completing at least 8 weeks of the initial therapy. Corticosteroid resistance in pediatric INS patients was independently associated with the black race, older age at presentation (>8 years), and female sex. The majority of blacks who were resistant to corticosteroids had a tissue diagnosis of MCD. Among the whites who were steroid-resistant, MCD and FSGS were diagnosed in similar proportions of cases. Thus, the tissue diagnosis in could not predict the response to corticosteroids. Nineteen percent of whites with FSGS were steroid-sensitive and none of the blacks with FSGS responded to corticosteroids. These data suggest that the histologic diagnosis of FSGS could not rule out response to corticosteroids, at least, in the white patient population. In summary, our data demonstrate that at this time, the therapeutic response to corticosteroids continues to be a valid approach for the initial evaluation and therapy of children diagnosed with INS at our center. Future studies should evaluate the mechanisms of changing characteristics of pediatric INS. The specific role of patient demographics, ethnicity, as well as genetic and environmental factors could be evaluated by a prospective, multicenter study.

Case Report: Complete Remission of C1q Nephropathy Treated With a Single Low-Dose Rituximab, a Reality or Coincidence?

C1q nephropathy is a glomerulopathy that is characterized by large amount of C1q deposits in the glomerular mesangium. It is a diagnosis of exclusion after ruling out systemic lupus erythematosus and membranoproliferative glomerulonephritis by systemic and serological examination. The pathogenesis of C1q nephropathy is unclear. In addition, there is very little generalizability in the treatment and prognosis for pediatric C1q nephropathy due to diversities in clinical manifestations and pathological types. Rituximab is a human/mouse chimeric monoclonal antibody against CD20, which is primarily used for treating lymphomas and, most recently, has been used to treat certain kidney diseases including C1q nephropathy. In this report, we used one quarter of the typical dose of rituximab for lymphoma treatment to achieve complete remission in a C1q nephropathy patient, significantly reducing deposition of immune complexes and glomerular damage. This case indicates that dosage reconsiderations may be necessary for rituximab in treatment of pediatric C1q nephropathy.

Clinical and pathologic features of nephropathy with C1q deposits

Aim. To determine the frequency, clinical and morphological features of a nephropathy with C1q deposits in chronic glomerulonephritis adult patients. Materials and methods. 296 specimens of kidneys of patients with a chronic glomerulonephritis (CGN) from 2014 for 2018 were analyzed. At the first step, specimens with C1q deposits in glomeruli revealed by immunofluorescent method were chosen. Lupus nephritis and primary membranoproliferative glomerulonephritis were exclusion criteria. At the second step, the retrospective analysis of the clinical characteristics was carried out. Results and discussion. Deposits of C1q in kidneys at 12 of 296 (4.05%) CGN were revealed, m:f ratio 2:1. Average age of the beginning of a disease was 32.1±14.7 years. At a morphological research in 8 membranous nephropathy (MN), in 2 mesangioproliferative glomerulonephritis (MesPGN), in 2 - nephrosclerosis was revealed. Among 12 patients in 5 the disease debuted a nephrotic syndrome, at the others - a proteinuria from 0.5 to 4.0 g/days with the subsequent formation of a nephrotic syndrome. In 5 of 12 patients the disease was characterized by a favor course with preserved kidney function. At 7 patients at the time of inspection decrease in function of kidneys [glomerular filtration rate (eGFR) 31 (30-34) ml/min] was noted. 5 had slow progressing of a renal failure. 2 of 12 progressed to renal failure (eGFR to 19 and 24 ml/min) within a year. Conclusion. Deposits of C1q in kidney were revealed in 4.05% of biopsy specimens in CGN. The most frequent morphological form was the membranous nephropathy. The clinical course was characterized by a nephrotic syndrome, more than at a half of patients - with renal dysfunction.

C1q nephropathy in adults is a form of focal segmental glomerulosclerosis in terms of clinical characteristics

Although C1q nephropathy (C1qN) was introduced three decades ago, the clinical significance and renal outcomes of C1qN remain unclear. This study aimed to evaluate the clinical characteristics of C1qN, including renal outcomes, by performing a matched comparison within a multicenter cohort. We enrolled 6,413 adult patients who underwent kidney biopsy between January 2000 and January 2018 at three tertiary hospitals in Korea. We compared the clinical characteristics of 23 patients with C1qN with those of patients with focal segmental glomerulosclerosis (FSGS) or minimal change disease (MCD) who were matched by age, sex, diabetic status, and a period of biopsy. Histological and clinical parameters in patients with C1qN were also evaluated according to the different pathological phenotypes. For a mean follow-up period of 92 months, 4 patients with C1qN (17.4%) developed end-stage renal disease (ESRD). None of the matched patients with MCD had ESRD, but 7 (30.4%) of patients with FSGS progressed to ESRD, which was not different from that of C1qN patients (p = 0.491). Laboratory and pathological findings, except segmental glomerulosclerosis, were not notably different between FSGS and C1qN. The presence of segmental glomerulosclerosis, mesangial hypercellularity, and podocyte effacement did not affect both the short- and long-term renal outcomes in patients with C1qN. Our study showed that the renal outcomes of C1qN are comparable with those of FSGS, and not with MCD. Specific pathological findings, including segmental glomerulosclerosis in C1qN, were not associated with renal outcomes, which may suggest homogeneity in the clinical features of C1qN.

C1q Nephropathy in a Patient of Neurofibromatosis Type 1: A Rare Case Report

C1q nephropathy is a rare glomerular disease defined by the presence of characteristic mesangial dominant or codominant C1q deposition on immunofluorescence microscopy. Neurofibromatosis type 1 (NF-1) is an autosomal dominant syndrome caused by a mutation of a gene located on chromosomal segment 17q11.2. Nephrotic syndrome has rarely been reported in patients of NF-1, and the relation of NF-1 with nephrotic syndrome is unclear. Here, we present a rare case of C1q nephropathy in a patient of NF-1.

Predominant but silent C1q deposits in mesangium on transplanted kidneys - long-term observational study

Background

C1q nephropathy (C1qN) was first described as glomerular disease characterized by predominant meangial C1q deposits in patients with proteinuria and no evidence of systemic lupus erythematosus. Several studies, however, revealed the clinical heterogeneity of C1qN, showing some cases with normal urinalysis. To confirm the existence of cases with predominant mesangial C1q deposits and negative or mild proteinuria and/or hematuria, we investigated renal graft biopsy specimens showing negative to mild proteinuria (less than or equal to 1+ by dip stick test) and/or hematuria.

Methods

Eligible participants were kidney transplant cases who corresponded to the criteria for C1qN and were followed more than 10 years. Their medical records were reviewed to determine the age at detection of predominant mesangial C1q deposits, gender, original renal disease and reason for renal graft biopsy, blood pressure, degree of proteinuria and hematuria, and serum creatinine levels.

Results

From 414 cases in adults and children, five pediatric patients (the male to female ratio, 1:1.5) were eligible. At the time when predominant mesangial C1q deposits were detected, 2 cases presented with mild proteinuria without hematuria, but the other 3 cases showed normal urinalysis. Light microscopy revealed minor glomerular abnormality in all the cases. Immunofluorescent study showed predominant mesangial C1q deposits with IgG, IgM and C3 in all cases. All selected specimens presented electron dense-depos in the mesangium. Ten years later from the detection, 2 cases continued to be normal urinalysis and 3 cases had mild proteinuria without hematuria. During this follow-up period, no cases presented with persistent proteinuria and/or hematuria greater than or equal to 2+ by dip stick test. And no cases developed systemic lupus erythematosus. Follow-up renal graft biopsies were performed once in 2 cases 8 years later from the detection. They showed minor glomerular abnormalities. C1q deposit disappeared in one case. In another case, immunofluorescent study was not examined.

Conclusions

This long-term observational study on transplanted kidneys confirms the existence of cases with predominant but silent C1q deposits in the mesangium who have negative or mild proteinuria.

Electronic supplementary material

The online version of this article (10.1186/s12882-018-0874-9) contains supplementary material, which is available to authorized users.

Outcome of childhood-onset full-house nephropathy

Background

Patients with full-house nephropathy (FHN) present renal lesions that are indistinguishable from those of lupus nephritis (LN) but lack the systemic features necessary to meet diagnostic criteria for systemic lupus erithematosus (SLE). Some have been reported to develop a delayed SLE with time. The clinical outcome of children having FHN without SLE has never been reported.

Methods

Children with biopsy-proven FHN were selected after excluding SLE cases by the absence of America College of Rheumatology criteria. The proportion of patients with complete (proteinuria <0.5 g/day) or partial remission (proteinuria ≤50% from baseline), relapse (estimated glomerular filtration rate <25% and/or proteinuria ≥50% from baseline) and progression to Stage III chronic kidney disease (CKD) was described according to age and gender groups with the Kaplan-Meier curve and compared with the Log-rank test. Entity of treatment was summarized by a score at induction (0-6 months) and maintenance (6-18 months). Cox-regression model was performed to test predictors of remission, relapse and progression to CKD.

Results

Among 42 patients (28 pre-pubertal) who met the inclusion criteria, 39 (92.9%) achieved partial and 32 (76.2%) complete remission of nephropathy over 2.78 and 7.51 months of follow-up. At 10 years, the probability of progressing to CKD was 4.8%. Of those achieving remission, 18% had a renal flare mainly within 4 years after remission. Pre-pubertal males achieved complete remission more frequently than other patients but often relapsed; pre-pubertal females were treated more aggressively. Cox-regression analysis did not find independent predictors of remission or relapse.

Conclusions

The outcome of the patients with FHN we investigated was encouraging. Recurrences are limited to the first 4 years following diagnosis, allowing progressive withdrawal of immunosuppression in patients achieving remission. Evaluation of risk factors for adverse outcome is necessary especially in pre-pubertal children.

[The clinical and morphological characteristics of C1q glomerulopathy]

C1q glomerulopathy is a rare variety of chronic glomerulonephritis manifested as C1q deposition revealed by immunofluorescence microscopy. The pathogenesis and etiology of the disease have not been studied. The paper deals with the results of clinical, morphological, immunofluorescence, and electron microscopic examinations in 13 patients with C1q glomerulopathy. Light microscopy more commonly revealed membranous nephropathy, mesangioproliferative glomerulonephritis, and nephrosclerosis. Immunofluorescence microscopy detected a C1q fraction in association with other deposits, more frequently IgM and IgG ones. A correlation was found between the clinical presentation and morphological form of chronic glomerulonephritis.

Pathology of Podocytopathies Causing Nephrotic Syndrome in Children

Nephrotic syndrome (NS) in children includes a diverse group of diseases that range from genetic diseases without any immunological defects to causes that are primarily due to immunological effects. Recent advances in molecular and genomic studies have resulted in a plethora of genetic defects that have been localized to the podocyte, the basic structure that is instrumental in normal filtration process. Although the disease can manifest from birth and into adulthood, the primary focus of this review would be to describe the novel genes and pathology of primary podocyte defects that cause NS in children. This review will restrict itself to the pathology of congenital NS, minimal change disease (MCD), and its variants and focal segmental glomerulosclerosis (FSGS). The two major types of congenital NS are Finnish type characterized by dilated sausage shaped tubules morphologically and diffuse mesangial sclerosis characterized by glomerulosclerosis. MCD has usually normal appearing biopsy features on light microscopy and needs electron microscopy for diagnosis, whereas FSGS in contrast has classic segmental sclerosing lesions identified in different portions of the glomeruli and tubular atrophy. This review summarizes the pathological characteristics of these conditions and also delves into the various genetic defects that have been described as the cause of these primary podocytopathies. Other secondary causes of NS in children, such as membranoproliferative and membranous glomerulonephritis, will not be covered in this review.

C1q Nephropathy: The Unique Underrecognized Pathological Entity

C1q nephropathy is a rare glomerular disease with characteristic mesangial C1q deposition noted on immunofluorescence microscopy. It is histologically defined and poorly understood. Light microscopic features are heterogeneous and comprise minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS), and proliferative glomerulonephritis. Clinical presentation is also diverse, and ranges from asymptomatic hematuria or proteinuria to frank nephritic or nephrotic syndrome in both children and adults. Hypertension and renal insufficiency at the time of diagnosis are common findings. Optimal treatment is not clear and is usually guided by the underlying light microscopic lesion. Corticosteroids are the mainstay of treatment, with immunosuppressive agents reserved for steroid resistant cases. The presence of nephrotic syndrome and FSGS appear to predict adverse outcomes as opposed to favorable outcomes in those with MCD. Further research is needed to establish C1q nephropathy as a universally recognized distinct clinical entity. In this paper, we discuss the current understanding of pathogenesis, histopathology, clinical features, therapeutic options, and outcomes of C1q nephropathy.

Resolution of C1q deposition but not of the clinical nephrotic syndrome after immunomodulating therapy in focal sclerosis

BACKGROUND

The natural evolution of C1q nephropathy (C1qNP) during immunosuppressive treatment is relatively little studied or understood.

CASE PRESENTATION

A 30 year-old Caucasian female was referred to us for further management of biopsy-proven C1qNP and severe nephrotic syndrome. Serologic work-up remained negative, including complement C3 and C4 levels and repeated testing for antinuclear antibodies. A renal biopsy revealed minimal change nephropathy vs. focal sclerosis on light microscopy and C1qNP on immunopathology. She has failed trials of high-dose oral prednisone, mycophenolate mofetil 1,500 mg twice a day and a subsequent regimen of monthly IV cyclophosphamide 750 mg × 9 cycles. She also received the maximum tolerated angiotensin-converting enzyme inhibitor and spironolactone therapy. Random urine protein-to-creatinine (UPC) ratio predicted proteinuria in the range between 5-35 gm/day, while serum creatinine rose progressively from 1.0 mg/dL to 1.4 mg/dL (to convert to μmol/L, multiply by 88.4). A decision was made to repeat renal biopsy to reassess the underlying histology. The biopsy revealed focal sclerosis but no C1q deposition.

CONCLUSIONS

Our case illustrates at least two points: first, an established pathologic diagnosis does not obviate the need for repeated renal biopsy later on, should diagnostic uncertainty persist. Second, histological diagnoses may evolve over time, especially in a patient receiving active and powerful immune-modulating treatment. In our case, the clinical nephrosis did not change with immunosuppressive therapy while C1q deposition ceased, making this latter entity likely the immunologically mediated process.

C1q nephropathy in children: clinical characteristics and outcome

BACKGROUND

C1q nephropathy has been suggested as a separate disease entity. C1q positivity has also been described in association with nephrotic syndrome (NS) as a potential marker for worse outcome. The aims of this study were to describe the clinical characteristics, laboratory parameters and outcomes of 35 children whose renal histology revealed predominant mesangial C1q deposition and to investigate if the experience at our institution supports the above hypothesis.

METHOD

Clinical and pathological characteristics of all children whose kidney biopsies showed positive C1q staining were retrospectively recorded. The outcome of children with minimal change nephrotic syndrome (MCNS) and predominant mesangial C1q deposition based on C1q staining was compared with that of a concurrent group of children with MCNS with no such immune staining.

RESULTS

The median age of the patient cohort was 4.5 years (range 6 months to 16 years), 69 % were boys and 88 % presented with nephrotic syndrome (NS). Children with C1q staining and MCNS had more relapses (p = 0.001) and shorter relapse-free periods (p = 0.033) than those with negative immunostaining, but the long-term outcomes were similar in both groups.

CONCLUSION

Our data do not support C1q nephropathy as a separate diagnostic category. Children with MCNS and mesangial C1q deposition (staining) showed more relapses but no difference in long term renal outcome.

Concurrent diabetic nephropathy and C1q nephropathy in a young male patient: The first report in literature

BACKGROUND

C1q nephropathy (C1qN) is an uncommon glomerulopathy with a significant deposition of C1q in mesangium without clinical evidence of lupus.According to the best of our knowledge, there is not any report on coincidence of diabetes mellitus and C1qN.

CASE PRESENTATION

In this report, we presented a 28 years-old-patient with type 1 diabetes and nephrotic range proteinuria, glomerular hematuria and C1q glomerulopathy in renal biopsy.

CONCLUSIONS

According to the best of our knowledge, there is no previous report about the association between type 1 DM and C1qN. Prevalence of autoimmune disease is higher in type 1 DM and this may explain the relation between DM and C1qN in our patient.

Do C1q or IgM nephropathies predict disease severity in children with minimal change nephrotic syndrome?

BACKGROUND

It has been suggested that C1q and immunoglobulin M (IgM) nephropathy are variants of minimal change nephrotic syndrome (MCNS). Many researchers believe that these two conditions signify a worse prognosis for children with MCNS in comparison with immunofluorescence (IF)-negative MCNS. The aim of our study was to determine the prognostic significance of C1q nephropathy and IgM nephropathy in children with MCNS.

METHODS

Fifty-five children with MCNS who had been biopsied over the course of 24 years at our institution were retrospectively categorized into three groups on the basis of IF microscopy findings: IF-negative MCNS (29/55 patients), MCNS with IgM nephropathy (19/55 patients), and MCNS with C1q nephropathy (7/55 patients). Clinical characteristics at disease presentation, clinical course, and renal outcome were compared between groups during the median follow-up period of 16.9 years (minimum 1.0, maximum 31.1 years).

RESULTS

No statistically significant differences in clinical characteristics at disease presentation, clinical course, and renal outcome were found. Children with IgM nephropathy, C1q nephropathy, and IF-negative MCNS were clinically indistinguishable.

CONCLUSIONS

We concluded that C1q or IgM nephropathy variants do not seem to signify a worse prognosis in children with MCNS in comparison with IF-negative MCNS.

Diverse clinical and histology presentation in c1q nephropathy

Patients presenting with nephrotic syndrome with or without nephritic illness rarely come across with the diagnosis of 'C1q nephropathy'. This entity is purely diagnosed with the help of immunofluorescence like IgA nephropathy. Clinical presentation is heterogenous, ranging from nephrotic range proteinuria to sub-nephrotic state; and with or without hematuria / renal insufficiency. Similarly, the concept of 'C1q nephroapthy' has periodically evolved since its original description by Jenette and Hipp in 1985. Here the pathophysiology, histologic findings / diagnostic and therapeutic options in patients with C1q nephropathy are discussed.

Non-nephronal hematuria misdiagnosed as C1q nephropathy: Look before you leap

A 19-year-old male presented with persistent macroscopic hematuria for last 3 months. On initial evaluation, he was found to have minimal proteinuria, normal renal function, and normal complement with negative lupus serology. Light microscopy, immunofluorescence and electron microscopy of renal tissue confirmed the presence of C1q nephropathy. Because of poor response to immunosuppressive agent (prednisolone and mycophenolate mofetil), passage of urinary clot once and vexing persistent macroscopic hematuria, alternative diagnosis was considered. Cystourethroscopy showed urethritis of prostatic urethra. Immunosuppressives were stopped and doxycycline started to which hematuria responded dramatically. This case report illustrates that hematuria in this patient was because of undiagnosed urethritis rather than incidental C1q nephropathy.

Positive C1q staining associated with poor renal outcome in membranoproliferative glomerulonephritis

BACKGROUND

Pathogenesis and clinical prognosis of membranoproliferative glomerulonephritis (MPGN) has not yet been established.

METHODS

We conducted a retrospective study of 41 patients with MPGN (type I and III) and examined the renal survival. In addition, factors contributing to survival time were analyzed.

RESULTS

Fourteen patients (34 %) were classified into the renal death group. Patients with nephrotic syndrome and positive C1q staining of glomerular deposits showed a particularly poor prognosis. Significantly higher frequency of nephrotic syndrome and higher urinary protein excretion were observed in the renal death group (p = 0.0002, p = 0.0002) than in the renal survival group. The intensity of C1q staining was positively correlated with the severity of the proteinuria (p = 0.004). Factors that influenced the survival time were positive C1q staining of glomerular deposits (p = 0.003), presence of nephrotic syndrome (p = 0.004), serum albumin (p = 0.02), and proteinuria (p = 0.04).

CONCLUSIONS

C1q staining in glomerular deposits and nephrotic syndrome were important factors influencing the prognosis and outcome in MPGN patients. C1q deposition may play a key role in the pathogenesis of MPGN, as evidenced by numerous observations, such as induction of proteinuria.

C1q nephropathy in a patient with Gitelman syndrome

Bartter syndrome can manifest in three different forms and is rarely concomitant with glomerular nephropathies. However, this association is more frequently observed in children. We report the case of a 50-year-old woman with Gitelman syndrome for the past 30 years who also had a nephrotic syndrome of recent appearance. Her renal biopsy revealed hyperplasia of the juxtaglomerular apparatus and mesangial deposits of C1q, with no clinical or serological evidence of systemic erythematous lupus. We have not found any reports of instances of association of Gitelman syndrome and nephrotic syndrome arising from C1q nephropathy in adult patients. Our case suggests the possible existence of an association between hypokalaemic tubular nephropathies and glomerular nephropathies that may cause nephrotic syndrome.

Focal segmental glomerulosclerosis and chronic kidney disease in pediatric patients

Focal segmental glomerulosclerosis (FSGS) is one of the most common forms of acquired glomerular disease leading to end-stage kidney disease. Its incidence is rising around the world. There is no proven therapy for those patients who do not respond to corticosteroids and it can recur in 20% to 25% of patients who receive a kidney transplant. The disease can be primary, or it can be secondary to various conditions including vesicoureteral reflux, obesity, medications, and infections. Recent advances have demonstrated the important role of genetic mutations in podocyte proteins as a cause of FSGS. There is an urgent need for randomized clinical trials to develop safe and effective therapy for FSGS that occurs in the native or transplanted kidney.

Resolution of clinical and pathologic features of C1q nephropathy after rituximab therapy

C1q nephropathy is a rare idiopathic glomerulopathy characterized by mesangial deposition of immunoglobulin and complement with C1q dominance or co-dominance, and the absence of clinical and laboratory evidence of systemic lupus erythematosus. Its clinical course is unpredictable and the response to corticosteroid or cytotoxic treatment is variable. Here, we report two cases of C1q nephropathy, one in a child and one in an adult, both presenting with impaired renal function and massive proteinuria. Both patients failed to respond to immunosuppressive medications; however, rituximab, an anti-CD20 antibody, was effective in preserving renal function in one patient and eliminating the need for hemodialysis in the other. In one patient, histologic regression of abnormalities was documented over 3 years post-treatment. Both patients have remained off other immunosuppressive medication for a prolonged period with stable renal function. These cases are, to our knowledge, the first reported successful treatment of C1q nephropathy with rituximab.

C1q deposition in the renal allograft: a report of 24 cases

C1q nephropathy is an uncommon glomerular disease characterized by dominant or codominant mesangial staining for C1q in the absence of systemic lupus erythematosus. There are no series in the literature addressing the significance of C1q deposition in the renal allograft. We retrospectively analyzed 24 patients, most of whom were white (83%) and male (63%), with a mean age at transplant of 31 years. None of the patients were diagnosed with C1q nephropathy in the native kidney or had any features of systemic lupus erythematosus. The mean time from transplant to detection of mesangial C1q deposits was 37 months (>12 months in 71% of cases). Half of the patients had a preceding infection. The indication for biopsy was surveillance (63%) or graft dysfunction (37%). At biopsy, 52% had proteinuria (>1g/day in only 17%). The mean creatinine was 1.8 mg per 100 ml. Only 9% developed hematuria and none had hypoalbuminemia. The glomerular pattern on light microscopy was mesangial hypercellularity (46%), focal segmental glomerulosclerosis (21%), or no lesions (33%). All cases showed intense (>or=2+) dominant (67%) or codominant (33%) mesangial staining for C1q on immunofluorescence. Mesangial electron-dense deposits were seen in 82% of cases. On follow-up (mean 1 year) of the 10 patients without rejection, most had stable creatinine with no or stable proteinuria, and none lost their graft. We conclude that C1q-dominant mesangial deposition in the renal allograft is a morphological pattern with no apparent clinical significance in the majority of patients. It is usually detected after the first year. The rate of preceding infection and the prevalence of proteinuria seem to be similar to the renal transplant recipients in general. Most cases show mesangial hypercellularity or no glomerular changes on light microscopy.

Is collapsing C1q nephropathy another MYH9-associated kidney disease? A case report

C1q nephropathy is a rare kidney disease that can present with nephrotic syndrome and typically has the histologic phenotype of either minimal change disease or focal segmental glomerulosclerosis (FSGS). Disagreement exists about whether it is a distinct immune complex-mediated glomerulopathy or it resides in the spectrum of FSGS-minimal change disease. Two African American patients with C1q nephropathy histologically presenting as the collapsing variant of FSGS (collapsing C1q nephropathy) and rapid loss of kidney function were genotyped for polymorphisms in the non-muscle myosin heavy chain 9 gene (MYH9). Both cases were homozygous for the MYH9 E1 risk haplotype, the variant strongly associated with idiopathic FSGS, collapsing FSGS in human immunodeficiency virus-associated nephropathy, and focal global glomerulosclerosis (historically attributed to hypertensive nephrosclerosis). Collapsing C1q nephropathy with rapid progression to end-stage renal disease appears to reside in the MYH9-associated disease spectrum.

C1q nephropathy in a child presenting with recurrent gross hematuria

C1q nephropathy is a rare glomerular disease characterized by mesangial immune deposits with dominant or codominant staining for C1q. The exact pathogenesis leading to the mesangial immune deposits of C1q remains unknown. C1q nephropathy often presents with proteinuria in the nephrotic range, with an unpredictable or poor response to corticosteroid therapy. It is seen more commonly in older children and young adults and is more common in African Americans compared with Caucasians. We present a 4-year-old African American girl who presented with recurrent gross hematuria in the absence of proteinuria or hypertension and whose renal biopsy demonstrated dominant mesangial deposits of C1q. We conclude that C1q nephropathy should be considered in patients who present with recurrent gross hematuria.

Management patterns of childhood-onset nephrotic syndrome

As an initial effort to identify opportunities to improve the management of children with nephrotic syndrome, the goal of this study was to assess the present-day management of children with primary nephrotic syndrome. A web-based survey was designed to assess the current management styles of all pediatric nephrology faculties at ten participating institutions. Ninety-one percent completed the initial survey. The duration of initial glucocorticoid therapy ranged from 4 to 24 weeks. Physicians reported that the recommendation for kidney biopsy was dependent on the response to initial corticosteroid therapy, with the minority always recommending a biopsy for frequently relapsing or steroid-dependent cases. All responding physicians recommended a kidney biopsy in steroid-resistant cases. Treatment strategies were reported to vary based upon the steroid response pattern and, where available, kidney histopathology. Striking variations in therapeutic preferences were described when alternatives to glucocorticoids were considered. The variability of management practices among pediatric nephrologists in the USA combined with the changing characteristics of our pediatric population raise concerns about our future strategies for improving healthcare for children coping with nephrotic syndrome. This variability is not unique to children's healthcare or to nephrology. However, a systematic approach to patient care and improvement in health outcomes has been shown to substantially improve morbidity and mortality outcomes in children with chronic health conditions.

C1q nephropathy: a true immune complex disease or an immunologic epiphenomenon?

We describe a 16-year-old Caucasian boy who presented with steroid-sensitive nephrotic syndrome aged 2 years. His clinical course was one of frequent relapses and severe steroid dependence. To manage this, he was sequentially treated with levamisole, then oral cyclophosphamide before being started on ciclosporin. A renal biopsy performed prior to commencement of ciclosporin confirmed minimal change disease on light microscopy. The immunohistochemistry and electron microscopy findings were in keeping with this. His complement levels were normal and his lupus serology negative. He remained on ciclosporin therapy for 8 years and had two further renal biopsies to detect ciclosporin-induced renal damage. Both biopsies showed evidence of increasing amounts of C1q deposition on immunohistochemistry and the presence of immune deposits on electron microscopy. As he had continued negative lupus serology, this was compatible with a diagnosis of C1q nephropathy. In addition both biopsies had changes compatible with chronic mild ciclosporin nephrotoxicity. This case is the first report describing in detail a paediatric patient with evolving C1q nephropathy who was treated successfully with rituximab. We discuss the role of C1q in this clinicopathological entity and question its significance.

Current status and issues of C1q nephropathy

C1q nephropathy, first proposed by Jennette and Hipp [Am J Clin Pathol 83:415-420, 1985; Am J Kidney Dis 6:103-110, 1985], was described as a distinct glomerular disease entity characterized by extensive mesangial deposition of C1q, with associated mesangial immune complexes, and the absence of any clinical and laboratory evidence of systemic lupus erythematosus. Now, 20 years since the first report, the disease entity is gradually attaining recognition, particularly in the field of pediatrics. C1q is the subcomponent of C1 in the classical pathway of complement activation. Generally, C1q deposition is caused by the activation of C1 by immunoglobulin G (IgG) and IgM; therefore, C1q nephropathy is considered as an immune complex glomerulonephritis. However, in C1q nephropathy, it remains unclear whether the deposition of C1q in the glomeruli is in response to the deposition of immunoglobulin or immune complex, or whether deposition is non-specific trapping that accompanies increased glomerular protein trafficking associated with proteinuria. Since not only the pathogenesis of C1q deposition in glomeruli but also its significance are still uncertain, it has not yet been established as an independent disease. From recent publications of the clinical and pathological characterizations, C1q nephropathy has been thought to be a subgroup of primary focal segmental glomerular sclerosis. However, many reports describe different symptoms, histopathologies, therapeutic responses and prognoses, suggesting that C1q nephropathy is not a single disease entity, but that it may be a combination of several disease groups. There are many uncertain areas requiring further investigation, though it is hoped that a detailed examination of future cases will clarify the subgroups making up C1q nephropathy and their clinicopathological characteristics, and will lead to the establishment of C1q nephropathy as an independent disease entity.

C1q nephropathy and minimal change nephrotic syndrome

C1q nephropathy (C1qN) is an uncommon disorder seen in children and adults with nephrotic syndrome and non-specific urinary findings. It has been described with minimal change nephrotic syndrome (MCNS), focal segmental glomerulonephritis and isolated mesangial proliferative glomerulonephritis. We describe nine children with MCNS and mesangial C1q deposition. These children had a median age of 2.7 years at diagnosis (range 1.3-15 years), 56% were male and 78% were Hispanic. We compared these children to concurrent patients with nephrotic syndrome and biopsy-proven MCNS. We found that the C1qN patients were more likely than MCNS children to require chronic immunosuppression with calcineurin inhibitors or mycophenolate mofetil to maintain remission. However, all children were able to achieve and sustain clinical remission of nephrotic syndrome. Children with C1qN and minimal change histology have an increased frequency of frequently relapsing and steroid-unresponsive disease, but they can attain prolonged remission and stable renal function with calcineurin inhibitor or mycophenolate mofetil therapy.

Focal segmental glomerulosclerosis: a morphologic diagnosis in evolution

CONTEXT

The diagnosis of focal segmental glomerulosclerosis (FSGS) is a descriptive pathologic diagnosis that in certain clinical situations (ie, primary or idiopathic) becomes its own disease. The clinical diversity, varied histology, and nonspecific morphologic features of FSGS all contribute to the complexity and problematic nature in making a pathologic diagnosis of FSGS. The definitions of the disease and of the morphologic features have evolved during the last century.

OBJECTIVE

To review historic and morphologic features of FSGS in order to demonstrate a practical approach in achieving a pathologic diagnosis of FSGS on kidney tissue.

DATA SOURCES

In 2004 a working proposal on the pathologic (morphologic) classification of FSGS was published in an attempt to unify the complexity of diagnosing FSGS, and it has shown to be both reproducible and with unique clinical implications for each defined FSGS variant.

CONCLUSIONS

An accurate diagnosis of FSGS can be challenging. During the last few decades, numerous new scientific discoveries have enriched our knowledge of pathogenetic mechanisms of nephrotic syndrome. Thus, it is expected there will be a need for a further modification to a morphologic classification and that the pathologist's role in diagnosing FSGS will remain in evolution. This review recapitulates the history of the pathologic diagnosis of FSGS and a current morphologic classification, hopefully opening up a discussion for further modifications that reflect the status of knowledge evolving in the 21st century.

A single-center study of C1q nephropathy in children

C1q nephropathy (C1qN) is a rare idiopathic glomerulopathy typically seen in adolescents and young adults. All kidney biopsies done from 2002 to 2007 were analyzed (264). Thirteen cases of C1qN from 212 (6.6%) native biopsies and one case out of 52 (1.9%) transplant biopsies were reviewed regarding demographic features, clinical presentation, histopathology, treatment, and outcome. Age varied from 1 to 18 years; half were boys. Ten children (71.4%) presented with nephrotic syndrome (NS). The most common histopathology found was diffuse mesangial proliferative glomerulonephritis (DMP) by light microscopy (LM), with diffuse granular staining for C1q predominantly in the mesangium. Children with either NS or persistent gross hematuria received prednisone and angiotensin-converting enzyme inhibitors (ACEi) (11). Median follow-up was 36 months. Steroid response was complete in 6 patients (54.5%). Those with steroid resistance (5) or steroid dependence (2) received further immunosuppression with mycophenolate mofetil (MMF) or tacrolimus (Tac). Three children achieved complete remission and four partial remission. Frequent relapses were seen in 4/14 patients. Renal survival was 100%. Our report reveals a high incidence of C1qN in pediatric patients, with variable clinical presentation. Despite a high incidence of steroid resistance among those with NS, an excellent response was observed with the addition of further immunosuppression.

Rituximab treatment of collapsing C1q glomerulopathy: clinical and histopathological evolution

A 13-year-old girl with obesity and hyperinsulinism developed steroid-resistant nephrotic syndrome due to collapsing glomerulopathy with dominant C1q-containing mesangial immune deposits (CG/C1qN). She became overtly diabetic while receiving alternate-day prednisone and tacrolimus, requiring insulin injections. Despite the addition of mycophenolate mofetil to the treatment regimen, renal function subsequently declined. Rituximab (four weekly doses of 375 mg/m2) was tried 6 months after initial presentation and 3 months after weaning all glucocorticoids. Glomerular filtration rate (GFR) and proteinuria improved. Unexpectedly, blood sugar control normalized 6 weeks after antibody infusion. Rituximab was readministered 20 months after the first course because of deteriorating renal function, but the effect on GFR and proteinuria was modest. A retrospective analysis revealed that tubulointerstitial infiltrates present in the biopsies prior to treatment with rituximab contained numerous CD20+ and CD3+ (CD4 > CD8) lymphocyte aggregates. Rebiopsy 10 weeks after repeat rituximab therapy demonstrated the elimination of B-cell infiltrates and the apparent decrease of interstitial T-cell infiltrates, yet persistent, advanced global glomerulosclerosis, interstitial fibrosis and tubular atrophy. In conclusion, CG/C1qN was associated with B- and T-cell-rich tubulointerstitial infiltrates. B-cell-directed therapy delayed clinical progression during early disease but failed to prevent or ameliorate chronic changes, despite effective tissue B-cell clearance. The incidental resolution of diabetes was noted after rituximab treatment.

Clinicopathologic correlation and outcome of C1q nephropathy

BACKGROUND AND OBJECTIVES

The number of patients with C1q nephropathy (C1qN) in previous reports is small and the duration of follow-up is short. Our study describes the clinicopathologic correlation and clinical outcome through the mean follow-up period of 7.2 yr in 61 patients.

DESIGN, SETTINGS, PARTICIPANTS, & MEASUREMENTS

Sixty-one patients, 1 to 67 yr of age, with C1qN were enrolled in this study.

RESULTS

According to presentation at onset, patients were divided into two groups: asymptomatic urinary abnormalities (asymptomatic) (n = 36) and nephrotic syndrome (NS) (n = 25). Light microscopy showed minimal change disease (MCD) in 46 patients (75%), mesangial proliferative glomerulonephritis in 7 (12%), and focal segmental glomerulosclerosis (FSGS) in 8 (13%). The prevalence of MCD was higher in the NS group than in the asymptomatic group. Nine patients in the asymptomatic group and all patients in the NS group were treated with prednisolone and/or cyclosporine. Normal urinalysis was found in 10 patients in asymptomatic group and 8 in NS group during the follow-up. Thirteen patients in the NS group were frequent relapsers at the latest follow-up. Three patients with FSGS developed chronic renal failure 8 to 15 yr after the diagnosis. C1q deposits disappeared in 3 of 8 patients receiving repeat biopsy, and 2 of these 3 showed FSGS.

CONCLUSIONS

The prognosis of C1qN is good, associated with MCD in a large number. In some patients, C1q deposits disappear through the follow-up period. FSGS may develop in some patients on repeat biopsies. Further investigation is critically needed to settle this issue.

Pathology, clinical presentations, and outcomes of C1q nephropathy

C1q nephropathy is an uncommon glomerular disease with characteristic features on immunofluorescence microscopy. In this report, clinicopathologic correlations and outcomes are presented for 72 patients with C1q nephropathy. The study comprised 82 kidney biopsies from 28 children and 54 adults with male preponderance (68%). Immunofluorescence microscopy showed dominant or co-dominant staining for C1q in the mesangium and occasional glomerular capillary walls. Electron-dense deposits were observed in 48 of 53 cases. Light microscopy revealed no lesions (n = 27), focal segmental glomerulosclerosis (FSGS; n = 11), proliferative glomerulonephritis (n = 20), or various other lesions (n = 14). Clinical presentations in the patients who had no lesions histology were normal urine examination (7%), asymptomatic hematuria and/or proteinuria (22%), and nephrotic syndrome (minimal change-like lesion; 63%), which frequently relapsed. All patients with FSGS presented with nephrotic syndrome. Those with proliferative glomerulonephritis usually presented with chronic kidney disease (75%) or asymptomatic urine abnormalities (20%). Of the patients with sufficient follow-up data, complete remission of the nephrotic syndrome occurred in 77% of those with a minimal change-like lesion, progression to end-stage renal disease occurred in 33% of those with FSGS, and renal disease remained stable in 57% of those with proliferative glomerulonephritis. In conclusion, this study identified two predominant clinicopathologic subsets of C1q nephropathy: (1) Podocytopathy with a minimal change-like lesion or FSGS, which typically presents with nephrotic syndrome, and (2) a typical immune complex-mediated glomerular disease that varies from no glomerular lesions to diverse forms of glomerular proliferation, which typically presents as chronic kidney disease. Clinical presentation, histology, outcomes, and presumably pathogenesis of C1q nephropathy are heterogeneous.

C1q nephropathy in two young sisters

C1q nephropathy (C1qNP) is a controversial and uncommon form of glomerulonephritis, characterized by mesangial immunoglobulin and complement deposits, predominantly C1q, with no evidence of systemic lupus erythematosus. Clinically, it may present as nephrotic syndrome and non-nephrotic proteinuria per se or associated with microhematuria, hypertension, or renal insufficiency. We describe two sisters with C1qNP, who presented with steroid-resistant nephrotic syndrome. Both sisters presented before the age of 2 years, and they showed a poor response to other immunosuppressive therapy. Both girls had normal serum complement levels, negative antinuclear antibodies (ANAs) and negative hepatitis B antigen. Renal biopsy in both patients showed histological features of mesangioproliferative glomerulonephritis, with diffuse "full-house" positive immunofluorescence reaction in the mesangial area. The immunofluorescence reaction for C1q was most intense and co-dominant with IgG in both patients. Correspondingly, electron microscopy demonstrated dense deposits mainly in the mesangial areas too. We report on two young sisters with the characteristic features of C1qNP presented in early childhood. To the best of our knowledge, this is the first report of C1qNP in siblings.

Proteinuria in a boy with infectious mononucleosis, C1q nephropathy, and Dent's disease

C1q nephropathy is a proliferative glomerulopathy with extensive mesangial deposition of C1q. A three-year old boy presented with a nephrotic-range proteinuria during an acute phase of Epstein-Barr virus (EBV) infection, and he had a family history of Dent's disease. The renal biopsy findings were compatible with C1q nephropathy. However, EBV in situ hybridization was negative. The CLCN5 gene analysis revealed an R637X hemizygous mutation, which was the same as that detected in his maternal cousin, the proband of the family. The causal relationship between EBV infection and C1q nephropathy remains to be determined. Moreover, the effects of underlying Dent's disease in the process of C1q nephropathy has to be considered.

A proposed taxonomy for the podocytopathies: a reassessment of the primary nephrotic diseases

A spectrum of proteinuric glomerular diseases results from podocyte abnormalities. The understanding of these podocytopathies has greatly expanded in recent years, particularly with the discovery of more than a dozen genetic mutations that are associated with loss of podocyte functional integrity. It is apparent that classification of the podocytopathies on the basis of morphology alone is inadequate to capture fully the complexity of these disorders. Herein is proposed a taxonomy for the podocytopathies that classifies along two dimensions: Histopathology, including podocyte phenotype and glomerular morphology (minimal-change nephropathy, focal segmental glomerulosclerosis, diffuse mesangial sclerosis, and collapsing glomerulopathy), and etiology (idiopathic, genetic, and reactive forms). A more complete understanding of the similarities and differences among podocyte diseases will help the renal pathologist and the nephrologist communicate more effectively about the diagnosis; this in turn will help the nephrologist provide more accurate prognostic information and select the optimal therapy for these often problematic diseases. It is proposed that final diagnosis of the podocytopathies should result from close collaboration between renal pathologists and nephrologists and should whenever possible include three elements: Morphologic entity, etiologic form, and specific pathogenic mechanism or association.

C1q nephropathy in association with Gitelman syndrome: a case report

There have been rare reports of glomerulopathies developing in patients with Bartter syndrome (BS) and its milder variant, Gitelman syndrome (GS). We present the first case of C1q nephropathy (C1qN) in an African American child with GS. This child was diagnosed with GS at 9 years of age and subsequently developed nephrotic range proteinuria 3 years later. Renal biopsy revealed mesangial hypercellularity and focal segmental glomerulosclerosis (FSGS). The segmental lesions were generally located at the vascular pole. Dominant C1q (2+) staining along with IgG (1-2+) was demonstrated in the mesangium, which correlated with scattered electron dense mesangial deposits demonstrated by electron microscopy. Treatment with an angiotensin-converting enzyme inhibitor led to an improvement in proteinuria to near-normal values (urine protein/creatinine ratio down to 0.5), but the creatinine clearance declined to approximately 58 ml/min/1.73 m(2). This case highlights the possible association between the milder hypokalemic tubulopathy, GS, and glomerular disease, including C1qN. Prompt evaluation of proteinuria with renal biopsy in these patients is recommended to detect significant glomerular pathology. Further research is needed to define risk factors for this complication.

Cellular focal segmental glomerulosclerosis: Clinical and pathologic features

Five pathologic variants of idiopathic focal segmental glomerulosclerosis (FSGS) are recognized: collapsing (COLL), cellular (CELL), glomerular tip lesion (GTL), perihilar, and not otherwise specified (NOS). The prognostic significance of CELL FSGS has not been determined. We compared the presenting clinical and pathologic characteristics in 225 patients with CELL (N=22), COLL (N=56), GTL (N=60), and NOS (N=87) variants of idiopathic FSGS. CELL, COLL, and tip lesion all showed greater frequency and severity of nephrotic syndrome, and shorter time to biopsy compared to NOS. Predictors of end-stage renal disease (ESRD) for all FSGS patients included initial serum creatinine, % global sclerosis, % COLL lesions, chronic tubulo-interstitial injury score, and lack of remission response. COLL FSGS had the highest rate of renal insufficiency at presentation, most extensive glomerular involvement and chronic tubulo-interstitial disease, fewest remissions (13.2%), and highest rate of ESRD (65.3%). GTL patients were older and showed the highest remission rate (75.8%) and lowest rate of ESRD (5.7%). CELL variant showed intermediate rates of remission (44.5%) and ESRD (27.8%) compared to COLL and tip lesion. CELL variant may include cases of unsampled tip or COLL lesion, underscoring the importance of adequate sampling. Our data support the view that CELL and COLL FSGS are not equivalent and validates an approach to pathologic classification that distinguishes between COLL, CELL, and tip lesion variants of FSGS.