Sporadic Focal Segmental Glomerulosclerosis Research Articles

Pediatric focal segmental glomerulosclerosis: favorable transplantation outcome with plasma exchange

BackgroundAlthough kidney transplantation (KTX) is the treatment of choice for pediatric end stage kidney disease (ESKD); concerns for recurrence in cases of focal segmental glomerulosclerosis (FSGS) are still present. This study aimed to investigate the outcome of KTX in children with ESKD secondary to FSGS, with implementation of preemptive perioperative plasma exchange (PE) for non-genetically proven patients.MethodsForty FSGS pediatric kidney transplant recipients were studied. Of them: 12 patients (30%) had genetically proven NPHS2 mutations/familial and 28 (70%) were sporadic FSGS patients. All sporadic patients electively received 6 perioperative PE sessions. Patients with recurrence of proteinuria (n = 13; including 3 patients with genetic/familial and 10 patients with sporadic FSGS) were managed with PE and Rituximab (RTX). Kaplan-Meier curves were used to analyze graft and recurrence free survival data.ResultsThe mean follow-up duration after KTX was 3.8 ± 2.86 years. Recurrence of proteinuria was encountered early postoperative in 11 patients (27.5%) and late (1.6 and 2.9 years after KTX) in 2 patients (5%). All patients with early recurrence achieved complete remission, while patients with late recurrence developed graft failure. Current serum creatinine and proteinuria levels were not different in patients received PE (n = 31) and patients did not PE (n = 9) (p = 0.308 and 0.287 respectively). Current serum creatinine and proteinuria levels in sporadic patients (n = 28) after prophylactic perioperative PE were not different from those of genetic/ familial patients (n = 12) (p = 0.303 and 0.144 respectively). Proteinuria was less in patients underwent native nephrectomy than others immediately postoperative and at assessment (p = 0.002 & 0.0031 respectively). One-year graft and patient survival was 93.8% with a mean 1-year serum creatinine of 0.67 ± 0.25 mg/dl. Three graft losses (7.5%) were due to chronic rejection 3.3, 3.75 and 4.17 years after KTX and 2 patients’ mortality (5%) occurred early postoperative (first 2 weeks).ConclusionFSGS transplanted children have favorable outcomes with perioperative PE for non-genetically proven cases. Early recurrence after KTX can be successfully managed with PE and RTX.

Rho-GTPase Activating Protein myosin MYO9A identified as a novel candidate gene for monogenic focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a podocytopathy leading to kidney failure, whose molecular cause frequently remains unresolved. Here, we describe a rare MYO9A loss of function nonsense heterozygous mutation (p.Arg701∗) as a possible contributor to disease in a sibling pair with familial FSGS/proteinuria. MYO9A variants of uncertain significance were identified by whole exome sequencing in a cohort of 94 biopsy proven patients with FSGS. MYO9A is an unconventional myosin with a Rho-GAP domain that controls epithelial cell junction assembly, crosslinks and bundles actin and deactivates the small GTPase protein encoded by the RHOA gene. RhoA activity is associated with cytoskeleton regulation of actin stress fiber formation and actomyosin contractility. Myo9A was detected in mouse and human podocytes invitro and invivo. Knockin mice carrying the p.Arg701∗MYO9A (Myo9AR701X) generated by gene editing developed proteinuria, podocyte effacement and FSGS. Kidneys and podocytes from Myo9AR701X/+ mutant mice revealed Myo9A haploinsufficiency, increased RhoA activity, decreased Myo9A-actin-calmodulin interaction, impaired podocyte attachment and migration. Our results indicate that Myo9A is a novel component of the podocyte cytoskeletal apparatus that regulates RhoA activity and podocyte function. Thus, Myo9AR701X/+ knock-in mice recapitulate the proband FSGS phenotype, demonstrate that p.R701X Myo9A is an FSGS-causing mutation in mice and suggest that heterozygous loss-of-function MYO9A mutations may cause a novel form of human autosomal dominant FSGS. Hence, identification of MYO9A pathogenic variants in additional individuals with familial or sporadic FSGS is needed to ascertain the gene contribution to disease.

Clinical and laboratory features that differentiate familial from sporadic focal segmental glomerulosclerosis in adolescents and adults

Background: Focal segmental glomerulosclerosis (FSGS) is an important cause of end-stage kidney disease in children and adults. Although most cases are sporadic (s), familial (f) presentation is also described. The purpose of the present study was to establish clinical and laboratory profiles of fFSGS vs. primary sFSGS, contributing to the distinguishing diagnosis in clinical practice and best management, in particular when mutation analysis is not available. Methods: Demographic, clinical and laboratorial parameters were studied in 124 patients 12 years and older with FSGS, subdivided in sFSGS (n=89) and fFSGS (n=35). Results: General and clinical features were similar, as well as serum creatinine at disease presentation. Proteinuria levels were more frequently ≥ 3g/day in sFSGS (63.8%) than in fFSGS (44%, p=0.080), and serum albumin levels were < 3.0 g/dL in 45.8% and 20%, respectively (p=0.046). The groups were statistically different regarding steroid resistance, corresponding to 60% in sFSGS and 100% in fFSGS (p=0.001). Conclusions: The studied groups were clinically similar, except that proteinuria tended to be higher (nephrotic range) and serum albumin was lower in sFSGS vs. fFSGS. In addition, all treated fFSGS patients were steroid resistant. At presentation it is important to characterize if the patient has fFSGS, that will contribute to further disease management, and disease history will be the first clue for such differential diagnosis.

Prevalence of the NPHS2 variants p.R229Q, p.A242V, and p.R138Q in patients with focal segmental glomerulosclerosis.

NPHS2 gene variants are associated with focal segmental glomerulosclerosis (FSGS) and steroid-resistant nephrotic syndrome (SRNS). In this study, the prevalence of NPHS2 variants p.R229Q, p.A242V, and p.R138Q was investigated in patients with familial or sporadic FSGS. The sample consisted of 40 children and 70 adults diagnosed with FSGS confirmed by renal biopsy. Clinical and laboratory parameters were evaluated. Genotyping for the three single nucleotide polymorphisms (SNPs) was performed by real-time polymerase chain reaction: two variants in exon 5 (p.R229Q and p.A242V) and one in exon 3 (p.R138Q). Variants were correlated with ethnicity, clinical presentation, treatment response, and renal outcomes. Among the 40 children analyzed, 20% had familial and 80% sporadic FSGS and among adults, 4.3% had familial and 95.7% sporadic FSGS, respectively. Overall, SRNS was found in 70% of adults and 90% in children. Among children, variants were detected in 2 (5%) with sporadic FSGS, p.R229Q and p.A242V in 1 each. Among adults, variants were present in 9 (12.9%) patients, all with sporadic FSGS, p.R229Q in 4 and p.A242V in 5. No patient had the p.R138Q variant. Among adults, a trend of higher proteinuria at the end of follow-up (p=0.06) was found in patients carrying a variant. There was no significant association between NPHS2 variants with the clinical presentation, dependence on immunosuppressive treatment, or renal outcomes. Regarding ethnicity, all patients carrying the p.R229Q variant were White, while 67% of carriers of the p.A242V variant were Black. In these patients with familial or sporadic FSGS, the prevalence of p.R229Q and p.A242V variants in children was 5% and in adults 12.9%. More studies of patients with FSGS could better define a strategy for genetic analysis and therapeutic management.

SUN-190 GFB-887, a small molecule inhibitor of TRPC5, protects against podocyte injury and attenuates proteinuria in models of FSGS

Focal segmental glomerulosclerosis (FSGS) is a rare podocytopathy with a high likelihood of progression to end stage renal disease. The Ca2+-permeable transient receptor potential canonical 5 (TRPC5) channel is a critical mediator of proteinuria in FSGS. Activation of the TRPC5 pathway in podocytes culminates in activation of Rac1, which is the primary driver of proteinuria in many forms of familial and sporadic FSGS. Inhibition of TRPC5 channel activity has been shown to protect against proteinuria and podocyte loss in AT1R transgenic and Dahl salt-sensitive rats. We performed high throughput screening of a structurally diverse compound collection followed by lead optimization for the development of several potent TRPC5 inhibitors. We characterized TRPC5 inhibitors in vitrousing a mouse podocyte cell line and podocyte injury models derived from human inducible pluripotent stem cells (hiPSC), and in two in vivomodels of FSGS, the unilaterally nephrectomized deoxycorticosterone acetate (DOCA)-salt rat model and the puromycin aminonucleoside nephrosis (PAN) rat model Here we report the identification of GFB-887, a potent, selective and orally bioavailable small molecule inhibitor of TRPC5. Potency and selectivity across TRP channels were determined using FLIPR based assays and electrophysiology. We show that TRPC5 inhibition protects against loss of stress fibers induced by protamine sulfate, a known activator of TRPC5, and restores stress fibers in podocytes after knockdown of synaptopodin. We further show that inhibition of TRPC5 suppresses pathogenic podocyte motility in a scratch assay. Finally, we demonstrate that inhibition of TRPC5 attenuates proteinuria in hypertension-induced FSGS in DOCA-salt rat model without altering blood pressure, and in non-hypertensive FSGS in the PAN rat model suggesting direct glomerular protection in vivo. We have identified GFB-887 as a new selective small molecule inhibitor of TRPC5 for the treatment of proteinuria in FSGS

A comprehensive analysis of NPHS1 gene mutations in patients with sporadic focal segmental glomerulosclerosis

BackgroundFocal segmental glomerulosclerosis (FSGS) is still one of the common causes of refractory nephrotic syndrome. Nephrin, encoded by podocyte-specific NPHS1 gene, participated in the pathogenesis of FSGS. The sites of NPHS1 mutations in FSGS is not clarified very well. In this study, we investigated the specific mutations of NPHS1 gene in Chinese patients with sporadic FSGS.MethodsA total of 309 patients with sporadic FSGS were collected and screened for NPHS1 mutations by second-generation sequencing. The variants were compared with those extracted from 2504 healthy controls in the 1000 Genomes Project. The possible pathogenic roles of missense variants were predicted by three different software. We also compared these candidate causal mutations with those summarized from the previous studies.ResultsThirty-two genetic mutations of NPHS1 gene were identified in FSGS patients, including 12 synonymous mutations, 17 missense mutations, 1 splicing mutation, and 2 intron mutations, of which c.G3315A (p.S1105S) was the most common variant (261/309). A novel missense mutation c.G2638 T (p.V880F) and a novel splicing mutation 35830957 C > T were identified in FSGS patients. The frequencies of the four synonymous mutations (c.C294T [p.I98I], c.C2223T [p.T741 T], c.C2289T [p.V763 V], c.G3315A [p.S1105S]) were much higher in FSGS patients than in controls. The frequencies of the four missense mutations (c.G349A [p.E117K], c.G1339A [p.E447K], c.G1802C [p.G601A], c.C2398T [p.R800C]) were much higher and one (c.A3230G [p.N1077S]) was lower in FSGS patients than in controls. Five missense mutations, c.C616A (p.P206T), c.G1802C (p.G601A), c.C2309T (p.P770L), c.G2869C (p.V957 L), and c.C3274T (p.R1092C), were predicted to be pathogenic mutations by software analysis.ConclusionsNPHS1 gene mutations were quite common in sporadic FSGS patients. We strongly recommend mutation analysis of the NPHS1 gene in the clinical management of FSGS patients.

APOL1 risk genotype in Europe: Data in patients with focal segmental glomerulosclerosis and after renal transplantation

Apolipoprotein L1 (APOL1) risk variants are strongly associated with sporadic focal segmental glomerulosclerosis in populations with African ancestry. We determined the frequency of G1/G2 variants in patients with steroid-resistant nephrotic syndrome/focal segmental glomerulosclerosis with African or French West Indies origin in France and its relationships with other steroid-resistant nephrotic syndrome genes. In a cohort of 152 patients (139 families), the APOL1 risk variants were genotyped: the two risk allele (high risk) genotype was found in 43.1% of subjects compared to 18.9% in a control population (P<0.0001). Compared to patients in the low risk group, patients in the high-risk group were more likely to originate from French West Indies than from Africa. APOL1 high-risk genotype was more frequent in young adult patients, but it was also found in children and it was associated with a bad renal prognosis. APOL1 high-risk genotype was usually not associated with other causative mutation in known monogenic steroid-resistant nephrotic syndrome genes and families in which multiple individuals have focal segmental glomerulosclerosis may have APOL1-associated disease. After renal transplantation, recipients of deceased-donor kidney transplantation from individuals with recent African ancestry possessing two APOL1 high-risk variants have slightly shorter allograft survival. Effects of APOL1 are independent of other traditional risk factors. Recently it was shown that black living kidney donors homozygous for APOL1 high-risk alleles have significantly lower glomerular filtration rate and increased risk of end-stage renal disease after donation. However, APOL1 genotype may not summarize by itself the totality of this risk. We showed that living kidney donors of African ancestry in France with low-risk APOL1 genotype have lower postdonation eGFR increase and lower baseline kidney volume compared to Caucasian donors.

APOL1 risk genotype in European steroid-resistant nephrotic syndrome and/or focal segmental glomerulosclerosis patients of different African ancestries

Apolipoprotein L1 (APOL1) risk variants are strongly associated with sporadic focal segmental glomerulosclerosis (FSGS) in populations with African ancestry. We determined the frequency of G1/G2 variants in steroid-resistant nephrotic syndrome (SRNS)/FSGS patients with African or French West Indies ancestry in France and its relationships with other SRNS genes. In a cohort of 152 patients (139 families), the APOL1 risk variants were genotyped by direct Sanger sequencing and pathogenic mutations were screened by next-generation sequencing with a panel including 35 SRNS genes. The two risk allele [high-risk (HR)] genotypes were found in 43.1% (66/152) of subjects compared with 18.9% (106/562) in a control population (P < 0.0001): 33 patients homozygous for APOL1 G1 alleles, 4 homozygous for G2 and 29 compound heterozygous for G1 and G2. Compared with patients in the low-risk (LR) group, patients in the HR group were more likely to originate from the French West Indies than from Africa [45/66 (68.2%) versus 30/86 (34.9%); P < 0.0001]. There were more familial cases in the HR group [27 (41.5%) versus 8 (11.4%); P < 0.0001]. However, causative mutations in monogenic SRNS genes were found in only 1 patient in the HR group compared with 16 patients (14 families) in the LR group (P = 0.0006). At diagnosis, patients in the HR group without other mutations were more often adults [35 (53.8%) versus 19 (27.1%); P = 0.003] and had a lower estimated glomerular filtration rate (78.9 versus 98.8 mL/min/1.73 m2; P = 0.02). The HR genotype is frequent in FSGS patients with African ancestry in our cohort, especially in those originating from the West Indies, and confer a poor renal prognosis. It is usually not associated with other causative mutations in monogenic SRNS genes.

A role for genetic susceptibility in sporadic focal segmental glomerulosclerosis.

Focal segmental glomerulosclerosis (FSGS) is a syndrome that involves kidney podocyte dysfunction and causes chronic kidney disease. Multiple factors including chemical toxicity, inflammation, and infection underlie FSGS; however, highly penetrant disease genes have been identified in a small fraction of patients with a family history of FSGS. Variants of apolipoprotein L1 (APOL1) have been linked to FSGS in African Americans with HIV or hypertension, supporting the proposal that genetic factors enhance FSGS susceptibility. Here, we used sequencing to investigate whether genetics plays a role in the majority of FSGS cases that are identified as primary or sporadic FSGS and have no known cause. Given the limited number of biopsy-proven cases with ethnically matched controls, we devised an analytic strategy to identify and rank potential candidate genes and used an animal model for validation. Nine candidate FSGS susceptibility genes were identified in our patient cohort, and three were validated using a high-throughput mouse method that we developed. Specifically, we introduced a podocyte-specific, doxycycline-inducible transactivator into a murine embryonic stem cell line with an FSGS-susceptible genetic background that allows shRNA-mediated targeting of candidate genes in the adult kidney. Our analysis supports a broader role for genetic susceptibility of both sporadic and familial cases of FSGS and provides a tool to rapidly evaluate candidate FSGS-associated genes.

Sequencing rare and common APOL1 coding variants to determine kidney disease risk

A third of African Americans with sporadic focal segmental glomerulosclerosis (FSGS) or HIV-associated nephropathy (HIVAN) do not carry APOL1 renal risk genotypes. This raises the possibility that other APOL1 variants may contribute to kidney disease. To address this question, we sequenced all APOL1 exons in 1, 437 Americans of African and European decent, including 464 patients with biopsy-proven FSGS/HIVAN. Testing for association with 33 common and rare variants with FSGS/HIVAN revealed no association independent of strong recessive G1 and G2 effects. Seeking additional variants that might have been under selection by pathogens and could represent candidates for kidney disease risk, we also sequenced an additional 1, 112 individuals representing 53 global populations. Except for G1 and G2, none of the 7 common codon-altering variants showed evidence of selection or could restore lysis against trypanosomes causing human African trypanosomiasis. Thus, only APOL1 G1 and G2 confer renal risk and other common and rare APOL1 missense variants, including the archaic G3 haplotype, do not contribute to sporadic FSGS and HIVAN in the United States population. Hence, in most potential clinical or screening applications, our study suggests that sequencing APOL1 exons is unlikely to bring additional information compared to genotyping only APOL1 G1 and G2 risk alleles.

Collagen (COL4A) mutations are the most frequent mutations underlying adult focal segmental glomerulosclerosis.

Multiple genes underlying focal segmental glomerulosclerosis (FSGS) and/or steroid-resistant nephrotic syndrome (SRNS) have been identified, with the recent inclusion of collagen IV mutations responsible for Alport disease (AD) or thin basement membrane nephropathy (TBMN). We aimed to investigate the distribution of gene mutations in adult patients with primary FSGS/SRNS by targeted next generation sequencing (NGS). Eighty-one adults from 76 families were recruited; 24 families had a history of renal disease. A targeted NGS panel was designed and applied, covering 39 genes implicated in FSGS/SRNS including COL4A3-5. Confirmed pathogenic mutations were found in 10 patients (6 with family history) from 9 families (diagnostic rate 12%). Probably pathogenic mutations were identified in an additional six patients (combined diagnostic rate 20%). Definitely pathogenic mutations were identified in 22% of patients with family history and 10% without. Mutations in COL4A3-5 were present in eight patients from six families, representing 56% of definitely pathogenic mutations, and establishing a diagnosis of AD in six patients and TBMN in two patients. Collagen mutations were identified in 38% of families with familial FSGS, and 3% with sporadic FSGS, with over half the mutations occurring in COL4A5. Patients with collagen mutations were younger at presentation and more likely to have family history, haematuria and glomerular basement membrane abnormalities. We show that collagen IV mutations, including COL4A5, frequently underlie FSGS and should be considered, particularly with a positive family history. Targeted NGS improves diagnostic efficiency by investigating many candidate genes in parallel.

COL4A3 mutations cause focal segmental glomerulosclerosis.

Focal segmental glomerulosclerosis (FSGS) is a histologically identifiable glomerular injury often leading to proteinuria and renal failure. To identify its causal genes, whole-exome sequencing and Sanger sequencing were performed on a large Chinese cohort that comprised 40 FSGS families, 50 sporadic FSGS patients, 9 independent autosomal recessive Alport's syndrome (ARAS) patients, and 190 ethnically matched healthy controls. Patients with extrarenal manifestations, indicating systemic diseases or other known hereditary renal diseases, were excluded. Heterozygous COL4A3 mutations were identified in five (12.5%) FSGS families and one (2%) sporadic FSGS patient. All identified mutations disrupted highly conserved protein sequences and none of them was found in either public databases or the 190 healthy controls. Of the FSGS patients with heterozygous COL4A3 mutations, segmental thinning of the glomerular base membrane (GBM) was only detected in the patient with electronic microscopy examination results available. Five ARAS patients (55.6%) had homozygous or compound-heterozygous mutations in COL4A3 or COL4A4. Serious changes in the GBM, hearing loss, and ocular abnormalities were found in 100%, 80%, and 40% of the ARAS patients, respectively. Overall, a new subgroup of FSGS patients resulting from heterozygous COL4A3 mutations was identified. The mutations are relatively frequent in families diagnosed with inherited forms of FSGS. Thus, we suggest screening for COL4A3 mutations in familial FSGS patients.

Genetic causes of proteinuria and nephrotic syndrome: Impact on podocyte pathobiology

In the past 20 years, multiple genetic mutations have been identified in patients with congenital nephrotic syndrome (CNS) and both familial and sporadic focal segmental glomerulosclerosis (FSGS). Characterization of the genetic basis of CNS and FSGS has led to the recognition of the importance of podocyte injury to the development of glomerulosclerosis. Genetic mutations induce injury due to effects on the podocyte's structure, actin cytoskeleton, calcium signaling, and lysosomal and mitochondrial function. Transgenic animal studies have contributed to our understanding of podocyte pathobiology. Podocyte endoplasmic reticulum stress response, cell polarity, and autophagy play a role in maintenance of podocyte health. Further investigations related to the effects of genetic mutations on podocytes may identify new pathways for targeting therapeutics for nephrotic syndrome.

Podocyte-associated gene mutation screening in a heterogeneous cohort of patients with sporadic focal segmental glomerulosclerosis

The utility of genetic testing in sporadic focal segmental glomerulosclerosis (FSGS) is unclear. We sought to determine the frequency of podocyte-related gene mutations in a heterogeneous population of adults and children with biopsy-proven FSGS. The prevalence of pathogenic mutations in five genes (NPHS2, TRPC6, ACTN4, INF2 and PLCE1) and of APOL1 risk alleles (G1 and G2) was ascertained in children and adults diagnosed between 1984 and 2011 with FSGS by renal biopsy. Clinical data were extracted from medical records. A total of 65 patients (28 children, 37 adults) with sporadic FSGS were identified (34 females, 31 males), with a mean age of 25 ± 16 years (range from 3 to 62 years). The majority of patients were African American (39 African American, 21 White and 2 Hispanic). We identified biallelic pathogenic NPHS2 mutations in 2 of 28 (7.1%) children, both of whom were of non-Hispanic Caucasian background. A homozygous NPHS2 p.R138Q/p.R138Q mutation was detected in a 5-year-old Caucasian female. Two compound heterozygous NPHS2 mutations p.R138Q/p.R229Q were identified in a 7-year-old Caucasian male patient. One novel, potentially pathogenic non-synonymous variant in INF2 was identified in an African American patient. The proportion of African Americans with two APOL1 risk alleles was 69.2%. This study delineates a role for genetic testing for NPHS2 in children with biopsy-proven sporadic FSGS. Further studies which specify clinical and pathological details of patients will help further define whether there are specific populations that warrant systematic testing of other podocyte-related genes in sporadic FSGS.

Genetic causes of focal segmental glomerulosclerosis: implications for clinical practice

Focal segmental glomerulosclerosis (FSGS) is a common cause of steroid-resistant nephrotic syndrome in children and adults. Although FSGS is considered a podocyte disease, the aetiology is diverse. In recent years, many inheritable genetic forms of FSGS have been described, caused by mutations in proteins that are important for podocyte function. In the present commentary, we review these genetic causes of FSGS and describe their prevalence in familial and sporadic FSGS. In routine clinical practice, the decision to perform the costly DNA analysis should be based on the assessment if the results affect the care of the individual patient with respect to the evaluation of extra-renal manifestations, treatment decisions, transplantation and genetic counselling.

α-Actinin-4 and CLP36 Protein Deficiencies Contribute to Podocyte Defects in Multiple Human Glomerulopathies

Genetic alterations of α-actinin-4 can cause podocyte injury through multiple mechanisms. Although a mechanism involving gain-of-α-actinin-4 function was well described and is responsible for a dominantly inherited form of human focal segmental glomerulosclerosis (FSGS), evidence supporting mechanisms involving loss-of-α-actinin-4 function in human glomerular diseases remains elusive. Here we show that α-actinin-4 deficiency occurs in multiple human primary glomerulopathies including sporadic FSGS, minimal change disease, and IgA nephropathy. Furthermore, we identify a close correlation between the levels of α-actinin-4 and CLP36, which form a complex in normal podocytes, in human glomerular diseases. siRNA-mediated depletion of α-actinin-4 in human podocytes resulted in a marked reduction of the CLP36 level. Additionally, two FSGS-associated α-actinin-4 mutations (R310Q and Q348R) inhibited the complex formation between α-actinin-4 and CLP36. Inhibition of the α-actinin-4-CLP36 complex, like loss of α-actinin-4, markedly reduced the level of CLP36 in podocytes. Finally, reduction of the CLP36 level or disruption of the α-actinin-4-CLP36 complex significantly inhibited RhoA activity and generation of traction force in podocytes. Our studies reveal a critical role of the α-actinin-4-CLP36 complex in podocytes and provide an explanation as to how α-actinin-4 deficiency or mutations found in human patients could contribute to podocyte defects and glomerular failure through a loss-of-function mechanism.

Elevated asymmetric dimethylarginine (ADMA) and inverse correlation between circulating ADMA and glomerular filtration rate in children with sporadic focal segmental glomerulosclerosis (FSGS)

Steroid-resistant nephrotic syndromes (NS) with focal and segmental glomerulosclerosis (FSGS) can be differentiated into sporadic and syndromic forms. In sporadic NS, a circulating FSGS-factor is discussed in the pathogenesis and is thought to inhibit the synthesis of nitric oxide (NO) from L-arginine by blocking the NO synthase (NOS). Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of all types of NOS. In a previous study we did not find an elevation of ADMA in a syndromic form of FSGS, the Schimke-immuno-osseous dysplasia. Here we report for the first time data on the L-arginine/NO pathway in sporadic FSGS of childhood. Nine children (5 to 18 years of age) suffering from sporadic FSGS and age-matched healthy controls were investigated. ADMA in plasma and urine as well as L-arginine in plasma were determined by gas chromatography-tandem mass spectrometry. The NO metabolites nitrate and nitrite were measured in plasma and urine by gas chromatography-mass spectrometry (GC-MS). The ADMA metabolite dimethylamine (DMA) was measured in urine by GC-MS. We found elevated plasma levels of ADMA in children suffering from sporadic FSGS compared to healthy controls (851 nmol/L versus 684 nmol/L, P = 0.008). An inverse correlation between ADMA and glomerular filtration rate (GFR) was found in sporadic FSGS (Pearson's correlation coefficient -0.784, P = 0.012). Our study suggests that ADMA synthesis is elevated in sporadic FSGS. This finding argues for the involvement of ADMA in the pathogenesis of this disease in childhood.

NPHS2 Variation in Sporadic Focal Segmental Glomerulosclerosis

Mutations in NPHS2, the gene that encodes podocin, are well-established causes of both familial and sporadic steroid-resistant focal segmental glomerulosclerosis (FSGS) in the pediatric population, but have not been well-characterized in late-onset disease. To investigate the role of NPHS2 polymorphisms in sporadic cases of late-onset FSGS, we studied 377 biopsy-confirmed FSGS cases and 919 controls. We identified 18 single nucleotide polymorphisms (SNPs) by resequencing a subgroup of cases and controls, and subsequently genotyped African-American and European-American cases and controls for five missense SNPs, three SNPs within introns, and four SNPs in the 3' untranslated region. No homozygotes or compound heterozygotes were observed for any missense mutation. R138Q carriers were more frequent among FSGS cases relative to controls (OR = 4.9, P = 0.06), but heterozygosity for the other four missense mutations was equally distributed among FSGS cases and controls. Finally, a common haplotype of noncoding SNPs carried by 20% of African-Americans, but not observed in European-Americans, was strongly associated with a 50% reduction in risk for sporadic FSGS (OR = 0.5, P = 0.001). These results indicate that genetic variation or mutation of NPHS2 may play a role in late-onset sporadic FSGS.

Recurrent focal glomerulosclerosis in the era of genetics of podocyte proteins: theory and therapy

Focal segmental glomerulosclerosis (FSGS) is the most frequent cause of intractable proteinuria in children and adults and is emerging as a major glomerular cause of chronic kidney disease [1]. Most of the aspects related to its pathogenesis remain unknown, one major issue being post-transplant recurrence. Recent advances in molecular genetics of FSGS led to the identification of several genes responsible for familial forms. In general, they code for proteins of the podocyte and are specifically localized in the glomerular slit-diaphragm where they play a critical role in the control of glomerular permeability. The clinical implications of one of them, that is NPHS2 coding for podocin, are obvious as it’s involvement has been extended to sporadic FSGS [2–4]. Experience with inherited sporadic FSGS due to NPHS2 mutations is accumulating and shows strong clinical homologies with idiopathic FSGS, in spite of clear pathogenic differences. This offers an invaluable opportunity for a critical reevaluation of the mechanisms, which are presently thought to be involved in the pathogenesis of idiopathic FSGS and in its recurrence after renal transplantation.

Recurrence of focal segmental glomerulosclerosis after renal transplantation in patients with mutations of podocin

Background:Posttransplant recurrence of focal segmental glomerulosclerosis (FSGS) occurs in a relevant proportion of FSGS patients and represents an important clinical emergency. It is taken as a proof of the existence of circulating permeability plasma factor(s) that are also putative effectors of original proteinuria in these patients. Familial forms of FSGS do not recur, but the discovery of numerous patients with sporadic FSGS and mutations of podocin (NPHS2, that is actually an inherited disease) who received a renal graft require a re-evaluation of the problem. Methods:To evaluate the incidence of posttransplant recurrence of FSGS in patients with NPHS2, the authors screened for podocin mutations in 53 patients with the clinical and pathologic stigmata of FSGS who had renal failure and who had undergone renal transplantation. Results.Twelve children were found to carry a homozygous (n9) or a heterozygous (n4) mutation of podocin and were classified, according to current criteria, as patients with inherited FSGS. In 5 patients of this group (38%), proteinuria recurred after renal graft and in 2, renal biopsy results showed recurrence of FSGS. Prerecurrence serum of 3 patients of this cohort was tested for antipodocin antibodies with indirect immuno-Western utilizing human podocyte extracts and were found negative. The rate of FSGS recurrence was comparable in non-NPHS2-FSGS children (12 of 27) and adults (3 of 13). Also clinical outcome of recurrence and response to plasmapheresis and immunosuppressors were comparable, suggesting a common mechanism. Conclusion:These data show a high rate of FSGS recurrence in patients with NPHS2 mutations that is comparable with idiopathic FSGS and describe the successful therapeutic approach. Recurrence of an apparently inherited disease should stimulate a critical review of the mechanisms of recurrence and of original proteinuria in these cases.