NPHS2 Mutations Research Articles

ADCK4-Associated Glomerulopathy Causes Adolescence-Onset FSGS.

Hereditary defects of coenzyme Q10 biosynthesis cause steroid-resistant nephrotic syndrome (SRNS) as part of multiorgan involvement but may also contribute to isolated SRNS. Here, we report 26 patients from 12 families with recessive mutations in ADCK4. Mutation detection rate was 1.9% among 534 consecutively screened cases. Patients with ADCK4 mutations showed a largely renal-limited phenotype, with three subjects exhibiting occasional seizures, one subject exhibiting mild mental retardation, and one subject exhibiting retinitis pigmentosa. ADCK4 nephropathy presented during adolescence (median age, 14.1 years) with nephrotic-range proteinuria in 44% of patients and advanced CKD in 46% of patients at time of diagnosis. Renal biopsy specimens uniformly showed FSGS. Whereas 47% and 36% of patients with mutations in WT1 and NPHS2, respectively, progressed to ESRD before 10 years of age, ESRD occurred almost exclusively in the second decade of life in ADCK4 nephropathy. However, CKD progressed much faster during adolescence in ADCK4 than in WT1 and NPHS2 nephropathy, resulting in similar cumulative ESRD rates (>85% for each disorder) in the third decade of life. In conclusion, ADCK4-related glomerulopathy is an important novel differential diagnosis in adolescents with SRNS/FSGS and/or CKD of unknown origin.

Response to cyclosporine in steroid-resistant nephrotic syndrome: discontinuation is possible.

Steroid-resistant nephrotic syndrome (SRNS) is still regarded as a serious disease although treatment with cyclosporine (CSA) has improved outcome. However, the duration of treatment in responders is unclear, and treatment of patients with genetic causes is a matter of debate. Thirty-six patients with SRNS were studied retrospectively. Median age at presentation was 3.2 (range, 0.06-15.0) and median follow-up 15.5 years (range, 1.8-27.7), respectively; 23 (64%) had focal segmental glomerulosclerosis (FSGS) on biopsy. In 33/36 patients (92%), genetic testing was performed for at least three most common genes known to be mutated in SRNS. Nineteen patients (53%), especially those with minimal change nephrotic syndrome (MCNS) at initial biopsy (p < 0.002), entered complete remission with CSA monotherapy, including one patient with compound heterozygous NPHS1 and dominant ACTN4 mutation, respectively. Ten patients entered partial remission (28%, all FSGS), including two with NPHS2 mutations. Seven patients (six FSGS, one MCNS) did not respond to treatment. In 15 of 19 responders to CSA, treatment was stopped after a median of 3.1 years (range, 0.5-14) and no further relapses occurred in 11/15 (73%) patients with median follow-up of 9.7 years. CSA monotherapy is effective in SRNS. Discontinuation of CSA is possible in many patients with complete remission.

Genetic abnormalities and prognosis in patients with congenital and infantile nephrotic syndrome.

Congenital nephrotic syndrome (CNS) and infantile nephrotic syndrome (INS) are caused primarily by mutations in genes that encode structural and regulatory proteins of the glomerular filtration barrier. The aim of this study was to determine genotype-phenotype correlations and prognosis in patients with CNS and INS. NPHS1, NPHS2, LAMB2 and the eighth and ninth exons of WT1 were sequenced in 80 and 22 patients with CNS and INS, respectively. Genotype-phenotype correlations and survival were evaluated. Causative mutations were identified in 64.7 % of patients, of which NPHS1 mutations were the most common (37.4 %). The mutation detection rate was twofold higher in CNS patients than in INS patients (72.5 vs. 36.2 %). The most commonly mutated gene in CNS patients was NPHS1 (46.3 %) versus NPHS2 (13.6 %) and WT1 (13.6 %) in INS patients. NPHS2 mutations, female patients with NPHS1 mutations, and NPHS1 mutations affecting the transmembrane or intracellular domains of nephrin were associated with longer survival. Based on our present findings, the likelihood of identification of a genetic cause decreases with increasing age at diagnosis. The underlying genetic abnormality should be identified as early as possible, as this knowledge will facilitate clinicians in their prognostic prediction and enable patients to receive appropriate genetic counseling.

Pierson syndrome: A case report with a neonatal cardiac association based on a novel mutation in the LAMB2 gene

Congenital nephrotic syndrome (CNS) combined with eye abnormalities including microcoria (small pupils that don't respond to light) and abnormal lens shape can suggest a clinical diagnosis of Pierson syndrome (which mainly affects the kidneys and eyes). Mutations in the genes NPHS1, NPHS2, and WT1 are known to account for the majority of CNS cases, whereas a definitive diagnosis of Pierson syndrome can be established by the detection of a causative mutation in both copies of a patient's LAMB2 gene (encoding laminin β2). CNS can manifest in utero (ultrasound may reveal hyperechogenic kidneys and oligohydramnios), or during the first 3 months of life. Pierson syndrome is an autosomal recessive disorder comprised of CNS and distinct ocular abnormalities. The prognosis of this extremely rare disorder is very poor, with the most babies developing end-stage renal disease. Those who do survive tend to show the neurodevelopmental delay and visual loss. We report a case of neonatal Pierson syndrome in conjunction with complex cyanotic cardiac disease in which a novel homozygous mutation in the LAMB2 gene was detected. The clinical association of Pierson syndrome with heart manifestation is a novel finding, reported here for the 1 st time.

NPHS2 variation in Chinese southern infants with late steroid-resistant nephrotic syndrome

NPHS2 mutations are responsible for autosomal recessive familial steroid-resistant nephrotic syndrome (SRNS) with minor glomerular abnormalities or focal segmental glomerulosclerosis (FSGS), which is characterized by early childhood onset and rapid progression to chronic renal insufficiency. This gene mutation is also responsible for an adolescent onset form of autosomal recessive familial FSGS with heavy proteinuria. Many infants with late steroid-resistant nephrotic syndrome (late SRNS) are prone to an implicated clinical and therapeutic course. The etiopathogenesis and the long-term prognosis of late SRNS remain obscure. Considering the similar steroid resistance between late and initial SRNS, analysis of NPHS2 variation was performed in 70 sporadic Chinese infants with late SRNS and 70 controls in the present study to investigate the possible role of NPHS2 gene in late SRNS. The variation analysis revealed three polymorphisms (288C > T heterozygous in exon 2, 954T > C heterozygous and homozygous, and 1038A > G heterozygous in exon 8) in 22 out of 70 patients studied. In conclusion, NPHS2 gene mutations are not a major cause of chronic renal insufficiency caused by late SRNS in Chinese southern infants.

NPHS2mutation analysis and primary nephrotic syndrome in southern Indians

Nephrotic syndrome is one of the most commonly diagnosed primary kidney diseases and its progressive forms can lead to chronic kidney disease and or end-stage renal disease. Steroid-resistant nephrotic syndrome is defined by resistance to standard steroid therapy and it remains one of the most intractable causes of kidney failure. Mutations in NPHS2, which encodes for podocin, an integral membrane protein of the glomerular epithelial cells (podocytes), represent a frequent cause of steroid-resistant nephrotic syndrome worldwide. This study was aimed at screening for known NPHS2 mutations in Indians with nephrotic syndrome. We screened a cohort of 484 subjects from the southern Indian population for the presence of four missense mutations G92C, P118L, R138Q and D160G within the NPHS2 gene using tetra primer ARMS PCR. Our results revealed that these mutations were seen only among the patients (14.02%) and were absent in the controls, suggesting their disease-causing nature. Further categorization revealed that these mutations were together responsible for 18.5% of steroid-resistant cases in our study group. Conversely, the studied mutations were not found in the controls as well as in the patients with steroid-sensitive nephrotic syndrome. This is the first such report from India. More studies are warranted to establish the frequency of NPHS2 mutations in the Asian-Indian population and such analysis may help in developing mutation(s)-specific therapeutic interventions in the future.

Lmx1b and FoxC combinatorially regulate podocin expression in podocytes.

Podocin is a key protein of the kidney podocyte slit diaphragm protein complex, an important part of the glomerular filtration barrier. Mutations in the human podocin gene NPHS2 cause familial or sporadic forms of renal disease owing to the disruption of filtration barrier integrity. The exclusive expression of NPHS2 in podocytes reflects its unique function and raises interesting questions about its transcriptional regulation. Here, we further define a 2.5-kb zebrafish nphs2 promoter fragment previously described and identify a 49-bp podocyte-specific transcriptional enhancer using Tol2-mediated G0 transgenesis in zebrafish. Within this enhancer, we identified a cis-acting element composed of two adjacent DNA-binding sites (FLAT-E and forkhead) bound by transcription factors Lmx1b and FoxC. In zebrafish, double knockdown of Lmx1b and FoxC orthologs using morpholino doses that caused no or minimal phenotypic changes upon individual knockdown completely disrupted podocyte development in 40% of injected embryos. Co-overexpression of the two genes potently induced endogenous nphs2 expression in zebrafish podocytes. We found that the NPHS2 promoter also contains a cis-acting Lmx1b-FoxC motif that binds LMX1B and FoxC2. Furthermore, a genome-wide search identified several genes that carry the Lmx1b-FoxC motif in their promoter regions. Among these candidates, motif-driven podocyte enhancer activity of CCNC and MEIS2 was functionally analyzed in vivo. Our results show that podocyte expression of some genes is combinatorially regulated by two transcription factors interacting synergistically with a common enhancer. This finding provides insights into transcriptional mechanisms required for normal and pathologic podocyte functions.

Rapid detection of monogenic causes of childhood-onset steroid-resistant nephrotic syndrome.

In steroid-resistant nephrotic syndrome (SRNS), >21 single-gene causes are known. However, mutation analysis of all known SRNS genes is time and cost intensive. This report describes a new high-throughput method of mutation analysis using a PCR-based microfluidic technology that allows rapid simultaneous mutation analysis of 21 single-gene causes of SRNS in a large number of individuals. This study screened individuals with SRNS; samples were submitted for mutation analysis from international sources between 1996 and 2012. For proof of principle, a pilot cohort of 48 individuals who harbored known mutations in known SRNS genes was evaluated. After improvements to the method, 48 individuals with an unknown cause of SRNS were then examined in a subsequent diagnostic study. The analysis included 16 recessive SRNS genes and 5 dominant SRNS genes. A 10-fold primer multiplexing was applied, allowing PCR-based amplification of 474 amplicons in 21 genes for 48 DNA samples simultaneously. Forty-eight individuals were indexed in a barcode PCR, and high-throughput sequencing was performed. All disease-causing variants were confirmed via Sanger sequencing. The pilot study identified the genetic cause of disease in 42 of 48 (87.5%) of the affected individuals. The diagnostic study detected the genetic cause of disease in 16 of 48 (33%) of the affected individuals with a previously unknown cause of SRNS. Seven novel disease-causing mutations in PLCE1 (n=5), NPHS1 (n=1), and LAMB2 (n=1) were identified in <3 weeks. Use of this method could reduce costs to 1/29th of the cost of Sanger sequencing. This highly parallel approach allows rapid (<3 weeks) mutation analysis of 21 genes known to cause SRNS at a greatly reduced cost (1/29th) compared with traditional mutation analysis techniques. It detects mutations in about 33% of childhood-onset SRNS cases.

Steroid-resistant nephrotic syndrome with mutations in NPHS2 (podocin): report from a three-generation family.

Genetic causes of steroid-resistant nephrotic syndrome are being increasingly recognized. Mutations in NPHS2, which encodes the glomerular protein podocin, account for up to 17% of sporadic and 40% of familial cases, where they display an autosomal-recessive pattern of inheritance. This report describes a non-consanguineous family with three generations of individuals who are either compound heterozygotes for mutations in NPHS2 or who have inherited a mutation and a non-neutral polymorphism (R229Q). As well as providing an aetiological explanation, identifying pathogenic mutations and considering genotype-phenotype correlations can provide prognostic information and lead to changes in genetic counselling and management.

Mutation-dependent recessive inheritance of NPHS2-associated steroid-resistant nephrotic syndrome

Monogenic disorders result from defects in a single gene. According to Mendel's laws, these disorders are inherited in either a recessive or dominant fashion. Autosomal-recessive disorders require a disease-causing variant on both alleles, and according to our current understanding, their pathogenicities are not influenced by each other. Here we present an autosomal-recessive disorder, nephrotic syndrome type 2 (MIM 600995), in which the pathogenicity of an NPHS2 allele encoding p.Arg229Gln depends on the trans-associated mutation. We show that, contrary to expectations, this allele leads to a disease phenotype only when it is associated specifically with certain 3' NPHS2 mutations because of an altered heterodimerization and mislocalization of the encoded p.Arg229Gln podocin. The disease-associated 3' mutations exert a dominant-negative effect on p.Arg229Gln podocin but behave as recessive alleles when associated with wild-type podocin. Therefore, the transmission rates for couples carrying the disease-associated mutations and p.Arg229Gln may be substantially different from those expected in autosomal-recessive disorders.

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.

Steroid Sensitive Nephrotic Syndrome in Children

Nephrotic Syndrome (NS) is one of the most frequent glomerular diseases seen in children. Children who go into complete remissin following treatment with corticosteroids are classified as having “steroid sensitive” NS. In developed countries over 80% of children with idiopathic NS have steroid sensitive disease although response to steroids is somewhat tempered in developing countries, especially in black children, the majority of whom have steroid resistant disease. The exact pathogenesis of this condition remains elusive. Podocyte injury and proteinuria are the two main issues in the pathogenesis. Recent studies suggest alterations in both innate and adaptive immune responses. There is release of cytokines by T-cells as well as a strong contribution of B-cell immunity. Genetic studies have reported human leucocyte antigen (HLA) class II antigens DR and DQ associations linked to steroid sensitive NS and in small case studies, single gene mutations e.g. PLCE1 although to date no homozygous mutations in NPHS1 or NPHS2 and WT-1 genes have been reported. Most children with steroid sensitive NS have multiple relapses and a significant percentage also develop steroid dependent NS. These children receive multiples courses of steroids and are at high risk of developing steroid toxicity. Patient with frequent relapses who develop steroid dependency thus require alternative treatment. Steroids sparing agents used include levamisole, cyclophosphamide, mycophenolate mofetil (MMF), calcineurin inhibitors (cyclosporine and tacrolimus), rituximab and vincristine. The steroid-sparing effects of these agents have greatly reduced the adverse effects seen with long-term use of steroids. Despite the wide arsenal of agents available, therapy needs to be individualised to achieve optimal care of each child. More randomised controlled trials are required to evaluate the therapeutic and economic efficacy of this agent, define criteria for selection of patients for use of particular agents and to determine the safety profile of these drugs in children. This article reviews the epidemiology, pathogenesis, clinical presentation, diagnosis, complications, management and long term outcome of children with steroid sensitive NS.

Mutational analysis of podocyte genes in children with sporadic steroid-resistant nephrotic syndrome.

Recent studies have demonstrated that mutations in 4 podocyte genes, NPHS1, NPHS2, CD2AP, and WT1, are associated with the pathogenesis of steroid-resistant nephrotic syndrome (SRNS). Systematic investigation of all 4 genes for sporadic SRNS in China has not been performed. We examined 10 Chinese children with sporadic SRNS who showed no response to immunosuppressive agents and 20 SRNS controls who exhibited a response to prolonged steroid or immunosuppressive treatment and achieved complete remission. We analyzed mutations in the 4 podocyte genes, NPHS1, NPHS2, CD2AP, and WT1. Mutational analysis was performed using polymerase chain reaction and direct sequencing. Of the 10 SRNS children who showed no response to immunosuppressive agents, the compound heterozygous NPHS1 mutations 2677A>G (T893A) and *142T>C were identified in 1 patient, while a heterozygous mutation in WT1, 1180C>T (R394W), was found in another patient. Of the 20 SRNS children showing complete remission who responded to prolonged steroid therapy or immunosuppressive agents, 4 heterozygous NPHS1 mutations, 928G>A, IVS8+30C>T, IVS21+14G>A, and IVS25-23C>T, were identified in 4 patients and a heterozygous CD2AP mutation, IVS7-135G>A, was identified in 1 patient. Our results indicate the necessity of genetic examination for mutations in podocyte genes in Chinese SRNS children who show no response to immunosuppressive agents.

NPHS2Mutations in Steroid-Resistant Nephrotic Syndrome: A Mutation Update and the Associated Phenotypic Spectrum

Mutations in the NPHS2 gene encoding podocin are implicated in an autosomal-recessive form of nonsyndromic steroid-resistant nephrotic syndrome in both pediatric and adult patients. Patients with homozygous or compound heterozygous mutations commonly present with steroid-resistant nephrotic syndrome before the age of 6 years and rapidly progress to end-stage kidney disease with a very low prevalence of recurrence after renal transplantation. Here, we reviewed all the NPHS2 mutations published between October 1999 and September 2013, and also all novel mutations identified in our personal cohort and in international genetic laboratories. We identified 25 novel pathogenic mutations in addition to the 101 already described. The mutations are distributed along the entire coding region and lead to all kinds of alterations including 53 missense, 17 nonsense, 11 small insertions, 26 small deletions, 16 splicing, two indel mutations, and one mutation in the stop codon. In addition, 43 variants were classified as variants of unknown significance, as these missense changes were exclusively described in the heterozygous state and/or considered benign by prediction software. Genotype-phenotype analyses established correlations between specific variants and age at onset, ethnicity, or clinical evolution. We created a Web database using the Leiden Open Variation Database (www.lovd.nl/NPHS2) software that will allow the inclusion of future reports.

Steroid-resistant nephrotic syndrome: impact of genetic testing

BACKGROUND AND OBJECTIVESMutations in several genes are known to cause steroid-resistant nephrotic syndome (SRNS), most commonly in NPHS1, NPHS2, and WT1. Our aims were to determine the frequency of mutations in these genes in children with SRNS, the response of patients with SRNS to various immunosuppressants, and the disease outcome, and to review the predictive value of genetic testing and renal biopsy result.DESIGN AND SETTINGSA retrospective review was performed of the medical records for all children with SRNS who were treated and followed-up in the Pediatric Nephrology Unit of King Abdulaziz University Hospital (KAUH), Jeddah, Saudi Arabia from 2002–2012.PATIENTS AND METHODSWe retrospectively reviewed the medical records of children above 1 year of age, who presented with SRNS to KAUH, Jeddah, Saudi Arabia, in the 10-year interval from 2002–2012 and for whom the results of genetic testing for NPHS1, NPHS2, and WT1 were available. We compared the clinical phenotype, including response to treatment and renal outcome to genotype data.RESULTSWe identified 44 children with a clinical diagnosis of SRNS in whom results of genetic testing were available. Presumably disease-causing mutations were detected in 5 children (11.4%) of which 3 (6.8%) had NPHS2 mutation and 2 (4.5%) had NPHS1 mutation. Renal biopsy revealed minimal change disease (MCD) or variants in 17 children, focal segmental glomerulosclerosis (FSGS) in 23 children, membranoproliferative changes (MPGN) in 2 children, and IgA nephropathy in another 2 children. Children with MCD on biopsy were more likely to respond to treatment than those with FSGS. None of those with an identified genetic cause showed any response to treatment.CONCLUSIONThe frequency of identified disease-causing mutations in children older than 1 year with SRNS presented to KAUH was 11.4%, and these patients showed no response to treatment. Initial testing for gene mutation in children with SRNS may obviate the need for biopsy, and the use of immunosuppressive treatment in children with disease due to NPHS1 or NPHS2 mutations. Renal biopsy was useful in predicting response in those without genetic mutations.

Functional analysis of NPHS1 mutations in Japanese patients.

Many mutations in the NPHS1 gene were detected among patients with congenital nephrotic syndrome. Functional analysis of those mutations was done with a stable-expression cell line. Nevertheless, establishing such a cell line is time-consuming. We established an easier method using automatic counting software for functional analysis with transient-transfection cells rather than a stable-expression cell line. We demonstrated maltrafficking to the plasma membrane of abnormal nephrin for immunostaining on transient-expression cells by comparison without Triton X (detecting proteins on the cell membrane only) and with Triton X (detecting proteins both on the cell membrane and inside the cell cytoplasm). We obtained relevant results with data obtained previously using a stable-expression cell line. Furthermore, we conducted functional analysis of NPHS1 mutations in Japanese patients with congenital nephrotic syndrome using this simple method, which revealed that all pathogenic mutations impaired trafficking to the protein plasma membrane. Functional analysis using transient-expression cells with automatic counting software was useful to demonstrate maltrafficking to the plasma membrane of a protein. All pathogenic mutations detected in Japanese patients impaired trafficking to the protein plasma membrane.

English

Introduction The aim of this study was to determine pathological variants of childhood focal segmental glomerulosclerosis and assess efficacy of prednisolone + methylprednisolone + cyclosporin A treatment. Materials and methods This retrospective cohort study included 134 native Kazakh children (3 months–17 years) with nephrotic syndrome hospitalised in the Nephrology Department of the Republic Children’s Clinical Hospital from 2004 to 2011. Kidney biopsy and pathological investigations were performed in 38 nephrotic syndrome patients with proven steroid resistance. Results Focal segmental glomerulosclerosis was confirmed in 38 (28.4%) patients (treatment group). The main focal segmental glomerulosclerosis variants were glomerular tip lesions and not otherwise specified types. Historical (did not undergo kidney biopsy) controls were treated with cyclosporin A or alkylating agents. Prednisolone + methylprednisolone + cyclosporin A immunosuppressive therapy was highly effective, allowing complete remission in 88.9% patients with minimum side effects. Patients with the not otherwise specified variant (NPHS2 and WT1 mutations) did not achieve remission. Combination cyclosporin A treatment was significantly more effective than alkylating agent treatment in steroid-resistant nephrotic syndrome patients without genetic mutations. Conclusion Tip lesions are predominant in childhood steroid-resistant nephrotic syndrome. Prednisolone + methylprednisolone + cyclosporin A therapy is safe and effective for childhood focal segmental glomerulosclerosis. Establishing a podocyte mutation profile is important to predict treatment outcome.

Mutation c.106delG (p.Ala36fs*6) associée au syndrome néphrotique congénital type finlandais : premier cas diagnostiqué au Togo

ObjectiveTo report the first case of congenital nephrotic syndrome of the Finnish type (SNCF) in Togo associated with a new mutation of NPHS1. ObservationOur study focused on a female infant of 10months, born premature at 34weeks 6days, followed from birth to pure SNC discovered the 10th day of life. Monitoring and pregnancy outcome unremarkable. It is the third in a family of three children, the first two are killed in a similar table but not explored before 1year of age. The diagnosis is confirmed by the SNCF genetic study NPHS1 gene encoding nephrin performed in our patient and her parents showed a double mutation of which c.[106delG]+[2728T>C] and p. at the nucleotide level. [Ala36fs*6]+[Ser91OPro] at the protein level inherited from each parent. The change was made to the 10th month of death in life after sepsis in a third of cortico-resistance. ConclusionThe SNCF, autosomal recessive disease early, which remains a serious diagnosis, is genetic. This new mutation could she explained the severity of the SNCF in this family?

Genetic screening in adolescents with steroid-resistant nephrotic syndrome

Genetic screening paradigms for congenital and infantile nephrotic syndrome are well established; however, screening in adolescents has received only minor attention. To help rectify this, we analyzed an unselected adolescent cohort of the international PodoNet registry to develop a rational screening approach based on 227 patients with nonsyndromic steroid-resistant nephrotic syndrome aged 10-20 years. Of these, 21% had a positive family history. Autosomal dominant cases were screened for WT1, TRPC6, ACTN4, and INF2 mutations. All other patients had the NPHS2 gene screened, and WT1 was tested in sporadic cases. In addition, 40 sporadic cases had the entire coding region of INF2 tested. Of the autosomal recessive and the sporadic cases, 13 and 6%, respectively, were found to have podocin-associated nephrotic syndrome, and 56% of them were compound heterozygous for the nonneutral p.R229Q polymorphism. Four percent of the sporadic and 10% of the autosomal dominant cases had a mutation in WT1. Pathogenic INF2 mutations were found in 20% of the dominant but none of the sporadic cases. In a large cohort of adolescents including both familial and sporadic disease, NPHS2 mutations explained about 7% and WT1 4% of cases, whereas INF2 proved relevant only in autosomal dominant familial disease. Thus, screening of the entire coding sequence of NPHS2 and exons 8-9 of WT1 appears to be the most rational and cost-effective screening approach in sporadic juvenile steroid-resistant nephrotic syndrome.

Mutational analysis in podocin-associated hereditary nephrotic syndrome in Polish patients: founder effect in the Kashubian population

Hereditary nephrotic syndrome is caused by mutations in a number of different genes, the most common being NPHS2. The aim of the study was to identify the spectrum of NPHS2 mutations in Polish patients with the disease. A total of 141 children with steroid-resistant nephrotic syndrome (SRNS) were enrolled in the study. Mutational analysis included the entire coding sequence and intron boundaries of the NPHS2 gene. Restriction fragment length polymorphism (RFLP) and TaqMan genotyping assay were applied to detect selected NPHS2 sequence variants in 575 population-matched controls. Twenty patients (14 %) had homozygous or compound heterozygous NPHS2 mutations, the most frequent being c.1032delT found in 11 children and p.R138Q found in four patients. Carriers of the c.1032delT allele were exclusively found in the Pomeranian (Kashubian) region, suggesting a founder effect origin. The 14 % NPHS2 gene mutation detection rate is similar to that observed in other populations. The heterogeneity of mutations detected in the studied group confirms the requirement of genetic testing the entire NPHS2 coding sequence in Polish patients, with the exception of Kashubs, who should be initially screened for the c.1032delT deletion.