Author Correction: The copy number variation landscape of congenital anomalies of the kidney and urinary tract.

In the version of this article initially published, affiliation 38 incorrectly read "ICNU-Nephrology and Urology Department, Barcelona, Spain"; "Renal Division, Hospital Clinic, IDIBAPS, University of Barcelona, Barcelona, Spain" is the correct affiliation. The error has been corrected in the HTML and PDF versions of the article.

The copy number variation landscape of congenital anomalies of the kidney and urinary tract.

Congenital anomalies of the kidney and urinary tract (CAKUT) are a major cause of pediatric kidney failure. We performed a genome-wide analysis of copy number variants (CNVs) in 2,824 cases and 21,498 controls. Affected individuals carried a significant burden of rare exonic (that is, affecting coding regions) CNVs and were enriched for known genomic disorders (GD). Kidney anomaly (KA) cases were most enriched for exonic CNVs, encompassing GD-CNVs and novel deletions; obstructive uropathy (OU) had a lower CNV burden and an intermediate prevalence of GD-CNVs; and vesicoureteral reflux (VUR) had the fewest GD-CNVs but was enriched for novel exonic CNVs, particularly duplications. Six loci (1q21, 4p16.1-p16.3, 16p11.2, 16p13.11, 17q12 and 22q11.2) accounted for 65% of patients with GD-CNVs. Deletions at 17q12, 4p16.1-p16.3 and 22q11.2 were specific for KA; the 16p11.2 locus showed extensive pleiotropy. Using a multidisciplinary approach, we identified TBX6 as a driver for the CAKUT subphenotypes in the 16p11.2 microdeletion syndrome.

Genetic Drivers of Kidney Defects in the DiGeorge Syndrome.

BACKGROUND: The DiGeorge syndrome, the most common of the microdeletion syndromes, affects multiple organs, including the heart, the nervous system, and the kidney. It is caused by deletions on chromosome 22q11.2; the genetic driver of the kidney defects is unknown. METHODS: We conducted a genomewide search for structural variants in two cohorts: 2080 patients with congenital kidney and urinary tract anomalies and 22,094 controls. We performed exome and targeted resequencing in samples obtained from 586 additional patients with congenital kidney anomalies. We also carried out functional studies using zebrafish and mice. RESULTS: We identified heterozygous deletions of 22q11.2 in 1.1% of the patients with congenital kidney anomalies and in 0.01% of population controls (odds ratio, 81.5; P=4.5×10-14). We localized the main drivers of renal disease in the DiGeorge syndrome to a 370-kb region containing nine genes. In zebrafish embryos, an induced loss of function in snap29, aifm3, and crkl resulted in renal defects; the loss of crkl alone was sufficient to induce defects. Five of 586 patients with congenital urinary anomalies had newly identified, heterozygous protein-altering variants, including a premature termination codon, in CRKL. The inactivation of Crkl in the mouse model induced developmental defects similar to those observed in patients with congenital urinary anomalies. CONCLUSIONS: We identified a recurrent 370-kb deletion at the 22q11.2 locus as a driver of kidney defects in the DiGeorge syndrome and in sporadic congenital kidney and urinary tract anomalies. Of the nine genes at this locus, SNAP29, AIFM3, and CRKL appear to be critical to the phenotype, with haploinsufficiency of CRKL emerging as the main genetic driver. (Funded by the National Institutes of Health and others.).

[Familial Focal Segmental Glomerulosclerosis, a vademecum for clinical nephrologist]. / Glomerulosclerosi Focale e Segmentaria Familiare: vademecum per il nefrologo clinico.

The new genomic technologies (Next Generation Sequencing, NGS) are opening a new era in Genomic Medicine. This simple guide gives a state-of-the-art description of the genes that cause Focal Segmental Glomerulosclerosis and nephrotic syndrome.

Phenotypic expansion of DGKE-associated diseases.

Atypical hemolytic uremic syndrome (aHUS) is usually characterized by uncontrolled complement activation. The recent discovery of loss-of-function mutations in DGKE in patients with aHUS and normal complement levels challenged this observation. DGKE, encoding diacylglycerol kinase-ε, has not been implicated in the complement cascade but hypothetically leads to a prothrombotic state. The discovery of this novel mechanism has potential implications for the treatment of infants with aHUS, who are increasingly treated with complement blocking agents. In this study, we used homozygosity mapping and whole-exome sequencing to identify a novel truncating mutation in DGKE (p.K101X) in a consanguineous family with patients affected by thrombotic microangiopathy characterized by significant serum complement activation and consumption of the complement fraction C3. Aggressive plasma infusion therapy controlled systemic symptoms and prevented renal failure, suggesting that this treatment can significantly affect the natural history of this aggressive disease. Our study expands the clinical phenotypes associated with mutations in DGKE and challenges the benefits of complement blockade treatment in such patients. Mechanistic studies of DGKE and aHUS are, therefore, essential to the design of appropriate therapeutic strategies in patients with DGKE mutations.

Mutations in DSTYK and dominant urinary tract malformations.

BACKGROUND: Congenital abnormalities of the kidney and the urinary tract are the most common cause of pediatric kidney failure. These disorders are highly heterogeneous, and the etiologic factors are poorly understood. METHODS: We performed genomewide linkage analysis and whole-exome sequencing in a family with an autosomal dominant form of congenital abnormalities of the kidney or urinary tract (seven affected family members). We also performed a sequence analysis in 311 unrelated patients, as well as histologic and functional studies. RESULTS: Linkage analysis identified five regions of the genome that were shared among all affected family members. Exome sequencing identified a single, rare, deleterious variant within these linkage intervals, a heterozygous splice-site mutation in the dual serine-threonine and tyrosine protein kinase gene (DSTYK). This variant, which resulted in aberrant splicing of messenger RNA, was present in all affected family members. Additional, independent DSTYK mutations, including nonsense and splice-site mutations, were detected in 7 of 311 unrelated patients. DSTYK is highly expressed in the maturing epithelia of all major organs, localizing to cell membranes. Knockdown in zebrafish resulted in developmental defects in multiple organs, which suggested loss of fibroblast growth factor (FGF) signaling. Consistent with this finding is the observation that DSTYK colocalizes with FGF receptors in the ureteric bud and metanephric mesenchyme. DSTYK knockdown in human embryonic kidney cells inhibited FGF-stimulated phosphorylation of extracellular-signal-regulated kinase (ERK), the principal signal downstream of receptor tyrosine kinases. CONCLUSIONS: We detected independent DSTYK mutations in 2.3% of patients with congenital abnormalities of the kidney or urinary tract, a finding that suggests that DSTYK is a major determinant of human urinary tract development, downstream of FGF signaling. (Funded by the National Institutes of Health and others.).

Copy-number disorders are a common cause of congenital kidney malformations.

We examined the burden of large, rare, copy-number variants (CNVs) in 192 individuals with renal hypodysplasia (RHD) and replicated findings in 330 RHD cases from two independent cohorts. CNV distribution was significantly skewed toward larger gene-disrupting events in RHD cases compared to 4,733 ethnicity-matched controls (p = 4.8 × 10(-11)). This excess was attributable to known and novel (i.e., not present in any database or in the literature) genomic disorders. All together, 55/522 (10.5%) RHD cases harbored 34 distinct known genomic disorders, which were detected in only 0.2% of 13,839 population controls (p = 1.2 × 10(-58)). Another 32 (6.1%) RHD cases harbored large gene-disrupting CNVs that were absent from or extremely rare in the 13,839 population controls, identifying 38 potential novel or rare genomic disorders for this trait. Deletions at the HNF1B locus and the DiGeorge/velocardiofacial locus were most frequent. However, the majority of disorders were detected in a single individual. Genomic disorders were detected in 22.5% of individuals with multiple malformations and 14.5% of individuals with isolated urinary-tract defects; 14 individuals harbored two or more diagnostic or rare CNVs. Strikingly, the majority of the known CNV disorders detected in the RHD cohort have previous associations with developmental delay or neuropsychiatric diseases. Up to 16.6% of individuals with kidney malformations had a molecular diagnosis attributable to a copy-number disorder, suggesting kidney malformations as a sentinel manifestation of pathogenic genomic imbalances. A search for pathogenic CNVs should be considered in this population for the diagnosis of their specific genomic disorders and for the evaluation of the potential for developmental delay.

Exome sequencing identified MYO1E and NEIL1 as candidate genes for human autosomal recessive steroid-resistant nephrotic syndrome.

To identify gene loci associated with steroid-resistant nephrotic syndrome (SRNS), we utilized homozygosity mapping and exome sequencing in a consanguineous pedigree with three affected siblings. High-density genotyping identified three segments of homozygosity spanning 33.6 Mb on chromosomes 5, 10, and 15 containing 296 candidate genes. Exome sequencing identified two homozygous missense variants within the chromosome 15 segment; an A159P substitution in myosin 1E (MYO1E), encoding a podocyte cytoskeletal protein; and an E181K substitution in nei endonuclease VIII-like 1 (NEIL1), encoding a base-excision DNA repair enzyme. Both variants disrupt highly conserved protein sequences and were absent in public databases, 247 healthy controls, and 286 patients with nephrotic syndrome. The MYO1E A159P variant is noteworthy, as it is expected to impair ligand binding and actin interaction in the MYO1E motor domain. The predicted loss of function is consistent with the previous demonstration that Myo1e inactivation produces nephrotic syndrome in mice. Screening 71 additional patients with SRNS, however, did not identify independent NEIL1 or MYO1E mutations, suggesting larger sequencing efforts are needed to uncover which mutation is responsible for the phenotype. Our findings demonstrate the utility of exome sequencing for rapidly identifying candidate genes for human SRNS.

Hyperinsulinemia and insulin resistance, early cardiovascular risk factors in children with chronic kidney disease.

BACKGROUND/AIMS: Pediatric chronic kidney disease (CKD) is associated with increased risk of cardiovascular disease. Still, hyperinsulinemia and insulin resistance, common cardiovascular risk factors, are not extensively investigated in children with CKD. We hypothesize that insulin abnormalities are present also in pediatric mild to moderate CKD, and associated with inflammation and malnutrition. METHODS: We enrolled 26 children with CKD, and 34 healthy controls for analyses of blood samples and body composition. Insulin resistance was assessed using the homeostasis model assessment for insulin resistance (HOMA-IR). RESULTS: The patients had higher insulin levels and HOMA-IR compared to the controls (p < 0.01 and p < 0.005), and they correlated inversely with estimated glomerular filtration rate (rho = -0.52, p < 0.01; rho = -0.37, p = 0.08). No association was found with inflammation or malnutrition. CONCLUSION: High insulin levels and HOMA-IR appear to be common in pediatric CKD patients, already in mild to moderate renal failure. We hypothesize that hyperinsulinemia and insulin resistance alone might be important risk factors for cardiovascular disease in children with CKD.

Localization of a gene for nonsyndromic renal hypodysplasia to chromosome 1p32-33.

Nonsyndromic defects in the urinary tract are the most common cause of end-stage renal failure in children and account for a significant proportion of adult nephropathy. The genetic basis of these disorders is not fully understood. We studied seven multiplex kindreds ascertained via an index case with a nonsyndromic solitary kidney or renal hypodysplasia. Systematic ultrasonographic screening revealed that many family members harbor malformations, such as solitary kidneys, hypodysplasia, or ureteric abnormalities (in a total of 29 affected individuals). A genomewide scan identified significant linkage to a 6.9-Mb segment on chromosome 1p32-33 under an autosomal dominant model with reduced penetrance (peak LOD score 3.5 at D1S2652 in the largest kindred). Altogether, three of the seven families showed positive LOD scores at this interval, demonstrating heterogeneity of the trait (peak HLOD 3.9, with 45% of families linked). The chromosome 1p32-33 interval contains 52 transcription units, and at least 23 of these are expressed at stage E12.5 in the murine ureteric bud and/or metanephric mesenchyme. These data show that autosomal dominant nonsyndromic renal hypodysplasia and associated urinary tract malformations are genetically heterogeneous and identify a locus for this common cause of human kidney failure.

Phenotypic and genetic heterogeneity in Dent's disease--the results of an Italian collaborative study.

BACKGROUND: Dent's disease is an inherited tubulopathy caused by CLCN5 gene mutations. While a typical phenotype characterized by low-molecular-weight (LMW) proteinuria, hypercalciuria, nephrocalcinosis, nephrolithiasis, rickets and progressive renal failure in various combinations often enables a clinical diagnosis, less severe sub-clinical cases may go under-diagnosed. METHODS: By single-strand conformation polymorphism analysis and direct sequencing, we screened 40 male patients from 40 unrelated families for CLCN5 gene mutations. Twenty-four of these patients had the prominent features of Dent's disease, including LMW proteinuria, hypercalciuria and nephrocalcinosis. RESULTS: We identified 24 mutations in the CLCN5 gene in 21/24 patients with a typical phenotype and in 3/16 patients with a partial clinical picture of Dent's disease. Overall, 10 novel CLCN5 mutations were identified (E6fsX11, W58fsX97, 267 del E, Y272C, N340K, F444fsX448, W547X, Q600X, IVS3 +2 G>C and IVS3 -1 G>A), extending the number of mutations identified so far from 75 to 85. The CLCN5 coding sequence was normal in three patients. In the group with an incomplete Dent's disease phenotype, we detected two intronic mutations and one silent substitution leading to the up regulation of an alternatively spliced isoform. CONCLUSIONS: Our data confirm the genetic heterogeneity of Dent's disease. In most classic cases, the clinical diagnosis is confirmed by genetic tests.

Angiotensin-converting enzyme (ACE) haplotypes and cyclosporine A (CsA) response: a model of the complex relationship between ACE quantitative trait locus and pathological phenotypes.

It is highly controversial to define the role of angiotensin-converting enzyme (ACE) polymorphisms in essential hypertension. We studied a group of patients in whom hypertension was the major side effect of treatment by cyclosporine A (CsA). This study group comprised 227 Italian patients with nephrotic syndrome, 103 of which were treated with CsA and had different outcome. Forty-nine patients developed serious hypertension that was reversed after withdrawal of drug. ACE haplotypes were determined by a combination of molecular and statistical methods after verifying genotypes of six intragenic single nucleotide polymorphisms in 304 Italian blood donors and assembling them in clades (A, B, C) that include 95% of observed haplotypes. The association between ACE clade combinations and serum enzymatic levels confirmed the previous results about a role of an unidentified genetic variant at the 5' of the intragenic recombination site located near intron 7. ACE clades were then determined in patients, and regression methods were used to analyze variables associated with CsA responsivity and progression to renal failure. ACE genotype and responsiveness to CsA were strictly associated, because homozygosis for ACE B clade was able to influence CsA sensitivity. This highlights the role of 5' variants, which differentiate clades B and C. Other genetic markers were tested to search for possible additive effects. We found that PAI-1 4G allele was associated with progression to renal failure in the group of CsA-treated patients. Our results are in agreement with the hypothesis, raised after experimental results obtained in mouse models, that the effect of ACE polymorphisms on blood pressure is detectable once environmental factors, like CsA treatment in our case, overcome physiological homeostatic mechanisms.

Cyclosporine in patients with steroid-resistant nephrotic syndrome: an open-label, nonrandomized, retrospective study.

BACKGROUND: Steroid-resistant nephrotic syndrome (SRNS) with focal segmental glomerulosclerosis has emerged as a leading cause of end-stage renal failure (ESRF) in children and adults. In the past decade, immunosuppressive drugs such as cyclosporine (CsA) and cyclophosphamide have been introduced for the treatment of SRNS, but data on long-term clinical outcome (over years) are lacking. OBJECTIVE: The current study considered the clinical outcome of patients with SRNS who had been treated with CsA for >2 years. The primary objective was to evaluate renal function after years of treatment compared with nontreated or CsA-resistant patients. A secondary objective was to identify renal effects related to the use of CsA, with a major emphasis on renal fibrosis. METHODS: In this open-label, nonrandomized, retrospective study, the outcomes of patients of all ages with sporadic SRNS who had been followed up for >2 years (between 1970 and 2002) at 4 Italian clinical institutions were evaluated. Preliminary molecular screenings for genes encoding proteins of the slit-diaphragm (eg, podocin, nephrin, alpha-actinin) were performed to exclude inherited forms of sporadic SRNS. RESULTS: A total of 157 patients were studied; mutations were found in 18 patients (11%). Of the remaining 139 patients (84 men, 55 women; median [interquartile range (IQR)] age at onset of proteinuria, 12 [4-32] years), 84 (60%) were nontreated and 55 (40%) were treated with CsA. Of these 55 treated patients, 35 (64%) were found to be resistant (ie, persistence of proteinuria after 2 months) or intolerant (ie, malignant hypertension or worsening of renal function), and CsA was withdrawn. The median (IQR) durations of follow-up for CsA-resistant and nontreated patients were 41 (23-92) and 48 (28-106) months, respectively. Twenty patients (36%) were responsive to CsA and were followed up for a median (IQR) of 81 (47-115) months. Progression Lo ESRF occurred in 10% of CsA-responsive patients versus 60% of CsA-resistant patients and 62% of nontreated patients (P = 0.002). No sign of renal fibrosis related to drug toxicity was observed in renal biopsies performed at 5-year intervals. CONCLUSIONS: This retrospective analysis of SRNS documented a persistent antiproteinuric effect of long-term CsA (>2 years) in the absence of renal fibrosis. Although sensitivity to CsA was associated with normal renal function, resistance or intolerance was associated with progression to ESRF These data suggest that CsA may have a role in the treatment of patients with SRNS.

Broadening the spectrum of diseases related to podocin mutations.

A total of 179 children with sporadic nephrotic syndrome were screened for podocin mutations: 120 with steroid resistance, and 59 with steroid dependence/frequent relapses. Fourteen steroid-resistant patients presented homozygous mutations that were associated with early onset of proteinuria and variable renal lesions, including one case with mesangial C3 deposition. Single mutations of podocin were found in four steroid-resistant and in four steroid-dependent; five patients had the same mutation (P20L). Among these, two had steroid/cyclosporin resistance, two had steroid dependence, and one responded to cyclosporin. The common variant R229Q of podocin, recently associated with late-onset focal segmental glomerulosclerosis, had an overall allelic frequency of 4.2% versus 2.5% in controls. To further define the implication of R229Q, a familial case was characterized with two nephrotic siblings presenting the association of the R229Q with A297V mutation that were inherited from healthy mother and father, respectively. Immunohistochemistry with anti-podocin antibodies revealed markedly decreased expression of the protein in their kidneys. All carriers of heterozygous coding podocin mutation or R229Q were screened for nephrin mutation that was found in heterozygosity associated with R229Q in one patient. Finally, podocin loss of heterozygosity was excluded in one heterozygous child by characterizing cDNA from dissected glomeruli. These data outline the clinical features of sporadic nephrotic syndrome due to podocin mutations (homozygous and heterozygous) in a representative population with broad phenotype, including patients with good response to drugs. The pathogenetic implication of single podocin defects per se in proteinuria must be further investigated in view of the possibility that detection of a second mutation could have been missed. A suggested alternative is the involvement of other gene(s) or factor(s).

Apolipoprotein E in idiopathic nephrotic syndrome and focal segmental glomerulosclerosis.

BACKGROUND: Hyperlipemia characterizes nephrotic syndrome (NS) and contributes to the progression of the underlying nephropathy. The data in the literature support an implication of apolipoprotein E (apoE) in both hyperlipemia and focal segmental glomerulosclerosis (FSGS), a malignant condition associated with NS. METHODS: The apoE genotype was determined in 209 nephrotic patients, who were classified according to age and their response to steroids as resistant children (N = 96) and adults (43), and steroid dependent (33) and steroid responder (37) children. A total of 123 presented the histological features of FSGS. In a subgroup of 28 patients, serum and urinary levels of apoE and renal deposits were evaluated by immunofluorescence. RESULTS: The allelic frequencies of the three major haplotypes epsilon2, epsilon3, and epsilon4 were the same in nephrotic patients versus controls, and homozygosity for epsilon3epsilon3 was comparably the most frequent genotype (70 vs. 71%) followed by epsilon3epsilon4, epsilon2epsilon3, epsilon2epsilon4, epsilon4epsilon4. Serum levels of apoE were fivefold higher in NS and in FSGS patients than in controls, with a direct correlation with hypercholesterolemia and proteinuria. ApoE genotypes did not influence serum levels. Urinary levels were 1/10,000 of serum with an increment in nephrotic urines. Finally, immunofluorescence demonstrated the absence of apoE in sclerotic glomeruli, while comparably nephrotic patients with membranous nephropathy had an increased glomerular expression of apoE. CONCLUSIONS: ApoE is dysregulated in NS with a marked increment in serum, which is a part of the complex lipid metabolism. Down-regulation of glomerular apoE instead is a peculiarity of FSGS and may contribute to the pathogenesis of the disease. The normal distribution of apoE genotypes in nephrotic patients with FSGS excludes a pathogenetic role of genetic variants.

Homocysteine, folate, vitamin B12 levels, and C677T MTHFR mutation in children with renal failure.

Hyperhomocysteinemia is well documented in chronic renal failure (CRF) and premature and progressive occlusive vascular disease is common in CRF. The combined effects of renal failure, folate and vitamin B(12) levels, and a common mutation (C677T) in the methylenetetrahydrofolate reductase (MTHFR) gene that leads to total plasma homocysteine (tHcy) elevation in CRF children were investigated. Forty-two children (15 females) with CRF, mean age 10.3+/-4.7 years, were included. The mean glomerular filtration rate (GFR) was 37.3+/-16.9 ml/min per 1.73 m(2). The control group comprised 33 children (18 females) with a mean age of 8.6+/-3.4 years. There were 40% of CRF patients with hyperhomocysteinemia. Folate and vitamin B(12) deficiencies were identified in 14% (n=6) and 5% (n=2), respectively, of all patients. On univariate analysis, the tHcy serum concentration was negatively correlated with the plasma folate concentration (P<0.05) in controls, and with GFR (P<0.05) in patients. On multiple regression analysis for the predictors of tHcy serum concentrations, folic and vitamin B(12 )were significant in controls, whereas only GFR was significant in CRF children. In our patients no effect of the MTHFR polymorphism on tHcy levels was seen This result, in addition to the limited number of patients, may partially be explained by the low prevalence of folate deficiency in our patients.

Free amino acids in plasma, red blood cells, polymorphonuclear leukocytes, and muscle in normal and uraemic children.

BACKGROUND: The aims of this study were to investigate free amino acid (AA) concentrations in plasma, red blood cells (RBC), polymorphonuclear granulocytes (PMN), and muscle, sampled at the same time, in normal and uraemic children. METHODS: Twelve apparently well-nourished chronically uraemic children (five females) aged a mean of 9.4+/-4.8 (range 1.7--17.7) years and 13 age-matched normal children were studied. Venous blood and muscle samples for AA analyses were taken simultaneously after an overnight fast. RESULTS: The intracellular AA patterns in the three cellular compartments were qualitatively similar, but the absolute intracellular concentrations were higher in muscle than in PMN, which had higher values than in RBC. The AA patterns in plasma, RBC, PMN, and muscle in the uraemic children have many similarities; typical features being low branched-chain AA (BCAA), tyrosine, and serine concentrations and variably high concentrations of some non-essential AA. Among the individual AA, there were only few correlations between their concentrations in the three cell compartments. CONCLUSIONS: The lack of correlation between the concentrations in RBC, PMN, and muscle for most of the AA indicates that there is no close association in the same subject between individual free AA concentrations in various types of cells, presumably because of differences in metabolism and function. Consequently, one should be cautious in assuming that AA concentrations, determined in RBC or PMN, reflect the concentrations in muscle cells. Therefore, these preliminary observations do not support the hypothesis that RBC and PMN AA analysis can be considered as a suitable alternative to muscle AA determination.

Prevalence, genetics, and clinical features of patients carrying podocin mutations in steroid-resistant nonfamilial focal segmental glomerulosclerosis.

Podocin mutations (NPHS2 gene) are responsible for the autosomal recessive form of steroid-resistant nephrotic syndrome. As a result of a screening for these gene alterations in a cohort of Italian patients with nonfamilial nephrotic syndrome and histologic focal segmental glomerulosclerosis (FSGS), nine patients with NPHS2 gene homozygous or composite heterozygous mutations were found. In addition to the previously described defects, two novel mutations at exon 4 were identified (frameshift, L169P); four single nucleotide polymorphisms (SNPs) and one dinucleotide repeat were also identified. On the basis of haplotype analysis, a founder effect was suggested for the 419delG mutation, the most frequently observed in the patients studied. Patients carrying NPHS2 mutations and without a family history of nephrotic syndrome were indistinguishable from those with idiopathic FSGS on the basis of the clinical phenotype. Two of the nine patients had normal renal function at 3 and 10 yr of age, despite the presence of the nephrotic syndrome. The other seven had reached end-stage renal failure at a mean age of 9.6 yr (range, 4 to 17 yr) and had received renal allografts. In those presenting with end-stage renal failure, the clinical and laboratory features both before and after transplantation were similar, including the age at onset, the amount of proteinuria, and the absence of any response to steroids and other immunosuppressants. Finally, two children presented recurrence of mild proteinuria after transplantation, which promptly remitted after plasmapheresis combined with cyclophosphamide. These data demonstrate that podocin mutations in nonfamilial cases of steroid-resistant nephrotic syndrome are frequent and may be due in one case to a founder effect. The pretransplantation and posttransplantation outcomes in the group of patients with mutations of the podocin gene are similar to classical idiopathic FSGS, including the possibility of recurrence of proteinuria that is mild and responsive to plasmapheresis. These observations support a role of molecular screening of the podocin gene in patients with nephrotic syndrome before immunosuppressive treatment is started.