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WT1 splice-site mutations are rarely associated with primary steroid-resistant focal and segmental glomerulosclerosis.BackgroundDonor splice-site de novo heterozygous mutations in intron 9 of the Wilms' tumor gene (WT1) have been reported in Frasier syndrome, which is defined by the association of focal and segmental glomerulosclerosis (FSGS), male pseudohermaphroditism, and gonadoblastoma. These splice-site mutations alter theWT1 alternative splicing leading to twoWT1 isoforms, with (+) or without (-) three amino acids, lysine-threonine-serine (KTS), between zinc fingers 3 and 4. The aim of this work was to investigate the possibility that some cases of primary steroid-resistant nephrotic syndrome associated with FSGS may be caused byWT1 splice-site mutations.MethodsWe analyzedWT1 exons 8 and 9 and the surrounding exon/intron boundary DNA sequences in 37 children with nonfamilial primary steroid-resistant nephrotic syndrome. Semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to determine the relative ratio of +KTS/-KTS transcripts from immortalized lymphocyte RNA.ResultsOne boy with FSGS and associated pathologies (diaphragmatic hernia, proximal hypospadias, and unilateral testicular ectopia) was found to carry the heterozygous 1228 +4 C→T splice-site mutation. RT-PCR quantitation of the +KTS/-KTS transcripts from immortalized lymphocyte RNA of this patient showed a diminution of the +KTS/-KTS isoform ratio (0.43), which is identical to that reported in patients with Frasier syndrome. Using the same approach, healthy control subjects have +KTS/-KTS ratios ranging from 1.50 to 2.00.ConclusionsThis study expands the range of the phenotypic presentation of the intron 9 splice-siteWT1 mutations and adds to the already reported heterogeneity of primary steroid-resistant nephrotic syndromes. We suggest that these mutations are not likely to be a common cause of isolated steroid-resistant nephrotic syndrome, and recommend aWT1 exon 9/intron 9 splice-site study in children with primary steroid-resistant nephrotic syndrome if genital or diaphragmatic anomalies are associated. The identification of suchWT1 mutations has practical implications for the management of these patients.

The twin-to-twin transfusion syndrome (TTS) results from an unbalanced blood supply through placental anastomoses in monochorionic twins. It induces growth restriction, renal tubular dysgenesis, and oliguria in the donor and visceromegaly and polyuria in the recipient. A better understanding of its pathophysiology could contribute to improving the management of TTS, which still carries a high perinatal mortality in both twins. As well as several other candidates, the renin-angiotensin system might be involved in TTS. To evaluate its role in the pathogenesis of the syndrome, we studied the kidneys of 21 twin pairs who died from TTS at 19 to 30 weeks, compared with 39 individuals in a control group, using light microscopy, immunohistochemistry, and in situ hybridization. The overexpression of the renin protein and transcript with frequent evidence of renin synthesis by mesangial cells was observed in the donor kidneys, presumably as a consequence of chronic renal hypoperfusion. This upregulation of renin synthesis might be beneficial to restore euvolemia. In severe cases of TTS, however, angiotensin-II-induced vasoconstriction acts as an additional deleterious factor by further reducing the renal blood flow in donors. In recipients, renin expression was virtually absent, possibly because it was down-regulated by hypervolemia. However, in addition to congestion and hemorrhagic infarction, there were severe glomerular and arterial lesions resembling those observed in polycythemia- or hypertension-induced microangiopathy. We speculate that fetal hypertension in the recipient might be partly mediated by the transfer of circulating renin produced by the donor, through the placental vascular shunts.

Denys-Drash syndrome is a rare disorder of urogenital development characterized by the association of early onset glomerulopathy caused by diffuse mesangial sclerosis, gonadal dysgenesis leading to pseudohermaphroditism in males, and a high risk of developing Wilms’ tumor. The syndrome is caused by dominant negative point mutations in the WT1 gene that encodes a tumor suppressor transcription factor normally expressed in podocytes. Mutations usually affect the zinc fingers of the WT1 protein. The basic defect is unknown in most cases of isolated diffuse mesangial sclerosis, a disease characterized by the same glomerular changes as in Denys-Drash syndrome but possibly transmitted as an autosomal recessive trait. Here we show that the distribution of WT1 is abnormal in most patients with Denys-Drash syndrome : WT1 nuclear staining of podocytes is decreased or absent. This finding is consistent with the decreased DNA binding capacity of the mutated protein. One target gene of WT1 is PAX2, the expression of which is down-regulated in podocytes during early stages of nephrogenesis. We demonstrate that WT1 mislocalization is associated with abnormal podocyte expression of PAX2 protein and RNA. We suggest that persistent expression of PAX2 is likely to result from the loss of WT1 dependent transcriptional repression and may participate in the pathological mechanisms leading to glomerular dysfunction. Abnormal distribution of WT1 and PAX2 was also observed in isolated diffuse mesangial sclerosis suggesting that a defect in WT1 could also be operative in isolated diffuse mesangial sclerosis. Primary involvement of PAX2 is an alternative hypothesis because persistent expression of PAX2 in transgenic mice is associated with the occurrence of early and severe glomerulopathy.

Familial juvenile nephronophthisis (NPH) is an autosomal recessive interstitial nephritis leading to terminal renal failure around puberty. Associations with extrarenal symptoms have been reported, mainly with Leber amaurosis (termed Senior-Løken syndrome). By means of linkage analysis a gene NPH1 for the purely renal form of NPH has been localized to chromosome 2. Genetic heterogeneity has been shown between NPH and Senior-Løken syndrome and also within the group of isolated NPH cases. Further characterization of the NPH1 region led to the isolation of large homozygous deletions in approximately 70% of patients with NPH. The detection of these deletions by PCR represents a simple noninvasive method for precise diagnosis in the majority of patients suspected of having NPH.

International audience; Since the recent publication of data showing favorable outcomes for patients with HIV-1 and ESRD, kidney transplantation has become a therapeutic option in this population. However, reports have documented unexplained reduced allograft survival in these patients. We hypothesized that the unrecognized infection of the transplanted kidney by HIV-1 can compromise long-term allograft function. Using electron microscopy and molecular biology, we examined protocol renal transplant biopsies from 19 recipients with HIV-1 who did not have detectable levels of plasma HIV-1 RNA at transplantation. We found that HIV-1 infected the kidney allograft in 68% of these patients. Notably, HIV-1 infection was detected in either podocytes predominately (38% of recipients) or tubular cells only (62% of recipients). Podocyte infection associated with podocyte apoptosis and loss of differentiation markers as well as a faster decline in allograft function compared with tubular cell infection. In allografts with tubular cell infection, epithelial cells of the proximal convoluted tubules frequently contained abnormal mitochondria, and both patients who developed features of subclinical acute cellular rejection had allografts with tubular cell infection. Finally, we provide a novel noninvasive test for determining HIV-1 infection of the kidney allograft by measuring HIV-1 DNA and RNA levels in patients' urine. In conclusion, HIV-1 can infect kidney allografts after transplantation despite undetectable viremia, and this infection might influence graft outcome.

An alteration in cell/matrix interactions is one of the suggested mechanisms leading to cyst formation in polycystic kidney diseases. Most of these interactions are mediated by beta 1-integrins, a subfamily of integrin receptors, formed by the association of the beta 1-chain with different alpha-subunits. To date, no study on alpha-integrin subunit distribution during the early stages of cyst development has been reported. Using immunofluorescence, we analyzed the distribution of alpha-integrin subunits (alpha 1, alpha 2, alpha 3, alpha 5, and alpha 6) and basement membrane proteins in kidneys of fetuses with autosomal dominant (ADPKD) or autosomal recessive polycystic kidney disease (ARPKD). The distribution was compared with that observed in normal fetal and post-natal kidneys, and in fetal cystic dysplasia and Meckel syndrome. Marked increase in alpha 1-integrin staining was observed in normal and cystic collecting duct cells of both polycystic diseases (PKD), compared with normal and cystic controls. The distribution of integrin subunits alpha 2, alpha 3, and alpha 6 was irregular in cyst epithelial cells of PKD and cystic controls. The increased expression of the alpha 1-subunit specifically observed in PKD collecting duct cells may be an early consequence of the genetic defect in ARPKD. In ADPKD it parallels the reported expression of polycystin, the protein product of PKD1. The irregular expression of alpha 2, alpha 3, and alpha 6 integrin subunits observed in all types of cysts suggests that cell/matrix interactions are altered early and may participate in the development of cysts, perhaps by contributing to the deregulation of cell survival in cystic diseases.

Diffuse leiomyomatosis (DL) with Alport syndrome (AS) has been shown to be associated with contiguous gene deletions of the COL4A5 and COL4A6 genes, with the COL4A6 breakpoint of the deletions invariably located in the large intron 2 of the gene. We describe four YAC clones covering the locus and a refined restriction map of the entire COL4A6 gene. These resources have allowed us to make a precise estimate of the size of COL4A6 introns 2 and 3, as well as the size of the gene itself. We also describe five novel deletions which, in conjunction with previous reports, allow the definition of a 90-kb critical region in which to search for a gene or other entity involved in the pathogenesis of DL.

LMX1B encodes a homeodomain-containing transcription factor that is essential during development. Mutations in LMX1B cause nail-patella syndrome, characterized by dysplasia of the patellae, nails, and elbows and FSGS with specific ultrastructural lesions of the glomerular basement membrane (GBM). By linkage analysis and exome sequencing, we unexpectedly identified an LMX1B mutation segregating with disease in a pedigree of five patients with autosomal dominant FSGS but without either extrarenal features or ultrastructural abnormalities of the GBM suggestive of nail-patella-like renal disease. Subsequently, we screened 73 additional unrelated families with FSGS and found mutations involving the same amino acid (R246) in 2 families. An LMX1B in silico homology model suggested that the mutated residue plays an important role in strengthening the interaction between the LMX1B homeodomain and DNA; both identified mutations would be expected to diminish such interactions. In summary, these results suggest that isolated FSGS could result from mutations in genes that are also involved in syndromic forms of FSGS. This highlights the need to include these genes in all diagnostic approaches to FSGS that involve next-generation sequencing.

Focal and segmental glomerulosclerosis (FSGS) is a non-specific scarring process of the glomerulus, initially described in idiopathic nephrotic syndrome. The distribution of types I, III, IV, V, and VI collagen and of the alpha 1, alpha 3, alpha 4, alpha 5, and alpha 6 chains of type IV collagen was studied by immunohistochemistry in sclerotic lesions of nine nephrotic children. Dual immunofluorescence and high-resolution immunogold labelling were used to determine the precise distribution of the antigens. No changes were detected in normal glomeruli of patients compared with controls. In FSGS, type IV collagen [alpha 1(IV)2 alpha 2(IV)], and to a lesser degree type VI, accumulates in the two components of the lesion: the enlarged mesangial matrix and the material deposited between the pushed-out podocytes and the alpha 3-alpha 5(IV)-positive glomerular basement membrane. Staining for alpha 6(IV) and types I, III, and V collagen was practically negative. These results suggest that the matrix components of the sclerotic lesion are produced solely by glomerular cells. Changes in the relative distribution of type IV collagen chains, characterized by the presence of collagen [alpha 1(IV)2 alpha 2(IV)] in close contact with the podocytes, strongly suggest a switch in the podocyte programme of collagen synthesis.

In membranous glomerulonephritis (MGN), thickening of the glomerular basement membrane (GBM) is partly due to the accumulation of basement membrane material between and around immune deposits located on the epithelial aspect of the GBM. We investigated the distribution of type IV collagen chains (alpha 1/alpha 2, alpha 3, alpha 4, alpha 5, alpha 6) and of types I, III, V, and VI collagen in the glomeruli from 16 patients, by indirect immunofluorescence in 13 and the high-resolution immunogold technique in 6. No changes were detected in stage I MGN. The spiky projections of the GBM in stage II MGN and the basement membrane layers encircling immune deposits in stage III contained the alpha 3, alpha 4, and alpha 5 chains of type IV collagen. In contrast, the alpha 1/alpha 2 chains of type IV, as well as type VI collagen accumulated in the subendothelial aspect of the GBM. No significant staining for types I, III, and V collagens or for the alpha 6 chain of type IV collagen was detected. The results show that, as in the normal glomeruli, the different chains of type IV collagen are not co-distributed in the glomerular extracellular matrix in MGN. They also indicate that type IV collagen chains and type IV collagen play an important role in the thickening of the GBM in human MGN.

SUMMARY: We report in this paper two siblings aged 8 and 17 months who were clinically diagnosed with familial steroid-resistant nephrotic syndrome (SRNS). By mutation screening of the NPHS2 gene, a homozygous missense mutation, P118L, was detected in both children. This study is the first systematic investigation of NPHS2 gene mutations in Turkish children with familial SRNS. If this mutation is a hot spot of mutation in the Turkish population, screening this novel mutation in Turkish children with SRNS may be of great clinical use to prevent unnecessary treatment modalities, provide accurate genetic counselling and predict the prognosis of the disease.

A gene (NPH1) responsible for approximately 90% of the purely renal form of familial juvenile nephronophthisis, a progressive tubulo-interstitial kidney disorder, maps to human chromosome 2. We report the construction of a YAC-based contig spanning the critical NPH1 region and the flanking genetic markers. This physical map was integrated with a refined genetic map that restricted the NPH1 interval to about 2 cM; this interval corresponds in a maximum physical distance of 3.5 Mb. The entire contig covers 9 cM between the loci D2S135 and D2S121. The maximum physical distance between these two markers is approximately 11.3 Mb. Forty-five sequence-tagged sites, including six genes, have been located within this contig. PAX8, a member of the human paired box gene family, that is expressed in the developing kidney, was assigned outside the restricted NPH1 critical region and cannot therefore be regarded as a candidate gene. This set of overlapping clones represents a useful resource for further targeted development of genetic markers and for the characterization of candidate genes responsible for juvenile nephronophthisis.

Idiopathic nephrotic syndrome (INS) in childhood is characterized by massive proteinuria and minimal glomerular changes. Most patients with INS respond to steroid therapy. INS is generally regarded as a sporadic disease with favorable outcome. We investigated a distinct subgroup of nephrosis--the familial form of steroid resistant INS (SRN). These patients always progress to end-stage renal failure within a few years and show absence of recurrence of the disease after renal transplantation. The occurrence of the disorder in siblings and the high incidence of inbreeding in these families made an autosomal recessive mode of inheritance very likely. We performed whole genome linkage analysis in nine multiplex families of European or Northern African origin. Our results allowed us to assign a disease locus (SRN1) to a defined chromosomal region on 1q25-1q31, thus confirming the existence of a distinct entity of autosomal recessive nephrosis. Exclusion of linkage to the entire region in one family proves genetic heterogeneity.

The angiotensin I converting enzyme inhibitor (ACEI) perindopril (2 mg/kg body weight), the peripheral vasodilator dihydralazine (DHL) (25 mg/kg body weight) or distilled water was given daily from birth to day 14 to neonatal rats. Blood pressure, plasma creatinine, plasma renin activity (PRA), substrate (PRS) and concentration (PRC) and renin content of kidney tissue sections were evaluated on days 14 and 28. By day 14, a high mortality in the ACEI group was observed. ACEI, but not DHL, led to a significant fall (P < 0.01) in blood pressure, 57 +/- 11 versus 89 +/- 25 in the DHL group and 103 +/- 24 mmHg in controls, and to a dramatic increase in plasma creatinine. PRA and PRS were undetectable in ACEI-treated rats; in contrast, PRC and renal staining with anti-renin antibody were significantly increased in ACEI rats. On day 28, the blood pressure was normal in all groups and plasma creatinine returned to the normal range in ACEI rats. PRA, PRS and PRC were not significantly different in the ACEI group and controls. These results suggest that the renin-angiotensin system (RAS) plays a major postnatal role in the neonatal rat. Inhibition of the RAS during the first 2 weeks of life leads to high mortality, severe hypotension, reversible renal failure and a defect in circulating angiotensinogen.

Renal tubular dysgenesis (RTD) is a severe foetal disorder characterised by the absence or poor development of proximal tubules, early onset and persistent anuria (leading to oligohydramnios and the Potter sequence) and ossification defects of the skull. In most cases, early death occurs from pulmonary hypoplasia, anuria and refractory arterial hypotension. RTD may be acquired during foetal development or inherited as an autosomal recessive disease. Inherited RTD is genetically heterogeneous and linked to mutations in the genes encoding the major components of the renin-angiotensin system (RAS): angiotensinogen, renin, angiotensin-converting enzyme or angiotensin II receptor type 1. Mutations result in either the absence of production or lack of efficacy of angiotensin II. Secondary RTD has been observed in various situations, particularly in the donor twin of severe twin-to-twin transfusion syndrome, in foetuses affected with congenital haemochromatosis or in foetuses exposed to RAS blockers. All cases result in renal hypoperfusion. These examples illustrate the importance of a functional RAS in the maintenance of blood pressure and renal blood flow for humans during foetal life. The diagnosis of RTD in an anuric foetus with normal renal sonography results is important for the management of the foetus or neonate. Depending on the genetic or secondary cause of the disease, such findings can lead to genetic counselling or the prevention of recurrence in subsequent pregnancies.

CKD is a frequent long-term complication after SBTx. CNIs are a well-known factor, but probably not the only cause. We assessed the incidence, risk factors, and severity of CKD in 27 children with SBTx (15 combined liver/SBTx) and prednisone/TAC-based maintenance immunosuppression. Median follow-up was seven yr (3-21). A renal biopsy was performed in 14 patients, 1-18 yr post-SBTx. A reduced GFR was observed in 17 children (63%) during the follow-up with none requiring dialysis. CNI toxicity was observed in 11/14 biopsies, as early as two yr post-transplant, and could occur with a normal mGFR. The dose of TAC was reduced by 50% in 13 patients with CKD and/or significant kidney histological lesions, and six were also given MMF. This led to a significant improvement in renal function: mGFR normalized in eight patients and improved or stabilized in five. No rejection occurred. At last follow-up, 37% had CKD stage 2 and 15% had CKD stage 3. In conclusion, CKD is frequent in children after SBTx and probably multifactorial. Less nephrotoxic immunosuppressive protocols may improve mGFR and should be further considered. The kidney histology helps in designing personalized immunosuppression strategies for patients.

Autosomal recessive renal tubular dysgenesis (RTD) is a severe disorder of renal tubular development characterized by early onset and persistent fetal anuria leading to oligohydramnios and the Potter sequence, associated with skull ossification defects. Early death occurs in most cases from anuria, pulmonary hypoplasia, and refractory arterial hypotension. The disease is linked to mutations in the genes encoding several components of the renin-angiotensin system (RAS): AGT (angiotensinogen), REN (renin), ACE (angiotensin-converting enzyme), and AGTR1 (angiotensin II receptor type 1). Here, we review the series of 54 distinct mutations identified in 48 unrelated families. Most of them are novel and ACE mutations are the most frequent, observed in two-thirds of families (64.6%). The severity of the clinical course was similar whatever the mutated gene, which underlines the importance of a functional RAS in the maintenance of blood pressure and renal blood flow during the life of a human fetus. Renal hypoperfusion, whether genetic or secondary to a variety of diseases, precludes the normal development/ differentiation of proximal tubules. The identification of the disease on the basis of precise clinical and histological analyses and the characterization of the genetic defects allow genetic counseling and early prenatal diagnosis.

Familial juvenile nephronophthisis (NPH) is an autosomal recessive progressive tubulo-interstitial kidney disorder, responsible for 6-10% of end-stage renal failure in children, and is frequently associated with Leber amaurosis (termed Senior-Løken syndrome). The biochemical basis of NPH is unknown. We recently reported linkage of the purely renal form of NPH to three markers on chromosome 2. Our results also suggested the existence of genetic heterogeneity between NPH and SLS. To map this NPH gene more precisely, we have now tested the segregation of six new microsatellite markers and five additional families. Haplotype analyses show unequivocally that four NPH families are not linked to the chromosome 2 markers, although there are no clinical or pathological features discernible in these families that could separate them from the families linked to the chromosome 2 NPH locus (NPH1). This reveals genetic heterogeneity in the purely renal form of NPH. In situ hybridization of YAC clones isolated with two closely linked markers assigned the NPH1 region to 2q13. Furthermore, based on haplotype analysis and specific recombination events, the NPH1 gene has been placed between D2S293/D2S340 and D2S121, a genetic interval of about 5-7 cM.

A case of Meckel-Gruber syndrome was diagnosed by embryoscopy at 10 menstrual weeks, allowing for early termination of pregnancy. Post-mortem examination confirmed the presence of polydactyly and bilateral cystic lesions of the mesonephros and metanephros. Both the forming nephrons and the collecting ducts were involved in the formation of renal cysts.

WT1 was initially identified as a Wilms tumour suppressor gene through the study of children presenting the contiguous gene syndrome WAGR ( W ilms tumor, A niridia, G enitourinary malformations, mental R etardation) due to large constitutional deletions of DNA in band 11p13 ([1][1],[2][2]). This 10

Backgrounds: Charcot–Marie–Tooth neuropathy has been reported to be associated with renal diseases, mostly focal segmental glomerulosclerosis (FSGS). However, the common mechanisms underlying the neuropathy and FSGS remain unknown. Mutations in INF2 were recently identified in patients with autosomal dominant FSGS. INF2 encodes a formin protein that interacts with the Rho-GTPase CDC42 and myelin and lymphocyte protein (MAL) that are implicated in essential steps of myelination and myelin maintenance. We therefore hypothesized that INF2 may be responsible for cases of Charcot–Marie–Tooth neuropathy associated with FSGS., Methods: We performed direct genotyping of INF2 in 16 index patients with Charcot–Marie–Tooth neuropathy and FSGS who did not have a mutation in PMP22 or MPZ, encoding peripheral myelin protein 22 and myelin protein zero, respectively. Histologic and functional studies were also conducted., Methods: We identified nine new heterozygous mutations in 12 of the 16 index patients (75%), all located in exons 2 and 3, encoding the diaphanous-inhibitory domain of INF2. Patients presented with an intermediate form of Charcot–Marie–Tooth neuropathy as well as a glomerulopathy with FSGS on kidney biopsy. Immunohistochemical analysis revealed strong INF2 expression in Schwann-cell cytoplasm and podocytes. Moreover, we demonstrated that INF2 colocalizes and interacts with MAL in Schwann cells. The INF2 mutants perturbed the INF2–MAL–CDC42 pathway, resulting in cytoskeleton disorganization, enhanced INF2 binding to CDC42 and mislocalization of INF2, MAL, and CDC42., Conclusions: INF2 mutations appear to cause many cases of FSGS-associated Charcot–Marie–Tooth neuropathy, showing that INF2 is involved in a disease affecting both the kidney glomerulus and the peripheral nervous system. These findings provide new insights into the pathophysiological mechanisms linking formin proteins to podocyte and Schwann-cell function., Funded by the Agence Nationale de la Recherche and others.Supported by grants from the Association pour l'Utilisation du Rein Artificiel (to Dr. Antignac), Association Française contre les Myopathies (ANR-08-GENOPAT-017-01, to Dr. Antignac), Agence Nationale de la Recherche (PodoNet project number ANR-07-E-RARE-011-01 in the ERA-Net Consortium [JTC2007], to Dr. Antignac, and ANR-06-MRAR-024-01, to Dr. Leguern), Fondation pour la Recherche Médicale (project number DMP 2010-11-20-386, to Dr. Antignac, and doctoral funding, to Dr. Boyer), Association des Malades du Syndrome Néphrotique (to Dr. Mollet), Fonds de la Recherche en Santé du Québec (Fellowship Training Award to Dr. Benoit), and Ministerio de Ciencia e Innovación (BFU2009-07886 and CONSOLIDER COAT CSD2009-00016, to Dr. Alonso).

A new type of hereditary glomerulopathy was observed in ten children presenting with early and progressive glomerular symptoms, often associated with hypertension. Light microscopy showed a diffuse increase in the mesangial matrix and generalized widening of the capillary walls. Electron-microscopic examination of renal tissue, after phosphotungstic acid treatment, revealed the presence of fibrillar collagen within the mesangial matrix and the subendothelial aspect of the glomerular basement membrane, adjacent to normal lamina densa. Immunohistochemical studies identified the fibrillar collagen not usually present within the glomerular extracellular matrix as type III collagen. Clinical and family studies ruled out the diagnosis of nail-patella syndrome, an autosomal dominant disorder with typical extrarenal symptoms, which is also characterized by the presence of fibrillar collagen within the glomerular basement membranes. The poor renal outcome, the possible extrarenal haematological and pulmonary involvement and the transmission as an autosomal recessive trait strongly suggest that collagen type III glomerulopathy is a new type of hereditary disease. From the high incidence of superimposed haemolytic uraemic syndrome in patients or their siblings, it may be hypothesized that collagen type III glomerulopathy is the underlying defect in some of the familial cases of haemolytic uraemic syndromes.

Renal tubular dysgenesis (RTD) is a recessive autosomal disease characterized by persistent fetal anuria and perinatal death. During the systematic screening of mutations of the different genes of the renin-angiotensin system associated with RTD, two missense mutations in the renin gene were previously identified, the first affects one of the two catalytic aspartates (D38N) of renin, and the second, S69Y, is located upstream of the 'flap', a mobile β-hairpin structure which covers the substrate-binding site of renin. Here we report a novel renin mutation leading to the duplication of the tyrosine residue Y15dup, homologous to Y9 in some other aspartyl proteases, which seems to play a crucial role along the activation pathway. The biochemical and cellular mechanisms underlying renin inactivation were investigated. We expressed prorenin constructs harboring the identified point mutations in two established cell lines, able (AtT-20 cells) or unable (CHO cells) to process prorenin to renin and we evaluated the cellular localization of renin mutants and their functional properties. All three mutants were misfolded to different levels, were enzymatically inactive and exhibited abnormal intracellular trafficking. We suggest a misfolding of Y15dup renin, a partial misfolding of D38N prorenin and a misfolding of S69Y prorenin leading to complete absence of secretion. The structural consequences of the renin mutations were estimated by molecular modeling, which suggested some important structural alterations. This is the first characterization of the mechanisms underlying loss of renin function in RTD.

Steroid-resistant nephrotic syndrome (NS) remains one of the most intractable causes of end-stage renal disease in the first two decades of life. Several genes have been involved including NPHS1, NPHS2, WT1, PLCE1, and LAMB2. Our aim was to identify causative mutations in these genes, in 24 children belonging to 13 families with NS manifesting with various ages of onset. We performed haplotype analysis and direct exon sequencing of NPHS1, NPHS2, PLCE1, LAMB2, and the relevant exons 8 and 9 of WT1. Ten different pathogenic mutations were detected in seven families concerning four genes (NPHS1 (3/7), LAMB2 (2/7), NPHS2 (1/7), and WT1 (1/7)). Five of the detected mutations were novel; IVS9 + 2 T > C and p.D616G in NPHS1; p.E371fsX16 in NPHS2, and p.E705X and p.D1151fsX23 in LAMB2. Nine of 24 patients failed to be categorized by mutational analysis. Our study extends the spectrum of abnormalities underlying NS, by reporting novel mutations in the NPHS1 and NPHS2 genes and the first cases of LAMB2 mutations in Tunisia. Congenital and infantile NS can be explained by mutations in NPHS1, NPHS2, WT1, or LAMB2 genes. The identification of additional genes mutated in NS can be anticipated.

Summary Membranoproliferative glomerulonephritis type II is a rare renal disease, associated with uncontrolled activation of the complement alternative pathway because of C3 nephritic factor. Abnormalities in factor H have been rarely described in patients with membranoproliferative glomerulonephritis type II. We report the clinical history, molecular defect, and histologic description of 3 patients with factor H deficiency and various types of membranoproliferative glomerulonephritis. The 3 patients presented with severely decreased C3. Circulating factor H was undetectable. Complete factor H deficiency (CFH) was due to homozygous complement factor H mutations in short consesus repeat (SCR) 7, 10, and 11. Age at onset was 1 (patient 1), 17 (patient 2), and 33 years (patient 3). Symptoms at diagnosis included proteinuria of 0.5, 2.4, and 11 g/d, respectively, microhematuria, and normal renal function in all cases. The estimated glomerular filtration rate at last follow-up was 25, 43, and 112 mL/min per 1.73 m 2 , at ages of 29, 24, and 37 years, respectively. Renal biopsies disclosed a membranoproliferative glomerulonephritis type II with atypical discontinuous dense deposits in patient 1; a membranoproliferative glomerulonephritis type I with immunoglobin G (IgG), C1q, and abundant C3 deposits in patient 2; and a membranoproliferative glomerulonephritis with isolated C3 deposits without dense deposits in patient 3. This report of factor H–deficient patients emphasizes the diversity of the histologic lesions associated with factor H deficiencies and the role of the alternative pathway in several subtypes of membranoproliferative glomerulonephritis.

International audience; BACKGROUND: Mutations in the PLCE1 gene encoding phospholipase C epsilon 1 (PLCepsilon1) have been recently described in patients with early onset nephrotic syndrome (NS) and diffuse mesangial sclerosis (DMS). In addition, two cases of PLCE1 mutations associated with focal segmental glomerulosclerosis (FSGS) and later NS onset have been reported. METHOD: In order to better assess the spectrum of phenotypes associated with PLCE1 mutations, mutational analysis was performed in a worldwide cohort of 139 patients (95 familial cases belonging to 68 families and 44 sporadic cases) with steroid resistant NS presenting at a median age of 23.0 months (range 0-373). RESULTS: Homozygous or compound heterozygous mutations were identified in 33% (8/24) of DMS cases. PLCE1 mutations were found in 8% (6/78) of FSGS cases without NPHS2 mutations. Nine were novel mutations. No clear genotype-phenotype correlation was observed, with either truncating or missense mutations detected in both DMS and FSGS, and leading to a similar renal evolution. Surprisingly, three unaffected and unrelated individuals were also found to carry the homozygous mutations identified in their respective families. CONCLUSION: PLCE1 is a major gene of DMS and is mutated in a non-negligible proportion of FSGS cases without NPHS2 mutations. Although additional variants in 19 candidate genes (16 other PLC genes, BRAF,IQGAP1 and NPHS1) were not identified, it is speculated that other modifier genes or environmental factors may play a role in the renal phenotype variability observed in individuals bearing PLCE1 mutations. This observation needs to be considered in the genetic counselling offered to patients.

Mutations in NPHS1, which encodes nephrin, are the main causes of congenital nephrotic syndrome (CNS) in Finnish patients, whereas mutations in NPHS2, which encodes podocin, are typically responsible for childhood-onset steroid-resistant nephrotic syndrome in European populations. Genotype–phenotype correlations are not well understood in non-Finnish patients. We evaluated the clinical presentation, kidney histology, and disease progression in non-Finnish CNS cases by mutational screening in 107 families (117 cases) by sequencing the entire coding regions of NPHS1, NPHS2, PLCE1, WT1, LAMB2, PDSS2, COQ2, and NEPH1. We found that CNS describes a heterogeneous group of disorders in non-Finnish populations. We identified nephrin and podocin mutations in most families and only rarely found mutations in genes implicated in other hereditary forms of NS. In approximately 20% of cases, we could not identify the underlying genetic cause. Consistent with the major role of nephrin at the slit diaphragm, NPHS1 mutations associated with an earlier onset of disease and worse renal outcomes than NPHS2 mutations. Milder cases resulting from mutant NPHS1 had either two mutations in the cytoplasmic tail or two missense mutations in the extracellular domain, including at least one that preserved structure and function. In addition, we extend the spectrum of known NPHS1 mutations by describing long NPHS1 deletions. In summary, these data demonstrate that CNS is not a distinct clinical entity in non-Finnish populations but rather a clinically and genetically heterogeneous group of disorders.

Inherited renal tubular dysgenesis (RTD) is caused by mutations in the genes encoding components of the renin-angiotensin cascade: angiotensinogen, renin, angiotensin-converting enzyme (ACE), and angiotensin ΙΙ receptor type 1. It is characterized by oligohydramnios, prematurity, hypotension, hypocalvaria, and neonatal renal failure. The histological hallmark is the absence or poor development of renal proximal tubules. Except for a few cases, the prognosis has been thought to be universally poor, with patients dying either in utero or shortly after birth. We report a 3-year-old infant diagnosed clinically with RTD. The infant survived the neonatal period after 2 weeks of anuria subsequently subsiding. Hypotension and hyperkalemia normalized eventually with administration of fludrocortisone. A revision of renal tissue obtained from a sibling that died shortly after birth revealed normal glomeruli and distal tubules but no identifiable proximal tubules. A novel mutation in the ACE gene was found in the surviving child, who remains with stage 4 chronic kidney disease and normal neurodevelopment. As the number of surviving cases of RTD increases, it should be emphasized to the parents and the neonatal care team that it may not be universally fatal as previously reported. A trial of fludrocortisone may correct hyperkalemia and hypotension.

Autosomal recessive renal tubular dysgenesis (RTD) is a clinical disorder observed in fetuses, characterized by absence or poor development of proximal tubules and early onset and persistent oligohydramnios leading to the Potter sequence, associated with skull ossification defect. The disease is uniformly severe resulting in low blood pressure and perinatal death in most cases or in chronic renal disease in the few surviving patients. Based on the phenotype and the finding of striking changes in renal renin expression (absent or massive), we hypothesized and demonstrated that genetic defects in the renin-angiotensin system (RAS) components are the underlying causes of the disease. At the present time, molecular screening has been performed in 46 families (F) and homozygous or compound heterozygous mutations have been detected in 41. They affect the genes encoding renine (9F), angiotensinogen (3F), AT1 receptor (3F) and angiotensin converting enzyme (26F). These findings highlight the importance of the RAS during human kidney development. Moreover, the identification of the disease based on precise histological and immunohistological analysis, and the research of the genetic defect, now allow genetic counseling and early prenatal diagnosis.

Background Angiotensin-converting enzyme (ACE; Kininase II; CD143) hydrolyzes small peptides such as angiotensin I, bradykinin, substance P, LH-RH and several others and thus plays a key role in blood pressure regulation and vascular remodeling. Complete absence of ACE in humans leads to renal tubular dysgenesis (RTD), a severe disorder of renal tubule development characterized by persistent fetal anuria and perinatal death. Methodology/Principal Findings Patient with RTD in Lisbon, Portugal, maintained by peritoneal dialysis since birth, was found to have a homozygous substitution of Arg for Glu at position 1069 in the C-terminal domain of ACE (Q1069R) resulting in absence of plasma ACE activity; both parents and a brother who are heterozygous carriers of this mutation had exactly half-normal plasma ACE activity compared to healthy individuals. We hypothesized that the Q1069R substitution impaired ACE trafficking to the cell surface and led to accumulation of catalytically inactive ACE in the cell cytoplasm. CHO cells expressing wild-type (WT) vs. Q1069R-ACE demonstrated the mutant accumulates intracellularly and also that it is significantly degraded by intracellular proteases. Q1069R-ACE retained catalytic and immunological characteristics of WT-ACE N domain whereas it had 10–20% of the nativity of the WT-ACE C domain. A combination of chemical (sodium butyrate) or pharmacological (ACE inhibitor) chaperones with proteasome inhibitors (MG 132 or bortezomib) significantly restored trafficking of Q1069R-ACE to the cell surface and increased ACE activity in the cell culture media 4-fold. Conclusions/Significance Homozygous Q1069R substitution results in an ACE trafficking and processing defect which can be rescued, at least in cell culture, by a combination of chaperones and proteasome inhibitors. Further studies are required to determine whether similar treatment of individuals with this ACE mutation would provide therapeutic benefits such as concentration of primary urine.

Background Bardet–Biedl syndrome (BBS) is a genetically heterogeneous, multisystemic disorder characterised by progressive retinal dystrophy, obesity, hypogenitalism, learning difficulties, renal abnormalities and postaxial polydactyly, with only the last two antenatally observable. BBS is inherited as an autosomal recessive disorder, and 14 genes have been identified to date ( BBS1–BBS14 ). In addition, a complex digenic inheritance has been established in some families. Mutations of the BBS10 gene on chromosome 12q21.2 account for 20% of BBS cases. Methods Given the fact that mutations in BBS genes have already been found in Meckel-like fetuses, and in light of the major contribution of BBS10 to BBS, the BBS10 gene was sequenced in 20 fetal cases and a child diagnosed antenatally presenting with characteristic renal anomalies and polydactyly, but without biliary dysgenesis. Results Recessive mutations were identified at the BBS10 locus in five cases: four fetuses and a child. Interestingly, one of them had situs ambiguus, a rare feature in BBS. In the child, BBS gene screening identified a heterozygous BBS6 nonsense mutation in addition to the homozygous BBS10 mutation, in accordance with the suggested multigenic inheritance of the disease. Conclusions These results confirm that BBS is underdiagnosed antenatally and should systematically be suspected in fetuses with severe cystic kidneys leading to oligoamnios and fetal or perinatal death. Moreover, this study confirms the high frequency of BBS10 mutations, particularly of the p.Cys91LeufsX5 allele, including severe lethal cases.

Background. Cystinosis is caused by mutations in CTNS that encodes cystinosin, the lysosomal cystine transporter. The most severe and frequent form is characterized by a proximal tubulopathy that appears around 6 to 12 months of age. In the absence of treatment, end-stage renal disease is reached by 10 years. Ctns(-/-) mice of a mixed 129Sv x C57BL/6 genetic background show elevated renal cystine levels; however, proximal tubulopathy or end-stage renal disease is not observed. Methods. As renal phenotype can be influenced by genetic background, we generated congenic C57BL/6 and FVB/N Ctns(-/-) mice and assayed renal lesions and function by histological and biochemical studies. Results. C57BL/6 Ctns(-/-) mice showed significantly higher renal cystine levels than the FVB/N strain. Moreover, C57BL/6 mice presented with pronounced histological lesions of the proximal tubules as well as a tubulopathy and progressively developed chronic renal failure. In contrast, renal dysfunction was not observed in the FVB/N strain. Conclusions. Thus, the C57BL/6 strain represents the first Ctns(-/-) mouse model to show clear renal defects. In addition to highlighting the influence of genetic background on phenotype, the C57BL/6 Ctns(-/-) mice represent a useful model for further understanding cystinosin function in the kidney and, specifically, in the proximal tubules.

International audience; Meckel-Gruber syndrome (MKS) is a lethal fetal disorder characterized by diffuse renal cystic dysplasia, polydactyly, a brain malformation that is usually occipital encephalocele, and/or vermian agenesis, with intrahepatic biliary duct proliferation. Joubert syndrome (JBS) is a viable neurological disorder with a characteristic "molar tooth sign" (MTS) on axial images reflecting cerebellar vermian hypoplasia/dysplasia. Both conditions are classified as ciliopathies with an autosomal recessive mode of inheritance. Allelism of MKS and JBS has been reported for TMEM67/MKS3, CEP290/MKS4, and RPGRIP1L/MKS5. Recently, one homozygous splice mutation with a founder effect was reported in the CC2D2A gene in Finnish fetuses with MKS, defining the 6th locus for MKS. Shortly thereafter, CC2D2A mutations were also reported in JBS. The analysis of the CC2D2A gene in our series of MKS fetuses, identified 14 novel truncating mutations in 11 cases. These results confirm the involvement of CC2D2A in MKS and reveal a major contribution of CC2D2A to the disease. We also identified three missense CC2D2A mutations in two JBS cases. Therefore, and in accordance with the data reported regarding RPGRIP1L, our results indicate phenotype-genotype correlations, as missense and presumably hypomorphic mutations lead to JBS while all null alleles lead to MKS.

Introduction. Recurrence of nephrotic-range proteinuria in patients with idiopathic nephrotic syndrome (INS) and focal and segmental glomerulosclerosis (FSGS) on native kidneys is associated with poor graft survival. Identification of risk factors for recurrence is therefore an important issue. In 2004, Columbia University introduced a histological classification of FSGS that identifies five mutually exclusive variants. In non-transplant patients, the Columbia classification appears to predict the outcome and response to treatment better than clinical characteristics alone. However, the predictive value of this classification to assess the risk of recurrence after transplantation has not been addressed. Methods. We retrospectively studied 77 patients with INS and FSGS on native kidneys who underwent renal transplantation. Of these, 42 recipients experienced recurrence of nephrotic range proteinuria. Results. At time of recurrence, minimal-change disease (MCD) was the main histological feature. On serial biopsies, the incidence of MCD decreased over time, while the incidence of FSGS variants increased. The variant type observed in the native kidneys was not predictive of either recurrence or type of FSGS seen on the allograft. Patients with complete and sustained remission did not developed FSGS. Conclusion. In conclusion, the Columbia classification is of no help in predicting recurrence after renal transplantation or histological lesions in the case of recurrence of proteinuria.

Podocin is a critical component of the glomerular slit diaphragm, and genetic mutations lead to both familial and sporadic forms of steroid-resistant nephrotic syndrome. In mice, constitutive absence of podocin leads to rapidly progressive renal disease characterized by mesangiolysis and/or mesangial sclerosis and nephrotic syndrome. Using established Cre-loxP technology, we inactivated podocin in the adult mouse kidney in a podocyte-specific manner. Progressive loss of podocin in the glomerulus recapitulated albuminuria, hypercholesterolemia, hypertension, and renal failure seen in nephrotic syndrome in humans. Lesions of FSGS appeared after 4 wk, with subsequent development of diffuse glomerulosclerosis and tubulointerstitial damage. Interestingly, conditional inactivation of podocin at birth resulted in a gradient of glomerular lesions, including mesangial proliferation, demonstrating a developmental stage dependence of renal histologic patterns of injury. The development of significant albuminuria in this model occurred only after early and focal foot process effacement had progressed to diffuse involvement, with complete absence of podocin immunolabeling at the slit diaphragm. Finally, we identified novel potential mediators and perturbed molecular pathways, including cellular proliferation, in the course of progression of renal disease leading to glomerulosclerosis, using global gene expression profiling.

Alport syndrome is a hereditary, progressive, hematuric nephropathy characterized by glomerular basement membrane abnormalities with frequent hearing defects and ocular anomalies. The disease is associated with mutations in genes encoding the alpha3, alpha4, or alpha5 chains of type IV collagen, COL4A3, or COL4A4 in the autosomal forms of the disease, COL4A5 in the more frequent X-linked variety. Ultrastructural changes in the glomerular basement membrane and frequent abnormal expression of type IV collagen chains in renal and skin basement membranes are crucial elements for the diagnosis of Alport syndrome, determination of the mode of inheritance, and genetic counseling. Animal models have provided invaluable tools to study the mechanisms leading to progressive deterioration of the glomerular basement membrane and ultimately to renal failure, and to evaluate benefits of potential targeted therapies.

Mutations in the NPHS2 gene, which encodes podocin, are responsible for some cases of sporadic and familial autosomal recessive steroid-resistant nephrotic syndrome. Inter- and intrafamilial variability in the progression of renal disease among patients bearing NPHS2 mutations suggests a potential role for modifier genes. Using a mouse model in which the podocin gene is constitutively inactivated, we sought to identify genetic determinants of the development and progression of renal disease as a result of the nephrotic syndrome. We report that the evolution of renal disease as a result of nephrotic syndrome in Nphs2-null mice depends on genetic background. Furthermore, the maternal environment significantly interacts with genetic determinants to modify survival and progression of renal disease. Quantitative trait locus mapping suggested that these genetic determinants may be encoded for by genes on the distal end of chromosome 3, which are linked to proteinuria, and on the distal end of chromosome 7, which are linked to a composite trait of urea, creatinine, and potassium. These loci demonstrate epistatic interactions with other chromosomal regions, highlighting the complex genetics of renal disease progression. In summary, constitutive inactivation of podocin models the complex interactions between maternal and genetically determined factors on the progression of renal disease as a result of nephrotic syndrome in mice.

Over a 22-year period, eight patients affected with severe systemic or polyarticular juvenile chronic arthritis (JCA) developed systemic amyloidosis with nephrotic syndrome. They were treated with chlorambucil over 5-192 months (mean = 44 months). With treatment, an abrupt decrease in the severity of JCA was observed in six patients but two patients were chlorambucil resistant. After a mean follow-up period of 10 years from onset of renal symptoms, one chlorambucil-resistant patient died of end-stage renal failure; two patients have a persistent nephrotic syndrome; and five patients are free from proteinuria, of whom one has developed hypertension. A good correlation was observed between the response of the rheumatic disease to chlorambucil treatment and the clinical course of renal symptoms. Fourteen renal biopsies were performed in these eight patients. In all, amyloid deposits were of the AA type, which persisted on repeat biopsies. In addition, 15%-60% of glomeruli had become globally sclerotic by the second or third biopsies. At the ultrastructural level, modifications in the structure of amyloid deposits and reparative changes of the glomeruli, characterized by partial restoration of glomerular architecture, were observed in three patients with a favourable clinical course.

The hyperimmunoglobulinemia D syndrome (HIDS) is a well-defined entity resembling familial Mediterranean fever. HIDS is a systemic inflammatory disease associated with stimulation of T-cell-mediated immunity. These patients are at low risk for amyloidosis and are not known to develop nephropathy. We report a boy of Mediterranean ancestry who exhibited typical HIDS and end-stage renal failure. Kidney biopsy revealed pauci-immune crescentic glomerulonephritis (cGN). We hypothesized that the glomerular involvement was secondary to the cytokine network activation observed in HIDS. Thus, cGN should be considered as part of the syndrome, and kidney biopsy should be performed early in the course of the renal disease in patients with HIDS.

Alport syndrome is an inherited disorder characterized by progressive hematuric nephritis with structural defects of the glomerular basement membrane, and sensorineural deafness. Ocular abnormalities are frequently associated. The incidence is approximatively 1/5000. The renal disease is severe in male patients and should be responsible for 2% of end-stage renal failure. Alport syndrome is heterogeneous at the clinical and genetic levels. It occurs as a consequence of structural abnormalities in type IV collagen, the major constituent of basement membranes. Six genetically distinct chains of type IV collagen have been identified. Mutations in the COL4A5 gene located at Xq22, and encoding the alpha 5(IV) chain are responsible for X-linked Alport syndrome whereas COL4A3 or COL4A4 located "head to head" on chromosome 2 are involved in the rarer autosomal forms of the disease.

Renal tubular dysgenesis (RTD) is a clinical disorder either acquired during fetal development or inherited as an autosomal recessive condition. Inherited RTD is caused by mutations in the genes encoding the components of the renin-angiotensin system angiotensinogen, renin, angiotensin-converting enzyme and angiotensin II receptor type 1. Inherited RTD is characterized by early onset oligohydramnios, skull ossification defects, preterm birth and neonatal pulmonary and renal failure. The histological hallmark is the absence or poor development of proximal tubules. So far, all patients died either in utero or shortly after birth. We report the first patients with inherited RTD surviving the neonatal period and still being alive. Genetic and functional analysis of the renin-angiotensin system contributes to the diagnosis of RTD. In conclusion, the clinical diagnosis of inherited RTD is easily missed after birth without renal biopsy or information on affected family members. Genetic and functional analysis of the renin-angiotensin system contributes to correct diagnosis.

Joubert syndrome (JS) is an autosomal recessive disorder characterized by cerebellar vermis hypoplasia associated with hypotonia, developmental delay, abnormal respiratory patterns, and abnormal eye movements. The association of retinal dystrophy and renal anomalies defines JS type B. JS is a genetically heterogeneous condition with mutations in two genes, AHI1 and CEP290, identified to date. In addition, NPHP1 deletions identical to those that cause juvenile nephronophthisis have been identified in a subset of patients with a mild form of cerebellar and brainstem anomaly. Occipital encephalocele and/or polydactyly have occasionally been reported in some patients with JS, and these phenotypic features can also be observed in Meckel-Gruber syndrome (MKS). MKS is a rare, autosomal recessive lethal condition characterized by central nervous system malformations (typically, occipital meningoencephalocele), postaxial polydactyly, multicystic kidney dysplasia, and ductal proliferation in the portal area of the liver. Since there is obvious phenotypic overlap between JS and MKS, we hypothesized that mutations in the recently identified MKS genes, MKS1 on chromosome 17q and MKS3 on 8q, may be a cause of JS. After mutation analysis of MKS1 and MKS3 in a series of patients with JS (n=22), we identified MKS3 mutations in four patients with JS, thus defining MKS3 as the sixth JS locus (JBTS6). No MKS1 mutations were identified in this series, suggesting that the allelism is restricted to MKS3.

Background Wilms tumor, aniridia, genitourinary anomalies, and mental retardation (WAGR) syndrome is a genetic disorder caused by a deletion of band 11p13, which results in the loss of 1 allele of the Wilms tumor suppressor gene (WT1). It is not classically associated with nephropathies, but increased rates of renal failure are reported. Denys-Drash syndrome (DDS), caused by mutations in the WT1 gene affecting the third or second zinc finger, is characterized by a triad of glomerulopathy progressing rapidly to end-stage renal disease, male hermaphroditism, and Wilms tumor. In patients with DDS, small glomeruli were observed. Methods We reviewed histological findings of nontumoral kidney samples of 7 patients with WAGR syndrome at the time of tumor surgery. Results Median glomerular diameter was 110 ± 37 μm in patients with WAGR syndrome versus 125 ± 18.5 μm in controls ( P Conclusion The presence of small glomeruli in patients with WAGR syndrome, as in those with DDS, suggests a specific defect of WT1 function in development and a specific role of WT1 allele loss in the development of renal failure in these patients.

Alport syndrome (AS) is a hereditary disorder of type IV collagen characterized by the association of progressive hematuric nephritis and sensorineural hearing loss. An increase in proteinuria is linked with progressive renal failure. Preliminary data have shown that cyclosporin therapy reduces proteinuria, thereby suggesting that it may also slow the progression of AS nephropathy. We treated nine AS patients manifesting proteinuria1 g/m(2)/day and a glomerular filtration rate (GFR)50 ml/min/1.73 m(2) with cyclosporin for at least 6 months. At the end of this 6-month period, mean proteinuria had decreased from 2+/-1.06 to 0.65+/-0.73 g/day, and mean albuminemia had increased from 29+/-5.2 to 35+/-6.5 g/l. Mean inulin clearance had decreased from 102+/-29 to 74+/-16.3 ml/min/1.73 m(2). Cyclosporin treatment was stopped in four patients because of inefficacy or adverse effects and continued in the remaining five patients for an additional 14-42 months. At the end of this second treatment period, control renal biopsies revealed significant lesions of cyclosporin nephrotoxicity in three patients. Based on these results we conclude that while cyclosporin therapy can decrease proteinuria in most patients with AS, it may be associated with nephrotoxicity, thereby precluding its long-term use.

Background. Renal dysfunction is a major complication in heart transplant recipients treated with calcineurin inhibitors. The goal of the study was to investigate the effect of a reduction of calcineurin inhibitor dosage with the concomitant introduction of mycophenolate mofetil on both renal function and cardiac allograft function. Methods. Fourteen of 52 consecutive pediatric cardiac allograft recipients experienced a progressive decrease of renal function. A renal biopsy was performed before the dose of calcineurin inhibitors was reduced by 50% and azathioprine was replaced by mycophenolate mofetil. Renal function was evaluated by inulin clearance and maximal urinary osmo-lality before and yearly after the therapeutic changes. Acute rejection was monitored clinically, by echocardiography and endomyocardial biopsies. Results. Inulin clearance in the fourteen children decreased from 84.2 mL/min/1.73 m 2 at one year posttransplantation to 46.5±9.6 mL/min/1.73 m 2 at the time of the change in immunosuppressive therapy. Significant renal lesions were observed in the renal biopsies performed before the change. At 1 year, inulin clearance had increased by 67%. In six patients who had a second determination 2 years after the switch, inulin clearance was not significantly different from the value at 1 year. There were three reversible acute rejection episodes in three patients. The incidence of rejection episodes was not different from a control group of patients whose treatment was not changed. Conclusion. The reduction of calcineurin inhibitor dosage and replacement of azathioprine by mycophenolate mofetil is a safe way to improve renal function in children with heart transplants and calcineurin inhibitor induced nephrotoxicity.

Autosomal recessive polycystic kidney disease (ARPKD; MIM 263200) is an important childhood nephropathy, occurring in 1 in 20 000 live births.1 The clinical phenotype is dominated by dilatation of the renal collecting ducts, biliary dysgenesis, and portal tract fibrosis. Affected children often present in utero with enlarged, echogenic kidneys, as well as oligohydramnios secondary to poor urine output. Approximately 30% of affected neonates die shortly after birth as a result of severe pulmonary hypoplasia and secondary respiratory insufficiency. Those who survive the perinatal period express widely variable disease phenotypes with systemic hypertension, renal insufficiency, and portal hypertension due to portal tract fibrosis as the most common clinical features.2 Linkage analysis indicates that mutations in a single locus on chromosome 6p12 are responsible for all typical forms of ARPKD.3,4 Two groups working independently have identified PKHD1 (MIM 606702) as the locus responsible for ARPKD and have demonstrated that this novel gene is among the largest in the human genome, extending over at least 470 kb and including a minimum of 86 exons.5,6 Both PKHD1 and its mouse orthologue ( Pkhd1 ) encode a complex and extensive array of splice variants, with most abundant transcriptional expression in fetal and adult kidney and weaker expression in other tissues including liver and pancreas.5,7 The longest PKHD1 transcript includes 67 exons with an open reading frame (ORF) composed of 66 exons that encode a 4074 amino acid protein, polyductin/fibrocystin.5,6 The full length protein is predicted to have several immunoglobulin-like, plexin, transcription factor (IPT) domains and multiple parallel beta-helix 1 (PbH1) repeats in its approximately 3860 amino acid extracellular amino terminus; a single transmembrane (TM) spanning domain; and a short, cytoplasmic carboxyl terminus with potential phosphorylation sites. Alternatively spliced transcripts are predicted to fall into two broad groups. …

We report in this paper two siblings aged 8 and 17 months who were clinically diagnosed with familial steroid-resistant nephrotic syndrome (SRNS). By mutation screening of the NPHS2 gene, a homozygous missense mutation, P118L, was detected in both children. This study is the first systematic investigation of NPHS2 gene mutations in Turkish children with familial SRNS. If this mutation is a hot spot of mutation in the Turkish population, screening this novel mutation in Turkish children with SRNS may be of great clinical use to prevent unnecessary treatment modalities, provide accurate genetic counselling and predict the prognosis of the disease.