Lutz T. Weber

Mutations in Multiple PKD Genes May Explain Early and Severe Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is typically a late-onset disease caused by mutations in PKD1 or PKD2, but about 2% of patients with ADPKD show an early and severe phenotype that can be clinically indistinguishable from autosomal recessive polycystic kidney disease (ARPKD). The high recurrence risk in pedigrees with early and severe PKD strongly suggests a common familial modifying background, but the mechanisms underlying the extensive phenotypic variability observed among affected family members remain unknown. Here, we describe severely affected patients with PKD who carry, in addition to their expected familial germ-line defect, additional mutations in PKD genes, including HNF-1β, which likely aggravate the phenotype. Our findings are consistent with a common pathogenesis and dosage theory for PKD and may propose a general concept for the modification of disease expression in other so-called monogenic disorders.

Long-term follow-up after rituximab for steroid-dependent idiopathic nephrotic syndrome

BACKGROUNDnIn patients with refractory steroid-sensitive nephrotic syndrome (SSNS), treatment with rituximab has shown encouraging results; however, long-term follow-up data are not available.nnnMETHODSnWe performed a retrospective analysis of 37 patients (25 boys) with steroid-dependent nephrotic syndrome who were treated with rituximab (375 mg/m(2) given weekly for one to four courses). Long-term follow-up data (>2 years, median 36, range 24-92.8 months) are available for 29 patients (12 boys).nnnRESULTSnTwenty-six of 37 (70.3%) patients remained in remission after 12 months. Relapses occurred in 24 (64.8%) patients after a median of 9.6 (range 5.2-64.1) months. Time to first relapse was significantly shorter in patients receiving one or two compared to three or four initial infusions. In the 29 patients with long-term follow-up for >2 years, 12 (41%) patients remained in remission after the initial rituximab course for >24 months, 7 (24.1%) patients without further maintenance immunosuppression. Nineteen children received two to four repeated courses of rituximab increasing the total number of patients with long-term remission to 20 (69%), remission including 14 (48%) patients off immunosuppression. The proportion of patients with long-term remission was not related to the number of initial rituximab applications. No serious side effects were noted.nnnCONCLUSIONnRituximab is an effective treatment option in the short- and long-term control of treatment refractory SSNS. Further controlled studies are needed to address optimal patient selection, dose and safety of rituximab infusions.

Rapid Response to Cyclosporin A and Favorable Renal Outcome in Nongenetic Versus Genetic Steroid–Resistant Nephrotic Syndrome

BACKGROUND AND OBJECTIVESnTreatment of congenital nephrotic syndrome (CNS) and steroid-resistant nephrotic syndrome (SRNS) is demanding, and renal prognosis is poor. Numerous causative gene mutations have been identified in SRNS that affect the renal podocyte. In the era of high-throughput sequencing techniques, patients with nongenetic SRNS frequently escape the scientific interest. We here present the long-term data of the German CNS/SRNS Follow-Up Study, focusing on the response to cyclosporin A (CsA) in patients with nongenetic versus genetic disease.nnnDESIGN, SETTING, PARTICIPANTS, & MEASUREMENTSnCross-sectional and longitudinal clinical data were collected from 231 patients with CNS/SRNS treated at eight university pediatric nephrology units with a median observation time of 113 months (interquartile range, 50-178). Genotyping was performed systematically in all patients.nnnRESULTSnThe overall mutation detection rate was high at 57% (97% in CNS and 41% in SRNS); 85% of all mutations were identified by the analysis of three single genes only (NPHS1, NPHS2, and WT1), accounting for 92% of all mutations in patients with CNS and 79% of all mutations in patients with SRNS. Remission of the disease in nongenetic SRNS was observed in 78% of patients after a median treatment period of 2.5 months; 82% of nongenetic patients responded within 6 months of therapy, and 98% of patients with nongenetic SRNS and CsA-induced complete remission (normalbuminemia and no proteinuria) maintained a normal renal function. Genetic SRNS, on the contrary, is associated with a high rate of ESRD in 66% of patients. Only 3% of patients with genetic SRNS experienced a complete remission and 16% of patients with genetic SRNS experienced a partial remission after CsA therapy.nnnCONCLUSIONSnThe efficacy of CsA is high in nonhereditary SRNS, with an excellent prognosis of renal function in the large majority of patients. CsA should be given for a minimum period of 6 months in these patients with nongenetic SRNS. In genetic SRNS, response to CsA was low and restricted to exceptional patients.

Mycophenolate mofetil suspension in pediatric renal transplantation: three-year data from the tricontinental trial.

Abstract:u2002 Mycophenolate mofetil (MMF) is widely used to prevent acute rejection in adult solid organ transplant recipients, but data in children and adolescents are scarce. This prospective, multicenter, open‐labeled, single‐arm study investigated the efficacy and safety of an MMF‐based immunosuppressive regimen in 100 pediatric renal transplant recipients over a 3‐yr period of time. Three age groups were formed (<6u2003yr, nu2003=u200333; 6 to <12u2003yr, nu2003=u200334; 12–18u2003yr, nu2003=u200333). Basic immunosuppression consisted of MMF (600u2003mg/m2 b.i.d), cyclosporin A microemulsion and corticosteroids. Seventy‐three percent of patients were given anti‐lymphocyte antibody induction therapy, of whom 74% received anti‐thymocyte globulin. Patient and graft survival 3u2003yr after transplantation amounted to 98 and 95%, respectively. Twenty‐five percent of all patients suffered a biopsy‐proven acute rejection episode in the first 6u2003month post‐transplant. Children undergoing induction therapy exhibited a numerically lower rejection rate (21 vs. 37%, pu2003=u20030.11). Three years after transplantation, the acute rejection rate added up to 30% (26% with induction therapy vs. 41% without induction therapy, pu2003=u20030.21). The number of patients with acute rejection was lowest in the youngest age group (18%), in comparison with 39% in the 6 to <12u2003yr and 33% in the 12–18u2003yr age group, respectively. For the entire patient population, the rate of patients who withdrew prematurely because of adverse events was low (12%). The present study shows that MMF therapy in pediatric renal transplant recipients leads to an excellent patient and graft survival 3u2003yr post‐transplant with an acceptable safety profile.

Steroid withdrawal in pediatric and adult renal transplant recipients.

Corticosteroids are still a cornerstone in the immunosuppressive regimen in pediatric renal transplant recipients despite their numerous side effects, such as inhibition of longitudinal growth, body disfigurement, arterial hypertension, cardiovascular complications, osteopathy, and others. Previous attempts to spare steroids in cyclosporine (CsA)-based protocols have been associated with an increased risk for acute rejection episodes. The recent introduction of more-potent immunosuppressive medications, such as mycophenolate mofetil (MMF), have, however, renewed interest in steroid-sparing protocols to avoid or ameliorate steroid-associated side effects. Recent studies in Caucasian adult renal transplant recipients receiving CsA and MMF have shown a beneficial effect of late (≥6xa0months post transplant) steroid withdrawal on steroid-associated side effects without the burden of an increased rate of acute rejection episodes. These favorable results compared with previous reports in patients on CsA and azathioprine (AZA) can be ascribed to the higher immunosuppressive potency of MMF compared with AZA. We have shown in a retrospective case control study in 40 pediatric renal transplant recipients that late steroid withdrawal is safe and successful in stable patients under an immunosuppressive maintenance therapy with CsA and MMF. The Mid-European Study Group on Pediatric Renal Transplantation and the Arbeitsgemeinschaft für Pädiatrische Nephrologie are currently performing a prospective randomized trial to validate these observations.

SRL-based immunosuppression vs. CNI minimization in pediatric renal transplant recipients with chronic CNI nephrotoxicity

Abstract:u2002 Because calcineurin inhibitor (CNI)‐induced nephrotoxicity contributes significantly to late renal allograft loss, sirolimus (SRL)‐based, CNI‐free maintenance immunosuppression has been advocated, but data in the pediatric population are scarce. We therefore analyzed the efficacy and safety of an SRL‐based immunosuppressive regimen plus mycophenolate mofetil (MMF) and corticosteroids vs. CNI minimization (mean dose reduction by 39%) plus MMF and corticosteroids in 19 pediatric recipients with biopsy‐proven CNI‐induced nephrotoxicity in a single‐center case–control study. In the SRL group, we observed, oneu2003yr after study entry, an improvement of glomerular filtration rate (GFR) by 10.3u2003±u20033.0u2003mL/min/1.73u2003m2 (pu2003<u20030.05 vs. baseline) in seven of 10 patients and a stabilization in the remaining three, while in the CNI minimization group GFR improved by 17.7u2003±u20037.1u2003mL/min/1.73u2003m2 (pu2003<u20030.05) in six of nine recipients and stabilized in the remaining three. No patient in either group experienced an acute rejection episode. The main adverse event under SRL therapy was a transient hyperlipidemia in 70% of patients. In pediatric renal transplant recipients with declining graft function because of CNI‐induced nephrotoxicity, CNI withdrawal and switch to SRL‐based therapy or CNI minimization are associated with a comparable improvement of GFR after 12u2003months of observation.

Novel heterozygous COL4A3 mutation in a family with late-onset ESRD

Thin basement membrane nephropathy (TBMN) and Alport syndrome (ATS) are genetically heterogeneous conditions characterized by structural abnormalities in the glomerular basement membrane (GBM). TBMN presents with hematuria, minimal proteinuria, and normal renal function. Although TBMN is an autosomal dominant disease (COL4A3 and COL4A4), ATS can be inherited X-linked (COL4A5), autosomal recessive, or autosomal dominant (both COL4A3 and COL4A4). The clinical course of TBMN is usually benign, whereas ATS typically results in end-stage renal disease (ESRD). Nevertheless, there is a broad spectrum of clinical phenotypes caused by mutations in COL4A3 or COL4A4. We report an Italian family who presented with hematuria and mild proteinuria. Mutational analysis showed a novel heterozygous mutation p.G291E in exon 15 of the COL4A3 gene. Many different mutations in COL4A3 and COL4A4 that cause TBMN have already been identified, but most genetic variability in these genes has been found to cause autosomal ATS. A valid genotype–phenotype correlation for TBMN or ATS is not yet known. Therefore, it is important to identify new mutations by direct sequencing to clarify their clinical importance, to assess the prognosis of the disease, and to avoid renal biopsy.

C2 monitoring and absorption profiling of cyclosporine for optimization of immunosuppressive therapy in pediatric renal transplant recipients.

THE ABSORPTION phase of cyclosporine (CyA) (AUC0–4), that generally includes the maximal concentration (Cmax), is the period that displays the most pronounced intraand interindividual variability because it is characterized by rapid changes in whole blood concentrations. This variability is due among other reasons to different gastrointestinal absorption properties among patients. The absorption profile correlates better than trough levels with the immunosuppressive activity of CyA, measured by the suppression of intracellular calcineurin activity and maximum inhibition of IL-2 production. In adult patients, a single concentration taken 2 hours after CyA administration (C2) seems to be the best single pharmacokinetic parameter to predict AUC0–4. 3 In adult renal transplant recipients, immunosuppressive therapy with CyA may be optimized by absorption profiling or C2 monitoring. Comparable data for pediatric patients are lacking. We therefore investigated prospectively the pharmacokinetics of CyA microemulsion in pediatric renal transplant recipients over the first 6 months after grafting. The aims of the study were to assess whether there is association of the absorption profile of CyA (AUC0–4) with the drug’s immunosuppressive activity reflected by the incidence of acute rejection episodes (ARE); and whether the C2 level is a good parameter to predict AUC0–4 values in a cohort of pediatric renal transplant recipients.

Identification of 47 novel mutations in patients with Alport syndrome and thin basement membrane nephropathy.

BackgroundAlport syndrome (ATS) is a progressive hereditary nephropathy characterized by hematuria and proteinuria. It can be associated with extrarenal manifestations. In contrast, thin basement membrane nephropathy (TBMN) is characterized by microscopic hematuria, is largely asymptomatic, and is rarely associated with proteinuria and end-stage renal disease. Mutations have been identified in the COL4A5 gene in ATS and in the COL4A3 and COL4A4 genes in ATS and TBMN. To date, more than 1000 different mutations in COL4A5, COL4A3, and COL4A4 are known.MethodsIn this study mutational analysis by exon sequencing and multiplex ligation-dependent probe amplification was performed in a large European cohort of families with ATS and TBMN.ResultsMolecular diagnostic testing of 216 individuals led to the detection of 47 novel mutations, thereby expanding the spectrum of known mutations causing ATS and TBMN by up to 10 and 6xa0%, respectively, depending on the database. Remarkably, a high number of ATS patients with only single mutations in COL4A3 and COL4A4 were identified. Additionally, three ATS patients presented with synonymous sequence variants that possible affect correct mRNA splicing, as suggested by in silico analysis.ConclusionsThe results of this study clearly broaden the genotypic spectrum of known mutations for ATS and TBMN, which will in turn now facilitate future studies into genotype–phenotype correlations. Further studies should also examine the significance of single heterozygous mutations in COL4A3 and COL4A4 and of synonymous sequence variants associated with ATS.

Discontinuation of Eculizumab in a Patient With Atypical Hemolytic Uremic Syndrome Due to a Mutation in CFH

To the Editor: Dr Ardissino and colleagues recently reported on 16 patients with atypical hemolytic uremic syndrome (aHUS) who discontinued eculizumab treatment: 5 patients experienced relapse and 11 patients remained in stable remission. None of the patients in remission had a mutation in CFH, the gene encoding complement factor H, while 3 of the 5 patients with relapse harbored a CFH mutation. In light of these data, the authors discouraged discontinuation of eculizumab therapy in patients with CFH mutations. In another recent publication, Wetzels et al reported 3 patients with aHUS due to CFH mutations and discontinuation of eculizumab, with 1 patient experiencing relapse. The authors hypothesized that the location of the mutation within CFH might be critical and that patients with mutations in short consensus repeat (SCR) 19 and 20 of the gene are more prone to relapse. We describe a young girl presenting with aHUS at the age of 21 months who was treated with 2 doses of eculizumab (Fig 1). Genetic analysis revealed a novel heterozygous mutation in SCR19 of CFH that is predicted to produce a truncated protein due to the introduction of a premature stop codon at amino acid 1155 (p.Gly1155*). Segregation analysis revealed that this mutation was also present in the child’s healthy mother. Eculizumab therapy was discontinued after 4 weeks, and the child has been in stable remission for 15 months. This case illustrates that it might be possible to discontinue eculizumab therapy in patients with mutations in the carboxyterminal portion of CFH if regular monitoring and careful