Albert Bensman

Renal Phenotypes Related to Hepatocyte Nuclear Factor-1β (TCF2) Mutations in a Pediatric Cohort

The hepatocyte nuclear factor-1beta encoded by the TCF2 gene plays a role for the specific regulation of gene expression in various tissues such as liver, kidney, intestine, and pancreatic islets and is involved in the embryonic development of these organs. TCF2 mutations are known to be responsible for the maturity-onset diabetes of the young type 5 associated with renal manifestations. Several observations have suggested that TCF2 mutations may be involved in restricted renal phenotypes. Eighty children (median age at diagnosis 0.2 yr) with renal cysts, hyperechogenicity, hypoplasia, or single kidneys were studied. Quantitative multiplex PCR amplification of short fluorescence fragments for the search of large genomic rearrangements and sequencing for the detection of point mutations were performed. TCF2 anomalies were detected in one third of patients (25 of 80). The main alteration was the complete deletion of the TCF2 gene detected in 16 patients. Family screening revealed de novo TCF2 anomalies in nine of 17 probands with a high prevalence of deletions (seven of nine). TCF2 anomalies were associated with bilateral renal anomalies (P < 0.001) and bilateral cortical cysts (P < 0.001). However, abnormal renal function, detected in 40% of patients, was independent of the TCF2 genotype. No difference in renal function or severity of renal morphologic lesions was observed between patients with a TCF2 deletion and those with point mutations. In conclusion, TCF2 molecular anomalies are involved in restricted renal phenotype in childhood without alteration of glucose metabolism. These findings have important implications in the diagnosis of patients with renal dysplasia with cysts and their follow-up.

Phenotype–genotype correlation in antenatal and neonatal variants of Bartter syndrome

BACKGROUND Ante/neonatal Bartter syndrome (BS) is a hereditary salt-losing tubulopathy due to mutations in genes encoding proteins involved in NaCl reabsorption in the thick ascending limb of Henles loop. Our aim was to study the frequency, clinical characteristics and outcome of each genetic subtype. METHODS Charts of 42 children with mutations in KCNJ1 (n = 19), SLC12A1 (n = 13) CLCNKB (n = 6) or BSND (n = 4) were retrospectively analysed. The median follow-up was 8.3 [0.4-18.0] years. RESULTS We describe 24 new mutations: 10 in KCNJ1, 11 in SLC12A1 and 3 in CLCNKB. The onset of polyhydramnios, birth term, height and weight were similar for all groups; three patients had no history of polyhydramnios or premature birth and had CLCNKB mutations according to a less severe renal sodium wasting. Contrasting with these data, patients with CLCNKB had the lowest potassium (P = 0.006 versus KCNJ1 and P = 0.034 versus SLC12A1) and chloride plasma concentrations (P = 0.039 versus KCNJ1 and P = 0.024 versus SLC12A1) and the highest bicarbonataemia (P = 0.026 versus KCNJ1 and P = 0.014 versus SLC12A1). Deafness at diagnosis was constant in patients with BSND mutations; transient neonatal hyperkalaemia was present in two-thirds of the children with KCNJ1 mutations. Nephrocalcinosis was constant in KCNJ1 and SLC12A1 but not in BSND and CLCNKB patients. In most cases, water/electrolyte supplementation + indomethacin led to catch-up growth. Three patients developed chronic renal failure: one with KCNJ1 mutations during the second decade of age and two with CLCNKB and BSND mutations and without nephrocalcinosis during the first year of life. CONCLUSIONS We confirmed in a large cohort of ante/ neonatal BS that deafness, transient hyperkalaemia and severe hypokalaemic hypochloraemic alkalosis orientate molecular investigations to BSND, KCNJ1 and CLCNKB genes, respectively. Chronic renal failure is a rare event, associated in this cohort with three genotypes and not always associated with nephrocalcinosis.

Truncation of C-mip (Tc-mip), a new proximal signaling protein, induces c-maf Th2 transcription factor and cytoskeleton reorganization.

Several arguments suggest that minimal change nephrotic syndrome (MCNS) results from yet unknown systemic disorder of T cell function. By screening a cDNA library from T cell relapse, we identified a new pleckstrin homology (PH) domain-containing protein encoded by a gene located on chromosome 16q24. Two alternative transcripts were identified. The first species (c-mip) was expressed in fetal liver, kidney, and peripheral blood mononuclear cells (PBMCs), but weakly detected in PBMCs from MCNS patients. The second form (Tc-mip, standing for truncated c-maf inducing protein), corresponds to subtracted transcript and lacks the NH2-terminal PH domain. The expression of Tc-mip was restricted to fetal liver, thymus, and MCNS PBMCs where it was specifically recruited in CD4+ T cells subset. Overexpression of Tc-mip in T cell Jurkat induced c-maf, transactivated the interleukin 4 gene and down-regulated the interferon γ expression, characteristic of a Th2 commitment. Moreover, the overexpression of Tc-mip induced Src phosphorylation, T cell clustering, and a cellular redistribution of the cytoskeleton-associated L-plastin, by a PI3 kinase independent pathway. Tc-mip represents therefore the first identified protein, which links proximal signaling to c-maf induction.

Microsurgical creation and follow-up of arteriovenous fistulae for chronic haemodialysis in children

Three hundred and eighty children underwent 434 angioaccesses. Of these angioaccesses, 113 were constructed in 74 children weighing under 10 kg. Most accesses (n=340) were distal arteriovenous fistulae (AVF). After microsurgery there was a 96% immediate patency. Seventy percent of AVF, excluding distal ulnarbasilic AVF, were functional, sometimes after secondary superficialization of the vein. Eighty-five per cent of the distal radial-cephalic AVF are still patent after 2 years, 60% are still patent after 4 years. These radial-cephalic AVF required 65 repeat anastomoses, and 12 ligations of the proximal-radial artery in order to reduce to 50% the high blood flow (pre-reduction average index = 900 ml/min per m2). The patency rate of arteriovenousbridge grafts was not encouraging. The severity of stenoses in the proximal-venous trunks, sometimes related to previous catheterization, is emphasized. Advantages of the radial-cephalic wrist AVF in children are highlighted.

Phenotype and Genotype Characterization of Adenine Phosphoribosyltransferase Deficiency

Adenine phosphoribosyltransferase (APRT) deficiency is a rare autosomal recessive disorder causing 2,8-dihydroxyadenine stones and renal failure secondary to intratubular crystalline precipitation. Little is known regarding the clinical presentation of APRT deficiency, especially in the white population. We retrospectively reviewed all 53 cases of APRT deficiency (from 43 families) identified at a single institution between 1978 and 2009. The median age at diagnosis was 36.3 years (range 0.5 to 78.0 years). In many patients, a several-year delay separated the onset of symptoms and diagnosis. Of the 40 patients from 33 families with full clinical data available, 14 (35%) had decreased renal function at diagnosis. Diagnosis occurred in six (15%) patients after reaching ESRD, with five diagnoses made at the time of disease recurrence in a renal allograft. Eight (20%) patients reached ESRD during a median follow-up of 74 months. Thirty-one families underwent APRT sequencing, which identified 54 (87%) mutant alleles on the 62 chromosomes analyzed. We identified 18 distinct mutations. A single T insertion in a splice donor site in intron 4 (IVS4 + 2insT), which produces a truncated protein, accounted for 40.3% of the mutations. We detected the IVS4 + 2insT mutation in two (0.98%) of 204 chromosomes of healthy newborns. This report, which is the largest published series of APRT deficiency to date, highlights the underdiagnosis and potential severity of this disease. Early diagnosis is crucial for initiation of effective treatment with allopurinol and for prevention of renal complications.

Population Pharmacokinetics and Pharmacogenetics of Mycophenolic Acid Following Administration of Mycophenolate Mofetil in De Novo Pediatric Renal‐Transplant Patients

The objective was to develop a population pharmacokinetic‐pharmacogenetic model of mycophenolic acid following administration of mycophenolate mofetil (MMF) in de novo pediatric renal‐transplant patients and identify factors that explain variability. The pharmacokinetic samples were collected from 89 de novo pediatric renal‐transplant patients treated with MMF and studied during the first 60 postoperative days. All patients were genotyped for UGT1A8–A9, UGT2B7, and ABCC2. Population pharmacokinetic analysis was performed with the NONMEM and was validated using bootstrap visual predictive check. The pharmacokinetic data were best described by a 2‐compartment model with Erlang distribution to describe the absorption phase. The covariate analysis identified body weight as an individual factor influencing central volume of distribution and concomitant immunosuppressive medication and identified body weight and UGT2B7 802C>T genotype as individual factors influencing apparent oral clearance (CL/F) of MMF. CL/F in cyclosporine‐MMF‐treated patients was 33% higher than in tacrolimus‐MMF‐treated patients. The CL/F was significantly lower in patients with UGT2B7 802 C/C genotype compared with patients with UGT2B7 802 C/T and 802T/T genotypes, and this effect was independent of concomitant immunosuppressive medication or body weight. The population pharmacokinetic‐pharmacogenetic model of mycophenolic acid was validated. Body weight, concomitant medication, and UGT2B7 genotype contribute significantly to the interindividual variability of MMF disposition in pediatric renal‐transplant patients.

NF-κB p65 Antagonizes IL-4 Induction by c-maf in Minimal Change Nephrotic Syndrome

Mechanisms underlying the pathophysiology of minimal change nephrotic syndrome (MCNS), the most frequent of glomerular diseases in children, remain elusive, although recent arguments suggest that T cell dysfunction may be involved in the pathogenesis of this disease. Recently, we reported that activated T cells of these patients display a down-regulation of IL-12R β2 chain, suggesting an early commitment toward Th2 phenotype. In this study, we show that the short form of the proto-oncogene c-maf, a known activator of the IL-4 gene, is highly induced in MCNS T cells during relapse, where it translocates to the nuclear compartment and binds to the DNA responsive element. Unexpectedly, the nuclear localization of c-maf did not promote the IL-4 gene transcription in relapse. Using several approaches, we show in this study that RelA blunts IL-4 induction in T cells during the relapse in these patients. We demonstrate that the ex vivo inhibition of proteasome activity in T cells from relapse, which blocks NF-κB activity, strongly increases the IL-4 mRNA levels. Overexpression of c-maf in T cells induces a high level of IL-4 promoter-driven luciferase activity. In contrast, coexpression of c-maf with NF-κB RelA/p50, or RelA, but not p50, inhibits the c-maf-dependent IL-4 promoter activity. Finally, we demonstrated that, in T cell overexpressing RelA and c-maf, RelA expelled c-maf from its DNA binding site on IL-4 gene promoter, which results in active inhibition of IL-4 gene transcription. Altogether, these results suggest that the involvement of c-maf in Th2 commitment in MCNS operates through IL-4-independent mechanisms.

Successful anti-TNFalpha treatment in a child with posttransplant recurrent focal segmental glomerulosclerosis.

Posttransplant recurrence of focal and segmental glomulosclerosis (FSGS) occurs in ∼30% of patients, and remains after uncontrolled despite increased immunosuppression and plasma exchanges (PE) in ∼30% of cases. New immunosuppressive drugs might then be warranted. We report the case of a 15‐year‐old boy with FSGS leading to end‐stage renal disease (ESRD) who presented with an early posttransplant recurrence of disease. Reinforced immunosuppression and PE resulted in partial and transient disease control, but proteinuria significantly decreased with anti‐TNFα treatment (infliximab then etanercep). This is the first case report of successful anti‐TNFα treatment despite a constant high activity of FSGS, as demonstrated by relapse after discontinuation of anti‐TNFα agents.

Renal Granulomatous sarcoidosis in childhood: a report of 11 cases and a review of the literature

AbstractWe analysed retrospectively 11 children with renal granulomatous sarcoidosis confirmed by renal histology in order to describe the course and prognosis of the disease. Symptomatic sarcoidosis was diagnosed at a mean age of 10.1 years. Nine children had renal involvement at the time of diagnosis. In the course of the disease, nine patients developed renal failure and mild proteinuria, seven had transient sterile leucocyturia, four showed microscopic haematuria, seven had a urinary concentrating defect, and enlarged kidneys were seen in three patients. One child had hypercalcaemia and hypercalciuria, none had hypertension. Light microscopy of the kidney showed interstitial infiltration by mononuclear cells in all children, interstitial fibrosis in nine patients, epithelioid granulomas in seven, tubular involvement in eight, and mild glomerular involvement in seven patients. Renal immunofluorescence was negative. Ten children received prednisone for 1–11 years. After a mean follow up of 5.5 years, three patients had entered end-stage renal failure and one had chronic insufficiency after interruption of medical supervision and prednisone therapy. Conclusion Renal failure, proteinuria, leucocyturia, haematuria, and concentration defect are the prominent features of renal granulomatous sarcoidosis in children. Steroid therapy, adjusted according to disease activity, may prevent end-stage renal failure.

Tacrolimus nephrotoxicity: beware of the association of diarrhea, drug interaction and pharmacogenetics

Tacrolimus is known to potentially lead to adverse events in recipients with diarrhoea and/or calcium channel blocker (CCB) co-administration. We report a renal transplant recipient who suffered from severe nephrotoxicity related to a toxic tacrolimus trough concentration in both conditions, diarrhoea and CCB co-administration, and with genotyped CYP3A system and P-glycoprotein (P-gp) polymorphisms. To our knowledge, this is the first case to be investigated for such polymorphisms. Clinicians should be reminded of the possibility of highly increased levels of tacrolimus in situations of diarrhoea and/or co-administration of CCBs. It also highlights the key role in tacrolimus pharmacokinetics of the CYP3A system and P-gp polymorphisms, and their influence in high-risk situations when enzyme activity is already affected by enterocyte damage due to diarrhoea and CCB competition.