Ulrike John

Mutations in CYP24A1 and Idiopathic Infantile Hypercalcemia

BACKGROUND Vitamin D supplementation for the prevention of rickets is one of the oldest and most effective prophylactic measures in medicine, having virtually eradicated rickets in North America. Given the potentially toxic effects of vitamin D, the recommendations for the optimal dose are still debated, in part owing to the increased incidence of idiopathic infantile hypercalcemia in Britain in the 1950s during a period of high vitamin D supplementation in fortified milk products. We investigated the molecular basis of idiopathic infantile hypercalcemia, which is characterized by severe hypercalcemia, failure to thrive, vomiting, dehydration, and nephrocalcinosis. METHODS We used a candidate-gene approach in a cohort of familial cases of typical idiopathic infantile hypercalcemia with suspected autosomal recessive inheritance. Identified mutations in the vitamin D-metabolizing enzyme CYP24A1 were evaluated with the use of a mammalian expression system. RESULTS Sequence analysis of CYP24A1, which encodes 25-hydroxyvitamin D 24-hydroxylase, the key enzyme of 1,25-dihydroxyvitamin D(3) degradation, revealed recessive mutations in six affected children. In addition, CYP24A1 mutations were identified in a second cohort of infants in whom severe hypercalcemia had developed after bolus prophylaxis with vitamin D. Functional characterization revealed a complete loss of function in all CYP24A1 mutations. CONCLUSIONS The presence of CYP24A1 mutations explains the increased sensitivity to vitamin D in patients with idiopathic infantile hypercalcemia and is a genetic risk factor for the development of symptomatic hypercalcemia that may be triggered by vitamin D prophylaxis in otherwise apparently healthy infants.

Immunosuppression and Renal Outcome in Congenital and Pediatric Steroid-Resistant Nephrotic Syndrome

BACKGROUND AND OBJECTIVES Mutations in podocyte genes are associated with steroid-resistant nephrotic syndrome (SRNS), mostly affecting younger age groups. To date, it is unclear whether these patients benefit from intensified immunosuppression with cyclosporine A (CsA). The aim of this study was to evaluate the influence of podocyte gene defects in congenital nephrotic syndrome (CNS) and pediatric SRNS on the efficacy of CsA therapy and preservation of renal function. DESIGN, SETTINGS, PARTICIPANTS, & MEASUREMENTS Genotyping was performed in 91 CNS/SRNS patients, irrespective of age at manifestation or response to CsA. RESULTS Mutations were identified in 52% of families (11 NPHS1, 17 NPHS2, 11 WT1, 1 LAMB2, 3 TRPC6). Sixty-eight percent of patients with nongenetic SRNS responded to CsA, most of them achieved complete remission. In contrast, none of the patients with genetic CNS/SRNS experienced a complete remission and only two (17%) achieved a partial response, both affected by a WT1 mutation. Preservation of renal function was significantly better in children with nongenetic disease after a mean follow-up time of 8.6 years (ESRD in 29% versus 71%). CONCLUSIONS The mutation detection rate in our population was high (52%). Most patients with genetic CNS/SRNS did not benefit from CsA with significantly lower response rates compared with nongenetic patients and showed rapid progression to end-stage renal failure. These data strongly support the idea not to expose CNS/SRNS patients with inherited defects related to podocyte function to intensified immunosuppression with CsA.

Improved Acidosis Correction and Recovery of Mesothelial Cell Mass with Neutral-pH Bicarbonate Dialysis Solution among Children Undergoing Automated Peritoneal Dialysis

Acid-base balance and peritoneal membrane longevity are of utmost relevance for pediatric patients undergoing peritoneal dialysis (PD). PD fluids with neutral pH and reduced glucose degradation product contents are considered more biocompatible, because they preserve peritoneal cell functions in vitro. To investigate the clinical effects of a novel PD fluid buffered with 34 mM pure bicarbonate at neutral pH, a randomized, prospective, crossover comparison with conventional, acidic, 35 mM lactate PD fluid was performed for two consecutive 12-wk periods with 28 children (age, 6 mo to 15 yr) undergoing automated PD (APD). Blood bicarbonate levels and arterial pH were significantly higher after 3 mo of bicarbonate PD (24.6 +/- 2.3 mM and 7.43 +/- 0.06, respectively), compared with lactate PD (22.8 +/- 3.9 mM and 7.38 +/- 0.05, respectively; P < 0.05). This effect was reversible among patients who returned from bicarbonate to lactate fluid. Low initial pH and young patient age independently predicted increased blood pH during bicarbonate APD. Peritoneal equilibration tests revealed subtle changes in solute transport, with a less steep creatinine equilibration curve during bicarbonate dialysis, suggesting reduced peritoneal vasodilation. The peritoneal release of carcinogen antigen-125 increased twofold during bicarbonate APD (29 +/- 15 versus 15 +/- 8 U/ml per 4 h, P < 0.01), which is consistent with recovery of the mesothelial cell layer. This effect was fully reversed when the patients returned to lactate fluid. Effluent carcinogen antigen-125 levels were inversely correlated with peritoneal glucose exposure during lactate but not bicarbonate APD, indicating improved in vivo mesothelial cell tolerance of high-dose glucose with the neutral-pH PD fluid with reduced glucose degradation product content. Among children undergoing APD, neutral-pH, bicarbonate-buffered PD fluid provides more effective correction of metabolic acidosis and better preservation of peritoneal cell mass than do conventional, acidic, lactate-based fluids.

Successful withdrawal of steroids in pediatric renal transplant recipients receiving cyclosporine A and mycophenolate mofetil treatment : results after four years

Background. Despite their numerous systemic side effects, glucocorticoids (steroids) still form a cornerstone in immunosuppressive regimens in pediatric renal transplant recipients. The addition of mycophenolate mofetil (MMF) to a cyclosporine A (CsA)-based immunosuppressive regimen after renal transplantation may allow steroid withdrawal and amelioration or avoidance of steroid-specific side effects. Methods. In a retrospective case-control study, covering a mean follow-up period of 46±2.3 months and 40 patients aged 11.4±4.9 years, we analyzed the safety and efficacy of steroid withdrawal in pediatric renal transplant recipients receiving CsA micoroemulsion, MMF, and low-dose prednisone treatment. Results. Steroid withdrawal in all 20 pediatric renal transplant recipients receiving CsA and MMF was successful and not associated with an acute rejection episode; graft function remained stable. At baseline, the degree of growth retardation was comparable between the groups (mean height standard deviation scores [SDSs] −1.60±0.30 [withdrawal group] and −1.32±0.39 [case-control group]). After steroid withdrawal, prepubertal patients exhibited a significant catch-up growth with a mean height gain of 1.47±0.32 SDS, whereas height SDS did not improve in patients receiving steroids. Growth was also improved in pubertal patients who stopped taking steroids. Standardized body mass index in patients who stopped taking steroids decreased significantly by 49% from 0.87±0.31 SDS to 0.45±0.30 SDS. After steroid withdrawal, mean arterial blood pressure SDS decreased significantly by 45%. Moreover, the need for antihypertensive medication declined significantly in patients who stopped taking steroids. The white blood cell counts and hemoglobin levels were comparable between the groups. Conclusions. This study suggests that steroids can be safely and successfully withdrawn in selected pediatric renal transplant recipients receiving immunosuppressive maintenance therapy consisting of CsA and MMF.

Cluster of hemolytic-uremic syndrome caused by Shiga toxin-producing Escherichia coli O26:H11.

Background. The epidemiology and clinical characteristics of the hemolytic-uremic syndrome (HUS) caused by Escherichia coli O157:H7 are well-known, but HUS attributable to non-O157:H7 Shiga toxin (Stx)-producing E. coli (STEC) are less thoroughly described. Here we report a cluster of HUS cases caused by STEC O26:H11 the most common non-O157:H7 STEC isolated from sporadic cases of HUS in Europe. Methods. Three children between 13 and 17 months of age, living in the same small town, developed HUS within an interval of 5 days. We present clinical and microbiologic data on the patients and their infecting isolates. Results. The clinical course ranged from mild uncomplicated HUS to severe HUS complicated by multiorgan involvement. Microbiologic investigation demonstrated STEC of serotype O26:H11 in stools of all the patients. The phenotypic and molecular characterization of the STEC O26:H11 isolates demonstrated that these strains were identical and, unusual for STEC O26, they harbored the stx2 but not the stx1 gene. None of the patients had evidence of STEC O157:H7 infection either by culture or by E. coli O157 serology. The source of the STEC O26:H11 infection was undetermined. Conclusions. Our results demonstrate that diagnostic procedures based on the detection of stx genes and/or Stx production and subsequent subtyping of the isolates using molecular methods are necessary to identify such outbreaks caused by non-O157:H7 STEC.

Kidney growth and renal function in unilateral multicystic dysplastic kidney disease

Abstract. The natural history of multicystic dysplastic kidney (MCDK) is not well established. We analyzed kidney growth and renal function in 33 children with prenatally diagnosed unilateral MCDK in a long-term study. The mean observation period was 4.9 years with a range of 1–11.6 years. Abnormalities of the contralateral kidney were found in 10 of 33 patients (30%): ureteropelvic junction obstruction (5), ureterovesical junction obstruction (2), and vesicoureteral reflux (3). In 6 children the dysplastic kidney had been removed. Complete involution was observed in 48% and a decrease of size in 33% of 27 dysplastic kidneys. At the time of last examination, 27 of 29 children showed a volume of the contralateral kidney above the normal range (>145%). Hypertrophy of the contralateral kidney, defined as kidney length above 2 standard deviation scores (SDS), was seen in 24% of 33 children at birth, thus showing that hypertrophy of the contralateral kidney starts in utero and continues throughout childhood. The extent of contralateral hypertrophy was independent of associated abnormalities in this study. Mean creatinine was increased in the whole group (mean +1.13 SDS). Calculated creatinine clearance in 21 patients over 2 years was within normal limits, with a median of 102 ml/min per 1.73 m2 (range 84–143). Based on the results of this and previous studies, nephrectomy cannot be recommended in typical cases, but a regular follow-up of these patients seems necessary.

Improved growth and cardiovascular risk after late steroid withdrawal: 2-year results of a prospective, randomised trial in paediatric renal transplantation

BACKGROUND Long-term corticosteroid treatment impairs growth and increases cardiovascular risk factors. Hence, steroid withdrawal constitutes a major topic in paediatric renal transplantation and maintenance immunosuppression. METHODS The lack of data from randomised controlled trials caused us to conduct the first prospective, randomised, multicentre study on late steroid withdrawal among paediatric kidney allograft recipients treated with standard-dose cyclosporine microemulsion (CsA) and mycophenolate mofetil (MMF) for 2 years. Forty-two low- or regular-immunologic risk patients were randomly assigned, >or=1 year post-transplant, to continue taking or to withdraw steroids over 3 months. RESULTS Two years after steroid withdrawal, they showed a longitudinal growth superior to controls [mean height standard deviation score (SDS) gain, 0.6 +/- 0.1 SDS versus -0.2 +/- 0.1 SDS (P < 0.001)]. The prevalence of the metabolic syndrome declined significantly (P < 0.05), 2 years after steroid withdrawal, from 39% (9/23) to 6% (1/16). Steroid-free patients had less frequent arterial hypertension (50% versus 93% (P < 0.05)) and required fewer antihypertensive drugs [0.6 +/- 0.2 versus 1.5 +/- 0.3 (P < 0.05 versus control)]. Additionally, they had a significantly improved carbohydrate and lipid metabolism with fewer hypercholesterolaemia and hypertriglyceridaemia (P < 0.05 versus control). Patient and graft survival amounted to 100%. Allograft function remained stable 2 years after steroid withdrawal. The incidence of acute rejections was similar in the steroid-withdrawal group (1/23, 4%) and controls (2/19, 11%). CONCLUSION Late steroid withdrawal in selected CsA- and MMF-treated paediatric kidney transplant recipients improves growth, mitigates cardiovascular risk factors and reduces the prevalence of the metabolic syndrome, at no increased risk of acute rejection or unstable graft function.

(Val-)Ganciclovir prophylaxis reduces Epstein-Barr virus primary infection in pediatric renal transplantation

Epstein‐Barr virus (EBV) primary infection constitutes a serious risk for pediatric transplant recipients, particularly as regards the development of EBV‐related post‐transplant lymphoproliferative disease (PTLD). Currently, there is no established prophylactic regimen. We investigated the association between chemoprophylaxis with valganciclovir (VGCV) or ganciclovir (GCV) and the incidence of EBV viremia in EBV‐naïve pediatric renal transplant recipients (R−) who had received a graft from an EBV‐positive donor (D+) and are therefore at high risk of EBV primary infection. In a prospective, multicenter trial (n = 114), we compared a cohort on chemoprophylaxis (n = 20) with a similar control cohort without chemoprophylaxis (n = 8). Over the 1‐year study period, antiviral prophylaxis with VGCV/GCV was associated with a significantly decreased incidence of EBV primary infection: 9/20 patients (45%) in the prophylaxis group experienced an EBV primary infection compared to 8/8 controls (100%) (P < 0.0001). Chemoprophylaxis was associated with a significantly lower EBV viral load (P < 0.001). Type or intensity of immunosuppressive therapy did not influence the occurrence of EBV primary infection or the level/persistence of EBV viral load. Chemoprophylaxis with VGCV/GCV is associated with a reduced incidence of EBV viremia in high‐risk pediatric kidney allograft recipients in the first year post‐transplant.

Prospective, randomized trial on late steroid withdrawal in pediatric renal transplant recipients under cyclosporine microemulsion and mycophenolate mofetil.

Background. Many transplant centers practice late steroid withdrawal after pediatric renal transplantation, but evidence-based data on the overall risk-to-benefit ratio in this patient population are lacking. Methods. We therefore conducted the first prospective, randomized, open-label multicenter study to validate this strategy: 42 low-immunologic risk pediatric kidney allograft recipients, aged 10.3±4.3 years, on cyclosporine microemulsion, mycophenolate mofetil, and corticosteroids were randomly assigned, more than or equal to 1-year posttransplant, to continue steroids or to withdraw over 3 months. This report contains the 1-year results. Results. In response to steroid withdrawal, patients experienced a significant catch-up growth with a mean standardized height gain of 0.3±0.1 standard deviation score (SDS) per year (P<0.05 vs. control), whereas mean height SDS in the control group did not change (0.0±0.1 SDS). Standardized body mass index declined significantly by 0.68±0.23 SDS after steroid withdrawal, but rose significantly by 0.26±0.34 SDS in the control group. Patients off steroids had less frequent arterial hypertension (50% vs. 87.5% (P<0.05) and significantly lower serum cholesterol (by 21%) and triglyceride values (by 36%) than control patients. Patient and graft survival were 100%. The incidence of acute rejection episodes in the steroid-withdrawal group was 1 of 23 (4%) compared with 1 of 19 (5%) in controls. Transplant function remained stable in both groups. Conclusion. Late steroid withdrawal in low-immunologic risk European pediatric kidney transplant recipients on cyclosporine microemulsion and mycophenolate mofetil is not associated with an increased rate of acute rejection episodes, enables catch-up growth and ameliorates cardiovascular risk factors.

Blood Pressure, Renal Function, and Proteinuria in Children with Unilateral Renal Agenesis

Background/Aim: Unilateral renal agenesis (URA) is a model for a reduced nephron number that is believed to be a risk factor for blood pressure (BP) elevation and reduced renal function. The aim of the study was to investigate BP and renal function in children with URA. Methods: Data on children with URA from two pediatric nephrology centers were firstly retrospectively reviewed (renal ultrasound and scintigraphy, clinical BP, creatinine clearance, urinalysis). Children with normal renal ultrasound and scintigraphy were thereafter investigated using ambulatory BP monitoring. Results: Twenty-nine children with URA were investigated – 14 children with an abnormal kidney (mostly scarring) and 15 children with healthy kidneys. Hypertension was diagnosed on the basis of clinical BP in 57% of the children with abnormal kidneys and on the basis of ambulatory BP monitoring in 1 child (7%) with healthy kidneys. The mean ambulatory BP in children with normal kidneys was not significantly different from that in controls. Forty-three percent of the children with abnormal kidneys had a reduced renal function, but none of children with normal kidneys. Conclusions: Children with abnormalities of a solitary kidney have often hypertension, proteinuria, or a reduced renal function. In contrast, children with healthy solitary kidneys have BP and renal function similar to those of healthy children.