Efficacy and safety of intravenous immunoglobulin with rituximab versus rituximab alone in childhood-onset steroid-dependent and frequently relapsing nephrotic syndrome: protocol for a multicentre randomised controlled trial

INTRODUCTION

Guidelines for the treatment of steroid-dependent nephrotic syndrome (SDNS) and frequently relapsing nephrotic syndrome (FRNS) are lacking. Given the substantial impact of SDNS/FRNS on quality of life, strategies aiming to provide long-term remission while minimising treatment side effects are needed. Several studies confirm that rituximab is effective in preventing early relapses in SDNS/FRNS; however, the long-term relapse rate remains high (~70% at 2 years). This trial will assess the association of intravenous immunoglobulins (IVIgs) to rituximab in patients with SDNS/FRNS and inform clinicians on whether IVIg's immunomodulatory properties can alter the course of the disease and reduce the use of immunosuppressive drugs and their side effects.

METHODS AND ANALYSIS

We conduct an open-label multicentre, randomised, parallel group in a 1:1 ratio, controlled, superiority trial to assess the safety and efficacy of a single infusion of rituximab followed by IVIg compared with rituximab alone in childhood-onset FRNS/SDNS. The primary outcome is the occurrence of first relapse within 24 months. Patients are allocated to receive either rituximab alone (375 mg/m²) or rituximab followed by IVIg, which includes an initial Ig dose of 2 g/kg, followed by 1.5 g/kg injections once a month for the following 5 months (maximum dose: 100 g).

ETHICS AND DISSEMINATION

The study has been approved by the ethics committee (Comité de Protection des Personnes) of Ouest I and authorised by the French drug regulatory agency (Agence Nationale de Sécurité du Médicament et des Produits de Santé). Results of the primary study and the secondary aims will be disseminated through peer-reviewed publications.

TRIAL REGISTRATION NUMBER

NCT03560011.

Amniotic fluid peptides predict postnatal kidney survival in developmental kidney disease

Although a rare disease, bilateral congenital anomalies of the kidney and urinary tract (CAKUT) are the leading cause of end stage kidney disease in children. Ultrasound-based prenatal prediction of postnatal kidney survival in CAKUT pregnancies is far from accurate. To improve prediction, we conducted a prospective multicenter peptidome analysis of amniotic fluid spanning 140 evaluable fetuses with CAKUT. We identified a signature of 98 endogenous amniotic fluid peptides, mainly composed of fragments from extracellular matrix proteins and from the actin binding protein thymosin-β4. The peptide signature predicted postnatal kidney outcome with an area under the curve of 0.96 in the holdout validation set of patients with CAKUT with definite endpoint data. Additionally, this peptide signature was validated in a geographically independent sub-cohort of 12 patients (area under the curve 1.00) and displayed high specificity in non-CAKUT pregnancies (82 and 94% in 22 healthy fetuses and in 47 fetuses with congenital cytomegalovirus infection respectively). Change in amniotic fluid thymosin-β4 abundance was confirmed with ELISA. Knockout of thymosin-β4 in zebrafish altered proximal and distal tubule pronephros growth suggesting a possible role of thymosin β4 in fetal kidney development. Thus, recognition of the 98-peptide signature in amniotic fluid during diagnostic workup of prenatally detected fetuses with CAKUT can provide a long-sought evidence base for accurate management of the CAKUT disorder that is currently unavailable.

Red Blood Cell AE1/Band 3 Transports in Dominant Distal Renal Tubular Acidosis Patients

Introduction

Anion exchanger 1 (AE1) (SLC4A1 gene product) is a membrane protein expressed in both kidney and red blood cells (RBCs): it exchanges extracellular bicarbonate (HCO₃^–) for intracellular chloride (Cl^–) and participates in acid−base homeostasis. AE1 mutations in kidney α-intercalated cells can lead to distal renal tubular acidosis (dRTA). In RBC, AE1 (known as band 3) is also implicated in membrane stability: deletions can cause South Asian ovalocytosis (SAO).

Methods

We retrospectively collected clinical and biological data from patients harboring dRTA due to a SLC4A1 mutation and analyzed HCO₃^– and Cl^– transports (by stopped-flow spectrophotometry) and expression (by flow cytometry, fluorescence activated cell sorting, and Coomassie blue staining) in RBCs, as well as RBC membrane stability (ektacytometry).

Results

Fifteen patients were included. All experience nephrolithiasis and/or nephrocalcinosis, 2 had SAO and dRTA (dRTA SAO+), 13 dominant dRTA (dRTA SAO−). The latter did not exert specific RBC membrane anomalies. Both HCO₃^– and Cl^– transports were lower in patients with dRTA SAO+ than in those with dRTA SAO− or controls. Using 3 different extracellular probes, we report a decreased expression (by 52%, P < 0.05) in dRTA SAO+ patients by fluorescence activated cell sorting, whereas total amount of protein was not affected.

Conclusion

Band 3 transport function and expression in RBCs from dRTA SAO− patients is normal. However, in SAO RBCs, impaired conformation of AE1/band 3 corresponds to an impaired function. Thus, the driver of acid−base defect during dominant dRTA is probably an impaired membrane expression.

Metabolic acidosis is common and associates with disease progression in children with chronic kidney disease

Recent studies in adult chronic kidney disease (CKD) suggest that metabolic acidosis is associated with faster decline in estimated glomerular filtration rate (eGFR). Alkali therapies improve the course of kidney disease. Here we investigated the prevalence and determinants of abnormal serum bicarbonate values and whether metabolic acidosis may be deleterious to children with CKD. Associations between follow-up serum bicarbonate levels categorized as under 18, 18 to under 22, and 22 or more mmol/l and CKD outcomes in 704 children in the Cardiovascular Comorbidity in Children with CKD Study, a prospective cohort of pediatric patients with CKD stages 3-5, were studied. The eGFR and serum bicarbonate were measured every six months. At baseline, the median eGFR was 27 ml/min/1.73m² and median serum bicarbonate level 21 mmol/l. During a median follow-up of 3.3 years, the prevalence of metabolic acidosis (serum bicarbonate under 22 mmol/l) was 43%, 60%, and 45% in CKD stages 3, 4, and 5, respectively. In multivariable analysis, the presence of metabolic acidosis as a time-varying covariate was significantly associated with log serum parathyroid hormone through the entire follow-up, but no association with longitudinal growth was found. A total of 211 patients reached the composite endpoint (ESRD or 50% decline in eGFR). In a multivariable Cox model, children with time-varying serum bicarbonate under 18 mmol/l had a significantly higher risk of CKD progression compared to those with a serum bicarbonate of 22 or more mmol/l (adjusted hazard ratio 2.44; 95% confidence interval 1.43-4.15). Thus, metabolic acidosis is a common complication in pediatric patients with CKD and may be a risk factor for secondary hyperparathyroidism and kidney disease progression.

C3 glomerulopathy and eculizumab: a report on four paediatric cases

BACKGROUND

Eculizumab may be used to treat C3-glomerulopathy (C3G), a rare but severe glomerular disease.

DIAGNOSIS AND TREATMENT

Patients 1, 2 and 3 were diagnosed with nephritic syndrome with alternative complement pathway activation (low C3, C3Nef-positive) and C3G at the age of 9, 13 and 12 years, respectively. Treatment with eculizumab normalized proteinuria within 1, 2 and 7 months, respectively. Proteinuria relapsed when eculizumab was withdrawn, but the re-introduction of eculizumab normalized proteinuria. Patient 4 was diagnosed with C3G at 9 years of age, with progression to end-stage renal disease within 2 years, followed by a first renal transplantation (R-Tx) with early disease recurrence and graft loss within 39 months. After a second R-Tx, she rapidly presented with biological and histological recurrence: therapy with eculizumab was started, with no effect on proteinuria after 5 months, in a complex clinical setting (i.e. association of C3G recurrence, humoral rejection and BK nephritis). Eculizumab was withdrawn due to multiple viral reactivations, but the re-introduction of the drug a few months later enabled a moderate decrease in proteinuria.

CONCLUSION

These cases illustrate the efficacy of eculizumab, at least on native kidneys, in paediatric C3G. However, larger international studies are warranted to confirm the benefit and safety of eculizumab therapy.

Trichodysplasia spinulosa: a polyomavirus infection specifically targeting follicular keratinocytes in immunocompromised patients

Trichodysplasia spinulosa (TS) is a rare skin disease, caused by a specific polyomavirus, occurring in immunocompromised patients. The pathophysiological mechanisms of TS are not yet fully understood. By using polymerase chain reaction and skin biopsy immunostaining we report evidence, in a paediatric case, of follicular keratinocytes being the primary target of trichodysplasia spinulosa-associated polyomavirus.

Comprehensive PKD1 and PKD2 Mutation Analysis in Prenatal Autosomal Dominant Polycystic Kidney Disease

Prenatal forms of autosomal dominant polycystic kidney disease (ADPKD) are rare but can be recurrent in some families, suggesting a common genetic modifying background. Few patients have been reported carrying, in addition to the familial mutation, variation(s) in polycystic kidney disease 1 (PKD1) or HNF1 homeobox B (HNF1B), inherited from the unaffected parent, or biallelic polycystic kidney and hepatic disease 1 (PKHD1) mutations. To assess the frequency of additional variations in PKD1, PKD2, HNF1B, and PKHD1 associated with the familial PKD mutation in early ADPKD, these four genes were screened in 42 patients with early ADPKD in 41 families. Two patients were associated with de novo PKD1 mutations. Forty patients occurred in 39 families with known ADPKD and were associated with PKD1 mutation in 36 families and with PKD2 mutation in two families (no mutation identified in one family). Additional PKD variation(s) (inherited from the unaffected parent when tested) were identified in 15 of 42 patients (37.2%), whereas these variations were observed in 25 of 174 (14.4%, P=0.001) patients with adult ADPKD. No HNF1B variations or PKHD1 biallelic mutations were identified. These results suggest that, at least in some patients, the severity of the cystic disease is inversely correlated with the level of polycystin 1 function.

Towards a new point of view on the phenotype of patients with a 17q12 microdeletion syndrome

OBJECTIVE

17q12 microdeletion syndrome involves 15 genes, including HNF1B, and is considered to confer a high risk of neuropsychiatric disorders. Patients with HNF1B gene deletion diagnosed secondary to renal disorders are only very rarely reported to have neuropsychiatric disorders. Interestingly, however, when tested, patients with HNF1B gene deletion are found to have 17q12 deletion. This brings into question the extent to which 17q12 deletion is genuinely associated with severe neuropsychological disorders and in which patients. In this study, we sought to confirm 17q12 microdeletion in kidney patients initially diagnosed with HNF1B gene deletion and evaluate neuropsychological disorders in these patients compared with those with HNF1B point mutation.

PATIENTS AND DESIGN

Thirty-nine children with HNF1B disorders (26 with deletions) diagnosed secondary to renal abnormalities were included in this prospective study and tested for 17q12 microdeletion and neuropsychological disorders.

RESULTS

The same 17q12 microdeletion found in patients with neuropsychological disorders was identified in all of our patients with HNF1B deletion. Neurological examinations found no severe impairments except for one patient with autism. No significant differences were found between patients with deletions and those with point mutations as concerns learning abilities and schooling. Nevertheless, patients with deletions tended to have lower developmental quotients and more difficulties at school.

CONCLUSIONS

Complete deletion of the HNF1B gene and 17q12 microdeletion syndrome are actually the same genetic disorder. The neuropsychological phenotype of patients appears less severe when 17q12 deletion is diagnosed secondary to kidney rather than neuropsychological abnormalities. These data may influence antenatal counselling.

What about the renal function during childhood of children born from dialysed mothers?

INTRODUCTION

Pregnancy during dialysis is a high-risk condition which is becoming more and more common. The renal outcome of children born from such pregnancies needs to be investigated since renal development may be affected (i.e. exposure to uraemic toxins, therapies, intermittent haemodynamic changes during sessions, prematurity, growth retardation).

METHODS

We performed a single-centre prospective global and renal evaluation (inulin clearance or 2009 Schwartz formula in children <4 years) in 10 children from 7 mothers who underwent haemodialysis during pregnancy.

RESULTS

The median (range) age of mothers at the beginning of pregnancy was 30 (22-33) years, with maximal weekly haemodialysis duration of 18 (12-30) h. Systemic arterial hypertension was reported in 4 of 10 pregnancies, polyhydramnios in 3 and oligohydramnios in 1. The median (range) gestational age was 32 (29-39) weeks of gestation (WG). Seven children were born before 36 WG. The median (range) birth weight (BW) was 1735 (930-3430)g, and eight children had a BW <2500 g. One child had a PAX2 mutation requiring early renal transplantation and was thus excluded from further analysis. Even though glomerular filtration rate and blood pressure were normal in all other children, a significant urine albumin-to-creatinine ratio was found in three children and an increased urine beta-2-microglobulin concentration in an additional one, questioning the presence of an underlying silent reduction in nephron number.

CONCLUSIONS

Despite the small number of patients, this pilot study highlights the potential risk of renal impairment in children born from dialysed mothers. Further studies are required but until then, careful monitoring of these children is important.

Diagnosis, management, and prognosis of HNF1B nephropathy in adulthood

Mutations in HNF1B are responsible for a dominantly inherited disease with renal and nonrenal consequences, including maturity-onset diabetes of the young (MODY) type 5. While HNF1B nephropathy is typically responsible for bilateral renal cystic hypodysplasia in childhood, the adult phenotype is poorly described. To help define this we evaluated the clinical presentation, imaging findings, genetic changes, and disease progression in 27 adults from 20 families with HNF1B nephropathy. Whole-gene deletion was found in 11 families, point mutations in 9, and de novo mutations in half of the kindred tested. Renal involvement was extremely heterogeneous, with a tubulointerstitial profile at presentation and slowly progressive renal decline throughout adulthood as hallmarks of the disease. In 24 patients tested, there were cysts (≤5 per kidney) in 15, a solitary kidney in 5, hypokalemia in 11, and hypomagnesemia in 10 of 16 tested, all as characteristics pointing to HNF1B disease. Two patients presented with renal Fanconi syndrome and, overall, 4 progressed to end-stage renal failure. Extrarenal phenotypes consisted of diabetes mellitus in 13 of the 27 patients, including 11 with MODY, abnormal liver tests in 8 of 21, diverse genital tract abnormalities in 5 of 13 females, and infertility in 2 of 14 males. Thus, our findings provide data that are useful for recognition and diagnosis of HNF1B disease in adulthood and might help in renal management and genetic counseling.

Development of a Bayesian estimator for the therapeutic drug monitoring of mycophenolate mofetil in children with idiopathic nephrotic syndrome

The use of mycophenolate mofetil (MMF) in children with idiopathic nephrotic syndrome (INS) is increasing. However, the clinical benefit of its monitoring has been scarcely studied, and little is known about its pharmacokinetics in this context. The objectives of the present study were: (i) to study and model the pharmacokinetics of mycophenolic acid (MPA; the active moiety of MMF) in paediatric patients with INS given MMF, at all stages of the disease; (ii) to develop a Bayesian estimator (MAP-BE) for individual inter-dose area under the concentration-time curve (AUC) prediction in this population, using a limited blood sampling strategy (LSS). Full-pharmacokinetic (PK) profiles of MPA collected in paediatric inpatients with INS already treated with a maintenance immunosuppressive therapy based on MMF (with no calcineurin inhibitors; CNI) were studied. A classical iterative two-stage (ITS) method was applied to model the data and develop MAP-BEs using a one-compartment open model where the absorption is described by a double gamma law allowing the description of a potential enterohepatic recirculation. The performance of the MAP-BE developed for individual exposure assessment was evaluated by the bias and precision of predicted AUCs with respect to measured, trapezoidal AUCs (reference value), and by the proportion of predicted AUCs with absolute error >20%. These PK tools were tested in an independent group of patients. Sixty PK profiles of MPA from children receiving MMF in association to corticosteroids or given alone were included in the study. Forty-five of these PK profiles were used to develop a PK model and a MAP-BE, and 15 for their validation. In the building group, the PK model fitted accurately the PK profiles of MPA: mean residual error of modelled vs. reference AUC was m±SD=-0.015±0.092 (range: -0.153 to 0.204). The MAP-BE which allowed the estimation of MPA AUC on the basis of a 20 min-60 min-180 min LSS was then developed. In the independent group of patients, its mean residual error vs. reference AUCs was m±SD=-0.036±0.145 (range: -0.205 to 0.189). Thus, a PK model and its derived MAP-BE for MMF (without any associated CNI) when given to children with INS have been developed. Clinical trials using these PK tools could test the potential impact of the therapeutic drug monitoring of MMF based on the AUC on the clinical evolution of INS.

Long-term outcome of idiopathic steroid-resistant nephrotic syndrome: a multicenter study

Long-term outcome of idiopathic steroid-resistant nephrotic syndrome was retrospectively studied in 78 children in eight centers for the past 20 years. Median age at onset was 4.4 years (1.1-15.0 years) and the gender ratio was 1.4. Median follow-up period was 7.7 years (1.0-19.7 years). The disease in 45 patients (58%) was initially not steroid-responsive and in 33 (42%) it was later non-responsive. The main therapeutic strategies included administration of ciclosporine (CsA) alone (n = 29; 37%) and CsA + mycophenolate mofetil (n = 18; 23%). Actuarial patient survival rate after 15 years was 97%. Renal survival rate after 5 years, 10 years and 15 years was 75%, 58% and 53%, respectively. An age at onset of nephrotic syndrome (NS) > 10 years was the only independent predictor of end-stage renal disease (ESRD) in a multivariate analysis using a Cox regression model (P < 0.001). Twenty patients (26%) received transplants; ten showed recurrence of the NS: seven within 2 days, one within 2 weeks, and two within 3-5 months. Seven patients lost their grafts, four from recurrence. Owing to better management, kidney survival in idiopathic steroid-resistant nephrotic syndrome (SRNS) has improved during the past 20 years. Further prospective controlled trials will delineate the potential benefit of new immunosuppressive treatment.