Deferasirox-induced renal impairment in children: an increasing concern for pediatricians

BACKGROUND

Deferasirox (DFX) is an oral iron chelator with an established dose-dependent efficacy in transfusion-related iron overload. Whereas emerging long-term data confirm the safety of the drug, with transient moderate elevation of serum creatinine level, several authors have reported renal tubular dysfunction. The aim of this study was to evaluate tubular and glomerular function before and after the initiation of DFX therapy in a pediatric patient population.

METHODS

Ten children (4 girls, mean age 12.4 ± 3.9 years) enrolled in a routine blood transfusion program were treated with 24.8 ± 9.6 mg/kg per day of DFX, and renal function was assessed before and 17.2 ± 8.9 months after the initiation of DFX therapy.

RESULTS

Prior to treatment with DFX, all patients had a normal glomerular function rate (GFR) (125 ± 15 ml/min per 1.73 m(2)) and normal tubular function. Following the initiation of DFX therapy, the GFR decreased by approximately 20 % with one patient with a GFR of <80 mL/min per 1.73 m(2) and seven patients with a GFR of <100 mL/min per 1.73 m(2). Two patients experienced a generalized proximal tubular dysfunction whereas nine patients presented at least one sign of proximal tubular dysfunction.

CONCLUSIONS

Renal toxicity is a frequent adverse event of DFX treatment, presenting as both glomerular and proximal dysfunction. A routine renal assessment is therefore required to prevent chronic kidney disease that may result from prolonged tubular injury.

Dental abnormalities in Schimke immuno-osseous dysplasia

Described for the first time in 1971, Schimke immuno-osseous dysplasia (SIOD) is an autosomal-recessive multisystem disorder that is caused by bi-allelic mutations of SMARCAL1, which encodes a DNA annealing helicase. To define better the dental anomalies of SIOD, we reviewed the records from SIOD patients with identified bi-allelic SMARCAL1 mutations, and we found that 66.0% had microdontia, hypodontia, or malformed deciduous and permanent molars. Immunohistochemical analyses showed expression of SMARCAL1 in all developing teeth, raising the possibility that the malformations are cell-autonomous consequences of SMARCAL1 deficiency. We also found that stimulation of cultured skin fibroblasts from SIOD patients with the tooth morphogens WNT3A, BMP4, and TGFβ1 identified altered transcriptional responses, raising the hypothesis that the dental malformations arise in part from altered responses to developmental morphogens. To the best of our knowledge, this is the first systematic study of the dental anomalies associated with SIOD.

Cowden disease and multicystic dysplastic kidney: increased risk of renal cancer?

Unilateral multicystic dysplastic kidney is one of the most frequently identified urinary tract abnormalities in children. Although it can be an isolated finding, it is often associated with other anomalies of the kidney and urinary tract. It has also been described in association with other multisystemic disorders of known genetic aetiologies. Cowden disease (CD) is a rare autosomal-dominant disorder with age-related penetrance characterized by benign and malignant hamartomatous lesions affecting derivatives of all three germ cell layers. Hamartomas can emerge in virtually every organ, but are mostly found in the skin and gastrointestinal tract. We report a 7-year-old patient presenting with unilateral multicystic dysplastic kidney and CD, a hitherto unknown association in paediatrics, which raises the question of an increased risk of renal cancer.

Reduced elastogenesis: a clue to the arteriosclerosis and emphysematous changes in Schimke immuno-osseous dysplasia?

BACKGROUND

Arteriosclerosis and emphysema develop in individuals with Schimke immuno-osseous dysplasia (SIOD), a multisystem disorder caused by biallelic mutations in SMARCAL1 (SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily a-like 1). However, the mechanism by which the vascular and pulmonary disease arises in SIOD remains unknown.

METHODS

We reviewed the records of 65 patients with SMARCAL1 mutations. Molecular and immunohistochemical analyses were conducted on autopsy tissue from 4 SIOD patients.

RESULTS

Thirty-two of 63 patients had signs of arteriosclerosis and 3 of 51 had signs of emphysema. The arteriosclerosis was characterized by intimal and medial hyperplasia, smooth muscle cell hyperplasia and fragmented and disorganized elastin fibers, and the pulmonary disease was characterized by panlobular enlargement of air spaces. Consistent with a cell autonomous disorder, SMARCAL1 was expressed in arterial and lung tissue, and both the aorta and lung of SIOD patients had reduced expression of elastin and alterations in the expression of regulators of elastin gene expression.

CONCLUSIONS

This first comprehensive study of the vascular and pulmonary complications of SIOD shows that these commonly cause morbidity and mortality and might arise from impaired elastogenesis. Additionally, the effect of SMARCAL1 deficiency on elastin expression provides a model for understanding other features of SIOD.

The consequences of chronic kidney disease on bone metabolism and growth in children

Growth retardation, decreased final height and renal osteodystrophy (ROD) are common complications of childhood chronic kidney disease (CKD), resulting from a combination of abnormalities in the growth hormone (GH) axis, vitamin D deficiency, hyperparathyroidism, hypogonadism, inadequate nutrition, cachexia and drug toxicity. The impact of CKD-associated bone and mineral disorders (CKD-MBD) may be immediate (serum phosphate/calcium disequilibrium) or delayed (poor growth, ROD, fractures, vascular calcifications, increased morbidity and mortality). In 2012, the clinical management of CKD-MBD in children needs to focus on three main objectives: (i) to provide an optimal growth in order to maximize the final height with an early management with recombinant GH therapy when required, (ii) to equilibrate calcium/phosphate metabolism so as to obtain acceptable bone quality and cardiovascular status and (iii) to correct all metabolic and clinical abnormalities that can worsen bone disease, growth and cardiovascular disease, i.e. metabolic acidosis, anaemia, malnutrition and 25(OH)vitamin D deficiency. The aim of this review is to provide an overview of the mineral, bone and vascular abnormalities associated with CKD in children in terms of pathophysiology, diagnosis and clinical management.

Uric acid and IGF1 as possible determinants of FGF23 metabolism in children with normal renal function

BACKGROUND

Fibroblast growth factor 23 (FGF23) is a phosphaturic hormone and a suppressor of renal 1α hydroxylase. Although circulating values of FGF23 are increased in early chronic kidney disease (CKD), the interplay between FGF23 levels, growth and nutritional biomarkers has not been evaluated in children with normal renal function.

METHODS

We performed a secondary analysis of the cross-sectional observational INU23 study in 98 children (51 boys, mean age 10.5 ± 3.9 years) with preserved renal function (glomerular filtration rate (GFR) 114 ± 14 ml/min/1.73 m(2)).

RESULTS

In bivariate analyses, C-terminal FGF23 levels were positively related to phosphorus and uric acid levels. Intact FGF23 levels were positively associated with uric acid and insulin growth factor 1 (IGF1) levels, with similar results for age, body mass index (BMI), and 25OH vitamin D (25(OH)D). By multivariable analyses, 25(OH)D, uric acid, and phosphorus were independent predictors of C-terminal FGF23, while 25(OH)D, uric acid, and IGF1 were independent predictors of intact FGF23.

CONCLUSIONS

In children with preserved kidney function, the association between FGF23, uric acid, and IGF1 suggests that FGF23 could be an early nutritional indicator of high protein and phosphate intake. The association between FGF23 and IGF1 also suggests a relationship between FGF23 and growth, and warrants further investigation.

Cystinosin is a melanosomal protein that regulates melanin synthesis

Cystinosis is a rare autosomal recessive disease characterized by cystine crystal accumulation leading to multiorgan dysfunctions and caused by mutation in CTNS. CTNS encodes cystinosin, a cystine/H(+) symporter that exports cystine out of the lysosomes. Patients with cystinosis frequently exhibit blond hair and fair complexion, suggesting an alteration in melanogenesis. However, the pigmentation singularities of these patients have not been studied, and the role of cystinosin in melanogenesis has remained unknown. In our study, a clinical evaluation of 27 patients with cystinosis showed that 44% had a cutaneous pigmentation dilution compared to their relatives. Analysis of the hair melanin content in these patients by HPLC demonstrated a 50% decrease in eumelanin (4360 vs. 9360 ng/mg), and a 2-fold increase in pheomelanin (53 vs. 20 ng/mg), the yellow/red pigments. Cystinosin-deficient mice also showed a 4-fold increase in hair pheomelanin content. In vitro studies showed that cystinosin was located at melanosomes. CTNS silencing led to a 75% reduction of melanin synthesis that was caused by a degradation of tyrosinase by lysosomal proteases. Our results objectify the pigmentation defect in patients with cystinosis. We also identify the role of CTNS in melanogenesis and add a new gene to the list of the genes involved in the control of skin and hair pigmentation.

A randomized controlled crossover trial with delayed-release cysteamine bitartrate in nephropathic cystinosis: effectiveness on white blood cell cystine levels and comparison of safety

BACKGROUND AND OBJECTIVES

Immediate-release cysteamine bitartrate (Cystagon; Mylan Pharmaceuticals, Canonsburg, PA) may prevent or delay kidney transplantation and other serious outcomes in patients with cystinosis, but has never been subjected to a prospective clinical trial. Cystagon efficacy requires strict lifelong dosing every 6 hours. Such a dosing schedule and Cystagon-associated side effects are often cited by patients as reasons for nonadherence.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This open-label, randomized, controlled, crossover trial was powered to show that a new delayed-release formulation of cysteamine bitartrate, RP103, taken every 12 hours, was noninferior to Cystagon for maintenance of white blood cell (WBC) cystine at levels associated with optimal outcomes in the disease.

RESULTS

Forty-three patients were randomized. Using a mixed-effects statistical analysis model, the least-squares mean peak value of WBC cystine level was 0.62±0.05 nmol 1/2 cystine/mg protein after 12 hours under RP103 and 0.54±0.05 nmol 1/2 cystine/mg protein after 6 hours under Cystagon, a difference of 0.08±0.04 nmol 1/2 cystine/mg protein (95.8% confidence interval, 0-0.16). The average steady-state total daily dose of RP103 was 82% of the incoming steady-state total daily dose of Cystagon. There were three-fold more gastrointestinal side effects compared with using Cystagon.

CONCLUSIONS

A new delayed-release Q12H formulation of cysteamine bitartrate is not inferior to the Q6H formulation (Cystagon) in maintaining low WBC cystine levels in patients with cystinosis but at a lower total daily dose.

GFR estimation in adolescents and young adults

The performance of creatinine-based equations to obtain the estimated GFR in adolescents and young adults is poorly understood. We assessed creatinine-based GFR estimating equations in a cross-section of 751 adolescents and young adults (1054 measurements), using inulin clearance (measured GFR [mGFR]) as the reference method. We evaluated the following: Cockcroft-Gault, four-variable Modified Diet in Renal Disease, and the Chronic Kidney Disease Epidemiology Collaboration equations for adult participants, as well as the Schwartz 2009 and Schwartz-Lyon equations for pediatric age groups. Participants ranged in age from 10 to 26 years (mean 16.8 years); we divided the population into four groups according to age (10-12 years, 13-17 years, 18-21 years, and 21-25 years). Evaluation of the agreement between these formulas and mGFR (e.g., correlation, Bland-Altman plots, bias, and accuracy) showed that there was a good correlation between mGFR and both pediatric formulas in all age groups, whereas the adult formulas substantially overestimated mGFR. In conclusion, we recommend the use of pediatric equations to estimate GFR from childhood to early adulthood.

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis: phenotype-genotype correlation and outcome in 32 patients with CLDN16 or CLDN19 mutations

BACKGROUND AND OBJECTIVES

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis is a rare autosomal recessive renal tubular disease. It is caused by mutations in CLDN16 and CLDN19, encoding claudin-16 and -19, respectively. Familial hypomagnesemia with hypercalciuria and nephrocalcinosis is usually complicated by progressive CKD. The objectives of this study were to describe the clinical and genetic features of familial hypomagnesemia with hypercalciuria and nephrocalcinosis and analyze phenotype-genotype associations in patients with CLDN16 or CLDN19 mutations.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Data from 32 genetically confirmed patients (9 patients with CLDN16 and 23 patients with CLDN19 mutations) from 26 unrelated families were retrospectively reviewed.

RESULTS

Diagnosis was based on clinical criteria at a median age of 9.5 years and confirmed by genetic testing at a median age of 15.5 years. In total, 13 CLDN16 or CLDN19 mutations were identified, including 8 novel mutations. A founder effect was detected for the recurrent CLDN16 p.Ala139Val mutation in North African families and the CLDN19 p.Gly20Asp mutation in Spanish and French families. CKD was more frequently observed in patients with CLDN19 mutations: survival without CKD or ESRD was 56% at 20 years of age in CLDN19 versus 100% in CLDN16 mutations (log rank P<0.01). Ocular abnormalities were observed in 91% of patients with CLDN19 mutations and none of the patients with CLDN16 mutations (P<0.01). Treatments seem to have no effect on hypercalciuria and CKD progression.

CONCLUSIONS

Patients with CLDN19 mutations may display more severe renal impairment than patients with CLDN16 mutations. Ocular abnormalities were observed only in patients with CLDN19 mutations.

Pediatric en bloc kidney transplantation into pediatric recipients: the French experience

Chronic shortage of available donor organs has led to re-evaluation of the use of en bloc kidney transplants. Although excellent results have been reported in adult patients, experience in pediatric patients remains limited because of potential early complications and poor long-term graft outcome. We report 14 pediatric en bloc renal transplantations into 14 pediatric recipients, performed between 1990 and 2007 in France. We retrospectively analyzed demographic data, postoperative complications, and graft function with a median follow-up of five yr. Donor age ranged from four to 54 months. Complications were vascular graft thrombosis in four patients, leading to graft loss in two cases, and to excellent long-term graft function in the two others. Two hemorrhagic complications resulted in death in one case and in graft loss in the other. Six acute rejection episodes occurred in four patients. Median glomerular filtration rate at three months, one, five, and 10 yr was 90.8, 106, 87.8, and 66.1 mL/1.73 m(2) /min. We believe that en bloc transplantation may be an option for children with end-stage kidney disease.

Update of PAX2 mutations in renal coloboma syndrome and establishment of a locus-specific database

Renal coloboma syndrome, also known as papillorenal syndrome is an autosomal-dominant disorder characterized by ocular and renal malformations. Mutations in the paired-box gene, PAX2, have been identified in approximately half of individuals with classic findings of renal hypoplasia/dysplasia and abnormalities of the optic nerve. Prior to 2011, there was no actively maintained locus-specific database (LSDB) cataloguing the extent of genetic variation in the PAX2 gene and phenotypic variation in individuals with renal coloboma syndrome. Review of published cases and the collective diagnostic experience of three laboratories in the United States, France, and New Zealand identified 55 unique mutations in 173 individuals from 86 families. The three clinical laboratories participating in this collaboration contributed 28 novel variations in 68 individuals in 33 families, which represent a 50% increase in the number of variations, patients, and families published in the medical literature. An LSDB was created using the Leiden Open Variation Database platform: www.lovd.nl/PAX2. The most common findings reported in this series were abnormal renal structure or function (92% of individuals), ophthalmological abnormalities (77% of individuals), and hearing loss (7% of individuals). Additional clinical findings and genetic counseling implications are discussed.

Characteristics and outcomes of children with primary oxalosis requiring renal replacement therapy

BACKGROUND AND OBJECTIVES

Primary hyperoxaluria (PH) as a cause of ESRD in children is believed to have poor outcomes. Data on management and outcomes of these children remain scarce.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This study included patients aged <19 years who started renal replacement therapy (RRT) between 1979 and 2009 from 31 countries providing data to a large European registry.

RESULTS

Of 9247 incident patients receiving RRT, 100 patients had PH. PH children were significantly younger than non-PH children at the start of RRT. The median age at RRT of PH children decreased from 9.8 years in 1979-1989 to 1.5 years in 2000-2009. Survival was 86%, 79%, and 76% among PH patients at 1, 3, and 5 years after the start of RRT, compared with 97%, 94%, and 92% in non-PH patients, resulting in a three-fold increased risk of death over non-PH patients. PH and non-PH patient survival improved over time. Sixty-eight PH children received a first kidney (n=13) or liver-kidney transplantation (n=55). Although the comparison was hampered by the lower number of kidney transplantations primarily derived from the earlier era of RRT, kidney graft survival in PH patients was 82%, 79%, and 76% at 1, 3, and 5 years for liver-kidney transplantation and 46%, 28%, and 14% at 1, 3, and 5 years for kidney transplantation alone, compared with 95%, 90%, and 85% in non-PH patients.

CONCLUSIONS

The outcomes of PH children with ESRD are still poorer than in non-PH children but have substantially improved over time.

Characteristics and outcomes of children with primary oxalosis requiring renal replacement therapy

BACKGROUND AND OBJECTIVES

Primary hyperoxaluria (PH) as a cause of ESRD in children is believed to have poor outcomes. Data on management and outcomes of these children remain scarce.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This study included patients aged <19 years who started renal replacement therapy (RRT) between 1979 and 2009 from 31 countries providing data to a large European registry.

RESULTS

Of 9247 incident patients receiving RRT, 100 patients had PH. PH children were significantly younger than non-PH children at the start of RRT. The median age at RRT of PH children decreased from 9.8 years in 1979-1989 to 1.5 years in 2000-2009. Survival was 86%, 79%, and 76% among PH patients at 1, 3, and 5 years after the start of RRT, compared with 97%, 94%, and 92% in non-PH patients, resulting in a three-fold increased risk of death over non-PH patients. PH and non-PH patient survival improved over time. Sixty-eight PH children received a first kidney (n=13) or liver-kidney transplantation (n=55). Although the comparison was hampered by the lower number of kidney transplantations primarily derived from the earlier era of RRT, kidney graft survival in PH patients was 82%, 79%, and 76% at 1, 3, and 5 years for liver-kidney transplantation and 46%, 28%, and 14% at 1, 3, and 5 years for kidney transplantation alone, compared with 95%, 90%, and 85% in non-PH patients.

CONCLUSIONS

The outcomes of PH children with ESRD are still poorer than in non-PH children but have substantially improved over time.

[Kidney transplantation and infection in childhood]

Infectious risk is more important in the transplanted child than in adult because children are less often immunised against pathogens ant more exposed than adults to numerous infectious agents (virus but also bacteria including pneumococcus). The application of the standard immunisation schedule must be a permanent concern of transplantation (Tx) teams. Some vaccines that are not planned in the standard immunization schedule are particularly advised for the child and his family circle, as well as for caregivers. Immunisation response must be evaluated by a serological follow-up before Tx, in particular during the pre-Tx diagnostic work-up, then regularly after Tx. The more frequent absence of immunisation against Epstein Barr Virus (EBV) in children explains the increased frequency of post-transplant lymphoproliferative disorder at the pediatric age.

[Kidney transplantation in childhood: from milimeter to centimeters]

Graft survival is worse in recipient aged less than 5 years due to the greater risk of vascular thrombosis. Thrombosis may be prevented by the choice of the donor, method of surgery, perioperative hemodynamic optimisation and preventive anti-coagulation. Normal growth is a major objective of the management of transplanted children. The mean final height increased during the 20 last years to be between -1.63 and -0.92 SDS depending on age and period of the transplantation.

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.

Cysteamine therapy delays the progression of nephropathic cystinosis in late adolescents and adults

Nephropathic cystinosis is a multisystem autosomal recessive disease caused by cystine accumulation, which is usually treated by oral cysteamine. In order to determine long-term effects of this therapy, we enrolled 86 adult patients (mean age 26.7 years) diagnosed with nephropathic cystinosis, 75 of whom received cysteamine. Therapy was initiated at a mean age of 9.9 years with a mean duration of 17.4 years. By last follow-up, 78 patients had end-stage renal disease (mean age 11.1 years), 62 had hypothyroidism (mean age 13.4), 48 developed diabetes (mean age 17.1 years), and 32 had neuromuscular disorders (mean age 23.3 years). Initiating cysteamine therapy before 5 years of age significantly decreased the incidence and delayed the onset of end-stage renal disease, and significantly delayed the onset of hypothyroidism, diabetes, and neuromuscular disorders. The development of diabetes and hypothyroidism was still significantly delayed, however, in patients in whom therapy was initiated after 5 years of age, compared with untreated patients. The life expectancy was significantly improved in cysteamine-treated versus untreated patients. Thus, cysteamine decreases and delays the onset of complications and improves life expectancy in cystinosis. Hence, cysteamine therapy should be introduced as early as possible during childhood and maintained lifelong.