To provide the reader with understanding of neonatal physiology relating to fluids and electrolytes, and how optimal enteral and parenteral fluid provision should be provided during the transition from intra- to extrauterine life and during management of the various disorders that may occur in the neonatal period. Traditional recommendations of parenteral fluid volumes for late preterm and term infants may overestimate their fluid needs, placing them at risk for overhydration reflected by inadequate postnatal weight loss and hyponatremia. Preterm infants require larger parenteral fluid volumes than those born at term, due to their greater insensible water loss and high urine output related to their inability to adequately concentrate urine. However, care must be taken not to provide excessive fluids as it increases their risk of morbidity, mortality and adverse developmental outcomes. When providing neonates with fluids and electrolytes the uniqueness of their physiology needs to be considered. Meticulous monitoring of serum sodium, body weight and fluid balance is needed to optimize fluid and electrolyte management, especially in extremely preterm and sick infants. The volume and composition of fluid given must be adequate to maintain body homeostasis, but excessive fluid administration increases the risk of adverse neonatal outcomes.

Adenine phosphoribosyltransferase (APRT) deficiency is a rare autosomal recessive disorder of purine metabolism causing 2,8-dihydroxyadenine urinary tract stones and crystal nephropathy. Disease manifestations include acute kidney injury (AKI), progressive chronic kidney disease (CKD), and not infrequently, kidney failure. A significant proportion of affected individuals remain asymptomatic into adulthood. The diagnosis of APRT deficiency should be considered in all children presenting with renal colic, radiolucent urinary stones and/or AKI, as well as in infants with a history of reddish-brown diaper stain. Indeed, the disorder should be considered in any person with radiolucent urinary stones and in young and middle-aged individuals with progressive CKD, particularly when a kidney biopsy reveals tubulointerstitial nephropathy of unknown cause. The presence of biallelic pathogenic APRT mutations identified through targeted multi-gene panels or single-gene testing confirms the diagnosis of APRT deficiency. As kidney stone analysis can be false-positive, this method can only be considered suggestive of APRT deficiency, and confirmatory testing must be carried out in all cases. Timely diagnosis and treatment with a xanthine oxidoreductase inhibitor, either allopurinol or febuxostat, have in several studies, based on different levels of evidence, been found to be both highly effective and safe in APRT deficiency. Appropriate pharmacotherapy significantly reduces kidney stone recurrence, slows CKD progression and appears to prevent the development of kidney failure. The outcome of kidney transplantation in individuals with APRT deficiency is comparable to those with other causes of kidney failure when allopurinol or febuxostat therapy is initiated before the transplant procedure.

Adenine phosphoribosyltransferase (APRT) deficiency is a rare, autosomal recessive disorder characterized by urinary excretion of the poorly soluble 2,8-dihydroxyadenine (DHA), leading to kidney stones and chronic kidney disease. Treatment with the xanthine oxidoreductase (XOR) inhibitors allopurinol and febuxostat reduces DHA production. DHA and adenine were measured in 122 paired plasma and urine samples from 26 individuals with confirmed APRT deficiency, using ultra-performance liquid chromatography-tandem mass spectrometry assays. The relationship between plasma DHA and adenine concentrations, urine DHA-to-creatinine (DHA/Cr) and adenine-to-creatinine (adenine/Cr) ratios, and age and estimated glomerular filtration rate (eGFR) was evaluated in a subset of 87 paired plasma and urine samples from 23 individuals using Spearman's rank correlation. Allopurinol and febuxostat treatment reduced plasma DHA, with the median (range) concentration decreasing from 249 (123-1315) ng/mL in untreated individuals to below the limit of detection in those receiving higher doses. Plasma adenine increased during XOR inhibitor treatment. In untreated individuals, a strong negative correlation was observed between plasma DHA and eGFR (rs = -0.74, p < 0.0001). Plasma DHA correlated with urine DHA/Cr ratio in individuals treated with allopurinol or febuxostat (rs = 0.65, p < 0.0001), while no significant correlation was observed in untreated individuals (rs = -0.26, p = 0.14). Treatment with XOR inhibitors effectively reduces the plasma concentration and urinary excretion of DHA. The strong correlation between plasma DHA and eGFR, combined with the lack of correlation between plasma DHA and urine DHA/Cr ratio in untreated individuals, suggests that plasma DHA may be a more reliable marker of systemic DHA burden.

Adenine phosphoribosyltransferase (APRT) deficiency is a rare , hereditary disorder characterized by renal excretion of 2,8-dihydroxyadenine (DHA), leading to kidney stone formation and chronic kidney disease (CKD). Treatment with a xanthine oxidoreductase inhibitor, allopurinol or febuxostat, reduces urinary DHA excretion and slows the progression of CKD. The method currently used for therapeutic monitoring of APRT deficiency lacks specificity and thus, a more reliable measurement technique is needed. In this study, an ultra-performance liquid chromatography-tandem mass spectrometry method for simultaneous quantification of DHA, adenine, allopurinol, oxypurinol and febuxostat in human plasma was optimized and validated. Plasma samples were prepared with protein precipitation using acetonitrile followed by evaporation. The chemometric approach design of experiments was implemented to optimize gradient steepness, amount of organic solvent, flow rate, column temperature, cone voltage, desolvation temperature and desolvation flow rate. Experimental screening was conducted using fractional factorial design with addition of complementary experiments at the axial points for optimization of peak area, peak resolution and peak width. The assay was validated according to the US Food and Drug Administration guidelines for bioanalytical method validation over the concentration range of 50 to 5000 ng/mL for DHA, allopurinol and febuxostat, 100 to 5000 ng/mL for adenine and 50 to 12,000 ng/mL for oxypurinol, with r(2) >= 0.99. The analytical assay achieved acceptable performance of accuracy (-10.8 to 8.3 %) and precision (CV < 15 %). DHA, adenine, allopurinol, oxypurinol and febuxostat were stable in plasma samples after five freeze-thaw cycles at -80 degrees C and after storage at -80 degrees C for 12 months. The assay was evaluated for quantification of the five analytes in clinical plasma samples from six APRT deficiency patients and proved to be both efficient and accurate. The proposed assay will be valuable for guiding pharmacotherapy and thereby contribute to improved and more personalized care for patients with APRT deficiency.

BackgroundThere is a lack of information on the current healthcare systems for children with kidney diseases across Europe. The aim of this study was to explore the different national approaches to the organization and delivery of pediatric nephrology services within Europe.MethodsIn 2020, the European society for Paediatric Nephrology (ESPN) conducted a cross-sectional survey to identify the existing pediatric nephrology healthcare systems in 48 European countries covering a population of more than 200 million children.ResultsThe reported three most important priorities in the care of children with kidney diseases were better training of staff, more incentives for physicians to reduce staff shortages, and more hospital beds. Positive achievements in the field of pediatric nephrology included the establishment of new specialized pediatric nephrology centers, facilities for pediatric dialysis and transplant units in 18, 16, and 12 countries, respectively. The most common problems included no access to any type of dialysis (12), inadequate transplant programs for all ages of children (12), lack of well-trained physicians and dialysis nurses (12), inadequate reimbursement of hospitals for expensive therapies (10), and lack of multidisciplinary care by psychologists, dieticians, physiotherapists, social workers and vocational counsellors (6). Twenty-five of 48 countries (52%) expected to have a shortage of pediatric nephrologists in the year 2025, 63% of clinical nurses and 56% of dialysis nurses. All three groups of health care professionals were expected to be lacking in 38% of countries. Prenatal assessment and postnatal management of renal malformations by a multidisciplinary team including obstetricians, geneticists, pediatricians, and pediatric surgeons was available in one third of countries.ConclusionsOur study shows that there are still very marked differences in pediatric health care systems across the European countries and highlights the need need for appropriate services for children with kidney disease in all European countries.

Abstract Background and Aims Adenine phosphoribosyltransferase (APRT) deficiency is a rare autosomal recessive disorder of adenine metabolism that results in renal excretion of 2,8-dihydroxyadenine (DHA) in excessive amounts, leading to kidney stones and crystal nephropathy with associated inflammation and fibrosis. The effects of other kidney stone constituents, such as calcium oxalate and uric acid, have been thoroughly studied in cell culture models, both in monolayer and three-dimensional (3D) assays. However, the effect of DHA in cell culture models has not yet been investigated. This study aimed to establish a comprehensive cell culture model to investigate DHA crystal-induced kidney injury and to identify therapeutic targets for clinical intervention. Method Three lines of kidney cells (MDCK, HK-2, and HEK293) were utilized in monolayer and 3D assays, employing both liquid-liquid interface (LLI) and “on-top” of Matrigel culture models. DHA exposure, matching the quantities found in the urine of untreated patients with APRT deficiency, was used in conjunction with siRNA-mediated APRT gene knockdown to assess the changes in cellular phenotypes. Assessments included cell viability and migration assays, RT-PCR, western blotting, phase-contrast microscopy, and immunostaining. Paraffin-embedded kidney tissue samples from patients with APRT deficiency and healthy controls were obtained from the Landspitali National University Hospital Biobank (Icelandic IRB permit: VSN 21-117-V1) and phenotypically analyzed using immunohistochemistry (IHC) staining for collagen I (Col I), collagen III (Col III), and APRT. Results After 72 h of incubation with DHA at concentrations of 60, 120, 240, and 480 μg/mL, the viability of all cell lines decreased. Proliferation was evaluated using a scratch assay after treatment with DHA at two different concentrations (120 and 480 μg/mL) for 24 h, and all cell lines showed decreased migration at the highest concentration. Enhanced CD44 expression was observed in both HEK293 and MDCK cells with increasing DHA concentration. In a 3D environment “on-top” of Matrigel, MDCK cells maintained polarized structures despite accumulation of DHA and did not show an increased EMT phenotype compared with TGFβ-treated cells. HEK293 and HK-2 cells formed solid colonies with DHA accumulation within the colony. MDCK cells formed a polarized cell layer grown on Transwell polyester membranes and demonstrated trans-epithelial electrical resistance (TEER) in LLI, which decreased when the cells were treated with DHA at 120 and 480 μg/mL. APRT expression was significantly reduced in all cell lines after successful knockdown. Analysis of kidney tissue specimens using IHC showed increased expression of Col III in patients with APRT deficiency compared to healthy controls. Enhanced Col I expression was also observed in these patients, which, together with Col III, was consistent with increased fibrosis. Conclusion This study revealed that incubation with varying concentrations of DHA led to decreased viability and impaired migration in all cell lines tested. Increased CD44 expression suggests potential crystal binding to renal tubular epithelial cells when exposed to increasing DHA concentrations. In a 3D environment, MDCK cells maintained polarized structures with DHA accumulation without enhancement of the EMT phenotype. Treatment with DHA resulted in a decrease in TEER, indicating a defective barrier function. Increased expression of Col III and Col I was observed in kidney tissue samples from APRT-deficient patients, suggesting increased fibrosis. Overall, these findings highlight the impact of DHA on cell viability, proliferation, EMT, and barrier function, highlighting the role of DHA in kidney fibrosis in patients with APRT-deficiency.

PURPOSE:Childhood incontinence is stigmatized and underprioritized, and a basic understanding of its pathogenesis is missing. Our goal was to identify risk-conferring genetic variants in daytime urinary incontinence (DUI). MATERIALS AND METHODS:We conducted a genome-wide association study in the Danish iPSYCH2015 cohort. Cases (3024) were identified through DUI diagnosis codes and redeemed prescriptions for DUI medication in individuals aged 5 to 20 years. Controls (30,240), selected from the same sample, were matched to cases on sex and psychiatric diagnoses, if any, and down-sampled to a 1:10 case:control ratio. Replication was performed in the Icelandic deCODE cohort (5475 cases/287,773 controls). Single-nucleotide polymorphism heritability was calculated using the genome-based restricted maximum likelihood method. Cross-trait genetic correlation was estimated using linkage disequilibrium score regression. Polygenic risk scores generated with LDpred2-auto and BOLT-LMM were assessed for association. RESULTS:Variants on chromosome 6 (rs12210989, odds ratio [OR] 1.24, 95% CI 1.17-1.32, P = 3.21 × 10-12) and 20 (rs4809801, OR 1.18, 95% CI 1.11-1.25, P = 3.66 × 10-8) reached genome-wide significance and implicated the PRDM13 and RIPOR3 genes. Chromosome 6 findings were replicated (P = .024, OR 1.09, 95% CI 1.01-1.16). Liability scale heritability ranged from 10.20% (95% CI 6.40%-14.00%) to 15.30% (95% CI 9.66%-20.94%). DUI and nocturnal enuresis showed positive genetic correlation (rg = 1.28 ± 0.38, P = .0007). DUI was associated with attention-deficit/hyperactivity disorder (OR 1.098, 95% CI 1.046-1.152, P < .0001) and BMI (OR 1.129, 95% CI 1.081-1.178, P < .0001) polygenic risk. CONCLUSIONS:Common genetic variants contribute to the risk of childhood DUI, and genes important in neuronal development and detrusor smooth muscle activity were implicated. These findings may help guide identification of new treatment targets.

BackgroundPrimary, secondary and tertiary healthcare services in Europe create complex networks covering pediatric subspecialties, sociology, economics and politics. Two surveys of the European Society for Paediatric Nephrology (ESPN) in 1998 and 2017 revealed substantial disparities of kidney care among European countries. The purpose of the third ESPN survey is to further identify national differences in the conceptualization and organization of European pediatric kidney health care pathways during and outside normal working hours.MethodsIn 2020, a questionnaire was sent to one leading pediatric nephrologist from 48 of 53 European countries as defined by the World Health Organization. In order to exemplify care pathways in pediatric primary care nephrology, urinary tract infection (UTI) was chosen. Steroid sensitive nephrotic syndrome (SSNS) was chosen for pediatric rare disease nephrology and acute kidney injury (AKI) was analyzed for pediatric emergency nephrology.ResultsThe care pathways for European children and young people with urinary tract infections were variable and differed during standard working hours and also during night-time and weekends. During daytime, UTI care pathways included six different types of care givers. There was a shift from primary care services outside standard working hours to general outpatient polyclinic and hospital services. Children with SNSS were followed up by pediatric nephrologists in hospitals in 69% of countries. Patients presenting with community acquired AKI were admitted during regular working hours to secondary or tertiary care hospitals. During nights and weekends, an immediate shift to University Children's Hospitals was observed where treatment was started by intensive care pediatricians and pediatric nephrologists.ConclusionGaps and fragmentation of pediatric health services may lead to the risk of delayed or inadequate referral of European children with kidney disease to pediatric nephrologists. The diversity of patient pathways outside of normal working hours was identified as one of the major weaknesses in the service chain.

At-home urine sampling is commonly used to evaluate renal excretion of biomarkers for diagnostic purposes and therapeutic drug monitoring (TDM). While 24-hr collection is the preferred method, it is commonly associated with sampling errors resulting in incomplete or excessive urine collection. Therefore, more simple and precise sampling methods are needed. We present our studies of urine 2,8-dihydroxyadenine (DHA) quantification in patients with adenine phosphoribosyltransferase (APRT) deficiency, focusing on the comparison between single-void urine samples and 24-hr urine collections. Our findings show a strong correlation between DHA-to-creatinine ratio in first-morning void urine samples and 24-hr urinary DHA excretion. Hence, the use of single-void urine samples for quantification of DHA excretion in patients with APRT deficiency eliminates inaccuracies associated with sampling errors and is more convenient for patients. Simplified and more accurate assessment of urinary DHA excretion will improve TDM and hopefully result in improved outcomes of patients. Future studies will address the use of microsampling for quantification of DHA.

Although underlying mechanisms and the clinical course of kidney disease progression are well described, less is known about potential disease reversibility. Therefore, to analyze kidney recovery, we adapted a commonly used murine chronic kidney disease (CKD) model of 2,8- dihydroxyadenine (2,8-DHA) crystal-induced nephropathy to study disease recovery and efficacy of disease-modifying interventions. The recovery phase after CKD was characterized by improved kidney function after two weeks which remained stable thereafter. By contrast, even after eight weeks recovery, tubular injury and inflammation were only partially reduced, and fibrosis persisted. Deep-learning-based histologic analysis of 8,604 glomeruli and 596,614 tubular cross sections revealed numerous tubules had undergone either prominent dilation or complete atrophy, leading to atubular glomeruli and irreversible nephron loss. We confirmed these findings in a second CKD model, reversible unilateral ureteral obstruction, in which a rapid improvement of glomerular filtration rate during recovery also did not reflect the permanent histologic kidney injury. In 2,8-DHA nephropathy, increased drinking volume was highly effective in disease prevention. However, in therapeutic approaches, high fluid intake was only effective in moderate but not severe CKD and established tissue injury was again poorly reflective of kidney function parameters. The injury was particularly localized in the medulla, which is often not analyzed. Thus, recovery after crystal- or obstruction-induced CKD is characterized by ongoing tissue injury, fibrosis, and nephron loss, but not reflected by standard measures of kidney function. Hence, our data might aid in designing kidney recovery studies and suggest the need for biomarkers specifically monitoring intra-kidney tissue injury.