Consistency of metabolite associations with measured glomerular filtration rate in children and adults.

Background: There is interest in identifying novel filtration markers that lead to more accurate GFR estimates than current markers (creatinine and cystatin C) and are more consistent across demographic groups. We hypothesize that large-scale metabolomics can identify serum metabolites that are strongly influenced by glomerular filtration rate (GFR) and are more consistent across demographic variables than creatinine, which would be promising filtration markers for future investigation. Methods: We evaluated the consistency of associations between measured GFR (mGFR) and 887 common, known metabolites quantified by an untargeted chromatography- and spectroscopy-based metabolomics platform (Metabolon) performed on frozen blood samples from 580 participants in Chronic Kidney Disease in Children (CKiD), 674 participants in Modification of Diet in Renal Disease (MDRD) Study and 962 participants in African American Study of Kidney Disease and Hypertension (AASK). We evaluated metabolite-mGFR correlation association with metabolite class, molecular weight, assay platform and measurement coefficient of variation (CV). Among metabolites with strong negative correlations with mGFR (r < -0.5), we assessed additional variation by age (height in children), sex, race and body mass index (BMI). Results: A total of 561 metabolites (63%) were negatively correlated with mGFR. Correlations with mGFR were highly consistent across study, sex, race and BMI categories (correlation of metabolite-mGFR correlations between 0.88 and 0.95). Amino acids, carbohydrates and nucleotides were more often negatively correlated with mGFR compared with lipids, but there was no association with metabolite molecular weight, liquid chromatography/mass spectrometry platform and measurement CV. Among 114 metabolites with strong negative associations with mGFR (r < -0.5), 27 were consistently not associated with age (height in children), sex or race. Conclusions: The majority of metabolite-mGFR correlations were negative and consistent across sex, race, BMI and study. Metabolites with consistent strong negative correlations with mGFR and non-association with demographic variables may represent candidate markers to improve estimation of GFR.

Investigating the use of finerenone in children with chronic kidney disease and proteinuria: design of the FIONA and open-label extension studies.

INTRODUCTION: Proteinuria is a modifiable risk factor for chronic kidney disease (CKD) progression in children. Finerenone, a selective, non-steroidal, mineralocorticoid receptor antagonist (MRA) has been approved to treat adults with CKD associated with type 2 diabetes mellitus (T2DM) following results from the phase III clinical trials FIDELIO-DKD (NCT02540993) and FIGARO-DKD (NCT02545049). In a pre-specified pooled analysis of both studies (N = 13,026), finerenone was shown to have an acceptable safety profile and was efficacious in decreasing the risk of adverse kidney and cardiovascular outcomes and of proteinuria. OBJECTIVE: FIONA and the associated open-label extension (OLE) study aim to demonstrate that combining finerenone with an angiotensin-converting enzyme inhibitor (ACEi) or angiotensin receptor blocker (ARB) is safe, well-tolerated, and effective in sustainably reducing urinary protein excretion in children with CKD and proteinuria. DESIGN: FIONA (NCT05196035; Eudra-CT: 2021-002071-19) is a randomized (2:1), double-blind, placebo-controlled, multicenter, phase III study of 6 months' duration in approximately 219 pediatric patients. Patients must have a clinical diagnosis of CKD (an eGFR ≥ 30 mL/min/1.73 m2 if ≥ 1 to < 18 years or a serum creatinine level ≤ 0.40 mg/dL for infants 6 months to < 1 year) with significant proteinuria despite ACEi or ARB usage. The primary objective is to demonstrate that finerenone, added to an ACEi or ARB, is superior to placebo in reducing urinary protein excretion. FIONA OLE (NCT05457283; Eudra-CT: 2021-002905-89) is a single-arm, open-label study, enrolling participants who have completed FIONA. The primary objective of FIONA OLE is to provide long-term safety data. FIONA has two primary endpoints: urinary protein-to-creatinine ratio (UPCR) reduction of ≥ 30% from baseline to day 180 and percent change in UPCR from baseline to day 180. A sample size of 198 participants (aged 2 to < 18 years) in FIONA will provide at least 80% power to reject the null hypothesis of either of the two primary endpoints. CONCLUSION: FIONA is evaluating the use of finerenone in children with CKD and proteinuria. Should safety, tolerability, and efficacy be demonstrated, finerenone could become a useful additional therapeutic agent in managing proteinuria and improving kidney outcomes in children with CKD. TRIAL REGISTRATION: ClinicalTrials.gov NCT05196035. Registered on 19 January 2022.

Evidence of increased vascular stiffness and left ventricular hypertrophy in children with cystic kidney disease.

BACKGROUND: Cardiovascular disease (CVD) is the most common cause of mortality in chronic kidney disease (CKD). Children with early-onset CKD arguably experience the greatest lifetime CVD burden. We utilized data from the Chronic Kidney Disease in Children Cohort Study (CKiD) to evaluate two pediatric CKD cohorts: congenital anomalies of the kidney and urinary tract (CAKUT) and cystic kidney disease for CVD risks and outcomes. METHODS: CVD risk factors and outcomes including blood pressures, left ventricular hypertrophy (LVH), left ventricular mass index (LVMI), and ambulatory arterial stiffness index (AASI) scores were evaluated. RESULTS: Forty-one patients in the cystic kidney disease group were compared to 294 patients in the CAKUT group. Cystic kidney disease patients had higher cystatin-C levels, despite similar iGFR. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) indexes were higher in the CAKUT group, but a significantly higher proportion of cystic kidney disease patients was on anti-hypertensive medications. Cystic kidney disease patients had increased AASI scores and a higher incidence of LVH. CONCLUSIONS: This study provides a nuanced analysis of CVD risk factors and outcomes including AASI and LVH in two pediatric CKD cohorts. Cystic kidney disease patients had increased AASI scores, higher incidence of LVH, and higher rates of anti-hypertensive medication use which could imply a greater burden of CVD despite similar GFR. Our work suggests that additional mechanisms may contribute to vascular dysfunction in cystic kidney disease, and that these patients may need additional interventions to prevent the development of CVD. A higher resolution version of the Graphical abstract is available as Supplementary information.

Longitudinal changes of health-related quality of life in childhood chronic kidney disease.

BACKGROUND: Few longitudinal studies have evaluated the impact of chronic kidney disease (CKD) duration on health-related quality of life (HRQOL). The study's aim was to determine how HRQOL changes over time in childhood CKD. METHODS: Study participants were children in the chronic kidney disease in children (CKiD) cohort who completed the pediatric quality of life inventory (PedsQL) on three or more occasions over the course of two or more years. Generalized gamma (GG) mixed-effects models were applied to assess the effect of CKD duration on HRQOL while controlling for selected covariates. RESULTS: A total of 692 children (median age = 11.2) with a median of 8.3 years duration of CKD were evaluated. All subjects had a GFR greater than 15 ml/min/1.73 m2. GG models with child self-report PedsQL data indicated that longer CKD duration was associated with improved total HRQOL and the 4 domains of HRQOL. GG models with parent-proxy PedsQL data indicated that longer duration was associated with better emotional but worse school HRQOL. Increasing trajectories of child self-report HRQOL were observed in the majority of subjects, while parents less frequently reported increasing trajectories of HRQOL. There was no significant relationship between total HRQOL and time-varying GFR. CONCLUSIONS: Longer duration of the disease is associated with improved HRQOL on child self-report scales; however, parent-proxy results were less likely to demonstrate any significant change over time. This divergence could be due to greater optimism and accommodation of CKD in children. Clinicians can use these data to better understand the needs of pediatric CKD patients. A higher resolution version of the Graphical abstract is available as Supplementary information.

An automated histological classification system for precision diagnostics of kidney allografts.

For three decades, the international Banff classification has been the gold standard for kidney allograft rejection diagnosis, but this system has become complex over time with the integration of multimodal data and rules, leading to misclassifications that can have deleterious therapeutic consequences for patients. To improve diagnosis, we developed a decision-support system, based on an algorithm covering all classification rules and diagnostic scenarios, that automatically assigns kidney allograft diagnoses. We then tested its ability to reclassify rejection diagnoses for adult and pediatric kidney transplant recipients in three international multicentric cohorts and two large prospective clinical trials, including 4,409 biopsies from 3,054 patients (62.05% male and 37.95% female) followed in 20 transplant referral centers in Europe and North America. In the adult kidney transplant population, the Banff Automation System reclassified 83 out of 279 (29.75%) antibody-mediated rejection cases and 57 out of 105 (54.29%) T cell-mediated rejection cases, whereas 237 out of 3,239 (7.32%) biopsies diagnosed as non-rejection by pathologists were reclassified as rejection. In the pediatric population, the reclassification rates were 8 out of 26 (30.77%) for antibody-mediated rejection and 12 out of 39 (30.77%) for T cell-mediated rejection. Finally, we found that reclassification of the initial diagnoses by the Banff Automation System was associated with an improved risk stratification of long-term allograft outcomes. This study demonstrates the potential of an automated histological classification to improve transplant patient care by correcting diagnostic errors and standardizing allograft rejection diagnoses.ClinicalTrials.gov registration: NCT05306795 .

COL4A gene variants are common in children with hematuria and a family history of kidney disease.

BACKGROUND: Inherited kidney diseases are a common cause of chronic kidney disease (CKD) in children. Identification of a monogenic cause of CKD is more common in children than in adults. This study evaluated the diagnostic yield and phenotypic spectrum of children who received genetic testing through the KIDNEYCODE sponsored genetic testing program. METHODS: Unrelated children < 18 years of age who received panel testing through the KIDNEYCODE sponsored genetic testing program from September 2019 through August 2021 were included (N = 832). Eligible children met at least one of the following clinician-reported criteria: estimated GFR ≤ 90 ml/min/1.73 m2, hematuria, a family history of kidney disease, or suspected or biopsy confirmed Alport syndrome or focal segmental glomerulosclerosis (FSGS) in the tested individual or family member. RESULTS: A positive genetic diagnosis was observed in 234 children (28.1%, 95% CI [25.2-31.4%]) in genes associated with Alport syndrome (N = 213), FSGS (N = 9), or other disorders (N = 12). Among children with a family history of kidney disease, 30.8% had a positive genetic diagnosis. Among those with hematuria and a family history of CKD, the genetic diagnostic rate increased to 40.4%. CONCLUSIONS: Children with hematuria and a family history of CKD have a high likelihood of being diagnosed with a monogenic cause of kidney disease, identified through KIDNEYCODE panel testing, particularly COL4A variants. Early genetic diagnosis can be valuable in targeting appropriate therapy and identification of other at-risk family members. A higher resolution version of the Graphical abstract is available as Supplementary information.

Identification of Novel Genetic Risk Factors for Focal Segmental Glomerulosclerosis in Children: Results From the Chronic Kidney Disease in Children (CKiD) Cohort.

RATIONALE & OBJECTIVE: Focal segmental glomerulosclerosis (FSGS) is a major cause of pediatric nephrotic syndrome, and African Americans exhibit an increased risk for developing FSGS compared with other populations. Predisposing genetic factors have previously been described in adults. Here we performed genomic screening of primary FSGS in a pediatric African American population. STUDY DESIGN: Prospective cohort with case-control genetic association study design. SETTING & PARTICIPANTS: 140 African American children with chronic kidney disease from the Chronic Kidney Disease in Children (CKiD) cohort, including 32 cases with FSGS. PREDICTORS: Over 680,000 common single-nucleotide polymorphisms (SNPs) were tested for association. We also ran a pathway enrichment analysis and a human leucocyte antigen (HLA)-focused association study. OUTCOME: Primary biopsy-proven pediatric FSGS. ANALYTICAL APPROACH: Multivariate logistic regression models. RESULTS: The genome-wide association study revealed 169 SNPs from 14 independent loci significantly associated with FSGS (false discovery rate [FDR]<5%). We observed notable signals for genetic variants within the APOL1 (P=8.6×10-7; OR, 25.8 [95% CI, 7.1-94.0]), ALMS1 (P=1.3×10-7; 13.0% in FSGS cases vs 0% in controls), and FGFR4 (P=4.3×10-6; OR, 24.8 [95% CI, 6.3-97.7]) genes, all of which had previously been associated with adult FSGS, kidney function, or chronic kidney disease. We also highlighted novel, functionally relevant genes, including GRB2 (which encodes a slit diaphragm protein promoting podocyte structure through actin polymerization) and ITGB1 (which is linked to renal injuries). Our results suggest a major role for immune responses and antigen presentation in pediatric FSGS through (1) associations with SNPs in PTPRJ (or CD148, P=3.5×10-7), which plays a role in T-cell receptor signaling, (2) HLA-DRB1∗11:01 association (P=6.1×10-3; OR, 4.5 [95% CI, 1.5-13.0]), and (3) signaling pathway enrichment (P=1.3×10-6). LIMITATIONS: Sample size and no independent replication cohort with genomic data readily available. CONCLUSIONS: Our genetic study has identified functionally relevant risk factors and the importance of immune regulation for pediatric primary FSGS, which contributes to a better description of its molecular pathophysiological mechanisms. PLAIN-LANGUAGE SUMMARY: We assessed the genetic risk factors for primary focal segmental glomerulosclerosis (FSGS) by simultaneously testing over 680,000 genetic markers spread across the genome in 140 children, including 32 with FSGS lesions. Fourteen independent genetic regions were significantly associated with pediatric FSGS, including APOL1 and ALMS1-NAT8, which were previously found to be associated with FSGS and chronic kidney diseases in adults. Novel genes with relevant biological functions were also highlighted, such as GRB2 and FGFR4, which play a role in the kidney filtration barrier and in kidney cell differentiation, respectively. Finally, we revealed the importance of immune regulation in pediatric FSGS through associations involving cell surface proteins presenting antigens to the immune system and interacting with T-cell receptors.

Subcutaneous C.E.R.A. for the Maintenance Treatment of Anemia in Pediatric Patients With CKD: A Phase 2, Open-Label, Single-Arm, Multicenter Study.

RATIONALE & OBJECTIVE: The optimum starting dose of intravenous continuous erythropoietin receptor activator (C.E.R.A.) has been previously determined; this study ascertains the optimum starting dose of subcutaneous C.E.R.A. administration in pediatric patients. STUDY DESIGN: Phase 2, open-label, single-arm, multicenter study. SETTING & PARTICIPANTS: Patients aged 3 months to 17 years with renal anemia and chronic kidney disease (CKD; including those treated with maintenance dialysis and those not treated with dialysis) who were receiving maintenance treatment with erythropoiesis-stimulating agents (ESAs). INTERVENTION: Subcutaneous C.E.R.A. administration every 4 weeks (starting dose was based on defined conversion factors). OUTCOME: The primary outcome was the change in hemoglobin concentration between the baseline and evaluation period for each patient. Secondary efficacy measures and safety were also evaluated. RESULTS: Forty patients aged 0.4-17.7 years were enrolled. The study achieved its primary outcome: the mean change in hemoglobin concentration was an increase of 0.48g/dL; the 95% confidence interval (0.15-0.82) and standard deviation (±1.03) were within the prespecified boundaries (-1 to 1g/dL and<1.5g/dL, respectively). Mean hemoglobin concentrations were maintained within the target 10-12g/dL range in 24 of 38 patients and within±1g/dL of the baseline in 19 of 38 patients, and the median C.E.R.A. subcutaneous dose decreased over time. Efficacy in key subgroups (age group, dialysis type, prior ESA treatment) was consistent with the primary outcome. Thirty-eight patients completed the core period; 25 chose to enter the safety extension period. Safety was consistent with prior studies, with no new signals. LIMITATIONS: Single-arm and open-label study; small sample size. CONCLUSIONS: Pediatric patients with anemia secondary to CKD who were on, or not on, dialysis could be safely and effectively switched from maintenance ESAs to subcutaneous C.E.R.A. administered every 4 weeks, using defined dose-conversion factors to determine the optimum starting dose. FUNDING: F. Hoffmann-La Roche Ltd. TRIAL REGISTRATION: The SKIPPER trial registered at ClinicalTrials.gov with study number NCT03552393. PLAIN-LANGUAGE SUMMARY: Anemia, a complication of chronic kidney disease, is associated with poor quality of life and an increased risk of hospitalization and mortality. The current treatments for anemia include iron therapy and erythropoiesis-stimulating agents (ESAs); however, the relatively short half-lives of the ESAs epoetin alfa/beta or darbepoetin alfa may require more frequent dosing and hospital visits compared with the ESA known as continuous erythropoietin receptor activator (C.E.R.A.). A previous study demonstrated that children aged 5 years or more with anemia associated with chronic kidney disease who were on hemodialysis could be switched to intravenous C.E.R.A. from their existing epoetin alfa/beta or darbepoetin alfa treatment. This study provides evidence that subcutaneous C.E.R.A. can safely and effectively treat anemia in children, including those aged<5 years and regardless of whether they were on dialysis or the type of dialysis they received (peritoneal dialysis or hemodialysis).

Genomic Disorders in CKD across the Lifespan.

SIGNIFICANCE STATEMENT: Pathogenic structural genetic variants, also known as genomic disorders, have been associated with pediatric CKD. This study extends those results across the lifespan, with genomic disorders enriched in both pediatric and adult patients compared with controls. In the Chronic Renal Insufficiency Cohort study, genomic disorders were also associated with lower serum Mg, lower educational performance, and a higher risk of death. A phenome-wide association study confirmed the link between kidney disease and genomic disorders in an unbiased way. Systematic detection of genomic disorders can provide a molecular diagnosis and refine prediction of risk and prognosis. BACKGROUND: Genomic disorders (GDs) are associated with many comorbid outcomes, including CKD. Identification of GDs has diagnostic utility. METHODS: We examined the prevalence of GDs among participants in the Chronic Kidney Disease in Children (CKiD) cohort II ( n =248), Chronic Renal Insufficiency Cohort (CRIC) study ( n =3375), Columbia University CKD Biobank (CU-CKD; n =1986), and the Family Investigation of Nephropathy and Diabetes (FIND; n =1318) compared with 30,746 controls. We also performed a phenome-wide association analysis (PheWAS) of GDs in the electronic MEdical Records and GEnomics (eMERGE; n =11,146) cohort. RESULTS: We found nine out of 248 (3.6%) CKiD II participants carried a GD, replicating prior findings in pediatric CKD. We also identified GDs in 72 out of 6679 (1.1%) adult patients with CKD in the CRIC, CU-CKD, and FIND cohorts, compared with 199 out of 30,746 (0.65%) GDs in controls (OR, 1.7; 95% CI, 1.3 to 2.2). Among adults with CKD, we found recurrent GDs at the 1q21.1, 16p11.2, 17q12, and 22q11.2 loci. The 17q12 GD (diagnostic of renal cyst and diabetes syndrome) was most frequent, present in 1:252 patients with CKD and diabetes. In the PheWAS, dialysis and neuropsychiatric phenotypes were the top associations with GDs. In CRIC participants, GDs were associated with lower serum magnesium, lower educational achievement, and higher mortality risk. CONCLUSION: Undiagnosed GDs are detected both in children and adults with CKD. Identification of GDs in these patients can enable a precise genetic diagnosis, inform prognosis, and help stratify risk in clinical studies. GDs could also provide a molecular explanation for nephropathy and comorbidities, such as poorer neurocognition for a subset of patients.

Associations of body mass index (BMI) and BMI change with progression of chronic kidney disease in children.

BACKGROUND: Obesity is prevalent among children with chronic kidney disease (CKD) and is associated with cardiovascular disease and reduced quality of life. Its relationship with pediatric CKD progression has not been described. METHODS: We evaluated relationships between both body mass index (BMI) category (normal, overweight, obese) and BMI z-score (BMIz) change on CKD progression among participants of the Chronic Kidney Disease in Children study. Kaplan-Meier survival curves and multivariable parametric failure time models depict the association of baseline BMI category on time to kidney replacement therapy (KRT). Additionally, the annualized percentage change in estimated glomerular filtration rate (eGFR) was modeled against concurrent change in BMIz using multivariable linear regression with generalized estimating equations which allowed for quantification of the effect of BMIz change on annualized eGFR change. RESULTS: Participants had median age of 10.9 years [IQR: 6.5, 14.6], median eGFR of 50 ml/1.73 m2 [IQR: 37, 64] and 63% were male. 160 (27%) of 600 children with non-glomerular and 77 (31%) of 247 children with glomerular CKD progressed to KRT over a median of 5 years [IQR: 2, 8]. Times to KRT were not significantly associated with baseline BMI category. Children with non-glomerular CKD who were obese experienced significant improvement in eGFR (+ 0.62%; 95% CI: + 0.17%, + 1.08%) for every 0.1 standard deviation concurrent decrease in BMI. In participants with glomerular CKD who were obese, BMIz change was not significantly associated with annualized eGFR change. CONCLUSION: Obesity may represent a target of intervention to improve kidney function in children with non-glomerular CKD. A higher resolution version of the Graphical abstract is available as Supplementary information.

A longitudinal analysis of the effect of anemia on executive functions in children with mild to moderate chronic kidney disease.

BACKGROUND: Children with chronic kidney disease (CKD) are at risk for cognitive dysfunction. The aim of this study was to investigate associations between executive functions (EF), anemia, and iron deficiency. METHODS: A total of 688 children > 6 years of age enrolled in the Chronic Kidney Disease in Children (CKiD) study who underwent evaluation for EF were included. Hemoglobin (Hgb) was characterized as low (1st-5th percentile) or very low (< 1st percentile) compared to normative values for age, sex, and race irrespective of erythropoiesis-stimulating agent (ESA) usage. Longitudinal analysis was conducted using consecutive visit pairs, with anemia status defined as new onset, resolved, or persistent. Linear mixed models with random intercept were used and adjusted for key covariates. RESULTS: Anemia was present in 41% of children, and median Hgb was 11.8 gm/dl. New onset anemia was associated with lower digit span total score (- 0.75, 95% CI - 1.36, - 0.15, p = 0.01). Persistent anemia was associated with lower scores on color-word inhibition/switching (ß = - 0.98; 95% CI - 1.78, - 0.18, p = 0.02). Errors of omission were significantly higher (worse) in those with persistent anemia (ß = 2.67, 95% CI 0.18, 5.17, p = 0.04). Very low Hgb levels were significantly associated with lower color-word inhibition/switching scores (ß = - 1.33, 95% CI - 2.16, - 0.51; p = 0.002). Anemia and low GFR were associated with lower category fluency scores compared to non-anemic subjects with higher GFR (ß = - 1.09, 95% CI - 2.09, - 0.10, p = 0.03). CONCLUSIONS: The presence of anemia, in addition to its severity and duration in children with CKD, is associated with poorer scores on select measures of EF. A higher resolution version of the Graphical abstract is available as Supplementary information.

The KIDNEYCODE Program: Diagnostic Yield and Clinical Features of Individuals with CKD.

Background: Despite increasing recognition that CKD may have underlyi ng genetic causes, genetic testing remains limited. This study evaluated the diagnostic yield and phenotypic spectrum of CKD in individuals tested through the KIDNEYCODE sponsored genetic testing program. Methods: Unrelated individuals who received panel testing (17 genes) through the KIDNEYCODE sponsored genetic testing program were included. Individuals had to meet at least one of the following eligibility criteria: eGFR ≤90 ml/min per 1.73m2 and hematuria or a family history of kidney disease; or suspected/biopsy-confirmed Alport syndrome or FSGS in tested individuals or relatives. Results: Among 859 individuals, 234 (27%) had molecular diagnoses in genes associated with Alport syndrome (n=209), FSGS (n=12), polycystic kidney disease (n=6), and other disorders (n=8). Among those with positive findings in a COL4A gene, the majority were in COL4A5 (n=157, 72 hemizygous male and 85 heterozygous female individuals). A positive family history of CKD, regardless of whether clinical features were reported, was more predictive of a positive finding than was the presence of clinical features alone. For the 248 individuals who had kidney biopsies, a molecular diagnosis was returned for 49 individuals (20%). Most (n=41) individuals had a molecular diagnosis in a COL4A gene, 25 of whom had a previous Alport syndrome clinical diagnosis, and the remaining 16 had previous clinical diagnoses including FSGS (n=2), thin basement membrane disease (n=9), and hematuria (n=1). In total, 491 individuals had a previous clinical diagnosis, 148 (30%) of whom received a molecular diagnosis, the majority (89%, n=131) of which were concordant. Conclusions: Although skewed to identify individuals with Alport syndrome, these findings support the need to improve access to genetic testing for patients with CKD-particularly in the context of family history of kidney disease, hematuria, and hearing loss.

Urinary Polycyclic Aromatic Hydrocarbons in a Longitudinal Cohort of Children with CKD: A Case of Reverse Causation?

Background: Air pollution, which results in the formation of polycyclic aromatic hydrocarbons (PAHs), has been identified as a cause of renal function decline and a contributor to CKD. However, the results of cross-sectional studies investigating personal, integrated biomarkers of PAHs have been mixed. Longitudinal studies may be better suited to evaluate environmental drivers of kidney decline. The purpose of this study was to examine associations of serially measured urinary PAH metabolites with clinical and subclinical measures of kidney function over time among children with CKD. Methods: This study was conducted among 618 participants in the Chronic Kidney Disease in Children study, a cohort study of pediatric patients with CKD from the United States and Canada, between 2005 and 2015. In serially collected urine samples over time, nine PAH metabolites were measured. Clinical outcomes measured annually included eGFR, proteinuria, and BP. Subclinical biomarkers of tubular injury (kidney injury molecule-1 [KIM-1] and neutrophil gelatinase-associated lipocalin [NGAL]) and oxidant stress (8-hydroxy-2'-deoxyguanosine [8-OHdG] and F2-isoprostane) were assayed in urine samples. Results: Children were followed over an average (SD) of 3.0 (1.6) years and 2469 study visits (mean±SD, 4.0±1.6). Hydroxynaphthalene (NAP) or hydroxyphenanthrene (PHEN) metabolites were detected in >99% of samples and NAP concentrations were greater than PHEN concentrations. PHEN metabolites, driven by 3-PHEN, were associated with increased eGFR and reduced proteinuria, diastolic BP z-score, and NGAL concentrations over time. However, PAH metabolites were consistently associated with increased KIM-1 and 8-OHdG concentrations. Conclusions: Among children with CKD, these findings provoke the potential explanation of reverse causation, where renal function affects measured biomarker concentrations, even in the setting of a longitudinal study. Additional work is needed to determine if elevated KIM-1 and 8-OHdG excretion reflects site-specific injury to the proximal tubule mediated by low-grade oxidant stress.

Self-reported Race, Serum Creatinine, Cystatin C, and GFR in Children and Young Adults With Pediatric Kidney Diseases: A Report From the Chronic Kidney Disease in Children (CKiD) Study.

RATIONALE & OBJECTIVE: Recent reassessment of the use of race in estimated glomerular filtration rate (eGFR) in adults has instigated questions about the role of race in eGFR expressions for children. Little research has examined the associations of self-reported race with measured GFR (mGFR) adjusting for serum creatinine or cystatin C in children and young adults with chronic kidney disease (CKD). This study examined these associations and evaluated the performance of the previously published "U25" (under the age of 25 years) eGFR equations in a large cohort of children and young adults with CKD. STUDY DESIGN: Observational cohort study. SETTING & PARTICIPANTS: Participants in the Chronic Kidney Disease in Children (CKiD) study including 190 Black and 675 non-Black participants contributing 473 and 1,897 annual person-visits, respectively. EXPOSURE: Self- or parental-reported race (Black, non-Black). Adjustment for serum creatinine or cystatin C, body size, and socioeconomic status. OUTCOME: mGFR based on iohexol clearance. ANALYTICAL APPROACH: Linear regression with generalized estimating equations, stratified by age (<6, 6-12, 12-18, and ≥18 years) incorporating serum creatinine or serum cystatin C. Contrasting performance in different self-reported racial groups of the U25 eGFR equations. RESULTS: Self-reported Black race was significantly associated with 12.8% higher mGFR among children in regression models including serum creatinine. Self-reported Black race was significantly associated with 3.5% lower mGFR after adjustment for cystatin C overall but was not significant for those over 12 years. The results were similar after adjustment for body size and socioeconomic factors. The average of creatinine- and cystatin C-based U25 equations was unbiased by self-reported race groups. LIMITATIONS: Small number of children < 6 years; lean body mass was estimated. CONCLUSIONS: Differences in the creatinine-mGFR relationship by self-reported race were observed in children and young adults with CKD and were consistent with findings in adults. Smaller and opposite differences were observed for the cystatin C-mGFR relationship, especially in the younger age group. We recommend inclusion of children for future investigations of biomarkers to estimate GFR. Importantly, for GFR estimation among those under 25 years of age, the average of the new U25 creatinine and cystatin C equations without race coefficients yields unbiased estimates of mGFR.

Using Machine Learning to Identify Metabolomic Signatures of Pediatric Chronic Kidney Disease Etiology.

BACKGROUND: Untargeted plasma metabolomic profiling combined with machine learning (ML) may lead to discovery of metabolic profiles that inform our understanding of pediatric CKD causes. We sought to identify metabolomic signatures in pediatric CKD based on diagnosis: FSGS, obstructive uropathy (OU), aplasia/dysplasia/hypoplasia (A/D/H), and reflux nephropathy (RN). METHODS: Untargeted metabolomic quantification (GC-MS/LC-MS, Metabolon) was performed on plasma from 702 Chronic Kidney Disease in Children study participants (n: FSGS=63, OU=122, A/D/H=109, and RN=86). Lasso regression was used for feature selection, adjusting for clinical covariates. Four methods were then applied to stratify significance: logistic regression, support vector machine, random forest, and extreme gradient boosting. ML training was performed on 80% total cohort subsets and validated on 20% holdout subsets. Important features were selected based on being significant in at least two of the four modeling approaches. We additionally performed pathway enrichment analysis to identify metabolic subpathways associated with CKD cause. RESULTS: ML models were evaluated on holdout subsets with receiver-operator and precision-recall area-under-the-curve, F1 score, and Matthews correlation coefficient. ML models outperformed no-skill prediction. Metabolomic profiles were identified based on cause. FSGS was associated with the sphingomyelin-ceramide axis. FSGS was also associated with individual plasmalogen metabolites and the subpathway. OU was associated with gut microbiome-derived histidine metabolites. CONCLUSION: ML models identified metabolomic signatures based on CKD cause. Using ML techniques in conjunction with traditional biostatistics, we demonstrated that sphingomyelin-ceramide and plasmalogen dysmetabolism are associated with FSGS and that gut microbiome-derived histidine metabolites are associated with OU.

Ehrlichia-induced hemophagocytic lymphohistiocytosis in a pediatric kidney transplant recipient.

BACKGROUND: Kidney transplant patients are susceptible to a variety of infections in the post-transplant period due to the use of immunosuppressant medications. Ehrlichiosis is a rare infection in solid organ transplant recipients with signs and symptoms that mimic rejection and other viral infections. Hemophagocytic lymphohistiocytosis (HLH) is a potentially fatal hyperinflammatory syndrome that can be triggered by infections. METHODS: We describe a pediatric kidney transplant recipient who experienced secondary HLH due to ehrlichiosis within the initial post-transplant month. RESULT: Our patient improved after treatment with doxycycline, corticosteroids, and intravenous immunoglobulin (IVIG). CONCLUSION: Clinicians should consider infections such as ehrlichiosis as a potential cause of illness in febrile solid organ transplant recipients in immediate post-transplant period, especially when accompanied by a compatible exposure history.

Variability in CKD Biomarker Studies: Soluble Urokinase Plasminogen Activator Receptor (suPAR) and Kidney Disease Progression in the Chronic Kidney Disease in Children (CKiD) Study.

RATIONALE & OBJECTIVE: Biomarker studies are important for generating mechanistic insight and providing clinically useful predictors of chronic kidney disease (CKD) progression. However, variability across studies can often muddy the evidence waters. Here we evaluated real-world variability in biomarker studies using two published studies, independently conducted, of the novel plasma marker soluble urokinase-type plasminogen activator receptor (suPAR) for predicting CKD progression in children with CKD. STUDY DESIGN: A comparison of 2 prospective cohort studies. SETTING & PARTICIPANTS: 541 children from the Chronic Kidney Disease in Children (CKiD) study, median age 12 years, median glomerular filtration rate (GFR) of 54 mL/min/1.73m2. OUTCOME: The first occurrence of either a 50% decline in GFR from baseline or incident end-stage kidney disease. ANALYTICAL APPROACH: The suPAR plasma marker was measured using the Quantikine ELISA immunoassay in the first study and Meso Scale Discovery (MSD) platform in the second. The analytical approaches varied. We used suPAR data from the 2 assays and mimicked each analytical approach in an overlapping subset. RESULTS: We found that switching assays had the greatest impact on inferences, resulting in a 38% to 66% change in the magnitude of the effect estimates. Covariate and modeling choices resulted in an additional 8% to 40% variability in the effect estimate. The cumulative variability led to different inferences despite using a similar sample of CKiD participants and addressing the same question. LIMITATIONS: The estimated variability does not represent optimal repeatability but instead illustrates real-world variability that may be present in the CKD biomarker literature. CONCLUSIONS: Our results highlight the importance of validation, avoiding conclusions based on P value thresholds, and providing comparable metrics. Further transparency of data and equal weighting of negative and positive findings in explorations of novel biomarkers will allow investigators to more quickly weed out less promising biomarkers.

Metabolite Biomarkers of CKD Progression in Children.

BACKGROUND AND OBJECTIVES: Metabolomics facilitates the discovery of biomarkers and potential therapeutic targets for CKD progression. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We evaluated an untargeted metabolomics quantification of stored plasma samples from 645 Chronic Kidney Disease in Children (CKiD) participants. Metabolites were standardized and logarithmically transformed. Cox proportional hazards regression examined the association between 825 nondrug metabolites and progression to the composite outcome of KRT or 50% reduction of eGFR, adjusting for age, sex, race, body mass index, hypertension, glomerular versus nonglomerular diagnosis, proteinuria, and baseline eGFR. Stratified analyses were performed within subgroups of glomerular/nonglomerular diagnosis and baseline eGFR. RESULTS: Baseline characteristics were 391 (61%) male; median age 12 years; median eGFR 54 ml/min per 1.73 m2; 448 (69%) nonglomerular diagnosis. Over a median follow-up of 4.8 years, 209 (32%) participants developed the composite outcome. Unique association signals were identified in subgroups of baseline eGFR. Among participants with baseline eGFR ≥60 ml/min per 1.73 m2, two-fold higher levels of seven metabolites were significantly associated with higher hazards of KRT/halving of eGFR events: three involved in purine and pyrimidine metabolism (N6-carbamoylthreonyladenosine, hazard ratio, 16; 95% confidence interval, 4 to 60; 5,6-dihydrouridine, hazard ratio, 17; 95% confidence interval, 5 to 55; pseudouridine, hazard ratio, 39; 95% confidence interval, 8 to 200); two amino acids, C-glycosyltryptophan, hazard ratio, 24; 95% confidence interval 6 to 95 and lanthionine, hazard ratio, 3; 95% confidence interval, 2 to 5; the tricarboxylic acid cycle intermediate 2-methylcitrate/homocitrate, hazard ratio, 4; 95% confidence interval, 2 to 7; and gulonate, hazard ratio, 10; 95% confidence interval, 3 to 29. Among those with baseline eGFR <60 ml/min per 1.73 m2, a higher level of tetrahydrocortisol sulfate was associated with lower risk of progression (hazard ratio, 0.8; 95% confidence interval, 0.7 to 0.9). CONCLUSIONS: Untargeted plasma metabolomic profiling facilitated discovery of novel metabolite associations with CKD progression in children that were independent of established clinical predictors and highlight the role of select biologic pathways.

Glucose Derivative Induced Vasculopathy in Children on Chronic Peritoneal Dialysis.

[Figure: see text].

Organophosphate pesticides and progression of chronic kidney disease among children: A prospective cohort study.

BACKGROUND: Growing evidence suggests that exposure to environmental chemicals, such as pesticides, impacts renal function and chronic kidney disease (CKD). However, it is not clear if pesticides may affect CKD progression and no studies exist in children. OBJECTIVES: The objective of this study was to examine associations between serially measured urinary OP pesticide metabolites and clinical and laboratory measures of kidney function over time among children with CKD. METHODS: This study used data on 618 participants enrolled in the CKD in Children study (CKiD), a cohort study of pediatric CKD patients from the US and Canada. Children were followed over an average of 3.0 years (standard deviation (SD) = 1.6) between 2005 and 2015. In serially collected urine samples over time, six nonspecific dialkyl phosphate (DAP) metabolites of OP pesticides were measured. Biomarkers of tubular injury (kidney injury molecule-1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL)) and oxidant stress (8-hydroxy-2'-deoxyguanosine (8-OHdG) and F2-isoprostane) were determined in the same specimens. Estimated glomerular filtration rate (eGFR), proteinuria, and blood pressure were assessed annually. RESULTS: DAPs were associated with increased KIM-1 and 8-OHdG throughout follow-up. A standard deviation increase in ∑diethyl metabolites was associated with increases of 11.9% (95% Confidence Interval (CI): 4.8%, 19.4%) and 13.2% (95% CI: 9.3%, 17.2%) in KIM-1 and 8-OHdG over time, respectively. DAPs were associated with lower eGFR at baseline and higher eGFR over subsequent years. CONCLUSIONS: These findings provide preliminary evidence suggesting that urinary DAP metabolites are associated with subclinical kidney injury among children with CKD, which may signal the potential for clinical events to manifest in the future. The results from this study are significant from both a clinical and public health perspective, given that OP pesticide exposure is a modifiable risk factor.