Renal function, sex and age influence purines and pyrimidines in urine and could lead to diagnostic misinterpretation.

Glomerular filtration rate (GFR) is commonly used in clinical practice for the diagnosis and follow-up of chronic kidney disease. Screening for inborn errors of metabolism (IEM) is based on analysis of biomarkers in urine, reported by their ratio to urinary creatinine (crn). Impaired renal function may complicate the interpretation of several biomarkers used for screening of IEM. Our goal was to investigate the influence of kidney function, in terms of measured GFR (mGFR) on purines and pyrimidines in urine, in addition to the relationship to sex, age, pH and ketosis. Children (n = 96) with chronic kidney disease (CKD), in different CKD stages, were included. Urine samples were obtained prior to the injection of iohexol. Serum samples at 7 time-points were used to calculate mGFR based on iohexol plasma clearance. The association with sex, age, ketosis and pH was examined in samples of the laboratory production from 2015 to 2021 (n = 8192). Age was a highly significant covariate for all markers. GFR correlated positively to several purines and pyrimidines; the ratios hypoxanthine/crn, xanthine/crn and urate/crn (p = 2.0 × 10-14, < 3 × 10-15 and 7.2 × 10-4, respectively), and the ratios orotic acid/crn, uracil/crn, and carbamyl-ß-alanine/crn (p = 0.03, 1.4 × 10-6 and 0.003, respectively). The values of urate/crn, xanthine/crn, uracil/crn, and carbamyl-ß-alanine/crn were higher in females above 16 years of age. Ketosis and pH influenced some markers. In conclusion, decreased renal function interferes with the excretion of urinary purines and pyrimidines, and this could change decision limits substantially, e.g. result in false negative results in Lesch-Nyhan syndrome. SYNOPSIS: GFR influences purines and pyrimidines in urine. Clinical Trial Registration: ClinicalTrials.gov, Identifier NCT01092260, https://clinicaltrials.gov/ct2/show/NCT01092260?term=tondel&rank=2.

Increased Sphingomyelin and Free Sialic Acid in Cerebrospinal Fluid of Kearns-Sayre Syndrome: New Findings Using Untargeted Metabolomics.

BACKGROUND: Kearns-Sayre syndrome (KSS) is caused by duplications and/or deletions of mitochondrial DNA (mtDNA) and is typically diagnosed based on a classic triad of symptoms with chronic progressive external ophthalmoplegia (CPEO), retinitis pigmentosa, and onset before age 20 years. The present study aimed to diagnose two patients, on suspicion of KSS. METHODS: One of the patients went through a diagnostic odyssey, with normal results from several mtDNA analyses, both in blood and muscle, before the diagnosis was confirmed genetically. RESULTS: Two patients presented increased tau protein and low 5-methyltetrahydrofolate (5-MTHF) levels in the cerebrospinal fluid (CSF). Untargeted metabolomics on CSF samples also showed an increase in the levels of free sialic acid and sphingomyelin C16:0 (d18:1/C16:0), compared with four control groups (patients with mitochondrial disorders, nonmitochondrial disorders, low 5-MTHF, or increased tau proteins). CONCLUSIONS: It is the first time that elevated sphingomyelin C16:0 (d18:1/C16:0) and tau protein in KSS are reported. Using an untargeted metabolomics approach and standard laboratory methods, the study could shed new light on metabolism in KSS to better understand its complexity. In addition, the findings may suggest the combination of elevated free sialic acid, sphingomyelin C16:0 (d18:1/C16:0), and tau protein as well as low 5-MTHF as new biomarkers in the diagnostics of KSS.

Neutrophil Gelatinase-Associated Lipocalin (NGAL) and cystatin C are early biomarkers of acute kidney injury associated with cardiac surgery.

Acute kidney injury (AKI) is a serious complication in as much as half of the patients undergoing cardiac surgery, and early diagnosis and treatment are of the utmost importance. There is a need for robust biomarkers that can detect cardiac surgery-associated AKI (CSA-AKI) prior to rise in plasma creatinine, which typically occurs at least 48 h postoperatively. We compared pre- and 4, 12 and 48 h postoperative plasma (P) neutrophil gelatinase-associated lipocalin (NGAL), cystatin C, urea and creatinine, and urine (U) NGAL, as markers of AKI, in 49 patients (67% men, median age 65 years) scheduled for elective cardiac surgery (e.g. coronary artery bypass graft and/or valve replacement surgery) with the use of extracorporeal circulation. Patients with preoperative sepsis, renal replacement therapy, or estimated glomerular filtration rate <30 mL/min/1.73m2 were excluded. P- and U-NGAL were measured using the Roche Modular P (Roche Diagnostics®) NGAL immunoassay. According to AKIN/KDIGO criteria, nine patients (18%) were diagnosed with CSA-AKI. Compared to patients without CSA-AKI, these patients had significantly higher P-NGAL and P-cystatin C values 4 h (p-values .002 and <.001) and 12 h (p-values <.001 and <.001) postoperatively. The same differences were not observed for U-NGAL. Patients with AKI also had significantly higher P-creatinine 4 and 12 h postoperatively (p-values .001 and <.001), however the rise in P-creatinine was just above the upper reference limit. In conclusion, plasma NGAL and cystatin C seem to detect CSA-AKI earlier than the more commonly used biomarkers creatinine and urea.

Performance of Expanded Newborn Screening in Norway Supported by Post-Analytical Bioinformatics Tools and Rapid Second-Tier DNA Analyses.

In 2012, the Norwegian newborn screening program (NBS) was expanded (eNBS) from screening for two diseases to that for 23 diseases (20 inborn errors of metabolism, IEMs) and again in 2018, to include a total of 25 conditions (21 IEMs). Between 1 March 2012 and 29 February 2020, 461,369 newborns were screened for 20 IEMs in addition to phenylketonuria (PKU). Excluding PKU, there were 75 true-positive (TP) (1:6151) and 107 (1:4311) false-positive IEM cases. Twenty-one percent of the TP cases were symptomatic at the time of the NBS results, but in two-thirds, the screening result directed the exact diagnosis. Eighty-two percent of the TP cases had good health outcomes, evaluated in 2020. The yearly positive predictive value was increased from 26% to 54% by the use of the Region 4 Stork post-analytical interpretive tool (R4S)/Collaborative Laboratory Integrated Reports 2.0 (CLIR), second-tier biochemical testing and genetic confirmation using DNA extracted from the original dried blood spots. The incidence of IEMs increased by 46% after eNBS was introduced, predominantly due to the finding of attenuated phenotypes. The next step is defining which newborns would truly benefit from screening at the milder end of the disease spectrum. This will require coordinated international collaboration, including proper case definitions and outcome studies.

Growth Differentiation Factor 15 in Children with Chronic Kidney Disease and after Renal Transplantation.

Growth differentiation factor 15 (GDF-15) is strongly associated with cardiovascular disease (CVD). The aim of our study was to evaluate plasma and urinary levels of GDF-15 after pediatric renal transplantation (Rtx) and in children with chronic kidney disease (CKD) and its associations to cardiovascular risk factors. In this cross-sectional study, GDF-15 was measured in plasma and urine from 53 children with a renal transplant and 83 children with CKD and related to cardiovascular risk factors (hypertension, obesity, and cholesterol) and kidney function. Forty healthy children served as a control group. Plasma levels of GDF-15 (median and range) for a Tx (transplantation) cohort, CKD cohort, and healthy controls were, respectively, 865 ng/L (463-3039 ng/L), 508 ng/L (183-3279 ng/L), and 390 ng/L (306-657 ng/L). The CKD and Tx cohorts both had significantly higher GDF-15 levels than the control group (p < 0.001). Univariate associations between GDF-15 and hyperuricemia (p < 0.001), elevated triglycerides (p = 0.028), low HDL (p = 0.038), and obesity (p = 0.028) were found. However, mGFR (p < 0.001) and hemoglobin (p < 0.001) were the only significant predictors of GDF-15 in an adjusted analysis. Urinary GDF-15/creatinine ratios were 448 ng/mmol (74-5013 ng/mmol) and 540 ng/mmol (5-14960 ng/mmol) in the Tx cohort and CKD cohort, respectively. In the CKD cohort, it was weakly correlated to mGFR (r = -0.343, p = 0.002). Plasma levels of GDF-15 are elevated in children with CKD and after Rtx. The levels were not associated with traditional cardiovascular risk factors but strongly associated with renal function.

Measured GFR by Utilizing Population Pharmacokinetic Methods to Determine Iohexol Clearance.

INTRODUCTION: There is an increasing demand for accurately measured glomerular filtration rate (GFR). Iohexol serum clearance has become a new gold standard, but it is challenging when GFR is low and 24-hour sampling is required for accurate results. The primary aim of this study was to develop an iohexol pharmacokinetic population model for accurate determination of individual GFR using limited sampling for up to 5 hours also when renal function is <40 ml/min. METHODS: A nonparametric iohexol population pharmacokinetic model was developed with rich data from 176 patients. In a validation cohort of 43 patients, a model-determined GFR (iohexol clearance) using different limited sampling strategies for up to 5 hours was compared with the strategy currently used in routine care, a log-linear 2-point method. In all, 1526 iohexol concentrations were used, from patients ranging in age from 1 to 82 years and GFR from 14 to 149 ml/min. RESULTS: The clinical 2-point method showed insufficient agreement compared with reference values; 15% of GFR values had an error of greater than ±10% even when sampling for 24 hours when estimating GFR <40 ml/min per 1.73 m2 (standard procedure). Restricted sampling the first 5 hours with the population model required 4 samples to determine GFR accurately. This strategy showed excellent agreement with the reference; <3% of GFR values had an error greater than ±10 %. CONCLUSION: Using an iohexol population pharmacokinetic model allows for accurate determination of GFR within 5 hours when applying 4 optimally timed samples, even in patients with GFR <40 ml/min.

Dopa-responsive dystonia. / Doparesponsive dystonier.

BAKGRUNN: Doparesponsiv dystoni er en gruppe sykdommer som gir endrede nivåer av nevrotransmittere. Dette kan behandles med god effekt. Økt innsikt i patofysiologiske årsaksforhold har bedret forståelsen av sykdommene. KUNNSKAPSGRUNNLAG: Artikkelen bygger på 39 artikler fra et systematisk søk i databasen Medline, to nettsteder og en lærebok. RESULTATER: Doparesponsiv dystoni debuterer som oftest i barne- eller ungdomsårene og gir motoriske, kognitive, psykiatriske og/eller autonome symptomer og funn. Disse kan være uspesifikke og lett mistolkes som annen nevrologisk sykdom. Sykdommen skyldes feilkoding i ett enkelt gen og arves autosomalt recessivt eller dominant. Sykdomsgivende varianter er beskrevet fra tre ulike gener: guanosintrifosfat (GTP)-syklohydrolase-1-genet, sepiapterinreduktase-genet og tyrosinhydroksylase-genet. De sykdomsgivende variantene fører til enzymdefekt og gir tidlig debuterende dystoni, som responderer godt på levodopa. Nivåbestemmelse av pteriner, biogene monoaminer og deres metabolitter i spinalvæsken samt genetiske undersøkelser gir den eksakte diagnosen. FORTOLKNING: Dagens kunnskap baserer seg på kasuistikker og mindre pasientmaterialer. Her fremgår det at pasientgruppen har stor nytte av levodopa. Diagnostikken har blitt enklere de siste årene med nyere biokjemiske og molekylærgenetiske analysemetoder. Basert på dagens litteratur er det grunn til å tro at vi har udiagnostiserte pasienter i Norge med doparesponsiv dystoni.

Iohexol plasma clearance in children: validation of multiple formulas and single-point sampling times.

BACKGROUND: The non-ionic agent iohexol is increasingly used as the marker of choice for glomerular filtration rate (GFR) measurement. Estimates of GFR in children have low accuracy and limiting the number of blood-draws in this patient population is especially relevant. We have performed a study to evaluate different formulas for calculating measured GFR based on plasma iohexol clearance with blood sampling at only one time point (GFR1p) and to determine the optimal sampling time point. METHODS: Ninety-six children with chronic kidney disease (CKD) stage 1-5 (median age 9.2 years; range 3 months to 17.5 years) were examined in a cross-sectional study using iohexol clearance and blood sampling at seven time points within 5 h (GFR7p) as the reference method. Median GFR7p was 66 (range 6-153) mL/min/1.73 m2. The performances of six different single time-point formulas (Fleming, Ham and Piepsz, Groth and Aasted, Stake, Jacobsson- and Jacobsson-modified) were validated against the reference. The two-point GFR (GFR2p) was calculated according to the Jødal and Brøchner-Mortensen formula. RESULTS: The GFR1p calculated according to Fleming with sampling at 3 h (GFR1p3h-Fleming) had the best overall performance, with 82% of measures within 10% of the reference value (P10). In children with a GFR ≥ 30 mL/min/1.73 m2 (n = 78), the GFR1p3h-Fleming had a P10 of 92.3%, which is not significantly different (p = 0.29) from that of GFR2p (P10 = 96.2%). Considerable differences within and between the different formulas were found for different CKD stages and different time points for blood sampling. CONCLUSIONS: For determination of mGFR in children with CKD and an assumed GFR of ≥ 30 mL/min/1.73 m2 we recommend GFR1p3h-Fleming as the preferred single-point method as an alternative to GFR2p. For children with a GFR < 30 mL/min/1.73 m2, we recommend the slope-GFR with at least two blood samples. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov , Identifier NCT01092260, https://clinicaltrials.gov/ct2/show/NCT01092260?term=tondel&rank=2.

Iohexol plasma clearance in children: validation of multiple formulas and two-point sampling times.

BACKGROUND: In children, estimated glomerular filtration rate (eGFR) methods are hampered by inaccuracy, hence there is an obvious need for safe, simplified, and accurate measured GFR (mGFR) methods. The aim of this study was to evaluate different formulas and determine the optimal sampling points for calculating mGFR based on iohexol clearance measurements on blood samples drawn at two time points (GFR2p). METHODS: The GFR of 96 children with different stages of chronic kidney disease (CKD) (median age 9.2 years, range 3 months to 17.5 years) was determined using the iohexol plasma clearance, with blood sampling at seven time points within 5 h (GFR7p) as the reference method. Median GFR7p was 65.9 (range 6.3-153) mL/min/1.73 m2. The performance of seven different formulas with early and late normalization to body surface area (BSA) was validated against the reference. RESULTS: The highest percentage (95.8 %) of GFR2p within 10 % of the reference was calculated using the formula of Jødal and Brøchner-Mortensen (JBM) from 2009, with sampling at 2 and 5 h. Normalization to BSA before correction of the distribution phase improved the performance of the original Brøchner-Mortensen method from 1972; P10 of 92.7 % compared to P10 of 82.3 % with late normalization, and a similar result was obtained with other formulas. CONCLUSIONS: GFR2p performed well across a wide spectrum of GFR levels with the JBM formula. Several other formulas tested performed well provided that early BSA normalization was performed. Blood sampling at 2 and 5 h is recommended for an optimal GFR2p assessment.

Glomerular filtration rate measured by iohexol clearance: A comparison of venous samples and capillary blood spots.

BACKGROUND: Glomerular filtration rate (GFR) measured by iohexol clearance using venous samples is widely used. Capillary sampling on filter paper is easier to perform, may be less painful and spares the blood volume. The purpose of the study was to validate a blood spot method for measuring GFR in children aged 6 years or younger suffering from chronic kidney disease (CKD). METHODS: We examined 32 children with CKD, median age (range) 3.0 (0.3-6.2) years. Seven venous samples (10, 30/60, 120, 180, 210, 240, 300 min) were collected and GFR based on all samples was calculated for reference. Following injection of iohexol, blood spots were collected at 120, 180, 210 and 240 min and compared to the reference iohexol clearance. RESULTS: Median (range) reference GFR was 65 (6-122) mL/min/1.73 m(2). The 2, 3 and 4-point blood spot GFR were highly correlated to the reference GFR (r = 0.947, 0.945, 0.937). The mean relative bias between 2-point blood spot and reference GFR was 7.2%, and only 2.3% in the patients with reference GFR < 60 mL/min/1.73 m(2). The diagnostic accuracy for 2-point blood spot was: 87.5% and 96.9% within ± 15% (P15) and ± 30% (P30) of the reference GFR respectively. In patients with GFR < 60 mL/min/1.73 m(2), both P15 and P30 were 100%. CONCLUSIONS: GFR calculation based on blood spot iohexol measurement is an alternative method to traditional venous iohexol measurement in children. Our study demonstrates strong agreement between the blood spot and the venous GFR with acceptable bias, precision and diagnostic accuracy, especially in patients with GFR < 60 mL/min/1.73 m(2).