[Newborn blood spot screening (NBS) in Germany : Status quo and presentation of a concept for further development]. / Neugeborenen-Screening aus Trockenblut (NBS) in Deutschland : Status quo und Vorstellung eines Konzeptes zur Weiterentwicklung.

Newborn screening from dried blood spots (NBS) is a highly effective secondary prevention measure that has been established for many years. Against the background of the inclusion of "new diseases" that meet the screening criteria, a concept for the further advancement of NBS was developed on behalf of the GKV-Spitzenverband. This was based on a systematic literature review and a survey of the status quo of NBS in Germany using quantitative and qualitative methods.It is essential for the success of NBS that all newborns affected by a target disease are diagnosed and treated at an early stage and that the harm to be expected with each screening (e.g., due to false positive findings) is kept as low as possible. This requires the organisation of screening in the sense of an integrated programme through central coordination with standardised structures, continuous quality management and digitalisation in line with data protection requirements.Although in general NBS is being implemented successfully in Germany, the research project presented here also reveals weaknesses and a need for action. Proposals and recommendations were compiled in a concept paper, which shows approaches for further development of NBS in line with the current state of research in consideration of changing demands on the infrastructure and processes in the health system. This review article summarises the challenges, current status and possible solutions for the central topics of the concept paper.

[Consequences of the SARS-CoV-2 Pandemia on the Early Childhood Examinations]. / Auswirkungen der SARS-CoV-2 Pandemie auf die Früherkennungs-Untersuchungen bei Kindern.

Seit Mitte Mai wird berichtet, dass die Maßnahmen oder die Angst vor einer Infektion mit SARS-CoV-2 zu einem sekundären Gesundheitsrisiko führen könnten, weil Diagnosen, z. B. von Krebs- oder Herz-Kreislauferkrankungen, verspätet gestellt und Therapien, z. B. komplizierte operative Eingriffe mit Intensivpflege, verzögert durchgeführt werden (COVIDSurg Collaborative, Br J Surg 2020; DOI: 10.1002/bjs.11746; Kuhlen R et al., Dtsch Arztebl Int 2020; 117: 488-489). In der Kinder- und Jugendmedizin stehen die Fragen und Probleme des Schulunterrichts, der fehlenden sozialen Kontakte innerhalb der peer group und der häuslichen Gewalt im Vordergrund der Fragen zur Auswirkung der Pandemie auf die Gesundheit (Wade M et al., Psychiatry Res 2020; 290:113-143). Mögliche Auswirkungen auf die Umsetzung der Richtlinie des Gemeinsamen Bundesausschuss (G-BA) über die Früherkennung von Krankheiten bei Kinder (Vorsorge-Untersuchungen U1-U9) sind bislang nicht bekannt. Im Rahmen der SARS-CoV2 Kontaktbeschränkungen hatte der G-BA die Toleranzzeiten (Abrechnungsfristen) für die Vorsorge-Untersuchungen U6-U9 bis zum Ablauf von 3 Monaten nach Beendigung einer epidemischen Lage von nationaler Tragweite aufgehoben (BAnz AT 29.05.2020 B6).

Comparative meta-analysis of Kabuki syndrome with and without hyperinsulinaemic hypoglycaemia.

BACKGROUND AND OBJECTIVE: Kabuki syndrome (KS), caused by pathogenic variants in KMT2D or KDM6A, is associated with hyperinsulinaemic hypoglycaemia (HH) in 0.3%-4% of patients. We characterized the clinical, biochemical and molecular data of children with KS and HH compared to children with KS without HH in a multicentre meta-analysis. METHODS: Data of seven new and 17 already published children with KS and HH were compared to 373 recently published KS patients without HH regarding molecular and clinical characteristics. RESULTS: Seven new patients were identified with seven different pathogenic variants in KDM6A (n = 4) or KMT2D (n = 3). All presented with HH on the first day of life and were responsive to diazoxide. KS was diagnosed between 9 months and 14 years of age. In the meta-analysis, 24 KS patients with HH had a significantly higher frequency of variants in KDM6A compared to 373 KS patients without HH (50% vs 11.5%, P < .001), and KDM6A-KS was more likely to be associated with HH than KMT2D-KS (21.8% vs. 3.5%, P < .001). Sex distribution and other phenotypic features did not differ between KS with and without HH. CONCLUSION: The higher incidence of HH in KDM6A-KS compared to KMT2D-KS indicates that KDM6A loss of function variants predispose more specifically to beta cell dysfunction compared to KMT2D variants. As difficulties to assign syndromic characteristics to KS in early infancy often lead to delayed diagnosis, genetic testing for KS should be considered in children with HH, especially in the presence of other extrapancreatic/syndromic features.

Open-Source Technology for Real-Time Continuous Glucose Monitoring in the Neonatal Intensive Care Unit: Case Study in a Neonate With Transient Congenital Hyperinsulinism.

BACKGROUND: Use of real-time continuous glucose monitoring (rtCGM) systems has been shown to be a low-pain, safe, and effective method of preventing hypoglycemia and hyperglycemia in people with diabetes of various age groups. Evidence on rtCGM use in infants and in patients with conditions other than diabetes remains limited. OBJECTIVE: This case study describes the off-label use of rtCGM and the use of an open-source app for glucose monitoring in a newborn with prolonged hypoglycemia secondary to transient congenital hyperinsulinism during the perinatal period. METHODS: The Dexcom G6 rtCGM system (Dexcom, Inc) was introduced at 39 hours of age. Capillary blood glucose checks were performed regularly. In order to benefit from customizable alert settings and detect hypoglycemic episodes, the open-source rtCGM app xDrip+ was introduced at 9 days of age. RESULTS: Time in range (45-180 mg/dL) for interstitial glucose remained consistently above 90%, whereas time in hypoglycemia (<45 mg/dL) decreased. Mean glucose was maintained above 70 mg/dL at 72 hours of life and thereafter. Daily sensor glucose profiles showed cyclic fluctuations that were less pronounced over time. CONCLUSIONS: While off-label use of medication is both common practice and a necessity in newborn infants, there are few examples of off-label uses of medical devices, rtCGM being a notable exception. Real-time information allowed us to better understand glycemic patterns and to improve the quality of glycemic control accordingly. Severe hypoglycemia was prevented, and measurement of serum levels of insulin and further lab diagnostics were performed much faster, while the patient's individual burden caused by invasive procedures was reduced. Greater customizability of threshold and alert settings would be beneficial for user groups with glycemic instability other than people with diabetes, and for hospitalized newborn infants in particular. Further research in the field of personal and off-label rtCGM use, efficacy studies evaluating the accuracy of low glucose readings, and studies on the differences between algorithms in translating raw sensor data, as well as customization of commercially available rtCGM systems, is needed.

[Therapy Options for Infants with Congenital Cytomegalovirus Infection - Implications for Setting Up Neonatal Screening Programs]. / Therapeutische Optionen bei konnataler Zytomegalievirus (CMV)-Infektion ­ Implikationen für die Einführung eines Screeningprogramms.

INTRODUCTION: The number of diseases covered by universal neonatal screening in Germany has risen steadily from 1 (phenylketonuria) in 1968 to 17 (with hearing impairment and congenital hip dysplasia) in 2018. Treatment, however, of disorders diagnosed by screening may harm children, as failed neuroblastoma screening has shown. There are several pilot studies to detect congenital cytomegalovirus (CMV) infection but no consensus as to the treatment of the infants identified. METHODOLOGY: Systematic search for studies investigating therapy of congenital CMV infection, using PubMed and the WHO International Clinical Trials Registry Platform (ICTRP). RESULTS: We found only one controlled trial that randomized infants with symptomatic congenital CMV infection (involving the central nervous system) to treatment (intravenous ganciclovir for 6 weeks) or no treatment. Treatment was associated with significantly less hearing deterioration. A second trial comparing 6 weeks vs. 6 months of treatment with valganciclovir, an oral prodrug of ganciclovir, found no benefit for hearing but modestly improved developmental outcomes associated with 6 months of treatment. In contrast, an open-label registry reported benefits for infants with congenital CMV infection and isolated hearing who received valganciclovir for 12 months, with hearing improvement in 2/3 of cases after a median follow-up of 4½ years. CONCLUSIONS: Antiviral treatment of neonates with congenital CMV infection and few symptoms including isolated hearing loss remains controversial. A generally accepted therapy, however, is pivotal before introducing universal or targeted screening for congenital CMV infection.

Proopiomelanocortin Deficiency Treated with a Melanocortin-4 Receptor Agonist.

Patients with rare defects in the gene encoding proopiomelanocortin (POMC) have extreme early-onset obesity, hyperphagia, hypopigmentation, and hypocortisolism, resulting from the lack of the proopiomelanocortin-derived peptides melanocyte-stimulating hormone and corticotropin. In such patients, adrenal insufficiency must be treated with hydrocortisone early in life. No effective pharmacologic treatments have been available for the hyperphagia and obesity that characterize the condition. In this investigator-initiated, open-label study, two patients with proopiomelanocortin deficiency were treated with setmelanotide, a new melanocortin-4 receptor agonist. The patients had a sustainable reduction in hunger and substantial weight loss (51.0 kg after 42 weeks in Patient 1 and 20.5 kg after 12 weeks in Patient 2).

Newborn screening by tandem mass spectrometry confirms the high prevalence of sickle cell disease among German newborns.

Sickle cell disease (SCD) is a severe inherited blood disorder associated with significant morbidity and mortality in early childhood. Since simple interventions are available to prevent early fatal courses, SCD is a target condition of several national newborn screening (NBS) programs worldwide, but not in Germany. Traditionally, the diagnosis of SCD is made by high-performance liquid chromatography (HPLC), isoelectric focusing (IEF), or capillary electrophoresis (CE), but globally, most NBS programs in place are based on tandem mass spectrometry (MS/MS). Recently, several publications have shown that MS/MS is an appropriate screening technique to detect hemoglobin patterns suggestive of SCD in newborns, too. We have studied dried blood spot samples of 29,079 German newborns by both CE and MS/MS and observed a 100% congruence of test results. Seven babies had hemoglobin patterns characteristic of SCD (1:4154). Our study confirms that (a) the suitability of MS/MS as an adequate substitute for CE in NBS for SCD and (b) the high prevalence of SCD among German newborns. Our results support the thesis that German newborns should be screened for SCD by MS/MS.

Absorption and tolerability of taste-masked hydrocortisone granules in neonates, infants and children under 6 years of age with adrenal insufficiency.

OBJECTIVES: There is no licensed, dose-appropriate formulation of hydrocortisone for children with adrenal insufficiency (AI) and patients rely on compounded adult medication. The aim of this study was to evaluate the absorption, palatability and safety of Infacort® , an immediate-release, granule formulation of hydrocortisone with taste masking. STUDY DESIGN: Single site with satellites attended by a "flying" doctor from investigator site. Open-label, single-dose study in three consecutive child cohorts (n = 24) with AI; Cohort 1, children aged 2 to <6 years (n = 12); Cohort 2, infants aged 28 days to <2 years (n = 6); Cohort 3, neonates aged 1 to <28 days (n = 6). METHODS: Fasted children were given a single dose of Infacort® as dry granules administered directly from a capsule or spoon followed by a drink. The primary end-point was the maximum serum cortisol concentration up to 240 minutes after Infacort® administration. Secondary end-points were palatability and adverse events (AEs). RESULTS: All children showed an increase in cortisol above baseline after Infacort® (P < .0001), with geometric mean ± SD cortisol concentration at 60 minutes of 575.8 ± 299.5 nmol L-1 . There was no failure in administration of Infacort® , and 95.5% of parents/carers preferred Infacort® to their child's current medication. In 7 children who completed the palatability questionnaire, 80% of responses were very good or neutral, and 20% were adverse. No serious or severe treatment-emergent AEs were reported. CONCLUSIONS: Infacort® is well tolerated, easy to administer to neonates, infants and children and shows good absorption, with cortisol levels at 60 minutes after administration similar to physiological cortisol levels in healthy children.

Role of (68)Ga somatostatin receptor PET/CT in the detection of endogenous hyperinsulinaemic focus: an explorative study.

PURPOSE: To explore the role of (68)Ga-DOTATATE/DOTATOC PET/CT (SR PET/CT) in patients with suspicion of or histopathologically proven pancreatogenic hyperinsulinaemic hypoglycaemia. METHODS: We included 13 patients with histopathologically proven or a high clinical suspicion of pancreatogenic hyperinsulinaemia. All the patients underwent a SR PET/CT scan. The results were correlated with histopathological findings. Normalization of blood glucose levels after resection of the pancreatic lesion, as well as a cytological and/or pathological diagnosis of insulinoma, was considered the diagnostic gold standard for insulinoma. The diagnosis of nesidioblastosis was based on exclusion of an insulinoma and conclusive pathological examination of a segment of the pancreas. Malignant insulinoma was defined as the presence of locoregional or distant metastases. RESULTS: Based on histopathology, 13 patients were found to have pancreatic hyperinsulinaemia: two patients had malignant insulinoma, eight had nonmetastasized insulinoma, and three had nesidioblastosis. SR PET was positive in 11 of the 13 patients (84.6 %) with a final diagnosis of endogenous pancreatic hypoglycaemia. Histopathological staining confirmed 16 foci of hyperinsulinism (insulin positivity). SR PET detected 14 of the 16 lesions, resulting in a sensitivity of 87 %. One intrapancreatic spleen was falsely diagnosed as insulinoma focus on SR PET, resulting in positive predictive value of 93.3 %. Immunohistochemical staining of somatostatin receptor (SSR) subtype 2a was available in ten specimens: two nesidioblastosis, and seven benign and one malignant insulinoma. Eight out of the ten specimens (80 %) stained strongly to moderately positive. Seven of the eight SSR2a-positive lesions were picked up on SR PET. Based on the results of SR PET/CT, nine patients achieved complete remission of the hypoglycaemic events during follow-up. CONCLUSION: This explorative study suggests that SR PET in combination with CT may play a significant role in the detection and management of patients with pancreatogenic hyperinsulinaemic hypoglycaemia. A large proportion of insulinomas express SSR2a, and a larger study is needed to fully assess the diagnostic accuracy of SR PET in patients with insulinoma and nesidioblastosis compared with current localizing studies used in clinical practice.

Congenital Adrenal Hyperplasia with Non-functional Mutations in Both Alleles in a Clinically Unaffected Infant.

BACKGROUND: Results in neonatal screening programs aiming at detection of congenital adrenal hyperplasia (CAH) can only report elevated levels of 17-hydroxy-progesterone (17-OHP), without being able to differentiate presence or absence of salt loss. AIM: To predict presence or absence of salt loss in newborn infants with CAH. METHODS: The first specimen of suspected CAH in samples sent from People's Democratic Republic of Laos (Lao PDR) was investigated for known mutations in CAH associated with salt loss. RESULTS: Molecular genetic diagnosis revealed mutations associated with loss of function in both alleles; however, the infant was clinically unaffected even without any corticosteroid substitution therapy. CONCLUSIONS: Although molecular genetic methods can theoretically predict loss of function in CAH, our infant was clinically unaffected even without therapy at 6 years of age. We speculate that in CAH, remaining enzyme activity can be sufficiently high, despite the presence of loss of function mutations, which do not affect infants clinically.

Occurrence of giant focal forms of congenital hyperinsulinism with incorrect visualization by (18) F DOPA-PET/CT scanning.

CONTEXT: Congenital hyperinsulinism (CHI) is a rare disease characterized by severe hypoglycaemic episodes due to pathologically increased insulin secretion from the pancreatic beta cells. When untreated, CHI might result in irreversible brain damage and death. Currently, two major subtypes of CHI are known: a focal form, associated with local distribution of affected beta cells and a nonfocal form, affecting every single beta cell. The identification of focal forms is important, as the patients can be cured by limited surgery. (18) F DOPA-PET/CT is an established non-invasive approach to differentiate focal from nonfocal CHI. OBJECTIVE: The purpose of this study was to identify possible limitations of (18) F DOPA-PET/CT scan in patients with focal forms nonfocal CHI. DESIGN: A retrospective chart review of 32 patients (from 2008 through 2013) who underwent (18) F DOPA-PET/CT and partial pancreatectomy for focal CHI at the reference centres in Berlin, Germany and London, UK. RESULTS: In most cases (n = 29, 90·7%), (18) F DOPA-PET/CT was sufficient to localize the complete focal lesion. However, in some patients (n = 3, 9·3%), (18) F DOPA-PET/CT wrongly visualized only a small portion of the focal lesion. In this group of patients, a so-called 'giant focus' was detected in histopathological analysis during the surgery. CONCLUSIONS: Our data show that in most patients with focal CHI (18) F DOPA-PET/CT correctly predicts the size and anatomical localisation of the lesion. However, in those patients with a 'giant focal' lesion (18) F DOPA-PET/CT is unreliable for correct identification of 'giant focus' cases.

Model-Informed Target Morning 17α-Hydroxyprogesterone Concentrations in Dried Blood Spots for Pediatric Congenital Adrenal Hyperplasia Patients.

Monitoring cortisol replacement therapy in congenital adrenal hyperplasia (CAH) patients is vital to avoid serious adverse events such as adrenal crises due to cortisol underexposure or metabolic consequences due to cortisol overexposure. The less invasive dried blood spot (DBS) sampling is an advantageous alternative to traditional plasma sampling, especially in pediatric patients. However, target concentrations for important disease biomarkers such as 17α-hydroxyprogesterone (17-OHP) are unknown using DBS. Therefore, a modeling and simulation framework, including a pharmacokinetic/pharmacodynamic model linking plasma cortisol concentrations to DBS 17-OHP concentrations, was used to derive a target morning DBS 17-OHP concentration range of 2-8 nmol/L in pediatric CAH patients. Since either capillary or venous DBS sampling is becoming more common in the clinics, the clinical applicability of this work was shown by demonstrating the comparability of capillary and venous cortisol and 17-OHP concentrations collected by DBS sampling, using a Bland-Altman and Passing-Bablok analysis. The derived target morning DBS 17-OHP concentration range is a first step towards providing improved therapy monitoring using DBS sampling and adjusting hydrocortisone (synthetic cortisol) dosing in children with CAH. In the future, this framework can be used to assess further research questions, e.g., target replacement ranges for the entire day.

Screening Newborns for Low T Cell Receptor Excision Circles (TRECs) Fails to Detect Immunodeficiency, Centromeric Instability, and Facial Anomalies Syndrome.

BACKGROUND: Assessment of T-cell receptor excision circles (TRECs) in dried blood spots of newborns allows the detection of severe combined immunodeficiency (SCID) (T cells <300/µL at birth) with a presumed sensitivity of 100%. TREC screening also identifies patients with selected combined immunodeficiency (CID) (T cells >300/µL, yet <1500/µL at birth). Nevertheless, relevant CIDs that would benefit from early recognition and curative treatment pass undetected. OBJECTIVE: We hypothesized that TREC screening at birth cannot identify CIDs that develop with age. METHODS: We analyzed the number of TRECs in dried blood spots in archived Guthrie cards of 22 children who had been born in the Berlin-Brandenburg area between January 2006 and November 2018 and who had undergone hematopoietic stem-cell transplantation (HSCT) for inborn errors of immunity. RESULTS: All patients with SCID would have been identified by TREC screening, but only 4 of 6 with CID. One of these patients had immunodeficiency, centromeric instability, and facial anomalies syndrome type 2 (ICF2). Two of 3 patients with ICF whom we have been following up at our institution had TREC numbers above the cutoff value suggestive of SCID at birth. Yet all patients with ICF had a severe clinical course that would have justified earlier HSCT. CONCLUSIONS: In ICF, naïve T cells may be present at birth, yet they decline with age. Therefore, TREC screening cannot identify these patients. Early recognition is nevertheless crucial, as patients with ICF benefit from HSCT early in life.

Early-set POMC methylation variability is accompanied by increased risk for obesity and is addressable by MC4R agonist treatment.

Increasing evidence points toward epigenetic variants as a risk factor for developing obesity. We analyzed DNA methylation of the POMC (pro-opiomelanocortin) gene, which is pivotal for satiety regulation. We identified sex-specific and nongenetically determined POMC hypermethylation associated with a 1.4-fold (confidence interval, 1.03 to 2.04) increased individual risk of developing obesity. To investigate the early embryonic establishment of POMC methylation states, we established a human embryonic stem cell (hESC) model. Here, hESCs (WA01) were transferred into a naïve state, which was associated with a reduction of DNA methylation. Naïve hESCs were differentiated via a formative state into POMC-expressing hypothalamic neurons, which was accompanied by re-establishment of DNA methylation patterning. We observed that reduced POMC gene expression was associated with increased POMC methylation in POMC-expressing neurons. On the basis of these findings, we treated POMC-hypermethylated obese individuals (n = 5) with an MC4R agonist and observed a body weight reduction of 4.66 ± 2.16% (means ± SD) over a mean treatment duration of 38.4 ± 26.0 weeks. In summary, we identified an epigenetic obesity risk variant at the POMC gene fulfilling the criteria for a metastable epiallele established in early embryonic development that may be addressable by MC4R agonist treatment to reduce body weight.

Severe Acquired Primary Hypothyroidism in Children and its Influence on Growth: A Retrospective Analysis of 43 Cases.

INTRODUCTION: Severe acquired hypothyroidism in childhood is a rare condition, mostly caused by autoimmune thyroiditis. Scarce and inconsistent data based on small patient numbers exist concerning its impact on growth in height. METHODS: Patient files at a single centre university hospital over 8 years were retrospectively reviewed. We identified 43 patients (mean age 10.6 years, 3.3-15.25, 59% prepubertal, 88% females) in a cohort of children older than 3 years with an initial TSH>30 mIU/l and reduced T4 or fT4; congenital and drug-induced hypothyroidism were excluded. RESULTS: All patients had signs of autoimmune thyroiditis (93% positive autoantibodies, 95% typical ultrasonography, 63% goiter). Median TSH was 100 mIU/l [0.3-4 mIU/l]), median fT4 3.55 pg/ml [8-19 pg/ml], median T4 2.85 µg/dl [5.3-11 µg/dl]. Presenting symptoms included goiter (26%), tiredness (23%), weight gain (19%), and growth retardation (19%). The diagnosis was made incidentally in 26% patients. In 75% growth was retarded (median height standard deviation score (SDS)-0.55), in 17% height SDS was<-2 at diagnosis. Midparental height SDS at diagnosis correlated significantly with T4 and fT4 (r=0.77, p=0.0012 and r=0.53, p=0.021 respectively). Catch-up growth under T4 substitution was significantly greater in prepubertal than in pubertal children (p 0.049). CONCLUSION: This so far largest pediatric cohort with severe acquired hypothyroidism confirms a serious impact on growth which, however in most cases, showed a certain catch-up growth after adequate L-thyroxine therapy. The pubertal state seems to be important for catch-up growth. A significant number of patients were not diagnosed clinically, although affected by severe hypothyroidism.

Exploring Dried Blood Spot Cortisol Concentrations as an Alternative for Monitoring Pediatric Adrenal Insufficiency Patients: A Model-Based Analysis.

Congenital adrenal hyperplasia (CAH) is the most common form of adrenal insufficiency in childhood; it requires cortisol replacement therapy with hydrocortisone (HC, synthetic cortisol) from birth and therapy monitoring for successful treatment. In children, the less invasive dried blood spot (DBS) sampling with whole blood including red blood cells (RBCs) provides an advantageous alternative to plasma sampling. Potential differences in binding/association processes between plasma and DBS however need to be considered to correctly interpret DBS measurements for therapy monitoring. While capillary DBS samples would be used in clinical practice, venous cortisol DBS samples from children with adrenal insufficiency were analyzed due to data availability and to directly compare and thus understand potential differences between venous DBS and plasma. A previously published HC plasma pharmacokinetic (PK) model was extended by leveraging these DBS concentrations. In addition to previously characterized binding of cortisol to albumin (linear process) and corticosteroid-binding globulin (CBG; saturable process), DBS data enabled the characterization of a linear cortisol association with RBCs, and thereby providing a quantitative link between DBS and plasma cortisol concentrations. The ratio between the observed cortisol plasma and DBS concentrations varies highly from 2 to 8. Deterministic simulations of the different cortisol binding/association fractions demonstrated that with higher blood cortisol concentrations, saturation of cortisol binding to CBG was observed, leading to an increase in all other cortisol binding fractions. In conclusion, a mathematical PK model was developed which links DBS measurements to plasma exposure and thus allows for quantitative interpretation of measurements of DBS samples.

Insights in the maturational processes influencing hydrocortisone pharmacokinetics in congenital adrenal hyperplasia patients using a middle-out approach.

Introduction: Hydrocortisone is the standard of care in cortisol replacement therapy for congenital adrenal hyperplasia patients. Challenges in mimicking cortisol circadian rhythm and dosing individualization can be overcome by the support of mathematical modelling. Previously, a non-linear mixed-effects (NLME) model was developed based on clinical hydrocortisone pharmacokinetic (PK) pediatric and adult data. Additionally, a physiologically-based pharmacokinetic (PBPK) model was developed for adults and a pediatric model was obtained using maturation functions for relevant processes. In this work, a middle-out approach was applied. The aim was to investigate whether PBPK-derived maturation functions could provide a better description of hydrocortisone PK inter-individual variability when implemented in the NLME framework, with the goal of providing better individual predictions towards precision dosing at the patient level. Methods: Hydrocortisone PK data from 24 adrenal insufficiency pediatric patients and 30 adult healthy volunteers were used for NLME model development, while the PBPK model and maturation functions of clearance and cortisol binding globulin (CBG) were developed based on previous studies published in the literature. Results: Clearance (CL) estimates from both approaches were similar for children older than 1 year (CL/F increasing from around 150 L/h to 500 L/h), while CBG concentrations differed across the whole age range (CBGNLME stable around 0.5 µM vs. steady increase from 0.35 to 0.8 µM for CBG PBPK). PBPK-derived maturation functions were subsequently included in the NLME model. After inclusion of the maturation functions, none, a part of, or all parameters were re-estimated. However, the inclusion of CL and/or CBG maturation functions in the NLME model did not result in improved model performance for the CL maturation function (ΔOFV > -15.36) and the re-estimation of parameters using the CBG maturation function most often led to unstable models or individual CL prediction bias. Discussion: Three explanations for the observed discrepancies could be postulated, i) non-considered maturation of processes such as absorption or first-pass effect, ii) lack of patients between 1 and 12 months, iii) lack of correction of PBPK CL maturation functions derived from urinary concentration ratio data for the renal function relative to adults. These should be investigated in the future to determine how NLME and PBPK methods can work towards deriving insights into pediatric hydrocortisone PK.