Approach to the Patient: Challenging Cases of Pediatric Thyrotoxicosis.

Graves' disease (GD) is the leading cause of hyperthyroidism in children. However, compared to adults GD in children is a rare condition. In a recent guideline issued by the European Thyroid Association the diagnostic evaluation and treatment of pediatric GD is described extensively. In this article we go beyond the guideline and describe the potential challenges of establishing the right etiology of thyrotoxicosis in children, illustrated by cases of thyroid hormone resistance, autonomous functioning thyroid nodules and subacute thyroiditis with a thyrotoxic phase. In addition, we report therapeutic challenges in pediatric GD such as recurrent immunological flare-ups under anti-thyroid drug (ATD) treatment, innovative ways to improve ATD compliance and the role of definitive treatment in persistent complaints of malaise under ATD treatment.

Iodinated Contrast Induced Hypothyroidism in the Infant After Enteral Contrast Enema: A Case Report and Systematic Review.

Background: Excessive iodine intake triggers the Wolff-Chaikoff effect resulting in downregulation of thyroid hormone synthesis to prevent hyperthyroidism. Failure to escape the Wolff-Chaikoff effect can be seen especially in (premature born) infants and may result in prolonged iodine induced hypothyroidism. We describe a rare case of a preterm infant who developed severe iodinated contrast induced hypothyroidism after the use and prolonged stasis of enteral iodinated contrast media (ICM). In addition a systematic literature search was performed to evaluate all available data on this complication. Methods: A systematic literature search was performed in PubMed and Embase. Studies describing the effect of enteral ICM on thyroid function were considered eligible. The primary outcome was to determine the frequency of contrast induced hypothyroidism in infants after administration of enteral ICM. Results: The premature infant in our center developed severe iodinated contrast induced hypothyroidism after enteral ICM. In total, only two studies met our eligibility data, reporting eight patients. Out of these eight patients, four premature infants developed a contrast induced hypothyroidism after enteral administration of ICM. Conclusion: Data on severity, length and frequency of contrast induced hypothyroidism after exposure to enteral ICM is very scarce. The herein reported case and literature search illustrate the potential severity of the complication and underline the necessity of future studies on this topic. We recommend standardized monitoring of thyroid function after exposure to enteral ICM in newborns to prevent delayed diagnosis of severe contrast induced hypothyroidism until evidence based recommendations can be made.

Effects and Safety of Growth Hormone Treatment in Six Children with Pycnodysostosis.

INTRODUCTION: Pycnodysostosis is an extremely rare skeletal dysplasia caused by cathepsin K deficiency. It is characterized by extreme short stature with adult height (AH) in males typically less than 150 cm and in females less than 130 cm. Our objective was to evaluate the effect and safety of growth hormone (GH) treatment in 6 patients with pycnodysostosis treated according to the Dutch national pycnodysostosis guideline. CASE PRESENTATION: Six subjects (4 boys, 2 girls) presented with pycnodysostosis, treated with GH 1.4 mg/m2/day (∼0.046 mg/kg/day) for ≥1 year. Median (IQR) age at start of GH was 10.4 years (5.7; 12.2) and median height 113.5 cm (93.3; 129.3) (-4.2 SDS [-4.8; -3.6]). All children were prepubertal at start of GH. After 1 year of GH, median height gain was 7.6 cm (6.5; 8.5) (0.3 SDS [-0.3; 0.7]). Three children are still treated with GH, and the other three subjects reached AH: 1 boy reached an AH of 157.0 cm (-3.8 SDS) after 6.3 years of GH, and 2 girls reached an AH of 138.5 cm (-5.2 SDS) after 4.8 years of GH and 148.0 cm (-3.6 SDS) after 6.4 years of GH, respectively. This last girl received additional GnRH analogue treatment. In all subjects, height SDS remained stable or improved during and after GH treatment. No serious adverse advents were found. Serum IGF-I remained below the +2 SDS. CONCLUSION: Our data suggest that GH may prevent the decline in height which can be observed in children with pycnodysostosis. Further research is needed to confirm this. Also, the effect of other growth-promoting strategies such as treatment with an additional GnRH analogue warrants further investigation.

Analysis of Serum Free Thyroxine Concentrations in Healthy Term Neonates Underlines Need for Local and Laboratory-Specific Reference Interval: A Systematic Review and Meta-Analysis of Individual Participant Data.

Background: Initial evaluation of the hypothalamus-pituitary-thyroid axis is done by measuring serum free thyroxine (fT4) and thyrotropin concentrations. For correct interpretation of these measurements, reliable age-specific reference intervals (RIs) are fundamental. Since neonatal fT4 RIs conforming to the Clinical and Laboratory Standards Institute guidelines are not available for all assays, we set out to create literature-based uniform age-specific neonatal fT4 RIs that may be used for every assay. Methods: For meta-analysis of individual participant fT4 concentrations, we systematically searched MEDLINE and Embase (search date December 6, 2023; PROSPERO registration CRD42016041871). We searched for studies reporting fT4 concentrations in healthy term newborns aged 2-27 days, born to mothers without thyroid disease in iodine-sufficient regions. Authors were invited to supply data. Due to standardization differences between assays, data could not be combined for meta-analysis directly, and we attempted to normalize the data using two distinct methods. Results: We obtained 4206 fT4 concentrations from 20 studies that used 13 different assays from 6 manufacturers. First, we set out to normalize fT4 data using the mean and standard deviation of (assay-specific) adult RIs. fT4 concentrations were transformed into Z-scores, assuming a normal distribution. Using a linear mixed-effects model (LMM), we still found a significant difference between fT4 concentration across studies (p < 0.001), after this normalization. As a second approach, we normalized the fT4 concentrations using data from a method/assay comparison study. We used the relationship between the Cobas assay and the other assays as a reference point to convert all values to Cobas values. However, this method also failed to produce consistent results, with significant differences between the normalized data (LMM p < 0.001). Conclusions: We conclude that our attempts at normalizing fT4 assay results were unsuccessful. Confounders related to our unsuccessful analysis may be assay related and/or biological. These findings have significant implications for patient care, since relying on RIs from literature may result in erroneous interpretation of results. Therefore, we strongly recommend to establish local RIs for accurate interpretation of serum fT4 concentrations in neonates.

Corrigendum to "Expert management of congenital portosystemic shunts and their complications" [JHEP Reports 6 (2024)].

[This corrects the article DOI: 10.1016/j.jhepr.2023.100933.].

Tocilizumab for the fifth progression of cystic childhood craniopharyngioma-a case report.

We present the case of a 15-year-old girl, with a fifth cystic progression of an adamantinomatous craniopharyngioma after multiple surgeries and previous local radiotherapy. She had severe visual impairment, panhypopituitarism including diabetes insipidus, and several components of hypothalamic damage, including morbid obesity and severe fatigue. To prevent further late effects hampering her quality of survival, she was treated biweekly with intravenous tocilizumab, an anti-interleukin-6 agent, which stabilized the cyst for a prolonged time. Based on the biology of adamantinomatous craniopharyngioma, this immune-modulating treatment seems promising for the treatment of this cystic tumor in order to reduce surgery and delay or omit radiotherapy.

Optimizing the Dutch newborn screening for congenital hypothyroidism by incorporating amino acids and acylcarnitines in a machine learning-based model.

Objective: Congenital hypothyroidism (CH) is an inborn thyroid hormone (TH) deficiency mostly caused by thyroidal (primary CH) or hypothalamic/pituitary (central CH) disturbances. Most CH newborn screening (NBS) programs are thyroid-stimulating-hormone (TSH) based, thereby only detecting primary CH. The Dutch NBS is based on measuring total thyroxine (T4) from dried blood spots, aiming to detect primary and central CH at the cost of more false-positive referrals (FPRs) (positive predictive value (PPV) of 21% in 2007-2017). An artificial PPV of 26% was yielded when using a machine learning-based model on the adjusted dataset described based on the Dutch CH NBS. Recently, amino acids (AAs) and acylcarnitines (ACs) have been shown to be associated with TH concentration. We therefore aimed to investigate whether AAs and ACs measured during NBS can contribute to better performance of the CH screening in the Netherlands by using a revised machine learning-based model. Methods: Dutch NBS data between 2007 and 2017 (CH screening results, AAs and ACs) from 1079 FPRs, 515 newborns with primary (431) and central CH (84) and data from 1842 healthy controls were used. A random forest model including these data was developed. Results: The random forest model with an artificial sensitivity of 100% yielded a PPV of 48% and AUROC of 0.99. Besides T4 and TSH, tyrosine, and succinylacetone were the main parameters contributing to the model's performance. Conclusions: The PPV improved significantly (26-48%) by adding several AAs and ACs to our machine learning-based model, suggesting that adding these parameters benefits the current algorithm.

Neonatal screening for primary and central congenital hypothyroidism: is it time to go Dutch?

Thyroid hormone (TH) is indispensable for brain development in utero and during the first 2-3 years of life, and the negative effects of TH deficiency on brain development are irreversible. Detection of TH deficiency early in life by neonatal screening allows early treatment, thereby preventing brain damage. Inborn shortage of TH, also named congenital hypothyroidism (CH), can be the result of defective thyroid gland development or TH synthesis (primary or thyroidal CH (CH-T)). Primary CH is characterized by low blood TH and elevated thyroid-stimulating hormone (TSH) concentrations. Less frequently, CH is due to insufficient stimulation of the thyroid gland because of disturbed hypothalamic or pituitary function (central CH). Central CH is characterized by low TH concentrations, while TSH is normal, low or slightly elevated. Most newborn screening (NBS) programs for CH are primarily TSH based and thereby do not detect central CH. Only a few NBS programs worldwide aim to detect both forms of CH by different strategies. In the Netherlands, we have a unique T4-TSH-thyroxine-binding globulin (TBG) NBS algorithm for CH, which enables the detection of primary and central CH. Although the necessity of central CH detection by NBS is still under debate, it has been shown that most central CH patients have moderate-to-severe hypothyroidism instead of mild and that early detection of central CH by NBS probably improves its clinical outcome and clinical care for central CH patients with multiple pituitary hormone deficiency. We are therefore convinced that detection of central CH by NBS is of utmost importance.

The Effects of 5 Years of Growth Hormone Treatment on Growth and Body Composition in Patients with Temple Syndrome.

INTRODUCTION: Temple syndrome (TS14) is a rare imprinting disorder caused by maternal uniparental disomy of chromosome 14, paternal deletion of 14q32.2, or an isolated methylation defect. Most patients with TS14 develop precocious puberty. Some patients with TS14 are treated with growth hormone (GH). However, evidence for the effectiveness of GH treatment in patients with TS14 is limited. METHODS: This study describes the effect of GH treatment in 13 children and provides a subgroup analysis of 5 prepubertal children with TS14. We studied height, weight, body composition by dual-energy X-ray absorptiometry, resting energy expenditure (REE), and laboratory parameters during 5 years of GH treatment. RESULTS: In the entire group, mean (95% CI) height SDS increased significantly during 5 years of GH treatment from -1.78 (-2.52; -1.04) to 0.11 (-0.66; 0.87). Fat mass percentage SDS decreased significantly during the first year of GH, and lean body mass (LBM) SDS and LBM index increased significantly during 5 years of treatment. IGF-1 and IGF-BP3 levels rose rapidly during GH treatment, and the IGF-1/IGF-BP3 molar ratio remained relatively low. Thyroid hormone levels, fasting serum glucose, and insulin levels remained normal. In the prepubertal group, median (interquartile range [IQR]) height SDS, LBM SDS, and LBM index also increased. REE was normal at start and did not change during 1 year of treatment. Five patients reached adult height and their median (IQR) height SDS was 0.67 (-1.83; -0.01). CONCLUSION: GH treatment in patients with TS14 normalizes height SDS and improves body composition. There were no adverse effects or safety concerns during GH treatment.

Machine learning to improve false-positive results in the Dutch newborn screening for congenital hypothyroidism.

OBJECTIVE: The Dutch Congenital hypothyroidism (CH) Newborn Screening (NBS) algorithm for thyroidal and central congenital hypothyroidism (CH-T and CH-C, respectively) is primarily based on determination of thyroxine (T4) concentrations in dried blood spots, followed by thyroid-stimulating hormone (TSH) and thyroxine-binding globulin (TBG) measurements enabling detection of both CH-T and CH-C, with a positive predictive value (PPV) of 21%. A calculated T4/TBG ratio serves as an indirect measure for free T4. The aim of this study is to investigate whether machine learning techniques can help to improve the PPV of the algorithm without missing the positive cases that should have been detected with the current algorithm. DESIGN & METHODS: NBS data and parameters of CH patients and false-positive referrals in the period 2007-2017 and of a healthy reference population were included in the study. A random forest model was trained and tested using a stratified split and improved using synthetic minority oversampling technique (SMOTE). NBS data of 4668 newborns were included, containing 458 CH-T and 82 CH-C patients, 2332 false-positive referrals and 1670 healthy newborns. RESULTS: Variables determining identification of CH were (in order of importance) TSH, T4/TBG ratio, gestational age, TBG, T4 and age at NBS sampling. In a Receiver-Operating Characteristic (ROC) analysis on the test set, current sensitivity could be maintained, while increasing the PPV to 26%. CONCLUSIONS: Machine learning techniques have the potential to improve the PPV of the Dutch CH NBS. However, improved detection of currently missed cases is only possible with new, better predictors of especially CH-C and a better registration and inclusion of these cases in future models.

Meta-Analysis of DNA Methylation Datasets Shows Aberrant DNA Methylation of Thyroid Development or Function Genes in Down Syndrome.

Background: In Down syndrome (DS), there is high occurrence of congenital hypothyroidism (CH) and subclinical hypothyroidism (SH) early in life. The etiology of CH and early SH in DS remains unclear. Previous research has shown genome-wide transcriptional and epigenetic alterations in DS. Thus, we hypothesized that CH and early SH could be caused by epigenetically driven transcriptional downregulation of thyroid-related genes, through promoter region hypermethylation. Methods: We extracted whole blood DNA methylation (DNAm) profiles of DS and non-DS individuals from four independent Illumina array-based datasets (252 DS individuals and 519 non-DS individuals). The data were divided into discovery and validation datasets. Epigenome-wide association analysis was performed using a linear regression model, after which we filtered results for thyroid-related genes. Results: In the discovery dataset, we identified significant associations for DS in 18 thyroid-related genes. Twenty-one of 30 significant differentially methylated positions (DMPs) were also significant in the validation dataset. A meta-analysis of the discovery and validation datasets detected 31 DMPs, including 29 promoter-associated cytosine-guanine dinucleotides (CpG) with identical direction of effect across the datasets, and two differentially methylated regions. Twenty-seven DMPs were hypomethylated and promoter associated. The mean methylation difference of hypomethylated thyroid-related DMPs decreased with age. Conclusions: Contrary to our hypothesis of generalized hypermethylation of promoter regions of thyroid-related genes-indicative of epigenetic silencing of promoters and subsequent transcriptional downregulation, causing biochemical thyroid abnormalities in DS-we found an enrichment of hypomethylated DMPs annotated to promoter regions of these genes. This suggests that CH and early SH in DS are not caused by differential methylation of thyroid-related genes. Considering that epigenetic regulation is dynamic, we hypothesize that the observed thyroid-related gene DNAm changes could be a rescue phenomenon in an attempt to ameliorate the thyroid phenotype, through epigenetic upregulation of thyroid-related genes. This hypothesis is supported by the finding of decreasing methylation difference of thyroid-related genes with age. The prevalence of early SH declines with age, so hypothetically, epigenetic upregulation of thyroid-related genes also diminishes. While this study provides interesting insights, the exact origin of CH and early SH in DS remains unknown.

Temple Syndrome: Clinical Findings, Body Composition and Cognition in 15 Patients.

BACKGROUND: Temple syndrome (TS14) is an imprinting disorder caused by a maternal uniparental disomy of chromosome 14 (UPD(14)mat), paternal deletion of 14q32 or an isolated methylation defect of the MEG3-DMR. Studies on phenotypical characteristics in TS14 are scarce and patients with TS14 often experience delay in diagnosis, which has adverse effects on their health. TS14 is often characterized as either Prader-Willi-like, Silver-Russell-like or as a Silver-Russell spectrum disorder. METHODS: This study describes 15 patients with TS14 who visited the Dutch Reference Center for Prader-Willi-like from December 2018 to January 2022. RESULTS: Eight patients had UPD(14)mat and seven a methylation defect. The most common symptoms were intra-uterine growth retardation (IUGR) (100%), hypotonia (100%), precocious puberty (89%), small for gestational age (SGA) birth (67%), tube feeding after birth (53%) and psycho-behavioral problems (53%). Median (interquartile range (IQR)) IQ was 91.5 (84.25; 100.0), whilst many patients were enrolled in special education (54%). The median (IQR) fat mass % (FM%) SDS was 2.53 (2.26; 2.90) and lean body mass (LBM) SDS -2.03 (-3.22; -1.28). There were no significant differences in clinical characteristics between patients with a UPD(14)mat and a methylation defect. CONCLUSIONS: Our patients share a distinct phenotype consisting of IUGR, SGA birth, precocious puberty, hypotonia, tube feeding after birth, psycho-behavioral problems and abnormal body composition with a high FM% and low LBM. Whilst similarities with Prader-Willi syndrome (PWS) and Silver-Russell syndrome (SRS) exist, TS14 is a discernible syndrome, deserving a tailored clinical approach. Testing for TS14 should be considered in patients with a PWS or SRS phenotype in infancy if PWS/SRS testing is negative.

Identification of a Novel CYP11B2 Variant in a Family with Varying Degrees of Aldosterone Synthase Deficiency.

Isolated aldosterone synthase deficiency is a rare autosomal recessive disorder caused by pathogenic variants in CYP11B2, resulting in impaired aldosterone synthesis. We report on a neonate with isolated aldosterone synthase deficiency caused by a novel homozygous CYP11B2 variant Chr8:NM_000498.3:c.400G>A p.(Gly134Arg). The patient presented shortly after birth with severe signs of aldosterone deficiency. Interestingly, segregation analysis revealed that the patient's asymptomatic father was also homozygous for the CYP11B2 variant. Biochemical evaluation of the father indicated subclinical enzyme impairment, characterized by elevated aldosterone precursors. Apparently, this homozygous variant led to different clinical phenotypes in two affected relatives. In this manuscript we elaborate on the performed biochemical and genetic work-up and describe potential pitfalls of CYP11B2 sequencing due to its homology to CYP11B2.

The Effect of Pre-Thyroidectomy Calcitriol Prophylaxis on Post-Thyroidectomy Hypocalcaemia in Children.

INTRODUCTION: Transient or persistent hypoparathyroidism is one of the most well-known complications of total thyroidectomy and may lead to symptomatic hypocalcaemia. In children, treatment of post-thyroidectomy hypocalcaemia usually consists of postoperative calcium and/or vitamin D supplementation. In 2013, we implemented prophylactic pre-thyroidectomy calcitriol supplementation for all children undergoing total thyroidectomy at the Amsterdam UMC. The objective of this study was to evaluate the efficacy of this prophylactic calcitriol supplementation in preventing post-thyroidectomy hypocalcaemia in children. METHODS: In a retrospective case study, we included all children (age <18 years), who underwent a total or completion thyroidectomy in the Amsterdam UMC, between 2000 and 2020. Patients were divided into two groups, patients with preoperative calcitriol supplementation and those without (controls). Hypocalcaemia was defined as total serum calcium concentration of <2.0 mmol/L. The primary outcome measure was the occurrence of hypocalcaemia in the first 72 h after surgery. Secondary outcome measures were occurrence of symptomatic hypocalcaemia, need for medical intervention within the first 72 h after surgery, and length of hospitalization. RESULTS: A total of 51 patients were included; 26 with calcitriol prophylaxis and 25 controls. There was no significant difference in occurrence of hypocalcaemia (17/26 prophylaxis group; 18/25 control group). Median postoperative calcium concentrations in the first 72 h were significantly higher in the group with prophylaxis at 30-35 h (2.26 vs. 2.01 mmol/L) and 36-41 h (2.17 vs. 1.92 mmol/L). Occurrence of symptomatic hypocalcaemia, need for medical intervention, and length of hospitalization were not significantly different between the groups. CONCLUSION: Calcitriol prophylaxis resulted in somewhat higher postoperative calcium concentrations but did not reduce the occurrence of hypocalcaemia or affect clinical outcome measures such as occurrence of symptomatic hypocalcaemia and length of postoperative hospitalization.

Mild Isolated Congenital Central Hypothyroidism Due to a Novel Homozygous Variant in TSHB: A Case Report.

Pathogenic variants in TSHB are known to cause severe isolated central congenital hypothyroidism (CH). In this study, we present the clinical, biochemical, and genetic features of the first patient with a mild central CH phenotype. We identified a novel homozygous variant in TSHB: (Chr1: NM_000549.5):c.290A>G p.(Tyr97Cys) in a newborn girl detected by neonatal CH screening, whose central CH was initially overlooked because of misinterpretation of her plasma-free thyroxine (fT4) concentration. This report adds to the phenotypic spectrum of TSHB variants and underlines the importance of using age-specific fT4 reference intervals to diagnose central CH.

Complications After Thyroidectomy in Children: Lymph Node Dissection Is a Risk Factor for Permanent Hypocalcemia.

Background: Thyroidectomy is a treatment option in some benign thyroid disorders and the definitive treatment option for thyroid cancer. As postoperative mortality is extremely rare data on postoperative complications and long-term health consequences are important. Objective: To evaluate the frequencies of short- and long-term complications, and their risk factors in pediatric patients (0-18 years) who underwent a thyroidectomy in a tertiary children's hospital. Methods: A retrospective single center study was performed including all pediatric patients who underwent a thyroidectomy between January 2013 and February 2020. Results: Forty-eight patients were included in this study (mean age 14.6 years). Twenty-nine total thyroidectomies and 19 hemithyroidectomies were conducted. Thyroid carcinoma was the indication to perform a thyroidectomy in 12 patients, 36 patients underwent a thyroidectomy because of a benign thyroid disorder. Postoperative hypocalcemia was evaluated in patients who underwent a total thyroidectomy. Rapidly resolved hypocalcemia was observed in three patients (10.3%), transient hypocalcemia in 10 patients (34.5%) and permanent hypocalcemia in six patients (20.7%). Permanent hypocalcemia was only seen in patients who underwent a thyroidectomy combined with additional lymph node dissection because of thyroid carcinoma [thyroid carcinoma: OR 43.73, 95% CI (2.11-904.95); lymph node dissection: OR 76.14, 95% CI (3.49-458.98)]. Transient and permanent recurrent laryngeal nerve injury was reported in four (8.3%) and one (2.1%) of all patients, respectively. Conclusion: Permanent postoperative complications after thyroidectomy are rare in pediatric patients undergoing a thyroidectomy without lymph node dissection. However, in this age group permanent hypocalcemia occurs more frequently after thyroidectomy with additional lymph node dissection because of thyroid cancer. With respect to quality of life, especially of pediatric thyroid cancer patients, reducing this complication is an important goal.

Diagnosis and Management of Central Congenital Hypothyroidism.

Central congenital hypothyroidism (CH) is defined as thyroid hormone (TH) deficiency at birth due to insufficient stimulation by the pituitary of the thyroid gland. The incidence of central CH is currently estimated at around 1:13,000. Central CH may occur in isolation, but in the majority of cases (60%) it is part of combined pituitary hormone deficiencies (CPHD). In recent years several novel genetic causes of isolated central CH have been discovered (IGSF1, TBL1X, IRS4), and up to 90% of isolated central CH cases can be genetically explained. For CPHD the etiology usually remains unknown, although pituitary stalk interruption syndrome does seem to be the most common anatomic pituitary malformation associated with CPHD. Recent studies have shown that central CH is a more severe condition than previously thought, and that early detection and treatment leads to good neurodevelopmental outcome. However, in the neonatal period the clinical diagnosis is often missed despite hospital admission because of feeding problems, hypoglycemia and prolonged jaundice. This review provides an update on the etiology and prognosis of central CH, and a practical approach to diagnosis and management of this intriguing condition.

The Efficacy and Short- and Long-Term Side Effects of Radioactive Iodine Treatment in Pediatric Graves' Disease: A Systematic Review.

BACKGROUND: Graves's disease (GD) is the most common cause of hyperthyroidism. Maximal 30% of pediatric GD patients achieve remission with antithyroid drugs. The majority of patients therefore require definitive treatment. Both thyroidectomy and radioactive iodine (RAI) are often used as definitive treatment for GD. However, data on efficacy and short- and long-term side effects of RAI treatment for pediatric GD are relatively scarce. METHODS: A systematic review of the literature (PubMed and Embase) was performed to identify studies reporting the efficacy or short- and long-term side effects of RAI treatment in pediatric GD. RESULTS: Twenty-three studies evaluating 1,283 children and adolescents treated with RAI for GD were included. The treatment goal of RAI treatment changed over time, from trying to achieve euthyroidism in the past to aiming at complete thyroid destruction and subsequent hypothyroidism in the last 3 decades. The reported efficacy of a first RAI treatment when aiming at hypothyroidism ranged from 42.8 to 97.5%, depending on the activity administered. The efficacy seems to increase with higher RAI activities. When aiming at hypothyroidism, both short- and long-term side effects of treatment are very rare. Long-term side effects were mainly seen in patients in whom treatment aimed at achieving euthyroidism. CONCLUSION: RAI is a safe definitive treatment option for pediatric GD when aiming at complete thyroid destruction. When aiming at hypothyroidism, the efficacy of treatment seems to increase with a higher RAI activity. Prospective studies are needed to determine the optimal RAI dosing regimen in pediatric GD.

Defective Levothyroxine Response in a Patient with Dyshormonogenic Congenital Hypothyroidism Caused by a Concurrent Pathogenic Variant in Thyroid Hormone Receptor-ß.

Background: Pituitary resistance to thyroid hormone (PRTH) is often seen in congenital hypothyroidism (CH), presenting as elevated thyrotropin (TSH) values despite (high-)normal thyroid hormone (TH) values achieved by levothyroxine treatment. In this study, we describe a girl with CH who was referred because of difficulties interpreting thyroid function tests. She was thought to have PRTH associated with CH, but genetic studies discovered a pathogenic variant in THRB, causing resistance to TH (RTH-ß). Methods: Clinical, genetic, and biochemical data of the proband's family were collected. Results: The 3-year-old girl was diagnosed with CH due to a homozygous pathogenic c.470del p.(Asn157Thrfs*3) SLC5A5 variant in the neonatal period. She needed a notably high levothyroxine dose to normalize TSH, leading to high free thyroxine levels. There were no signs of hyperthyroidism. Sequencing identified a heterozygous pathogenic c.947G>A p.(Arg316His) THRB variant. Conclusions: To our knowledge, this is the first report of concomitant SLC5A5 and THRB variants causing CH and RTH-ß.