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Hypothalamic Integration Mechanisms, Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences, Amsterdam, The Netherlands
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Thyroid hormone (TH) plays a key role in regulating body temperature in mammals. Cold exposure stimulates the hypothalamus-pituitary-thyroid (HPT) axis at the hypothalamic level by activating hypophysiotropic thyrotropin-releasing hormone (TRH)-producing neurons, ultimately resulting in increased plasma TH concentrations. Importantly, the local TH metabolism within various cold-responsive organs enables tissue-specific action of TH on heat production and adaption to cold independently of the circulating TH levels. In addition to these neuroendocrine effects, TRH neurons in the hypothalamus also have neural connections with brown adipose tissue (BAT), probably contributing to regulation of thermogenesis by the autonomic nervous system. Recent studies have demonstrated that intrahypothalamic TH has profound metabolic effects on BAT, the liver, and the heart that are mediated via the autonomic nervous system. These effects originate in various hypothalamic nuclei, including the paraventricular nucleus (PVN), the ventromedial nucleus, and recently reported neurons in the anterior hypothalamic area, indicating a potential central function for TH on thermoregulation. Finally, although robust stimulation of the thermogenic program in BAT was shown upon TH administration in the ventromedial hypothalamus, the physiological relevance of these neurally mediated effects of TH is unclear at present. This review provides an overview of studies reporting the role of TH in cold defense, with a focus on recent literature evidencing the centrally mediated effects of TRH and TH.
Amsterdam Gastroenterology Endocrinology Metabolism, Amsterdam, the Netherlands
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Amsterdam Gastroenterology Endocrinology Metabolism, Amsterdam, the Netherlands
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Department of Laboratory Medicine, Endocrine Laboratory, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands
Amsterdam Reproduction & Development Research Institute, Amsterdam, the Netherlands
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Thyroid hormones play an essential role in regulating whole-body homeostasis. Deiodinases are known to convert thyroid hormone from the prohormone thyroxine (T4) to the bioactive hormone tri-iodothyronine (T3) and convert both T4 and T3 toward their inactive metabolites 3,3’,5’-tri-iodothyronine (rT3) and 3,3’-di-iodothyronine (3,3’-T2). Deiodinases are thus important for the regulation of intracellular thyroid hormone concentrations. This is known to be crucial both during development and adult life in regulating thyroid hormone-related gene transcription. This review discusses the importance of liver deiodinases in determining serum and liver thyroid hormone concentrations, liver metabolism and liver disease.
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Department of Pharmacology and Therapeutics, McGill University, Montreal, Quebec, Canada
Integrated Program in Neuroscience, McGill University, Montreal, Quebec, Canada
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Objective
Loss of function mutations in the insulin receptor substrate 4 (IRS4) gene cause a rare form of X-linked congenital central hypothyroidism in boys and men. Affected individuals show decreased thyroid-stimulating hormone (TSH) secretion. Members of the IRS family canonically act as scaffold proteins between tyrosine kinase receptors and downstream effectors. How loss of IRS4 affects TSH synthesis or secretion is unresolved. We therefore assessed IRS4’s role in the hypothalamic–pituitary–thyroid axis of Irs4 knockout mice.
Methods
We generated two global Irs4 knockout mouse lines harboring either two or four base-pair deletions that result in frameshifts and loss of most of the IRS4 protein.
Results
Under normal laboratory conditions, Irs4 knockout males did not exhibit impairments in pituitary expression of TSH subunit genes (Tshb or Cga) or in the thyrotropin-releasing hormone (TRH) receptor. Additionally, their serum thyroid hormone, triiodothyronine (T3) and thyroxine (T4), and hypothalamic Trh expression levels were normal. When Irs4 knockouts were rendered hypothyroid with a low-iodine diet supplemented with propylthiouracil for 3 weeks, their serum TSH increased similarly to wild-type males.
Conclusion
Overall, Irs4 knockout mice do not exhibit central hypothyroidism or otherwise appear to phenocopy IRS4 deficient patients. Compensation by another IRS protein may explain euthyroidism in these animals.
Amsterdam Gastroenterology Endocrinology Metabolism, Amsterdam, The Netherlands
Amsterdam Reproduction & Development Research Institute, Amsterdam, The Netherlands
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Department of Pediatric Endocrinology, Emma Children’s Hospital, Amsterdam UMC, location University of Amsterdam, Amsterdam, The Netherlands
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Amsterdam Gastroenterology Endocrinology Metabolism, Amsterdam, The Netherlands
Amsterdam Reproduction & Development Research Institute, Amsterdam, The Netherlands
Endocrine Laboratory, Department of Laboratory Medicine, Amsterdam UMC, location Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
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Department of Pediatric Endocrinology, Emma Children’s Hospital, Amsterdam UMC, location University of Amsterdam, Amsterdam, The Netherlands
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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.
Amsterdam Gastroenterology, Endocrinology & Metabolism (AGEM) Research Institute, Amsterdam UMC, Amsterdam, the Netherlands
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Department of Pediatric Endocrinology, Emma Children’s Hospital, Amsterdam University Medical Center, University of Amsterdam, Amsterdam, the Netherlands
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Department of Endocrinology, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands
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Department of Endocrinology, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands
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Amsterdam Gastroenterology, Endocrinology & Metabolism (AGEM) Research Institute, Amsterdam UMC, Amsterdam, the Netherlands
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Transducin β-like 1 X-linked receptor 1 (TBL1XR1) is a WD40 repeat-containing protein and part of the corepressor complex SMRT/NCoR that binds to the thyroid hormone receptor (TR). We recently described a mutation in TBL1XR1 in patients with Pierpont syndrome. A mouse model bearing this Tbl1xr1 mutation (Tbl1xr1Y446C/Y446C ) displays several aspects of the Pierpont phenotype. Although serum thyroid hormone (TH) concentrations were unremarkable in these mice, tissue TH action might be affected due to the role of TBL1XR1 in the SMRT/NCoR corepressor complex. The aim of the present study was to evaluate tissue TH metabolism and action in a variety of tissues of Tbl1xr1Y446C/Y446C mice. We studied the expression of genes involved in TH metabolism and action in tissues of naïve Tbl1xr1Y446C/Y446C mice and wild type (WT) mice. In addition, we measured deiodinase activity in liver (Dio1 and Dio3), kidney (Dio1 and Dio3) and BAT (Dio2). No striking differences were observed in the liver, hypothalamus, muscle and BAT between Tbl1xr1Y446C/Y446C and WT mice. Pituitary TRα1 mRNA expression was lower in Tbl1xr1Y446C/Y446C mice compared to WT, while the mRNA expression of Tshβ and the positively T3-regulated gene Nmb were significantly increased in mutant mice. Interestingly, Mct8 expression was markedly higher in WAT and kidney of mutants, resulting in (subtle) changes in T3-regulated gene expression in both WAT and kidney. In conclusion, mice harboring a mutation in TBL1XR1 display minor changes in cellular TH metabolism and action. TH transport via MCT8 might be affected as the expression is increased in WAT and kidney. The mechanisms involved need to be clarified.
Amsterdam Gastroenterology, Endocrinology & Metabolism, Amsterdam, The Netherlands
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Amsterdam Gastroenterology, Endocrinology & Metabolism, Amsterdam, The Netherlands
Amsterdam Reproduction & Development, Amsterdam, The Netherlands
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Amsterdam Gastroenterology, Endocrinology & Metabolism, Amsterdam, The Netherlands
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Amsterdam Public Health, Amsterdam, The Netherlands
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Amsterdam Gastroenterology, Endocrinology & Metabolism, Amsterdam, The Netherlands
Amsterdam Reproduction & Development, Amsterdam, The Netherlands
Department of Laboratory Medicine, Endocrine Laboratory, Amsterdam UMC Location Vrije Universiteit Amsterdam, Boelelaan, Amsterdam, The Netherlands
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Objective
International guidelines concerning subclinical hyperthyroidism and thyroid cancer advice absolute cut-off values for aiding clinical decisions in the low range of thyroid-stimulating hormone (TSH) concentrations. As TSH assays are known to be poorly standardized in the normal to high range, we performed a TSH assay method comparison focusing on the low range.
Methods
Sixty samples, selected to cover a wide range of TSH concentrations (<0.01 to 120 mIU/L) with oversampling in the lower range (<0.4 mIU/L), were used for the method comparison between three TSH immunoassays (Cobas, Alinity and Atellica). In addition, 20 samples were used to assess the coefficient of variation from duplicate measurements in these three methods.
Results
The TSH immunoassays showed standardization differences with a bias of 7–16% for the total range and 1–14% for the low range. This could lead to a different classification of 1.5% of all measured TSH concentrations <0.40 mIU/L measured in our laboratory over the last 6 months, regarding the clinically important cut-off value of TSH = 0.1 mIU/L. As the imprecision of the immunoassays varied from 1.6–5.5%, this could lead to a similar reclassification as the bias between immunoassays.
Conclusions
We established the standardization differences of frequently used TSH assays for the total and low concentration ranges. Based on the proportional bias and the imprecision, this effect seems to have limited clinical consequences for the low TSH concentration range. Nevertheless, as guidelines mention absolute TSH values to guide clinical decision-making, caution must be applied when interpreting values close to these cut-offs.
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Endocrine Laboratory, Department of Clinical Chemistry, Amsterdam Gastroenterology, Endocrinology & Metabolism, Amsterdam UMC, Vrije Universiteit, Amsterdam, The Netherlands
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Introduction: Newborn screening (NBS) for congenital hypothyroidism (CH) in the Netherlands consists of thyroxine (T4), thyroid-stimulating hormone (TSH), and T4-binding globulin (TBG) measurements to detect thyroidal CH and central CH (CH-C). CH-C is detected by T4 or a calculated T4/TBG ratio, which serves as an indirect measure of free T4. TSH and TBG are only measured in the lowest 20 and 5% of daily T4 values, respectively. A recent evaluation of the Dutch NBS for CH showed that the T4 and T4/TBG ratio contribute to the detection of CH-C but also lead to a low positive predictive value (PPV). Dried blood spot (DBS) reference intervals (RIs) are currently unknown and may contribute to improvement of our NBS algorithm. Materials and Methods: RIs of T4, TSH, TBG, and the T4/TBG ratio were determined according to Clinical & Laboratory Standards Institute guidelines in heel puncture cards from routine NBS in both sexes and at the common NBS sampling ages. Scatter plots were used to compare the healthy reference population to previously published data of CH-C patients and false positives. Results: Analyses of 1,670 heel puncture cards showed small differences between subgroups and led to the formulation of total sample DBS RIs for T4 (56–118 nmol/L), TSH (<2.6 mIU/L), TBG (116–271 nmol/L), and the T4/TBG ratio (>20). 46% of false-positive referrals based on T4 alone had a TBG below the RI, indicating preventable referral due to partial TBG deficiency. One case of CH-C also had partial TBG deficiency (TBG 59 and T4 12 nmol/L blood). Discussion/Conclusion: Established DBS RIs provided possibilities to improve the PPV of the Dutch CH NBS algorithm. We conclude that by taking partial TBG deficiency into account, approximately half of T4 false-positive referrals may be prevented while maintaining NBS sensitivity at the current level.
Amsterdam Gastroenterology, Endocrinology & Metabolism, Amsterdam, The Netherlands
Department of Clinical Chemistry, Endocrine Laboratory, Amsterdam UMC location University of Amsterdam, Amsterdam, The Netherlands
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Amsterdam Reproduction & Development Research Institute, Amsterdam, The Netherlands
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Department of Clinical Chemistry, Endocrine Laboratory, Amsterdam UMC location University of Amsterdam, Amsterdam, The Netherlands
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Department of Clinical Chemistry, Endocrine Laboratory, Amsterdam UMC location University of Amsterdam, Amsterdam, The Netherlands
Amsterdam Reproduction & Development Research Institute, Amsterdam, The Netherlands
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Amsterdam Gastroenterology, Endocrinology & Metabolism, Amsterdam, The Netherlands
Department of Clinical Chemistry, Endocrine Laboratory, Amsterdam UMC location University of Amsterdam, Amsterdam, The Netherlands
Amsterdam Reproduction & Development Research Institute, Amsterdam, The Netherlands
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Objective
Thyroid hormone measurements are often performed in pregnant women, as hypo- and hyperthyroidism during pregnancy can severely affect the fetus. Serum free thyroxine (fT4) measurements are well known for their analytical challenges, due to low serum concentrations and the subtle equilibrium between free and bound T4 (to thyroid-binding globulin (TBG), transthyretin and albumin). Pregnant women have high TBG concentrations due to an increase in human chorionic gonadotropin (hCG) and estrogen and lower albumin concentrations which change the equilibrium and may affect the validity of fT4 measurements in their samples. As accurate serum fT4 measurements in pregnant women are important for the long-term health of the fetus, we aimed to evaluate the accuracy of several fT4 immunoassays in the serum of pregnant women.
Methods
FT4 was measured in healthy controls and pregnant women using a candidate-reference method (LC-MS/MS) and five commercially available automated immunoassays (Alinity (Abbott), Atellica (Siemens), Cobas (Roche), Lumipulse (Fujirebio) and UniCel DXI (Beckman Coulter)). Method comparisons (Bland Altman plots and Passing and Bablok analyses) were performed.
Results
Serum samples from both healthy controls (n = 30) and pregnant women (n = 30; mean gestational age, 24.8 weeks) were collected. The fT4 immunoassays deviated +7 to +29% more from the LC-MS/MS in serum samples of pregnant women than healthy controls (falsely high).
Conclusions
Our results indicate that immunoassays overestimate fT4 in pregnant women, which might lead to an overestimation of thyroid status. Physicians and laboratory specialists should be aware of this phenomenon to avoid drawing false conclusions about thyroid function in pregnant women.
Amsterdam Gastroenterology, Endocrinology & Metabolism, Amsterdam, The Netherlands
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Amsterdam Gastroenterology, Endocrinology & Metabolism, Amsterdam, The Netherlands
Amsterdam Reproduction & Development Research Institute, Amsterdam, The Netherlands
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Amsterdam Public Health Research Institute, Amsterdam UMC, The Netherlands
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Department of Public Health and Primary Care, Leiden University Medical Center, Leiden, The Netherlands
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Department of Public Health and Primary Care, Leiden University Medical Center, Leiden, The Netherlands
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Amsterdam Gastroenterology, Endocrinology & Metabolism, Amsterdam, The Netherlands
Amsterdam Reproduction & Development Research Institute, Amsterdam, The Netherlands
Department of Laboratory Medicine, Endocrine Laboratory, Amsterdam UMC Location Vrije Universiteit Amsterdam, Boelelaan, Amsterdam, The Netherlands
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Laboratory Specialized Diagnostics & Research, Department of Laboratory Medicine, Amsterdam UMC, University of Amsterdam, Meibergdreef, Amsterdam, The Netherlands
Amsterdam Public Health Research Institute, Meibergdreef, Amsterdam, The Netherlands
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Background
Subclinical thyroid diseases are often the subject of debate concerning their clinical significance, the appropriateness of diagnostic testing, and possible treatment. This systematic review addresses the variation in international guidelines for subclinical hyperthyroidism, focusing on diagnostic workup, treatment, and follow-up recommendations.
Methods
Following the PRISMA guidelines, we searched PubMed, Embase, and guideline-specific databases and included clinical practice guidelines with recommendations on subclinical hyperthyroidism. Guideline recommendations were extracted, and quality assessment was performed using selected questions of the Appraisal of Guidelines for Research & Evaluation (AGREE) II instrument.
Results
Of the 2624 records screened, 22 guidelines were included, which were published between 2007 and 2021. Guideline quality was generally intermediate to low. Diagnostic approaches differed substantially, particularly in the extent of recommended testing. Treatment initiation depended on TSH levels, age, and comorbidities, but the level of detail regarding defining precise comorbidities varied. Recommendations for monitoring intervals for follow-up ranged from 3 to 12 months.
Conclusion
This review underscores the existing variability in (inter)national guidelines concerning subclinical hyperthyroidism. There isa need for clear recommendations in guidelines considering diagnostic workup, treatment, and follow-up of subclinical hyperthyroidism. In order to establish this, future research should focus on determining clear and evidence-based intervention thresholds.
Amsterdam Gastroenterology, Endocrinology and Metabolism, Amsterdam, The Netherlands
Department of Laboratory Medicine, Endocrine Laboratory, Amsterdam UMC location University of Amsterdam, Meibergdreef, Amsterdam, The Netherlands
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Department of Computer Science, Vrije Universiteit, Boelelaan, Amsterdam, The Netherlands
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Amsterdam Public Health, Amsterdam, The Netherlands
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Department of Endocrinology and Metabolism, Amsterdam UMC location University of Amsterdam, Meibergdreef, Amsterdam, The Netherlands
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Department of Paediatric Endocrinology, Emma Children’s Hospital, Amsterdam UMC, University of Amsterdam, Meibergdreef, Amsterdam, The Netherlands
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Department of Paediatric Endocrinology, Emma Children’s Hospital, Amsterdam UMC, University of Amsterdam, Meibergdreef, Amsterdam, The Netherlands
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Amsterdam Gastroenterology, Endocrinology and Metabolism, Amsterdam, The Netherlands
Department of Laboratory Medicine, Endocrine Laboratory, Amsterdam UMC location University of Amsterdam, Meibergdreef, Amsterdam, The Netherlands
Amsterdam Reproduction & Development Research Institute, Amsterdam, The Netherlands
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Department of Pediatrics, Division of Metabolic Disorders, Emma Children’s Hospital, Amsterdam UMC, University of Amsterdam, Meibergdreef, Amsterdam, The Netherlands
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Department of Laboratory Medicine, Amsterdam UMC, Vrije Universiteit, Boelelaan, Amsterdam, The Netherlands
Department of Laboratory Medicine, Amsterdam UMC, University of Amsterdam, Meibergdreef, Amsterdam, The Netherlands
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Department of Laboratory Medicine, Endocrine Laboratory, Amsterdam UMC location University of Amsterdam, Meibergdreef, Amsterdam, The Netherlands
Amsterdam Reproduction & Development Research Institute, Amsterdam, The Netherlands
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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.
