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Thyroid hormone (TH) exerts its biological activity via the TH receptors TRα1 and TRβ1/2, which are encoded by the THRA and THRB genes. The first patients with mutations in THRB were identified decades ago. These patients had a clinical syndrome of resistance to TH associated with high serum TH and nonsuppressed thyroid-stimulating hormone levels. Until recently, no patients with mutations in THRA had been identified. In an attempt to predict the clinical phenotype of such patients, different TRα1 mutant mouse models have been generated. These mice have a variable phenotype depending on the location and severity of the mutation. Recently, the first humans with mutations in THRA were identified. Their phenotype consists of relatively low serum T4 and high serum T3 levels (and thus an elevated T3/T4 ratio), growth retardation, delayed mental and bone development, and constipation. While, in retrospect, certain features present in humans can also be found in mouse models, the first humans carrying a defect in TRα1 were not suspected of having a THRA gene mutation initially. The current review focuses on the clinical consequences of TRα1 mutations.
Royal Victoria Infirmary, Newcastle upon Tyne, UK
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Queen Elizabeth Hospital, Gateshead, UK
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Subclinical hypothyroidism (SCH) should be considered in two categories according to the elevation in serum thyroid-stimulating hormone (TSH) level: mildly increased TSH levels (4.0-10.0 mU/l) and more severely increased TSH value (>10 mU/l). An initially raised serum TSH, with FT<sub>4</sub> within reference range, should be investigated with a repeat measurement of both serum TSH and FT<sub>4</sub>, along with thyroid peroxidase antibodies, preferably after a 2- to 3-month interval. Even in the absence of symptoms, replacement therapy with <smlcap>L</smlcap>-thyroxine is recommended for younger patients (<65-70 years) with serum TSH >10 mU/l. In younger SCH patients (serum TSH <10 mU/l) with symptoms suggestive of hypothyroidism, a trial of <smlcap>L</smlcap>-thyroxine replacement therapy should be considered. For such patients who have been started on <smlcap>L</smlcap>-thyroxine for symptoms attributed to SCH, response to treatment should be reviewed 3 or 4 months after a serum TSH within reference range is reached. If there is no improvement in symptoms, <smlcap>L</smlcap>-thyroxine therapy should generally be stopped. Age-specific local reference ranges for serum TSH should be considered in order to establish a diagnosis of SCH in older people. The oldest old subjects (>80-85 years) with elevated serum TSH ≤10 mU/l should be carefully followed with a wait-and-see strategy, generally avoiding hormonal treatment. If the decision is to treat SCH, then oral <smlcap>L</smlcap>-thyroxine, administered daily, is the treatment of choice. The serum TSH should be re-checked 2 months after starting <smlcap>L</smlcap>-thyroxine therapy, and dosage adjustments made accordingly. The aim for most adults should be to reach a stable serum TSH in the lower half of the reference range (0.4-2.5 mU/l). Once patients with SCH are commenced on <smlcap>L</smlcap>-thyroxine treatment, then serum TSH should be monitored at least annually thereafter.
Academic Center for Thyroid Diseases, Department of Internal Medicine, Erasmus Medical Center, Rotterdam, The Netherlands
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Objective
Evidence-based treatment guidelines for the management of postthyroidectomy hypocalcemia are absent. The aim of this study was to evaluate a newly developed symptom-based treatment algorithm including a protocolized attempt to phase out supplementation.
Methods
In a prospective multicenter study, patients were treated according to the new algorithm and compared to a historical cohort of patients treated with a biochemically based approach. The primary outcome was the proportion of patients receiving calcium and/or alfacalcidol supplementation. Secondary outcomes were calcium-related complications and predictors for supplementation.
Results
One hundred thirty-four patients were included prospectively, and compared to 392 historical patients. The new algorithm significantly reduced the proportion of patients treated with calcium and/or alfacalcidol during the first postoperative year (odds ratio (OR): 0.36 (95% CI: 0.23–0.54), P < 0.001), and persistently at 12 months follow-up (OR: 0.51 (95% CI: 0.28–0.90), P < 0.05). No severe calcium-related complications occurred, even though calcium-related visits to the emergency department and readmissions increased (OR: 11.5 (95% CI: 4.51–29.3), P <0.001) and (OR: 3.46 (95% CI: 1.58–7.57), P < 0.05), respectively. The proportional change in pre- to postoperative parathyroid hormone (PTH) was an independent predictor for supplementation (OR: 1.04 (95% CI: 1.02–1.07), P < 0.05).
Conclusions
Symptom-based management of postthyroidectomy hypocalcemia and a protocolized attempt to phase out supplementation safely reduced the proportion of patients receiving supplementation, although the number of calcium-related hospital visits increased. For the future, we envision a more individualized treatment approach for patients at risk for delayed symptomatic hypocalcemia, including the proportional change in pre- to post- operative PTH.
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Princess Máxima Center for Pediatric Oncology, Utrecht, The Netherlands
Oncode Institute, Utrecht, The Netherlands
Institute for Genome Stability in Ageing and Disease, CECAD Research Centre, Cologne, Germany
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Oncode Institute, Utrecht, The Netherlands
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Background
Thyroid hormone signaling is essential for development, metabolism, and response to stress but declines during aging, the cause of which is unknown. DNA damage accumulating with time is a main cause of aging, driving many age-related diseases. Previous studies in normal and premature aging mice, due to defective DNA repair, indicated reduced hepatic thyroid hormone signaling accompanied by decreased type 1 deiodinase (DIO1) and increased DIO3 activities. We investigated whether aging-related changes in deiodinase activity are driven by systemic signals or represent cell- or organ-autonomous changes.
Methods
We quantified liver and plasma thyroid hormone concentrations, deiodinase activities and expression of T3-responsive genes in mice with a global, liver-specific and for comparison brain-specific inactivation of Xpg, one of the endonucleases critically involved in multiple DNA repair pathways.
Results
Both in global and liver-specific Xpg knockout mice, hepatic DIO1 activity was decreased. Interestingly, hepatic DIO3 activity was increased in global, but not in liver-specific Xpg mutants. Selective Xpg deficiency and premature aging in the brain did not affect liver or systemic thyroid signaling. Concomitant with DIO1 inhibition, Xpg −/− and Alb-Xpg mice displayed reduced thyroid hormone-related gene expression changes, correlating with markers of liver damage and cellular senescence.
Conclusions
Our findings suggest that DIO1 activity during aging is predominantly modified in a tissue-autonomous manner driven by organ/cell-intrinsic accumulating DNA damage. The increase in hepatic DIO3 activity during aging largely depends on systemic signals, possibly reflecting the presence of circulating cells rather than activity in hepatocytes.
Rotterdam Thyroid Center, Department of Internal Medicine, Erasmus MC, Rotterdam, The Netherlands
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Rotterdam Thyroid Center, Department of Internal Medicine, Erasmus MC, Rotterdam, The Netherlands
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Rotterdam Thyroid Center, Department of Internal Medicine, Erasmus MC, Rotterdam, The Netherlands
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Rotterdam Thyroid Center, Department of Internal Medicine, Erasmus MC, Rotterdam, The Netherlands
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Background: Hypothyroidism has been associated with impaired urinary concentrating ability. However, previous reports on thyroid hormone and urinary concentrating ability in humans only studied a limited number of patients with autoimmune thyroid disease or used healthy controls instead of paired analysis within the same patients. Objective: To study the urinary concentrating ability in athyreotic patients with differentiated thyroid cancer on and off levothyroxine treatment as they are exposed to different thyroid states as part of their treatment in the absence of an autoimmune disease. Design and Methods: We studied 9 patients (mean age of 42.7 years) during severe hypothyroid state (withdrawal of levothyroxine before radioactive iodine therapy) and TSH-suppressed state (on levothyroxine therapy). At these two points, serum and urine samples were collected after 14 h of overnight fasting without any food or drink. Results: Serum and urine osmolality were not significantly different between on and off levothyroxine treatment. Serum creatinine levels were significantly higher in patients off versus on levothyroxine treatment (87.0 vs. 71.0 µmol/L, respectively; p = 0.044) and, correspondingly, the estimated glomerular filtration rate was significantly lower (89.6 vs. 93.1 mL/min, respectively; p = 0.038). Conclusion: Short-term, severe hypothyroidism has no effect on urinary concentrating ability. Our study confirms the well-known effects of thyroid hormone on serum creatinine concentrations.
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Background: Iodine deficiency disorders (IDD) represent a global health threat to individuals and societies. IDD prevention programmes have been introduced in many parts of the world. However, challenges remain, particularly in Europe due to fragmentation and diversity of approaches that are not harmonized. Objectives: This review is dedicated to the public-health impact of IDD prevention programmes. It sums up experiences collected by the EUthyroid consortium so far and provides information on stakeholders that should be involved in actions directed to improve the impact of IDD prevention. Methods: A joint European database for combining registry-based outcome and monitoring data as well as tools for harmonizing study methods were established. Methods for analyzing thyroglobulin from a dried blood spot are available for assessing the iodine status in the general population and at-risk groups. Mother-child cohorts are used for in-depth analysis of the potential impact of mild-to-moderate iodine deficiency on the neurocognitive development of the offspring. A decision-analytic model has been developed to evaluate the long-term effectiveness and cost effectiveness of IDD prevention programmes. Results: EUthyroid has produced tools and infrastructure to improve the quality of IDD monitoring and follows a dissemination strategy targeting policymakers and the general public. There are tight connections to major stakeholders in the field of IDD monitoring and prevention. Conclusions: EUthyroid has taken steps towards achieving a euthyroid Europe. Our challenge is to inspire a greater sense of urgency in both policymakers and the wider public to address this remediable deficit caused by IDD.
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DZHK (German Center for Cardiovascular Research), Partner Site Greifswald, Greifswald, Germany
Department of Psychiatry and Psychotherapy, University Medicine Greifswald, Greifswald, Germany
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Institute of Clinical Chemistry and Laboratory Medicine, University Medicine Greifswald, Germany
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Department of Epidemiology, Erasmus Medical Center, Rotterdam, The Netherlands
Department of Internal Medicine, Radboud University Medical Center, Nijmegen, The Netherlands
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Department of Epidemiology, Erasmus Medical Center, Rotterdam, The Netherlands
Department of Internal Medicine, Radboud University Medical Center, Nijmegen, The Netherlands
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Objective
Thyroid hormone (TH) transport represents a critical first step in governing intracellular TH regulation. It is still unknown whether the full repertoire of TH transporters has been identified. Members of the solute carrier (SLC) 22 family have substrates in common with the known TH transporters of the organic anion-transporting peptide family. Therefore, we screened the SLC22 family for TH transporters
Methods
Uptake of 1 nM of iodothyronines or sulfated iodothyronines in COS1 cells expressing SLC22 proteins was performed.
Results
We first tested 25 mouse (m) SLC22 proteins for TH uptake and found that the majority of the organic anion transporter (OAT) clade were capable of 3,3’,5-triiodothyronine and/or thyroxine (T4) transport. Based on phylogenetic tree analysis of the mouse and human (h) SLC22 family, we selected eight hSLC22s that grouped with the newly identified mouse TH transporters. Of these, four tested positive for uptake of one or more substrates, particularly hSLC22A11 showed robust (3-fold over control) uptake of T4. Uptake of sulfated iodothyronines was strongly (up to 17-fold) induced by some SLC22s, most notably SLC22A8, hSLC22A9, mSLC22A27 and mSLC22A29. Finally, the zebrafish orthologues of SLC22A6/8 drOatx and drSlc22a6l also transported almost all (sulfated) iodothyronines tested. The OAT inhibitors lesinurad and probenecid inhibited most SLC22 proteins.
Conclusions
Our results demonstrated that members of the OAT clade of the SLC22 family constitute a novel, evolutionary conserved group of transporters for (sulfated) iodothyronines. Future studies should reveal the relevance of these transporters in TH homeostasis and physiology.
