Thermoregulatory and Cardiovascular Consequences of a Transient Thyrotoxicosis and Recovery in Male Mice.

Thyroid hormones play a major role in body homeostasis, regulating energy expenditure and cardiovascular function. Given that obese people or athletes might consider rapid weight loss as beneficial, voluntary intoxication with T4 preparations is a growing cause for thyrotoxicosis. However, the long-lasting effects of transient thyrotoxicosis are poorly understood. Here we examined metabolic, thermoregulatory, and cardiovascular function upon induction and recovery from a 2-week thyrotoxicosis in male C57BL/6J mice. Our results showed that T4 treatment caused tachycardia, decreased hepatic glycogen stores, and higher body temperature as expected; however, we did not observe an increase in brown fat thermogenesis or decreased tail heat loss, suggesting that these tissues do not contribute to the hyperthermia induced by thyroid hormone. Most interestingly, when the T4 treatment was ended, a pronounced bradycardia was observed in the animals, which was likely caused by a rapid decline of T3 even below baseline levels. On the molecular level, this was accompanied by an overexpression of cardiac phospholamban and Serca2a mRNA, supporting the hypothesis that the heart depends more on T3 than T4. Our findings therefore demonstrate that a transient thyrotoxicosis can have pathological effects that even persist beyond the recovery of serum T4 levels, and in particular the observed bradycardia could be of clinical relevance when treating hyperthyroid patients.

Thyroid hormone drives the expression of mouse carbonic anhydrase Car4 in kidney, lung and brain.

Thyroid hormone is a well-known regulator of brain, lung and kidney development and function. However, the molecular mechanisms by which the hormone exerts its function have remained largely enigmatic, and only a limited set of target genes have been identified in these tissues. Using a mouse model with a mutation in thyroid hormone receptor α1 (TRα1), we here demonstrate that the expression of carbonic anhydrase 4 in lung and brain of the adult animal depends on intact TRα1 signaling. In the kidney, carbonic anhydrase 4 mRNA and protein are not affected by the mutant TRα1, but are acutely repressed by thyroid hormone. However, neither lung function--as measured by respiration rate and oxygen saturation--nor urine pH levels were affected by altered carbonic anhydrase 4 levels, suggesting that other carbonic anhydrases are likely to compensate. Taken together, our findings identify a previously unknown marker of TRα1 action in brain and lung, and provide a novel negatively regulated target gene to assess renal thyroid hormone status.

3-Iodothyroacetic acid lacks thermoregulatory and cardiovascular effects in vivo.

BACKGROUND AND PURPOSE: 3-Iodothyronamine (3-T1 AM) is an endogenous thyroid hormone derivative reported to induce strong hypothermia and bradycardia within minutes upon injection in rodents. Although 3-T1 AM is rapidly converted to several other metabolites in vivo, these strong pharmacological responses were solely attributed to 3-T1 AM, leaving potential contributions of downstream products untested. We therefore examined the cardiometabolic effects of 3-iodothyroacetic acid (TA1 ), the main degradation product of 3-T1 AM. EXPERIMENTAL APPROACH: We used a sensitive implantable radiotelemetry system in C57/Bl6J mice to study the effects of TA1 on body temperature and heart rate, as well as other metabolic parameters. KEY RESULTS: Interestingly, despite using pharmacological TA1 doses, we observed no effects on heart rate or body temperature after a single TA1 injection (50 mg·kg(-1) , i.p.) compared to sham-injected controls. Repeated administration of TA1 (5 mg·kg(-1) , i.p. for 7 days) likewise did not alter body weight, food and water intake, heart rate, blood pressure, brown adipose tissue (BAT) thermogenesis or body temperature. Moreover, mRNA expression of tissue specific genes in heart, kidney, liver, BAT and lung was also not altered by TA1 compared to sham-injected controls. CONCLUSIONS AND IMPLICATIONS: Our data therefore conclusively demonstrate that TA1 does not contribute to the cardiovascular or thermoregulatory effects observed after 3-T1 AM administration in mice, suggesting that the oxidative deamination constitutes an important deactivation mechanism for 3-T1 AM with possible implications for cardiovascular and thermoregulatory functions.

Inappropriate heat dissipation ignites brown fat thermogenesis in mice with a mutant thyroid hormone receptor α1.

Thyroid hormone is a major regulator of thermogenesis, acting both in peripheral organs and on central autonomic pathways. Mice heterozygous for a point mutation in thyroid hormone receptor α1 display increased thermogenesis as a consequence of high sympathetic brown fat stimulation. Surprisingly, despite the hypermetabolism, their body temperature is not elevated. Here we show, using isolated tail arteries, that defective thyroid hormone receptor α1 signaling impairs acetylcholine-mediated vascular relaxation as well as phenylephrine-induced vasoconstriction. Using infrared thermography on conscious animals, we demonstrate that these defects severely interfere with appropriate peripheral heat conservation and dissipation, which in turn leads to compensatory alterations in brown fat activity. Consequently, when the vasoconstrictive defect in mice heterozygous for a point mutation in thyroid hormone receptor α1 was reversed with the selective α1-adrenergic agonist midodrine, the inappropriate heat loss over their tail surface was reduced, normalizing brown fat activity and energy expenditure. Our analyses demonstrate that thyroid hormone plays a key role in vascular heat conservation and dissipation processes, adding a unique aspect to its well-documented functions in thermoregulation. The data thus facilitate understanding of temperature hypersensitivity in patients with thyroid disorders. Moreover, the previously unrecognized connection between cardiovascular regulation and metabolic activity revealed in this study challenges the interpretation of several experimental paradigms and questions some of the currently derived hypotheses on the role of thyroid hormone in thermogenesis.

Identification of thyroid hormone response elements in vivo using mice expressing a tagged thyroid hormone receptor α1.

TRα1 (thyroid hormone receptor α1) is well recognized for its importance in brain development. However, due to the difficulties in predicting TREs (thyroid hormone response elements) in silico and the lack of suitable antibodies against TRα1 for ChIP (chromatin immunoprecipitation), only a few direct TRα1 target genes have been identified in the brain. Here we demonstrate that mice expressing a TRα1-GFP (green fluorescent protein) fusion protein from the endogenous TRα locus provide a valuable animal model to identify TRα1 target genes. To this end, we analysed DNA-TRα1 interactions in vivo using ChIP with an anti-GFP antibody. We validated our system using established TREs from neurogranin and hairless, and by verifying additional TREs from known TRα1 target genes in brain and heart. Moreover, our model system enabled the identification of novel TRα1 target genes such as RNF166 (ring finger protein 166). Our results demonstrate that transgenic mice expressing a tagged nuclear receptor constitute a feasible approach to study receptor-DNA interactions in vivo, circumventing the need for specific antibodies. Models like the TRα1-GFP mice may thus pave the way for genome-wide mapping of nuclear receptor-binding sites, and advance the identification of novel target genes in vivo.

Thyroid hormone is required for hypothalamic neurons regulating cardiovascular functions.

Thyroid hormone is well known for its profound direct effects on cardiovascular function and metabolism. Recent evidence, however, suggests that the hormone also regulates these systems indirectly through the central nervous system. While some of the molecular mechanisms underlying the hormone's central control of metabolism have been identified, its actions in the central cardiovascular control have remained enigmatic. Here, we describe a previously unknown population of parvalbuminergic neurons in the anterior hypothalamus that requires thyroid hormone receptor signaling for proper development. Specific stereotaxic ablation of these cells in the mouse resulted in hypertension and temperature-dependent tachycardia, indicating a role in the central autonomic control of blood pressure and heart rate. Moreover, the neurons exhibited intrinsic temperature sensitivity in patch-clamping experiments, providing a new connection between cardiovascular function and core temperature. Thus, the data identify what we believe to be a novel hypothalamic cell population potentially important for understanding hypertension and indicate developmental hypothyroidism as an epigenetic risk factor for cardiovascular disorders. Furthermore, the findings may be beneficial for treatment of the recently identified patients that have a mutation in thyroid hormone receptor α1.

Serum copper as a novel biomarker for resistance to thyroid hormone.

Thyroid hormone action is mediated by the thyroid hormone receptors TRα1 and TRß. Defects in TRß lead to RTH (resistance to thyroid hormone) ß, a syndrome characterized by high levels of thyroid hormone and non-suppressed TSH (thyroid-stimulating hormone). However, a correct diagnosis of RTHß patients is difficult as the clinical picture varies. A biochemical serum marker indicative of defects in TRß signalling is needed and could simplify the diagnosis of RTHß, in particular the differentiation to TSH-secreting pituitary adenomas, which present with clinically similar symptoms. In the present paper we show that serum copper levels are regulated by thyroid hormone, which stimulates the synthesis and the export of the hepatic copper-transport protein ceruloplasmin into the serum. This is accompanied by a concerted reduction in the mRNA levels of other copper-containing proteins such as metallothioneins 1 and 2 or superoxide dismutase 1. The induction of serum copper is abolished in genetically hyperthyroid mice lacking TRß and human RTHß patients, demonstrating an important role of TRß for this process. Together with a previously reported TRα1 specific regulation of serum selenium, we show that the ratio of serum copper and selenium, which is largely independent of thyroid hormone levels, volume changes or sample degradation, can constitute a valuable novel biomarker for RTHß. Moreover, it could also provide a suitable large-scale screening parameter to identify RTHα patients, which have not been identified to date.

Multiple phenotypes in adult mice following inactivation of the Coxsackievirus and Adenovirus Receptor (Car) gene.

To determine the normal function of the Coxsackievirus and Adenovirus Receptor (CAR), a protein found in tight junctions and other intercellular complexes, we constructed a mouse line in which the CAR gene could be disrupted at any chosen time point in a broad spectrum of cell types and tissues. All knockouts examined displayed a dilated intestinal tract and atrophy of the exocrine pancreas with appearance of tubular complexes characteristic of acinar-to-ductal metaplasia. The mice also exhibited a complete atrio-ventricular block and abnormal thymopoiesis. These results demonstrate that CAR exerts important functions in the physiology of several organs in vivo.

Loss of thyroid hormone receptor ß is associated with increased progenitor proliferation and NeuroD positive cell number in the adult hippocampus.

Adult hippocampal neurogenesis is modulated by perturbations in thyroid hormone status; however the role of specific thyroid hormone receptors (TRs) in this process is not completely understood. We show here that loss of the TRß gene results in a significant increase in the proliferation of adult hippocampal progenitors, without any change in immature neuron number or in the neuronal and glial differentiation of progenitors. Using the mitotic marker 5'-bromo-2-deoxyuridine (BrdU) or the endogenous cell cycle marker, proliferating cell nuclear antigen (PCNA), we find a significant increase in the number of BrdU- and PCNA-immunopositive cells within the subgranular zone (SGZ) of the dentate gyrus subfield in TRß-/- mice. Further, we find that TRß-/- mice exhibit a significant increase in the numbers of NeuroD-positive cells within the SGZ, suggesting that the increased numbers of proliferating progenitors translate into enhanced numbers of neuroblasts. Interestingly, the number of BrdU-positive cells that persist 4 weeks post-BrdU injection is unaltered in TRß-/- mice, indicating that the enhanced proliferation does not result in increased hippocampal neurogenesis. This is also supported by the evidence of no change in the numbers of cells expressing markers of immature neurons such as doublecortin or polysialylated neural cell adhesion molecule. Furthermore, no change is observed in the neuronal or glial differentiation of BrdU-positive cells in the TRß-/- mice. Taken together, our results provide novel evidence for a role of TRß in modulating hippocampal progenitor cell division, and implicate this receptor in the effects of thyroid hormone on adult hippocampal neurogenesis.

Thyroid hormones regulate selenoprotein expression and selenium status in mice.

Impaired expression of selenium-containing proteins leads to perturbed thyroid hormone (TH) levels, indicating the central importance of selenium for TH homeostasis. Moreover, critically ill patients with declining serum selenium develop a syndrome of low circulating TH and a central downregulation of the hypothalamus-pituitary-thyroid axis. This prompted us to test the reciprocal effect, i.e., if TH status would also regulate selenoprotein expression and selenium levels. To investigate the TH dependency of selenium metabolism, we analyzed mice expressing a mutant TH receptor α1 (TRα1+m) that confers a receptor-mediated hypothyroidism. Serum selenium was reduced in these animals, which was a direct consequence of the mutant TRα1 and not related to their metabolic alterations. Accordingly, hyperthyroidism, genetically caused by the inactivation of TRß or by oral TH treatment of adult mice, increased serum selenium levels in TRα1+m and controls, thus demonstrating a novel and specific role for TRα1 in selenium metabolism. Furthermore, TH affected the mRNA levels for several enzymes involved in selenoprotein biosynthesis as well as serum selenoprotein P concentrations and the expression of other antioxidative selenoproteins. Taken together, our results show that TH positively affects the serum selenium status and regulates the expression of several selenoproteins. This demonstrates that selenium and TH metabolism are interconnected through a feed-forward regulation, which can in part explain the rapid parallel downregulation of both systems in critical illness.

The thyroid hormone receptor alpha1 protein is expressed in embryonic postmitotic neurons and persists in most adult neurons.

Thyroid hormone is essential for brain development where it acts mainly through the thyroid hormone receptor α1 (TRα1) isoform. However, the potential for the hormone to act in adult neurons has remained undefined due to difficulties in reliably determining the expression pattern of TR proteins in vivo. We therefore created a mouse strain that expresses TRα1 and green fluorescent protein as a chimeric protein from the Thra locus, allowing examination of TRα1 expression during fetal and postnatal development and in the adult. Furthermore, the use of antibodies against other markers enabled identification of TRα1 expression in subtypes of neurons and during specific stages of their maturation. TRα1 expression was first detected in postmitotic cells of the cortical plate in the embryonic telencephalon and preceded the expression of the mature neuronal protein NeuN. In the cerebellum, TRα1 expression was absent in proliferating cells of the external granular layer, but switched on as the cells migrated towards the internal granular layer. In addition, TRα1 was expressed transiently in developing Purkinje cells, but not in mature cells. Glial expression was found in tanycytes in the hypothalamus and in the cerebellum. In the adult brain, TRα1 expression was detected in essentially all neurons. Our data demonstrate that thyroid hormone, unexpectedly, has the capacity to play an important role in virtually all developing and adult neurons. Because the role of TRα1 in most neuronal cell types in vivo is largely unknown, our findings suggest that novel functions for thyroid hormone remain to be identified in the brain.

Unliganded thyroid hormone receptor alpha1 impairs adult hippocampal neurogenesis.

Thyroid hormone regulates adult hippocampal neurogenesis, a process involved in key functions, such as learning, memory, and mood regulation. We addressed the role of thyroid hormone receptor TRα1 in adult hippocampal neurogenesis, using mice harboring a TRα1 null allele (TRα1(-/-)), overexpressing TRα1 6-fold (TRα2(-/-)), and a mutant TRα1 (TRα1(+/m)) with a 10-fold lower affinity to the ligand. While hippocampal progenitor proliferation was unaltered, TRα1(-/-) mice exhibited a significant increase in doublecortin-positive immature neurons and increased survival of bromodeoxyuridine-positive (BrdU(+)) progenitors as compared to wild-type controls. In contrast, the TRα1(+/m) and the TRα2(-/-) mice, where the overexpressed TRα1 acts as an aporeceptor, showed a significant decline in surviving BrdU(+) progenitors. TRα1(-/-) and TRα2(-/-) mice showed opposing effects on neurogenic markers like polysialylated neural cell adhesion molecule and stathmin. The decreased progenitor survival in the TRα2(-/-) and TRα1(+/m) mice could be rescued by thyroid hormone treatment, as was the decline in neuronal differentiation seen in the TRα1(+/m) mice. These mice also exhibited a decrease in NeuroD(+) cell numbers in the dentate gyrus, suggesting an effect on early postmitotic progenitors. Our results provide the first evidence of a role for unliganded TRα1 in modulating the deleterious effects of hypothyroidism on adult hippocampal neurogenesis.

Enlarged lateral ventricles and aberrant behavior in mice overexpressing PDGF-B in embryonic neural stem cells.

Platelet-derived growth factor (PDGF) is important in central nervous system (CNS) development, and aberrant expression of PDGF and its receptors has been linked to developmental defects and brain tumorigenesis. We previously found that neural stem and progenitor cells in culture produce PDGF and respond to it by autocrine and/or paracrine signaling. We therefore aimed to examine CNS development after PDGF overexpression in neural stem cells in vivo. Transgenic mice were generated with PDGF-B under control of a minimal nestin enhancer element, which is specific for embryonic expression and will not drive adult expression in mice. The resulting mouse showed increased apoptosis in the developing striatum, which suggests a disturbed regulation of progenitor cells. Later in neurodevelopment, in early postnatal life, mice displayed enlarged lateral ventricles. This enlargement remained into adulthood and it was more pronounced in male mice than in transgenic female mice. Nevertheless, there was an overall normal composition of cell types and numbers in the brain and the transgenic mice were viable and fertile. Adult transgenic males, however, showed behavioral aberrations and locomotor dysfunction. Thus, a tightly regulated expression of PDGF during embryogenesis is required for normal brain development and function in mice.

Increased depressive behaviour in mice harboring the mutant thyroid hormone receptor alpha 1.

Clinical evidence indicates that hypothyroidism contributes to mood disorders. The present study tested if the mutant thyroid hormone receptor alpha 1 (TRalpha1) that causes a receptor-mediated hypothyroidism in the brain affects depressive and anxious behaviour in mice. Mice heterozygous for the TRalpha1 allele (TRalpha1+/m), yielding a receptor protein with a 10-fold reduced affinity to triiodothyronine (T3), and wildtype (wt) mice were subjected to several paradigms specifically testing depressive and anxious behaviour. Mutant and wt mice were either treated with T3 or vehicle. Untreated TRalpha1+/m animals displayed reduced locomotion, higher rates of helplessness in the shuttle box-, greater levels of anxiety in the startle response- and dark light box behavioural paradigms when compared to wt mice. Continuous T3-substitution therapy was effective in alleviating anxious and depressive behaviour without affecting locomotion in mutant mice. Notably, continuous T3-substitution reduced overall locomotion and increased helpless behaviour in wt mice when compared to untreated wt mice. The data suggest that receptor-mediated hypothyroidism caused by an unliganded thyroid hormone receptor alpha 1 leads to a depressive and anxious phenotype in mice, which is responsive to continuous T3-substitution and that an iatrogeneously induced hyperthyreoidism by continuous T3-administration leads to a hypolocomotive and depressive phenotype.

Adaptations of the autonomous nervous system controlling heart rate are impaired by a mutant thyroid hormone receptor-alpha1.

Thyroid hormone has profound direct effects on cardiac function, but the hormonal interactions with the autonomic control of heart rate are unclear. Because thyroid hormone receptor (TR)-alpha1 has been implicated in the autonomic control of brown adipose energy metabolism, it might also play an important role in the central autonomic control of heart rate. Thus, we aimed to analyze the role of TRalpha1 signaling in the autonomic control of heart rate using an implantable radio telemetry system. We identified that mice expressing the mutant TRalpha1R384C (TRalpha1+m mice) displayed a mild bradycardia, which becomes more pronounced during night activity or on stress and is accompanied by a reduced expression of nucleotide-gated potassium channel 2 mRNA in the heart. Pharmacological blockage with scopolamine and the beta-adrenergic receptor antagonist timolol revealed that the autonomic control of cardiac activity was similar to that in wild-type mice at room temperature. However, at thermoneutrality, in which the regulation of heart rate switches from sympathetic to parasympathetic in wild-type mice, TRalpha1+m mice maintained sympathetic stimulation and failed to activate parasympathetic signaling. Our findings demonstrate a novel role for TRalpha1 in the adaptation of cardiac activity by the autonomic nervous system and suggest that human patients with a similar mutation in TRalpha1 might exhibit a deficit in cardiac adaptation to stress or physical activity and an increased sensitivity to beta-blockers.

A mutant thyroid hormone receptor alpha1 alters hippocampal circuitry and reduces seizure susceptibility in mice.

Thyroid hormone deficiency during early developmental stages causes a multitude of functional and morphological deficits in the brain. In the present study we investigate the effects of a mutated thyroid hormone receptor TR alpha 1 and the resulting receptor-mediated hypothyroidism on the development of GABAergic neurotransmission and seizure susceptibility of neuronal networks. We show that mutant mice have a strong resistance to seizures induced by antagonizing the GABA(A) receptor complex. Likewise the hippocampal network of mutant mice shows a decreased likelihood to transform physiological into pathological rhythmic network activity such as seizure-like interictal waves. As we demonstrate the cellular basis for this behavior is formed by the excitatory nature of GABAergic neurotransmission in the mutant mice, possibly caused by altered Cl(-) homeostasis, and/or the altered patterning of calretinin-positive cells in the hippocampal hilus. This study is, to our knowledge, the first to show an effect of maternal and early postnatal hypothyroidism via TR alpha 1 on the development of GABAergic neurotransmission and susceptibility to epileptic seizures.

Physiological consequences of the TRalpha1 aporeceptor state.

Many patients have been characterized harboring a mutation in thyroid hormone receptor (TR) beta. Surprisingly none has yet been identified carrying a mutation in TRalpha1. To facilitate the identification of such patients, several animal models with a mutant TRalpha1 have been generated. While some phenotypic characteristics, such as an adult euthyroidism, are similar in the mutant mice, other aspects such as metabolism are quite variable. This review summarizes the most important consequences of a mutation in TRalpha1 in mice focusing on the TRalpha1-R384C mutation, and projects the insights from the animal models to a putative phenotype of patients with a mutated TRalpha1.

Interference of a mutant thyroid hormone receptor alpha1 with hepatic glucose metabolism.

Mice expressing the mutant thyroid hormone receptor TRalpha1R384C, which has a 10-fold reduced affinity to the ligand T(3), exhibit hypermetabolism due to an overactivation of the sympathetic nervous system. To define the consequences in the liver, we analyzed hepatic metabolism and the regulation of liver genes in the mutant mice. Our results showed that hepatic phosphoenolpyruvate-carboxykinase was up-regulated and pyruvate kinase mRNA down-regulated, contrary to what observed after T(3) treatment. In contrast, mice expressing a mutant TRalpha1L400R specifically in the liver did not show a dysregulation of these genes; however, when the TRalpha1L400R was expressed ubiquitously, the hepatic phenotype differed from TRalpha1R384C animals, suggesting that the localization of the mutation plays an important role for its consequences on glucose metabolism. Furthermore, we observed that glycogen stores were completely depleted in TRalpha1R384C animals, despite increased gluconeogenesis and decreased glycolysis. Exposure of the mutant mice to high maternal levels of thyroid hormone during fetal development leads to a normal liver phenotype in the adult. Our results show how genetic and maternal factors interact to determine the metabolic setpoint of the offspring and indicate an important role for maternal thyroid hormone in the susceptibility to metabolic disorders in adulthood.

Thyroid hormone receptor beta1 acts as a potent suppressor of tumor invasiveness and metastasis.

Loss of thyroid hormone receptors (TR) is a common feature in some tumors, although their role in tumor progression is currently unknown. We show here that expression of TRbeta1 in hepatocarcinoma and breast cancer cells reduces tumor growth, causes partial mesenchymal-to-epithelial cell transition, and has a striking inhibitory effect on invasiveness, extravasation, and metastasis formation in mice. In cultured cells, TRbeta1 abolishes anchorage-independent growth and migration, blocks responses to epidermal growth factor, insulin-like growth factor-I, and transforming growth factor beta, and regulates expression of genes that play a key role in tumorigenicity and metastatic growth. The receptor disrupts the mitogenic action of growth factors by suppressing activation of extracellular signal-regulated kinase and phosphatidylinositol 3-kinase signaling pathways that are crucial for cell proliferation and invasiveness. Furthermore, increased aggressiveness of skin tumors is found in genetically modified mice lacking TRs, further demonstrating the role of these receptors as inhibitors of tumor progression. These results define a novel role for the thyroid hormone receptor as a metastasis suppressor gene, providing a starting point for the development of novel therapeutic strategies for the treatment of human cancer.

Severe psychomotor and metabolic damages caused by a mutant thyroid hormone receptor alpha 1 in mice: can patients with a similar mutation be found and treated?

UNLABELLED: Individuals suffering from the resistance to thyroid hormone syndrome (RTH) have a mutation in thyroid hormone receptor (TR) beta. Surprisingly, no patient with a mutation in TRalpha1 has been found. To facilitate their identification, animal models with a RTH-like mutation in TRalpha1 have been generated. The mutations introduced into the mouse decrease affinity to ligand, resulting in a 'receptor-mediated hypothyroidism' in tissues expressing the mutant receptor: brain, heart and bone. The mice present minor perturbances in thyroid hormone homeostasis, but show major aberrancies in postnatal development, psychomotor behaviour and metabolism. These parameters are akin to those seen in endemic cretinism and untreated congenital hypothyroidism. Treatment of the mice with high doses of triiodothyronine leads to normalization or amelioration of the dysfunctions when applied at adequate developmental periods. CONCLUSION: Our studies on mice suggest the existence of a potentially debilitating disease caused by a mutant TRalpha1, and provide insights for identification and treatment of corresponding patients.