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Lange LM, Gonzalez-Latapi P, Rajalingam R, Tijssen MAJ, Ebrahimi-Fakhari D, Gabbert C, Ganos C, Ghosh R, Kumar KR, Lang AE, Rossi M, van der Veen S, van de Warrenburg B, Warner T, Lohmann K, Klein C, Marras C. Nomenclature of Genetic Movement Disorders: Recommendations of the International Parkinson and Movement Disorder Society Task Force - An Update. Mov Disord 2022; 37:905-935. [PMID: 35481685 DOI: 10.1002/mds.28982] [Citation(s) in RCA: 42] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Revised: 01/28/2022] [Accepted: 02/14/2022] [Indexed: 12/13/2022] Open
Abstract
In 2016, the Movement Disorder Society Task Force for the Nomenclature of Genetic Movement Disorders presented a new system for naming genetically determined movement disorders and provided a criterion-based list of confirmed monogenic movement disorders. Since then, a substantial number of novel disease-causing genes have been described, which warrant classification using this system. In addition, with this update, we further refined the system and propose dissolving the imaging-based categories of Primary Familial Brain Calcification and Neurodegeneration with Brain Iron Accumulation and reclassifying these genetic conditions according to their predominant phenotype. We also introduce the novel category of Mixed Movement Disorders (MxMD), which includes conditions linked to multiple equally prominent movement disorder phenotypes. In this article, we present updated lists of newly confirmed monogenic causes of movement disorders. We found a total of 89 different newly identified genes that warrant a prefix based on our criteria; 6 genes for parkinsonism, 21 for dystonia, 38 for dominant and recessive ataxia, 5 for chorea, 7 for myoclonus, 13 for spastic paraplegia, 3 for paroxysmal movement disorders, and 6 for mixed movement disorder phenotypes; 10 genes were linked to combined phenotypes and have been assigned two new prefixes. The updated lists represent a resource for clinicians and researchers alike and they have also been published on the website of the Task Force for the Nomenclature of Genetic Movement Disorders on the homepage of the International Parkinson and Movement Disorder Society (https://www.movementdisorders.org/MDS/About/Committees--Other-Groups/MDS-Task-Forces/Task-Force-on-Nomenclature-in-Movement-Disorders.htm). © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson Movement Disorder Society.
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Affiliation(s)
- Lara M Lange
- Institute of Neurogenetics, University of Lübeck, Lübeck, Germany
| | - Paulina Gonzalez-Latapi
- The Edmond J. Safra Program in Parkinson's Disease and The Morton and Gloria Shulman Movement Disorder Clinic, Toronto Western Hospital, University of Toronto, Toronto, Canada.,Ken and Ruth Davee Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA
| | - Rajasumi Rajalingam
- The Edmond J. Safra Program in Parkinson's Disease and The Morton and Gloria Shulman Movement Disorder Clinic, Toronto Western Hospital, University of Toronto, Toronto, Canada
| | - Marina A J Tijssen
- UMCG Expertise Centre Movement Disorders, Department of Neurology, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands
| | - Darius Ebrahimi-Fakhari
- Department of Neurology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA.,The Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, Massachusetts, USA
| | - Carolin Gabbert
- Institute of Neurogenetics, University of Lübeck, Lübeck, Germany
| | - Christos Ganos
- Department of Neurology, Charité University Hospital Berlin, Berlin, Germany
| | - Rhia Ghosh
- Huntington's Disease Centre, Department of Neurodegenerative Disease, UCL Queen Square Institute of Neurology, University College London, London, UK
| | - Kishore R Kumar
- Molecular Medicine Laboratory and Department of Neurology, Concord Repatriation General Hospital, Faculty of Medicine and Health, University of Sydney, Sydney, New South Wales, Australia.,Kinghorn Centre for Clinical Genomics, Garvan Institute of Medical Research, Darlinghurst, New South Wales, Australia
| | - Anthony E Lang
- The Edmond J. Safra Program in Parkinson's Disease and The Morton and Gloria Shulman Movement Disorder Clinic, Toronto Western Hospital, University of Toronto, Toronto, Canada
| | - Malco Rossi
- Movement Disorders Section, Neuroscience Department, Raul Carrea Institute for Neurological Research (FLENI), Buenos Aires, Argentina
| | - Sterre van der Veen
- UMCG Expertise Centre Movement Disorders, Department of Neurology, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands
| | - Bart van de Warrenburg
- Department of Neurology, Donders Institute for Brain, Cognition and Behavior, Center of Expertise for Parkinson and Movement Disorders, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Tom Warner
- Department of Clinical & Movement Neurosciences, UCL Queen Square Institute of Neurology, University College London, London, UK
| | - Katja Lohmann
- Institute of Neurogenetics, University of Lübeck, Lübeck, Germany
| | - Christine Klein
- Institute of Neurogenetics, University of Lübeck, Lübeck, Germany
| | - Connie Marras
- The Edmond J. Safra Program in Parkinson's Disease and The Morton and Gloria Shulman Movement Disorder Clinic, Toronto Western Hospital, University of Toronto, Toronto, Canada
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Subclinical hypothyroidism and Pelizaeus-Merzbacher Disease in same-sex twins: Case report. JOURNAL OF CLINICAL AND TRANSLATIONAL ENDOCRINOLOGY CASE REPORTS 2021. [DOI: 10.1016/j.jecr.2021.100097] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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3
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van Geest FS, Gunhanlar N, Groeneweg S, Visser WE. Monocarboxylate Transporter 8 Deficiency: From Pathophysiological Understanding to Therapy Development. Front Endocrinol (Lausanne) 2021; 12:723750. [PMID: 34539576 PMCID: PMC8440930 DOI: 10.3389/fendo.2021.723750] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Accepted: 08/13/2021] [Indexed: 01/18/2023] Open
Abstract
Genetic defects in the thyroid hormone transporter monocarboxylate transporter 8 (MCT8) result in MCT8 deficiency. This disorder is characterized by a combination of severe intellectual and motor disability, caused by decreased cerebral thyroid hormone signalling, and a chronic thyrotoxic state in peripheral tissues, caused by exposure to elevated serum T3 concentrations. In particular, MCT8 plays a crucial role in the transport of thyroid hormone across the blood-brain-barrier. The life expectancy of patients with MCT8 deficiency is strongly impaired. Absence of head control and being underweight at a young age, which are considered proxies of the severity of the neurocognitive and peripheral phenotype, respectively, are associated with higher mortality rate. The thyroid hormone analogue triiodothyroacetic acid is able to effectively and safely ameliorate the peripheral thyrotoxicosis; its effect on the neurocognitive phenotype is currently under investigation. Other possible therapies are at a pre-clinical stage. This review provides an overview of the current understanding of the physiological role of MCT8 and the pathophysiology, key clinical characteristics and developing treatment options for MCT8 deficiency.
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Groeneweg S, van Geest FS, Peeters RP, Heuer H, Visser WE. Thyroid Hormone Transporters. Endocr Rev 2020; 41:5637505. [PMID: 31754699 DOI: 10.1210/endrev/bnz008] [Citation(s) in RCA: 92] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/31/2019] [Accepted: 11/07/2019] [Indexed: 02/08/2023]
Abstract
Thyroid hormone transporters at the plasma membrane govern intracellular bioavailability of thyroid hormone. Monocarboxylate transporter (MCT) 8 and MCT10, organic anion transporting polypeptide (OATP) 1C1, and SLC17A4 are currently known as transporters displaying the highest specificity toward thyroid hormones. Structure-function studies using homology modeling and mutational screens have led to better understanding of the molecular basis of thyroid hormone transport. Mutations in MCT8 and in OATP1C1 have been associated with clinical disorders. Different animal models have provided insight into the functional role of thyroid hormone transporters, in particular MCT8. Different treatment strategies for MCT8 deficiency have been explored, of which thyroid hormone analogue therapy is currently applied in patients. Future studies may reveal the identity of as-yet-undiscovered thyroid hormone transporters. Complementary studies employing animal and human models will provide further insight into the role of transporters in health and disease. (Endocrine Reviews 41: 1 - 55, 2020).
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Affiliation(s)
- Stefan Groeneweg
- Department of Internal Medicine, Erasmus Medical Center, Rotterdam, the Netherlands Academic Center for Thyroid Diseases, Erasmus Medical Center, Rotterdam, the Netherlands
| | - Ferdy S van Geest
- Department of Internal Medicine, Erasmus Medical Center, Rotterdam, the Netherlands Academic Center for Thyroid Diseases, Erasmus Medical Center, Rotterdam, the Netherlands
| | - Robin P Peeters
- Department of Internal Medicine, Erasmus Medical Center, Rotterdam, the Netherlands Academic Center for Thyroid Diseases, Erasmus Medical Center, Rotterdam, the Netherlands
| | - Heike Heuer
- Department of Endocrinology, Diabetes and Metabolism, University Hospital Essen, University Duisburg-Essen, Essen, Germany
| | - W Edward Visser
- Department of Internal Medicine, Erasmus Medical Center, Rotterdam, the Netherlands Academic Center for Thyroid Diseases, Erasmus Medical Center, Rotterdam, the Netherlands
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Vancamp P, Demeneix BA, Remaud S. Monocarboxylate Transporter 8 Deficiency: Delayed or Permanent Hypomyelination? Front Endocrinol (Lausanne) 2020; 11:283. [PMID: 32477268 PMCID: PMC7237703 DOI: 10.3389/fendo.2020.00283] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/14/2020] [Accepted: 04/15/2020] [Indexed: 12/11/2022] Open
Abstract
Monocarboxylate transporter 8 (MCT8) deficiency or the Allan-Herndon-Dudley Syndrome (AHDS) is an X-linked psychomotor disability syndrome with around 320 clinical cases described worldwide. SLC16A2 gene mutations, encoding the thyroid hormone (TH) transporter MCT8, result in intellectual disability due to impaired TH uptake in the developing brain. MCT8 deficiency is a multi-organ affecting disease with a predominant neuronal cell-based pathology, with the glial component inadequately investigated. However, deficiency in myelin, a key component of white matter (WM) enabling fast nerve conduction, is a TH-dependent hallmark of the disease. Nevertheless, analysis of the myelin status in AHDS patients has led to conflicting interpretations. The majority of individual case studies reported delayed myelination, that was restored later in life. In contrast, post-mortem studies and high-resolution MRIs detected WM (micro-) abnormalities throughout adolescence, suggesting permanent hypomyelination. Thus, interpretations vary depending on methodology to investigate WM microstructure. Further, it is unknown whether the mutation within the MCT8 is linked to the severity of the myelin deficiency. Consequently, terminology is inconsistent among reports, and AHDS is occasionally misdiagnosed as another WM disorder. The evolutionary conserved TH signaling pathway that promotes the generation of myelinating oligodendrocytes enabled deciphering how the lack of MCT8 might affect myelinogenesis. Linking patient findings on myelination to those obtained from models of MCT8 deficiency revealed underlying pathophysiological mechanisms, but knowledge gaps remain, notably how myelination progresses both spatially and temporally in MCT8 deficiency. This limits predicting how myelin integrity might benefit therapeutically, and when to initiate. A recurrent observation in clinical trials is the absence of neurological improvement. Testing MCT8-independent thyromimetics in models, and evaluating treatments used in other demyelinating diseases, despite different etiologies, is crucial to propose new therapeutic strategies combatting this devastating disease.
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Affiliation(s)
- Pieter Vancamp
- UMR 7221 Molecular Physiology and Adaptation, Centre National de le Recherche Scientifique-Muséum National d'Histoire Naturelle, Paris, France
| | - Barbara A Demeneix
- UMR 7221 Molecular Physiology and Adaptation, Centre National de le Recherche Scientifique-Muséum National d'Histoire Naturelle, Paris, France
| | - Sylvie Remaud
- UMR 7221 Molecular Physiology and Adaptation, Centre National de le Recherche Scientifique-Muséum National d'Histoire Naturelle, Paris, France
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Remerand G, Boespflug-Tanguy O, Tonduti D, Touraine R, Rodriguez D, Curie A, Perreton N, Des Portes V, Sarret C. Expanding the phenotypic spectrum of Allan-Herndon-Dudley syndrome in patients with SLC16A2 mutations. Dev Med Child Neurol 2019; 61:1439-1447. [PMID: 31410843 DOI: 10.1111/dmcn.14332] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 07/07/2019] [Indexed: 01/01/2023]
Abstract
The aim of the study was to redefine the phenotype of Allan-Herndon-Dudley syndrome (AHDS), which is caused by mutations in the SLC16A2 gene that encodes the brain transporter of thyroid hormones. Clinical phenotypes, brain imaging, thyroid hormone profiles, and genetic data were compared to the existing literature. Twenty-four males aged 11 months to 29 years had a mutation in SLC16A2, including 12 novel mutations and five previously described mutations. Sixteen patients presented with profound developmental delay, three had severe intellectual disability with poor language and walking with an aid, four had moderate intellectual disability with language and walking abilities, and one had mild intellectual disability with hypotonia. Overall, eight had learned to walk, all had hypotonia, 17 had spasticity, 18 had dystonia, 12 had choreoathetosis, 19 had hypomyelination, and 10 had brain atrophy. Kyphoscoliosis (n=12), seizures (n=7), and pneumopathies (n=5) were the most severe complications. This study extends the phenotypic spectrum of AHDS to a mild intellectual disability with hypotonia. Developmental delay, hypotonia, hypomyelination, and thyroid hormone profile help to diagnose patients. Clinical course depends on initial severity, with stable acquisition after infancy; this may be adversely affected by neuro-orthopaedic, pulmonary, and epileptic complications. WHAT THIS PAPER ADDS: Mild intellectual disability is associated with SLC16A2 mutations. A thyroid hormone profile with a free T3 /T4 ratio higher than 0.75 can help diagnose patients. Patients with SLC16A2 mutations present a broad spectrum of neurological phenotypes that are also observed in other hypomyelinating disorders. Axial hypotonia is a consistent feature of Allan-Herndon-Dudley syndrome and leads to specific complications.
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Affiliation(s)
- Ganaelle Remerand
- Centre de Compétence des Leucodystrophies et Leucoencéphalopathies de Cause Rare, Pôle Femme et Enfant, Hôpital Estaing, Centre Hospitalier Universitaire de Clermont-Ferrand, Clermont-Ferrand, France
| | - Odile Boespflug-Tanguy
- Centre de Référence des Leucodystrophies et Leucoencéphalopathies de Cause Rare, Service de Neurologie Pédiatrique, Hôpital Robert Debré, Assistance Publique-Hôpitaux de Paris, Paris, France.,NeuroDiderot, INSERM UMR1141, Université Paris Diderot, Paris, France
| | - Davide Tonduti
- Unit of Child Neurology, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy.,Unit of Child Neurology, V. Buzzi Children's Hospital, Milan, Italy
| | - Renaud Touraine
- Service de Génétique, Centre Hospitalier Universitaire de Saint-Etienne, Saint-Etienne, France
| | - Diana Rodriguez
- Sorbonne Université, GRC no. 19, Pathologies Congénitales du Cervelet-LeucoDystrophies, Assistance Publique-Hôpitaux de Paris, Hôpital Armand Trousseau, Paris, France.,Centre de Référence Neurogénétique, Service de Neurologie Pédiatrique, Assistance Publique-Hôpitaux de Paris, Hôpital Armand Trousseau, Paris, France
| | - Aurore Curie
- Centre de Référence des Déficiences Intellectuelles de Cause Rare, Service de Neurologie Pédiatrique, Centre Hospitalier Universitaire de Lyon, Hôpital Femme-Mère-Enfant, Lyon, France
| | - Nathalie Perreton
- CIC 1407Inserm, Centre Hospitalo-Universitaire de Lyon, Lyon, France
| | - Vincent Des Portes
- Centre de Référence des Déficiences Intellectuelles de Cause Rare, Service de Neurologie Pédiatrique, Centre Hospitalier Universitaire de Lyon, Hôpital Femme-Mère-Enfant, Lyon, France
| | - Catherine Sarret
- Centre de Compétence des Leucodystrophies et Leucoencéphalopathies de Cause Rare, Pôle Femme et Enfant, Hôpital Estaing, Centre Hospitalier Universitaire de Clermont-Ferrand, Clermont-Ferrand, France.,IGCNC, Université Clermont Auvergne, CNRS, SIGMA Clermont, Institut Pascal, Clermont-Ferrand, France
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7
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Masnada S, Groenweg S, Saletti V, Chiapparini L, Castellotti B, Salsano E, Visser WE, Tonduti D. Novel mutations in SLC16A2 associated with a less severe phenotype of MCT8 deficiency. Metab Brain Dis 2019; 34:1565-1575. [PMID: 31332729 DOI: 10.1007/s11011-019-00464-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/18/2019] [Accepted: 07/08/2019] [Indexed: 02/08/2023]
Abstract
Mutations in the thyroid hormone transporter MCT8 cause severe intellectual and motor disability and abnormal serum thyroid function tests, a syndrome known as MCT8 deficiency (or: Allan-Herndon-Dudley syndrome, AHDS). Although the majority of patients are unable to sit or walk independently and do not develop any speech, some are able to walk and talk in simple sentences. Here, we report on two cases with such a less severe clinical phenotype and consequent gross delay in diagnosis. Genetic analyses revealed two novel hemizygous mutations in the SLC16A2 gene resulting in a p.Thr239Pro and a p.Leu543Pro substitution in the MCT8 protein. In vitro studies in transiently transfected COS-1 and JEG-3 cells, and ex vivo studies in patient-derived fibroblasts revealed substantial residual uptake capacity of both mutant proteins (Leu543Pro > Thr239Pro), providing an explanation for the less severe clinical phenotype. Both mutations impair MCT8 protein stability and interfere with proper subcellular trafficking. In one of the patients calcifications were observed in the basal ganglia at the age of 29 years; an abnormal neuroradiological feature at this age that has been linked to untreated (congenital) hypothyroidism and neural cretinism. Our studies extend on previous work by identifying two novel pathogenic mutations in SLC16A2 gene resulting in a mild clinical phenotype.
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Affiliation(s)
- Silvia Masnada
- Pediatric Neurology Unit, V. Buzzi Children's Hospital, Via Castelvetro 32, 20154, Milan, Italy
- Department of Brain and Behavioural Sciences, University of Pavia, Pavia, Italy
| | - Stefan Groenweg
- Department of Internal Medicine, Academic Center for Thyroid Diseases, Erasmus MC, University Medical Center, CN, Rotterdam, The Netherlands
| | - Veronica Saletti
- Child Neurology Department, IRCCS Foundation C. Besta Neurological Institute, Milan, Italy
| | - Luisa Chiapparini
- Neuroradiology Unit, IRCCS Foundation C. Besta Neurological Institute, Milan, Italy
| | - Barbara Castellotti
- Unit of Genetics of Neurodegenerative and Metabolic Diseases, IRCCS Foundation C. Besta Neurological Institute, Milan, Italy
| | - Ettore Salsano
- Unit of Neurodegenerative and Neurometabolic Rare Diseases, IRCCS Foundation C. Besta Neurological Institute, Milan, Italy
| | - W Edward Visser
- Department of Internal Medicine, Academic Center for Thyroid Diseases, Erasmus MC, University Medical Center, CN, Rotterdam, The Netherlands
| | - Davide Tonduti
- Pediatric Neurology Unit, V. Buzzi Children's Hospital, Via Castelvetro 32, 20154, Milan, Italy.
- Child Neurology Department, IRCCS Foundation C. Besta Neurological Institute, Milan, Italy.
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Abstract
Transport of thyroid hormone (TH) across the plasma membrane is essential for intracellular TH metabolism and action, and this is mediated by specific transporter proteins. During the last two decades several transporters capable of transporting TH have been identified, including monocarboxylate transporter 8 (MCT8), MCT10 and organic anion transporting polypeptide 1C1 (OATP1C1). In particular MCT8 and OATP1C1 are important for the regulation of local TH activity in the brain and thus for brain development. MCT8 is a protein containing 12 transmembrane domains, and is encoded by the SLC16A2 gene located on the X chromosome. It facilitates both TH uptake and efflux across the cell membrane. Male subjects with hemizygous mutations in MCT8 are afflicted with severe intellectual and motor disability, also known as the Allan-Herndon-Dudley syndrome (AHDS), which goes together with low serum T4 and high T3 levels. This review concerns molecular and clinical aspects of MCT8 function.
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Affiliation(s)
- Stefan Groeneweg
- Department of Internal Medicine, Erasmus University Medical Center, Rotterdam, The Netherlands.
| | - W Edward Visser
- Department of Internal Medicine, Erasmus University Medical Center, Rotterdam, The Netherlands.
| | - Theo J Visser
- Department of Internal Medicine, Erasmus University Medical Center, Rotterdam, The Netherlands.
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Abstract
Thyroid hormones (TH) are endocrine messengers essential for normal development and function of virtually every vertebrate. The hypothalamic-pituitary-thyroid axis is exquisitely modulated to maintain nearly constant TH (T4 and T3) levels in circulation. However peripheral tissues and the CNS control the intracellular availability of TH, suggesting that circulating concentrations of TH are not fully representative of what each cell type sees. Indeed, recent work in the field has identified that TH transporters, deiodinases and thyroid hormone receptor coregulators can strongly control tissue-specific sensitivity to a set amount of TH. Furthermore, the mechanism by which the thyroid hormone receptors regulate target gene expression can vary by gene, tissue and cellular context. This review will highlight novel insights into the machinery that controls the cellular response to TH, which include unique signaling cascades. These findings shed new light into the pathophysiology of human diseases caused by abnormal TH signaling.
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Affiliation(s)
- Arturo Mendoza
- Division of Endocrinology, Diabetes and Metabolism, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA
| | - Anthony N Hollenberg
- Division of Endocrinology, Diabetes and Metabolism, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA.
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Johannes J, Braun D, Kinne A, Rathmann D, Köhrle J, Schweizer U. Few Amino Acid Exchanges Expand the Substrate Spectrum of Monocarboxylate Transporter 10. Mol Endocrinol 2016; 30:796-808. [PMID: 27244477 PMCID: PMC5426580 DOI: 10.1210/me.2016-1037] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2016] [Accepted: 05/24/2016] [Indexed: 02/07/2023] Open
Abstract
Monocarboxylate transporters (MCTs) belong to the SLC16 family within the major facilitator superfamily of transmembrane transporters. MCT8 is a thyroid hormone transporter mutated in the Allan-Herndon-Dudley syndrome, a severe psychomotor retardation syndrome. MCT10 is closely related to MCT8 and is known as T-type amino acid transporter. Both transporters mediate T3 transport, but although MCT8 also transports rT3 and T4, these compounds are not efficiently transported by MCT10, which, in contrast, transports aromatic amino acids. Based on the 58% amino acid identity within the transmembrane regions among MCT8 and MCT10, we reasoned that substrate specificity may be primarily determined by a small number of amino acid differences between MCT8 and MCT10 along the substrate translocation channel. Inspecting the homology model of MCT8 and a structure-guided alignment between both proteins, we selected 8 amino acid positions and prepared chimeric MCT10 proteins with selected amino acids changed to the corresponding amino acids in MCT8. The MCT10 mutant harboring 8 amino acid substitutions was stably expressed in Madin-Darby canine kidney 1 cells and found to exhibit T4 transport activity. We then successively reduced the number of amino acid substitutions and eventually identified a minimal set of 2-3 amino acid exchanges which were sufficient to allow T4 transport. The resulting MCT10 chimeras exhibited KM values for T4 similar to MCT8 but transported T4 at a slower rate. The acquisition of T4 transport by MCT10 was associated with complete loss of the capacity to transport Phe, when Tyr184 was mutated to Phe.
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Affiliation(s)
- Jörg Johannes
- Institut für Biochemie und Molekularbiologie (J.J., D.B., U.S.), Rheinische Friedrich-Wilhelms-Universität, 53115 Bonn, Germany; and Institut für Experimentelle Endokrinologie (J.J., A.K., D.R., J.K.), Charité-Universitätsmedizin Berlin, 13353 Berlin, Germany
| | - Doreen Braun
- Institut für Biochemie und Molekularbiologie (J.J., D.B., U.S.), Rheinische Friedrich-Wilhelms-Universität, 53115 Bonn, Germany; and Institut für Experimentelle Endokrinologie (J.J., A.K., D.R., J.K.), Charité-Universitätsmedizin Berlin, 13353 Berlin, Germany
| | - Anita Kinne
- Institut für Biochemie und Molekularbiologie (J.J., D.B., U.S.), Rheinische Friedrich-Wilhelms-Universität, 53115 Bonn, Germany; and Institut für Experimentelle Endokrinologie (J.J., A.K., D.R., J.K.), Charité-Universitätsmedizin Berlin, 13353 Berlin, Germany
| | - Daniel Rathmann
- Institut für Biochemie und Molekularbiologie (J.J., D.B., U.S.), Rheinische Friedrich-Wilhelms-Universität, 53115 Bonn, Germany; and Institut für Experimentelle Endokrinologie (J.J., A.K., D.R., J.K.), Charité-Universitätsmedizin Berlin, 13353 Berlin, Germany
| | - Josef Köhrle
- Institut für Biochemie und Molekularbiologie (J.J., D.B., U.S.), Rheinische Friedrich-Wilhelms-Universität, 53115 Bonn, Germany; and Institut für Experimentelle Endokrinologie (J.J., A.K., D.R., J.K.), Charité-Universitätsmedizin Berlin, 13353 Berlin, Germany
| | - Ulrich Schweizer
- Institut für Biochemie und Molekularbiologie (J.J., D.B., U.S.), Rheinische Friedrich-Wilhelms-Universität, 53115 Bonn, Germany; and Institut für Experimentelle Endokrinologie (J.J., A.K., D.R., J.K.), Charité-Universitätsmedizin Berlin, 13353 Berlin, Germany
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