title: Thyroid hormone transport in developing brain.
abstract: OBJECTIVE
  To discuss the recent advances on thyroid hormone transport in the brain. A special attention is paid to the X-linked thyroid hormone cell transport (THCT) defect (also known as the Allan-Herndon-Dudley syndrome), caused by mutations of the specific thyroid hormone transporter MCT8 gene.
  
  
  RESULTS
  MCT8 is involved in thyroid hormone transport in the brain. MRI of patients with THCT defect showed myelination delays, probably related to impaired thyroid hormone action on oligodendrocytes. MCT8 is also expressed in the thyroid and has an important role in thyroid hormone secretion. The altered circulating concentrations of thyroid hormone in the patients are partly because of impaired secretion and altered peripheral metabolism. Increased deiodinase activity is important in the pathophysiology of the syndrome. High D1 activity in liver and kidney increases T4 and rT3 deiodination, and contributes to the increased serum T3. High D2 activity in the brain contributes to compensate the deficient T3 transport by increasing local T3 production.
  
  
  CONCLUSIONS
  Patients with suspected X-linked leukoencephalopathy should be screened for MCT8 gene mutations. Research on the brain pathophysiology of the THCT defect should focus on the specific role of Mct8 on oligodendrocytes and myelination.
authors.affiliation: Instituto de Investigaciones Biomédicas, Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, Madrid, Spain. jbernal@iib.uam.es
authors.forename: Juan
authors.initials: J
authors.lastname: Bernal
mesh_terms: D000818:Animals; D001692:Biological Transport; D001921:Brain / Q000196:embryology* / Q000378:metabolism; D006801:Humans; D038901:X-Linked Intellectual Disability / Q000378:metabolism; D027501:Monocarboxylic Acid Transporters / Q000235:genetics; D009123:Muscle Hypotonia / Q000378:metabolism; D009133:Muscular Atrophy / Q000378:metabolism; D027981:Symporters; D013963:Thyroid Hormones / Q000378:metabolism*; D013974:Thyroxine / Q000378:metabolism; D014284:Triiodothyronine / Q000378:metabolism
chemical_list: D027501:Monocarboxylic Acid Transporters; C090735:SLC16A2 protein, human; D027981:Symporters; D013963:Thyroid Hormones; D014284:Triiodothyronine; D013974:Thyroxine