Journal
CURRENT OPINION IN ENDOCRINOLOGY DIABETES AND OBESITY
Volume 18, Issue 5, Pages 295-299Publisher
LIPPINCOTT WILLIAMS & WILKINS
DOI: 10.1097/MED.0b013e32834a78b3
Keywords
Allan-Herndon-Dudley syndrome; brain development; deiodinases; leukoencephalopathy; thyroid gland; thyroid hormones; X-chromosome
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Funding
- Ministry of Science and Innovation [SAF2008-01168, SAF2008-00429E]
- European Union
- Center for Biomedical Research on Rare Diseases (CIBERER), an initiative of Instituto de Salud Carlos III, Spain
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Purpose of review 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. Recent findings 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. Summary 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.
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