MCT8: from gene to disease and therapeutic approach

Area of Science:

• Endocrinology and Metabolism
• Molecular Biology
• Neuroscience

Background:

• Thyroid hormone (TH) action relies on intracellular processes, necessitating membrane transport via specific transporters.
• MCT8 and MCT10 are key monocarboxylate transporters involved in TH transport across the plasma membrane.
• MCT8, located on the X chromosome, is crucial for TH transport in tissues like the liver, kidney, thyroid, and brain.

Purpose of the Study:

• To investigate the role of MCT8 in thyroid hormone transport and its implications in human health.
• To understand the molecular basis of psychomotor retardation and altered thyroid hormone levels associated with MCT8 mutations.
• To explore potential therapeutic strategies for conditions arising from MCT8 dysfunction.

Main Methods:

• Analysis of MCT8 gene location and mutations.
• Examination of MCT8 expression patterns in various tissues.
• Correlation of MCT8 mutations with clinical phenotypes, including psychomotor development and serum thyroid hormone levels.
• Investigation of thyroid hormone metabolism, conversion, and secretion in affected individuals.

Main Results:

• MCT8 mutations lead to severe psychomotor retardation in males.
• Affected individuals exhibit low serum thyroxine (T4) and high triiodothyronine (T3) levels.
• Impaired neuronal T3 uptake during development is implicated in psychomotor retardation.
• Increased T4 to T3 conversion in the kidney and altered thyroid hormone secretion contribute to abnormal hormone levels.

Conclusions:

• MCT8 is essential for normal thyroid hormone transport, particularly for neuronal development.
• MCT8 mutations result in a distinct clinical syndrome affecting both neurological function and thyroid hormone homeostasis.
• Therapeutic approaches involving T3 analogues that bypass MCT8-mediated transport offer a potential treatment strategy.