Thyroid hormone transporters.

BACKGROUND

Cellular uptake and release of thyroid hormone are mediated by transporters. Among these, monocarboxylate transporter 8 (MCT8) shows particularly high activity towards the active thyroid hormone 3,3',5-triiodothyronine (T(3)). MCT8 is expressed in different tissues, including the brain where it is predominantly localized in neurons. The MCT8 gene is located on the X chromosome.

CONCLUSIONS

Mutations in MCT8 have been identified in boys with severe psychomotor retardation who also have very high serum T(3) levels. Thyroid hormone is crucial for brain development, and mutations in MCT8 prevent the access of T(3) to its main target cells. Thus, mutations in MCT8 represent a novel mechanism for the pathogenesis of thyroid hormone resistance.