Role and Clinical Significance of Monocarboxylate Transporter 8 (MCT8) During Pregnancy.

The review aims to summarize the available research focusing on the importance of monocarboxylate transporter (MCT8) in thyroid hormone trafficking across the placenta and fetal development. A systematic search was carried out in PubMed; studies available in English related to "monocarboxylate transporter", "adverse pregnancy", "fetal development," and "thyroid hormone" were identified and assessed. The references within the resulting articles were manually searched. MCT8 is a highly active and selective thyroid hormone transporter that facilitates the cellular uptake of triiodothyronine (T3), thyroxine (T4), reverse triiodothyronine (rT3), and diiodothyronine (T2) in different tissues. MCT8 is expressed in the placenta from the first trimester onwards, allowing the transport of thyroid hormone from mother to fetus. Mutations in MCT8 cause an X-linked disorder known as Allan-Herndon-Dudley syndrome (AHDS), characterized by severe psychomotor impairment and peripheral thyrotoxicosis. Hence, any maternal thyroid dysfunction may cause severe consequences for the fetus and newborn. Further research regarding MCT8 gene expression, polymorphic variation, and adverse pregnancy outcomes must be done to establish that MCT8 is a novel prognostic marker for the early detection of pregnancy-related complications.