TG and Allan-Herndon-Dudley syndrome: MCT1 catalyzes the proton-linked transport of monocarboxylates, such as L-lactate across the plasma membrane, whereas MCT8 is essential for thyroid hormone transport across the BBB and it has been reported to be implicated in Allan–Herdon–Dudley syndrome (AHDS), an X-linked disorder characterized by neuropsychomotor abnormalities [29].