SLC16A2 and Allan-Herndon-Dudley syndrome: The family of monocarboxylate transporters (MCT) are of specific interest as MCT8 (solute carrier family 16 member 2, SCL16A2) was the first TH transporter identified to be causally involved in an inherited human disease, i.e., causative for the Allan–Herndon–Dudley syndrome (AHDS) [4,5].