SLC16A2 and Allan-Herndon-Dudley syndrome: TH transport across the BBB has a pivotal role for AHDS pathophysiology, as demonstrated by the expression of MCT8 in the human brain barriers along neurodevelopment [5, 6] and in different functional studies showing altered TH transport due to MCT8 inactivation using both in vivo [14] and in vitro models [15].