Allan-Herndon-Dudley syndrome (AHDS; OMIM #300523), also known as monocarboxylate transporter 8 (MCT8) deficiency, is an X-linked disorder caused by pathogenic variants in the solute carrier family 16 member 2 (SLC16A2) gene [1]. This evidence concerns the gene SLC16A2 and Allan-Herndon-Dudley syndrome.