Triiodothyroacetic acid treatment in MCT8 deficiency: a word of nuance

The Allan-Herndon-Dudley syndrome (AHDS) is caused by a defect in the thyroid hormone (TH) transporter MCT8 (1,2). The clinical phenotype comprises a “central” component due to impaired psychomotor development with severe intellectual disability, axial hypotonia and dystonia, and a ‘’peripheral’’ component dominated by signs of thyrotoxicosis, caused by elevated serum T3 levels. The combination of high serum T3, low or low-normal serum (F)T4 and normal to modestly elevated serum TSH levels are very typical for AHDS (3).