Until now, the THD related factors and their defects include: (1) defects in iodine uptake into thyroid follicular cells due to mutations in SLC5A5; (2) iodine organification defects due to mutations in TPO, DUOX2 and DUOXA2, encoding the peroxidase enzyme system; (3) defects in iodine transport (Pendred syndrome) due to mutations in the Pendrin gene (SLC26A4); (4) defects in thyroglobulin synthesis (TG), storage, or secretion; and (5) failure of iodine recycling due to mutations in IYD [6]. This evidence concerns the gene SLC26A4 and Pendred syndrome.