Mutations in genes critical for TH biosynthesis, including sodium iodide symporter (NIS; SLC5A5), pendrin (PDS; SLC26A4), thyroglobulin (TG), thyroperoxidase (TPO), thyroid stimulating hormone receptor (TSHR), and dual oxidase 2 (DUOX2), have been causally linked to thyroid dyshormonogenesis [11–13]. The gene discussed is TG; the disease is familial thyroid dyshormonogenesis.