TPO and thyroiditis: Thyroid dyshormonogenesis has been linked to mutations in the sodium iodide symporter (NIS), SLC26A4 (which encodes pendrin, a multifunctional anion exchanger), thyroid peroxidase (TPO), dual oxidase 2 (DUOX2), DUOX maturation factor 1 (DUOXA1), DUOX maturation factor 2 (DUOXA2), dehalogenase 1 (DEHAL1) and thyroglobulin (TG) genes (4).