TPO and cyclic hematopoiesis: Dyshormonogenic CH may occur because of biallelic mutations in anion transporters mediating thyroidal iodide uptake or efflux (SLC5A5/NIS or SLC26A4/pendrin, respectively); SLC26A7; TPO (the thyroid peroxidase enzyme), which catalyzes organification of iodide and the formation of thyroid hormones; and thyroglobulin (TG), upon which thyroid hormone biosynthesis and storage occur.