Thyroid dyshormonogenesis, which is caused by defects in thyroid hormone biosynthesis, accounts for approximately 10–15% of primary CH and is associated with the following genes: DUOX2, DUOXA2, DUOX1, TPO, TG, SLC26A4, SLC5A5 and TSHR (5, 7, 9, 10, 11). The gene discussed is SLC5A5; the disease is cyclic hematopoiesis.