TPO and cyclic hematopoiesis: Genetic screening of CH has been performed for research purpose and mainly eleven genes are related to CH such as TSHR, PAX8, NKX2-1, FOXE1, TG, TPO, SLC5A5, SLC26A4, IYD, DUOX2, and DUOXA2. Thyroid dysgenesis accounts for 80–85% cases, while 10 to 20% cases of CH are due to abnormalities in thyroid hormone synthesis [3].