PAX8 and cyclic hematopoiesis: To date, the five extensively studied TD candidate genes, FOXE1 (MIM*602617), NKX2-5 (MIM*600584), PAX8 (MIM*167415), TSHR (MIM+603372), and NKX2-1 (MIM*600635), appear to convincingly explain only <10% of the CH-TD cases, even when assessed using a NGS approach [3,7].