NKX2-5 and cyclic hematopoiesis: Recently, several gene defects of transcription factors {such as PAX8, NKX2-1 [encoding thyroid transcription factor (TTF)-1], FOXE1 (encoding TTF-2), NKX2-5 and thyroid-stimulating hormone receptor (TSHR)} have been determined among patients with permanent primary CH (8,16).