TTF2 and cyclic hematopoiesis: According to previous reports, the cause of CH in approximately 80–85% of patients is thyroid dysgenesis (including agenesis, ectopy, and hypoplasia), which is related to gene mutations in thyroid-stimulating hormone receptor (TSHR), paired box gene 8 (PAX8), thyroid transcription factor 1 (TTF1/NKX2-1), thyroid transcription factor 2 (TTF2/FOXE1), and NK2 transcription factor related locus 5 (NKX2-5).