Iodine deficiency is the most common cause of HT, but congenital HT and autoimmune HT are other varieties with different genetic causes [20] that cause central HT, primary HT, alterations in thyroid transcription factors (with which the FOXE1 gene is associated), dyshormonogenesis, and other genes such as the TG and TSH genes [19]. The gene discussed is FOXE1; the disease is hematocrit.