Thyroid hormone (TH) production is a tightly regulated process controlled by a classic negative feedback loop involving the hypothalamus, the pituitary, and the thyroid, which has led to the common name hypothalamus-pituitary-thyroid axis (Figure 1). The thyrotropin-releasing hormone (TRH) is produced in the hypothalamus. Once released, TRH reaches the pituitary gland and binds to the TRH receptor and stimulates the production and secretion of thyroid-stimulating hormone (TSH), also known as thyrotropin (Liu et al., 2019). In the thyroid, TSH binds to the TSH receptor (TSHR) and induces TH production. When needed,