The manifestations of resistance to thyroid hormone (RTH) syndrome vary as a spectrum of clinical findings between hypothyroidism and hyperthyroidism in different tissues, suggesting that due to the organ’s main receptors, which can be TRβ (liver, adipose tissues) or TRα (skeletal and cardiac muscles, vascular endothelium), TH deficiency, sufficiency, and excess may coexist at the same time in a patient. This evidence concerns the gene THRB and hyperthyroidism.