Expression changes of some of these genes have been used as sensitive indicators of the impact on the brain of situations leading to altered metabolism and/or transport of thyroid hormones, such as inactivation of the deiodinase genes Dio2 and Dio3, thyroid hormone transporter genes Mct8 and Oatp1c1, and the receptor genes Thra and Thrb, in addition to hypo or hyperthyroidism [5]–[9]. Here, DIO3 is linked to hyperthyroidism.