In view of the results obtained after intranasal administration of T4 to Wt and Mct8KO mice, it was essential 1) to establish if THs delivered intranasally can directly access the brain by nose-to-brain transport and 2) to reduce the amount of THs administered intranasally reaching the plasma in order to avoid worsening the peripheral hyperthyroidism characteristic of MCT8-deficient patients. Here, SLC16A2 is linked to hyperthyroidism.