However, from 2 to 4 weeks of continued exposure to iodine excess, organification and the synthesis of thyroid hormone return to normal, probably due to a decrease in the NIS activity, the sodium-iodide symporter, a carrier protein of iodine that captures iodine to the interior of the thyroid cell.8Some subjects cannot escape from this effect, and the iodine excess triggers the hypothyroidism.9Fetuses are particularly susceptible, as this escape ability is not totally mature until 36 weeks of pregnancy.4 Here, SLC5A5 is linked to hypothyroidism.