SLC5A5 and thyroid gland disorder: These tests can be used to differentiate a hyperactive thyroid, with increased uptake (e.g. Graves’ disease, toxic nodules), from an underactive thyroid with decreased iodine uptake, secondary to either thyroid damage or inactivation (e.g. thyroiditis, factitious thyrotoxicosis) or a blockade in thyroid uptake (e.g. mutation in NIS).