Influence of dietary iodine deficiency on the thyroid gland in Slc26a4-null mutant mice.

[pendred syndrome]

Pendred syndrome (PDS ) is an autosomal recessive disorder characterized by sensorineural hearing impairment and variable degree of goitrous enlargement of the thyroid gland with a partial defect in iodine organification . The thyroid function phenotype can range from normal function to overt hypothyroidism . It is caused by loss -of-function mutations in the SLC 26 A 4 (PDS ) gene . The severity of the goiter has been postulated to depend on the amount of dietary iodine intake . However , direct evidence has not been shown to support this hypothesis . Because Slc 26 a 4 -null mice have deafness but do not develop goiter , we fed the mutant mice a control diet or an iodine-deficient diet to evaluate whether iodine deficiency is a causative environmental factor for goiter development in PDS .We evaluated the thyroid volume in histological sections with the use of three -dimensional reconstitution software , we measured serum levels of total tri -iodothyronine (TT 3 ) and total thyroxine (TT 4 ) levels , and we studied the thyroid gland morphology by transmission electron microscopy .TT 4 levels became low but TT 3 levels did not change significantly after eight weeks of an iodine-deficient diet compared to levels in the control diet animals . Even in Slc 26 a 4 -null mice fed an iodine-deficient diet , the volume of the thyroid gland did not increase although the size of each epithelial cell increased with a concomitant decrease of thyroid colloidal area .An iodine-deficient diet did not induce goiter in Slc 26 a 4 -null mice , suggesting that other environmental , epigenetic or genetic factors are involved in goiter development in PDS .