Iodide Transport Defect and Breast Milk Iodine

Abstract

Background: Iodide transport defect (ITD) is a dyshormonogenetic congenital hypothyroidism caused by sodium/iodide symporter (NIS) gene mutations. In the lactating mammary gland, iodide is concentrated by NIS, and iodine for thyroid hormone synthesis is thereby supplied to the infant in the breast milk. Case Description: A 34-year-old Japanese woman was diagnosed with ITD caused by a homozygous NIS gene mutation T354P. She had begun treatment of primary hypothyroidism with levothyroxine at the age of 5. She delivered a baby at the age of 36. The iodine concentration in her breast milk was 54 µg/l. She took a 50-mg potassium iodide tablet daily to supply iodine in the breast milk, starting on the 5th day postpartum. Her breast milk iodine concentration increased to 90 µg/l (slightly above the minimum requirement level). The patient weaned her baby and stopped taking the daily potassium iodide tablet 6 weeks postpartum, and the baby began to be fed with relatively iodine-rich formula milk. The baby's thyroid function remained normal from birth until 6 months of age. Conclusion: Possible iodine deficiency in the infant breast-fed by an ITD patient should be kept in mind. Prophylactic iodine supplementation is essential for such infants in order to prevent severe iodine deficiency.

Effects of Inorganic Iodine Therapy Administered to Lactating Mothers With Graves Disease on Infant Thyroid Function

“…Supernatants of centrifuged breast milk samples and urine samples were stored at −20°C until further analysis. Iodine concentration measurements were outsourced to the Hitachi Chemical Clinical Laboratory (Tokyo, Japan), which implemented a microplate method based on the Sandell–Kolthoff reaction [ 15 ].…”

Implications of Na+/I- Symporter Transport to the Plasma Membrane for Thyroid Hormonogenesis and Radioiodide Therapy

“…Consistent with these findings, Ferrandino et al [35] recently developed an NIS knockout mouse model that recapitulated the conditions of ITDs and provided evidence that high dietary concentrations of I − make it possible for I − to enter the thyroid follicular cells—even in the absence of functional NIS expression—through low-affinity mechanisms, thus facilitating partial thyroid hormone biosynthesis. On a different note, Mizokami et al [36] demonstrated the importance of prophylactic iodine supplementation in healthy breast-fed newborns whose lactating mothers carry mutations in the SLC5A5 gene, as NIS mediates I − accumulation in breast milk, to prevent the development of hypothyroidism in the nursing newborn due to I − -deficient breast milk.…”

Genetic and Physiological Factors Affecting Human Milk Production and Composition

“…In addition, one mutation in the 5 untranslated region (a C→T transition at position-54) has also been reported [52]. Recently, a woman carrying the abovementioned homozygous T354P mutation in the NIS transporter was reported to produce iodine-deficient human milk [53]. In this case, the mother was treated with a daily dose of 50 mg potassium iodide starting on the fifth day postpartum until six weeks postpartum, when breastfeeding was ceased [53].…”

“…Recently, a woman carrying the abovementioned homozygous T354P mutation in the NIS transporter was reported to produce iodine-deficient human milk [53]. In this case, the mother was treated with a daily dose of 50 mg potassium iodide starting on the fifth day postpartum until six weeks postpartum, when breastfeeding was ceased [53]. Further research is needed to assess the impact of heterozygous mutations or other genetic alterations in the NIS transporter, which do not result in ITD, and thus are not diagnosed in most cases, based on human milk iodine concentration.…”