title: 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.
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  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.
authors: Tajiri Thyroid Clinic, Kumamoto, Japan.
authors: Tetsuya
authors: T
authors: Mizokami
authors: Tajiri Thyroid Clinic, Kumamoto, Japan; b Department of Medicine, Kuma Hospital, Kobe, Japan.
authors: Shuji
authors: S
authors: Fukata
authors: Department of Infection Control and Clinical Laboratory Medicine, Dokkyo Medical University, Tochigi, Japan.
authors: Akira
authors: A
authors: Hishinuma
authors: Department of Infection Control and Clinical Laboratory Medicine, Dokkyo Medical University, Tochigi, Japan.
authors: Takahiko
authors: T
authors: Kogai
authors: Tajiri Thyroid Clinic, Kumamoto, Japan.
authors: Katsuhiko
authors: K
authors: Hamada
authors: Tajiri Thyroid Clinic, Kumamoto, Japan.
authors: Tetsushi
authors: T
authors: Maruta
authors: Tajiri Thyroid Clinic, Kumamoto, Japan.
authors: Kiichiro
authors: K
authors: Higashi
authors: Tajiri Thyroid Clinic, Kumamoto, Japan.
authors: Junichi
authors: J
authors: Tajiri
keywords: Breast milk iodine; Iodide transport defect; NIS mutation; Sodium/iodide symporter