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.

Keywords:
Sodium/iodide symporter, Iodide transport defect, Breast milk iodine, NIS mutation
1.
Portulano C, Paroder-Belenitsky M, Carrasco N: The Na+/I- symporter (NIS): mechanism and medical impact. Endocr Rev 2014;35:106-149.
2.
Package insert of iodine measurement kit (Yodomonit, in Japanese). Hitachi Chemical Co., Ltd. 2012. http://www.info.pmda.go.jp/tgo/pack/21900AMZ00077000_A_01_01 (accessed April 10, 2016).
3.
Ohashi T, Yamaki M, Pandav CS, Karmarkar MG, Irie M: Simple microplate method for determination of urinary iodine. Clin Chem 2000;46:529-536.
4.
Fukata S, Hishinuma A, Nakatake N, Tajiri J: Diagnosis of iodide transport defect: do we need to measure the saliva/serum radioactive iodide ratio to diagnose iodide transport defect? Thyroid 2010;20:1419-1421.
5.
Kosugi S, Sato Y, Matsuda A, Ohyama Y, Fujieda K, Inomata H, Kameya T, Isozaki O, Jhiang SM: High prevalence of T354P sodium/iodide symporter gene mutation in Japanese patients with iodide transport defect who have heterogeneous clinical pictures. J Clin Endocrinol Metab 1998;83:4123-4129.
6.
Vulsma T, de Vijlder JJM: Genetic defects causing hypothyroidism; in Braverman LE, Cooper DS (eds): Werner and Ingbar's The Thyroid. A Fundamental and Clinical Text, ed 10. Philadelphia, Lippincott Williams and Wilkins, 2013, pp 535-551.
7.
Burns R, O'Herlihy C, Smyth PP: The placenta as a compensatory iodine storage organ. Thyroid 2011;21:541-546.
8.
Chan S, Kachilele S, Hobbs E, Bulmer JN, Boelaert K, McCabe CJ, Driver PM, Bradwell AR, Kester M, Visser TJ, Franklyn JA, Kilby MD: Placental iodothyronine deiodinase expression in normal and growth-restricted human pregnancies. J Clin Endocrinol Metab 2003;88:4488-4495.
9.
Laurberg P, Nøhr SB, Pedersen KM, Fuglsang E: Iodine nutrition in breast-fed infants is impaired by maternal smoking. J Clin Endocrinol Metab 2004;89:181-187.
10.
Andersen SL, Nøhr SB, Wu CS, Olsen J, Pedersen KM, Laurberg P: Thyroglobulin in smoking mothers and their newborns at delivery suggests autoregulation of placental iodide transport overcoming thiocyanate inhibition. Eur J Endocrinol 2013;168:723-731.
11.
Leung AM, Pearce EN, Braverman LE: Iodine nutrition in pregnancy and lactation. Endocrinol Metab Clin North Am 2011;40:765-777.
12.
Bazrafshan HR, Mohammadian S, Ordookhani A, Abedini A, Davoudy R, Pearce EN, Hedayati M, Azizi F, Braverman LE: An assessment of urinary and breast milk iodine concentrations in lactating mothers from Gorgan, Iran, 2003. Thyroid 2005;15:1165-1168.
13.
Zimmermann MB: Iodine deficiency and endemic cretinism; in Braverman LE, Cooper DS (eds): Werner and Ingbar's The Thyroid. A Fundamental and Clinical Text, ed 10. Philadelphia, Lippincott Williams and Wilkins, 2013, pp 217-241.
© 2016 European Thyroid Association Published by S. Karger AG, Basel
2016
Copyright / Drug Dosage / Disclaimer
Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
You do not currently have access to this content.