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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®


Reviewed May 2007

What is the official name of the SLC16A2 gene?

The official name of this gene is “solute carrier family 16, member 2 (thyroid hormone transporter).”

SLC16A2 is the gene's official symbol. The SLC16A2 gene is also known by other names, listed below.

What is the normal function of the SLC16A2 gene?

The SLC16A2 gene (also known as MCT8) provides instructions for making a protein that plays a critical role in nervous system development. This protein transports a particular hormone into nerve cells in the developing brain. This hormone, called triiodothyronine or T3, is produced by the thyroid (a butterfly-shaped gland in the lower neck). Once inside a nerve cell, T3 interacts with receptors in the nucleus that turn specific genes on or off. The activity of this hormone appears to be critical for the maturation of nerve cells, the movement of these cells to their proper locations (cell migration), and the formation of specialized cell outgrowths called dendrites. T3 may also play a role in the development of synapses, which are junctions between nerve cells where cell-to-cell communication occurs.

In addition to the nervous system, T3 is produced in the liver, kidney, heart, and several other tissues. T3 and other forms of thyroid hormone help regulate the development of many organs and control the rate of chemical reactions in the body (metabolism).

Does the SLC16A2 gene share characteristics with other genes?

The SLC16A2 gene belongs to a family of genes called SLC (solute carriers).

A gene family is a group of genes that share important characteristics. Classifying individual genes into families helps researchers describe how genes are related to each other. For more information, see What are gene families? ( in the Handbook.

How are changes in the SLC16A2 gene related to health conditions?

Allan-Herndon-Dudley syndrome - caused by mutations in the SLC16A2 gene

At least a dozen mutations in the SLC16A2 gene have been identified in people with the characteristic features of Allan-Herndon-Dudley syndrome. Some of these mutations insert or delete genetic material in the gene. Other mutations change single protein building blocks (amino acids) used to make the SLC16A2 protein. All of these genetic changes alter the structure and function of this protein, preventing it from transporting T3 into nerve cells effectively. A lack of this critical hormone in certain parts of the brain disrupts normal brain development, resulting in intellectual disability and problems with movement.

If T3 is not taken up by nerve cells, excess amounts of this hormone continue to circulate in the bloodstream. An increase in circulating T3 may be toxic to some organs, such as the liver. Researchers are working to determine whether increased T3 levels in the body contribute to the signs and symptoms of Allan-Herndon-Dudley syndrome.

Where is the SLC16A2 gene located?

Cytogenetic Location: Xq13.2

Molecular Location on the X chromosome: base pairs 74,421,493 to 74,533,929

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBI (

The SLC16A2 gene is located on the long (q) arm of the X chromosome at position 13.2.

The SLC16A2 gene is located on the long (q) arm of the X chromosome at position 13.2.

More precisely, the SLC16A2 gene is located from base pair 74,421,493 to base pair 74,533,929 on the X chromosome.

See How do geneticists indicate the location of a gene? ( in the Handbook.

Where can I find additional information about SLC16A2?

You and your healthcare professional may find the following resources about SLC16A2 helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the SLC16A2 gene or gene products?

  • DXS128E
  • MCT8
  • monocarboxylate transporter 8
  • solute carrier family 16, member 2 (monocarboxylic acid transporter 8)
  • solute carrier family 16 (monocarboxylic acid transporters), member 2
  • X-linked PEST-containing transporter
  • XPCT

See How are genetic conditions and genes named? ( in the Handbook.

What glossary definitions help with understanding SLC16A2?

acids ; carrier ; cell ; disability ; gene ; hormone ; kidney ; metabolism ; nerve cell ; nervous system ; nucleus ; protein ; solute ; syndrome ; T3 ; thyroid ; toxic ; triiodothyronine

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Dumitrescu AM, Liao XH, Weiss RE, Millen K, Refetoff S. Tissue-specific thyroid hormone deprivation and excess in monocarboxylate transporter (mct) 8-deficient mice. Endocrinology. 2006 Sep;147(9):4036-43. Epub 2006 May 18. (
  • Friesema EC, Grueters A, Biebermann H, Krude H, von Moers A, Reeser M, Barrett TG, Mancilla EE, Svensson J, Kester MH, Kuiper GG, Balkassmi S, Uitterlinden AG, Koehrle J, Rodien P, Halestrap AP, Visser TJ. Association between mutations in a thyroid hormone transporter and severe X-linked psychomotor retardation. Lancet. 2004 Oct 16-22;364(9443):1435-7. (
  • Friesema EC, Jansen J, Heuer H, Trajkovic M, Bauer K, Visser TJ. Mechanisms of disease: psychomotor retardation and high T3 levels caused by mutations in monocarboxylate transporter 8. Nat Clin Pract Endocrinol Metab. 2006 Sep;2(9):512-23. Review. (
  • Friesema EC, Kuiper GG, Jansen J, Visser TJ, Kester MH. Thyroid hormone transport by the human monocarboxylate transporter 8 and its rate-limiting role in intracellular metabolism. Mol Endocrinol. 2006 Nov;20(11):2761-72. Epub 2006 Aug 3. (
  • Herzovich V, Vaiani E, Marino R, Dratler G, Lazzati JM, Tilitzky S, Ramirez P, Iorcansky S, Rivarola MA, Belgorosky A. Unexpected peripheral markers of thyroid function in a patient with a novel mutation of the MCT8 thyroid hormone transporter gene. Horm Res. 2007;67(1):1-6. Epub 2006 Sep 15. (
  • Holden KR, Zuñiga OF, May MM, Su H, Molinero MR, Rogers RC, Schwartz CE. X-linked MCT8 gene mutations: characterization of the pediatric neurologic phenotype. J Child Neurol. 2005 Oct;20(10):852-7. (
  • Jansen J, Friesema EC, Kester MH, Milici C, Reeser M, Grüters A, Barrett TG, Mancilla EE, Svensson J, Wemeau JL, Busi da Silva Canalli MH, Lundgren J, McEntagart ME, Hopper N, Arts WF, Visser TJ. Functional analysis of monocarboxylate transporter 8 mutations identified in patients with X-linked psychomotor retardation and elevated serum triiodothyronine. J Clin Endocrinol Metab. 2007 Jun;92(6):2378-81. Epub 2007 Mar 13. (
  • Jansen J, Friesema EC, Milici C, Visser TJ. Thyroid hormone transporters in health and disease. Thyroid. 2005 Aug;15(8):757-68. Review. (
  • Kakinuma H, Itoh M, Takahashi H. A novel mutation in the monocarboxylate transporter 8 gene in a boy with putamen lesions and low free T4 levels in cerebrospinal fluid. J Pediatr. 2005 Oct;147(4):552-4. (
  • Maranduba CM, Friesema EC, Kok F, Kester MH, Jansen J, Sertié AL, Passos-Bueno MR, Visser TJ. Decreased cellular uptake and metabolism in Allan-Herndon-Dudley syndrome (AHDS) due to a novel mutation in the MCT8 thyroid hormone transporter. J Med Genet. 2006 May;43(5):457-60. Epub 2005 Jun 24. (
  • NCBI Gene (
  • Schwartz CE, May MM, Carpenter NJ, Rogers RC, Martin J, Bialer MG, Ward J, Sanabria J, Marsa S, Lewis JA, Echeverri R, Lubs HA, Voeller K, Simensen RJ, Stevenson RE. Allan-Herndon-Dudley syndrome and the monocarboxylate transporter 8 (MCT8) gene. Am J Hum Genet. 2005 Jul;77(1):41-53. Epub 2005 May 11. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: May 2007
Published: February 1, 2016