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SLC16A2 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

SLC16A2 gene

The SLC16A2 gene provides instructions for creating a protein essential for nervous system development and the regulation of thyroid hormone transport.

Normal Function

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 gland.

Once inside a nerve cell, T3 interacts with receptors in the nucleus to turn specific genes on or off. This activity is critical for the maturation of nerve cells, cell migration, and the formation of specialized cell outgrowths called dendrites. T3 may also play a role in the development of synapses, the junctions where cell-to-cell communication occurs. Beyond the nervous system, T3 is produced in the liver, kidney, heart, and other tissues, where it helps regulate organ development and metabolism.

Health Conditions Related to Genetic Changes

Allan-Herndon-Dudley syndrome

At least a dozen mutations in the SLC16A2 gene have been identified in people with Allan-Herndon-Dudley syndrome. These genetic changes, which include insertions, deletions, or single amino acid substitutions, alter the structure and function of the SLC16A2 protein. This prevents the effective transport of T3 into nerve cells, disrupting brain development and resulting in intellectual disability and movement problems.

Because T3 is not taken up by nerve cells, excess amounts circulate in the bloodstream, which may be toxic to organs such as the liver.

Other Names for This Gene

  • DXS128E
  • MCT8
  • monocarboxylate transporter 8
  • MOT8_HUMAN
  • solute carrier family 16 (monocarboxylic acid transporters), member 2
  • solute carrier family 16, member 2 (monocarboxylic acid transporter 8)
  • solute carrier family 16, member 2 (thyroid hormone transporter)
  • X-linked PEST-containing transporter
  • XPCT

Frequently Asked Questions

The condition primarily causes intellectual disability, hypotonia (low muscle tone), and movement disorders such as tremors or dystonia. While some motor symptoms like tremors may fluctuate or appear to improve slightly in adulthood, the underlying intellectual disability and developmental delays are generally permanent. Early intervention with physical and occupational therapy is crucial to maximize functional independence.
llan-Herndon-Dudley syndrome is inherited in an X-linked recessive pattern. This means the gene is located on the X chromosome. Males, who have only one X chromosome, are typically affected if they inherit the mutated gene. Females, who have two X chromosomes, are usually carriers and may have mild symptoms or be asymptomatic because their second, normal X chromosome produces enough functional protein to compensate.
In individuals with mutations in the SLC16A2 gene, the MCT8 transporter protein is defective and cannot move T3 into nerve cells. Because the hormone cannot enter the brain cells where it is normally used, it accumulates in the bloodstream. This results in elevated serum T3 levels, which can be toxic to other organs like the liver, even though the brain is deprived of the hormone it needs for development.
Standard thyroid hormone replacement therapy is not effective for treating the neurological symptoms of this syndrome. The issue is not a lack of thyroid hormone production by the gland, but rather the inability of the brain to transport T3 into cells. In fact, administering more thyroid hormone can sometimes worsen symptoms because it increases the already elevated levels of T3 circulating in the blood, potentially causing further toxicity to other organs.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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