The SLC16A2 gene gives cells instructions for a transporter that moves thyroid hormone into tissues, especially the brain. This gene helps your body use this hormone to support brain development, muscle control, and energy balance. When the transporter does not work properly, thyroid hormone cannot reach some cells well, and pathogenic variants can cause Allan-Herndon-Dudley syndrome, a condition linked to developmental delay, low muscle tone, and movement problems. Blood tests often show an unusual thyroid hormone pattern.
What is a gene?
Genes are stretches of DNA that carry instructions your cells use to make molecules or regulate processes in the body. Some genes hold the instructions for producing proteins, the working parts of cells. Others mainly help determine when certain processes happen, where they happen, and how strongly they occur. Taken together, genes affect how the body develops and works, and they can also shape how you respond to food, stress, or medications. To look into this topic more closely, you can find more in the LearnHub.
Overview
SLC16A2Gene function
What if the gene works
The SLC16A2 gene helps move thyroid hormone into cells, especially in the brain. This lets tissues use these signals for growth, brain development, and energy balance.
Risk
What if the gene does not work
Variants in the SLC16A2 gene can disrupt thyroid hormone transport into cells. This is linked to Allan-Herndon-Dudley syndrome, with developmental and movement problems that can range from milder to more severe, along with characteristic thyroid blood test changes.
Treatment
What does that mean for your treatment
Pathogenic variants in the SLC16A2 gene can make standard thyroid hormone treatment less useful, because hormone transport into certain tissues is impaired. Tiratricol (TRIAC) is an established treatment choice to lower high T3 levels and reduce body wide thyroid excess, while levothyroxine alone is usually not the main approach.
Conditions associated with SLC16A2
Gene function
What if the gene works
Your cells use the SLC16A2 gene to move thyroid hormone across their outer membrane. This allows many tissues, especially the brain, to respond to signals that help guide energy use, growth, and normal day-to-day activity. Understanding how the SLC16A2 gene works helps explain how thyroid hormone reaches the cells that need it.
The SLC16A2 gene makes a transporter that moves thyroid hormones, especially T3, across the cell membrane. This is a key part of thyroid hormone transport into cells, where the hormone can be used.
When thyroid hormone gets inside a cell, it can switch on gene programs that guide normal energy use, growth, and cell activity. The SLC16A2 gene helps tissues respond to these hormone signals in a steady way.
This transporter is especially important in brain cells, which rely on thyroid hormone during development and everyday function. It helps the brain receive and use an important signal for normal activity and maturation.
What is a variant?
A genetic variant is a minor change in a gene’s DNA sequence. These changes are common and help shape normal human diversity, including differences in appearance, metabolism, and the way the body responds to environmental influences. Many variants do not have any noticeable effect and are simply part of natural genetic variation. Sometimes, though, a variant changes how a gene works more substantially and may contribute to or cause a genetic condition.
Genetic variants
What if the gene does not work
Variants in the SLC16A2 gene can change how the MCT8 transporter is built, folded, or moved to the cell surface, which explains how SLC16A2 gene variants affect thyroid hormone transport. Some small DNA changes leave partial transport activity, while more disruptive changes can make the protein unstable, trap it inside the cell, or stop it from being made at all. Less residual activity is generally linked to earlier and more marked features of MCT8 deficiency, also called Allan-Herndon-Dudley syndrome.
How variants are linked to conditions
Pathogenic variants in the SLC16A2 gene cause Allan-Herndon-Dudley syndrome, so information about the SLC16A2 gene and Allan-Herndon-Dudley syndrome usually centers on this diagnosis. This X linked condition is associated with low muscle tone in infancy, major delays in sitting and walking, speech and learning difficulties, and later unusual muscle stiffness or movements. Females who carry a variant may have no symptoms or milder features.
A variant is not necessarily a diagnosis
Variants are a usual feature of human biology and are widely found across the population. Most do not directly affect health and instead reflect normal human variation. For many genes, having a variant associated with a condition points to a possible link, not a certain diagnosis, particularly when several genes and environmental influences also play a role. In some situations, though, one well-studied variant in a particular gene is enough to establish a diagnosis.
Are there things that can increase or change my risk?
For SLC16A2, risk is mostly set by the gene change itself and whether someone is male or female, since this condition is usually much more severe in males. Family history also matters because the gene is passed on the X chromosome. There is not enough evidence to say lifestyle changes lower the chance of having the condition.
Inheritance of SLC16A2 variants
Variants in the SLC16A2 gene are inherited in an X linked pattern. This means how SLC16A2 variants are inherited differs for sons and daughters because the gene sits on the X chromosome. A mother carrying a variant can pass it to any child, while a father with the variant passes his X chromosome to all daughters and none of his sons. Males who inherit the altered copy are more likely to be affected, while females who carry one altered copy may have no symptoms or milder features.
What does my SLC16A2 result mean for my family?
For families with a disease-causing change in the SLC16A2 gene, close relatives may also carry the same change. Because this gene is on the X chromosome, boys and men in the family are more likely to have symptoms, while girls and women may be carriers and can sometimes have mild features or none at all. Brothers, sisters, and the mother's side of the family are often the relatives most relevant to consider.
Genetic information
Genetic testing
How you find out about variants
To look for changes linked to this condition, SLC16A2 genetic testing uses a blood sample, saliva, or cheek swab to read the gene’s DNA code and check for variants. It can confirm whether a disease-causing SLC16A2 variant is present and may also clarify carrier status in female relatives.
When should I consider getting a genetic test?
Genetic testing for the SLC16A2 gene is worth considering when a child, often a boy, has major delays in sitting, walking, or talking, unusual muscle stiffness or floppiness, and thyroid blood tests that do not fit the usual pattern. Testing can also help when similar problems run in the family.
A genetic result is only one part of your health story
A genetic result can be informative, but what it can tell you varies based on the condition and the kind of variant involved. Over time, many factors, including lifestyle, environment, age, and medical history, influence how the body functions. For some conditions, especially those affected by many genes, genetic information offers context rather than certainty and is best viewed alongside other parts of care. In other situations, a genetic result may give a clear answer. In areas such as medication response, genetic results can help put personal experiences into context.
Pharmacogenetics
How variants shape your response to medicine
Genetic variation can affect how your body responds to medicines. Small differences in genes can change how a drug is absorbed, moved through the body, broken down, or reaches its target. This is one reason the same treatment may work well for one person, seem less effective for another, or cause more side effects in someone else.
What is Pharmacogenetics?
Pharmacogenetics looks at how genetic differences shape a person’s response to medications. It examines links between genes and drugs to help explain why the same treatment may work differently from one person to another. For many medications, genes affect both how strongly a drug works and how the body processes it. This information can support more informed, more individualized treatment decisions. If you want to explore this topic in greater detail, you can learn more in the LearnHub.
Drugs influenced by the SLC16A2 gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in guiding medication choice or dose, so general questions about medicines, side effects, or changing symptoms are best discussed with your doctor. SLC16A2 has been studied because it helps move thyroid hormone into cells, but this research has not led to routine medicine decisions.
History
SLC16A2 entered medical history through a family described in 1944 by William Allan, C. Nash Herndon, and Florence Dudley, who reported boys with a shared inherited pattern of developmental and movement differences. For many years, the condition was recognized clinically as Allan-Herndon-Dudley syndrome before the gene itself was identified. In recent decades, awareness of this gene’s role has grown. In 2004, researchers linked pathogenic variants in the SLC16A2 gene to the syndrome, giving families a clear genetic explanation for a condition that had long been observed but not fully understood. From these first observations, research expanded steadily. This genetic discovery helped connect earlier clinical reports with modern testing and more precise diagnosis.