The SLC5A5 gene gives thyroid cells the instructions to pull iodine from the bloodstream, which is a key step in making thyroid hormone. This gene helps your body keep energy use, growth, and brain development on track. If it does not work well, the thyroid may not collect enough iodine, which can lead to low thyroid hormone levels and sometimes an enlarged thyroid gland (goiter). In babies, this can cause congenital hypothyroidism, while older children and adults may develop symptoms of an underactive thyroid.
What is a gene?
Genes are sections of DNA that carry instructions your cells use to make molecules or regulate processes in the body. Some genes give the directions for making proteins, which are the functional parts of cells. Other genes mostly control when specific processes happen, where they occur, and how active they are. As a group, genes affect how the body develops and works, and they can influence how you respond to food, stress, or medicines. To go into this topic in more detail, you can visit the LearnHub.
Overview
SLC5A5Gene function
What if the gene works
The SLC5A5 gene helps thyroid cells pull iodine from the blood into the thyroid. This is a key step in making thyroid hormones, which support energy use, growth, and body temperature.
Risk
What if the gene does not work
Variants in the SLC5A5 gene can reduce iodine uptake into the thyroid, causing iodide transport defect and congenital hypothyroidism. Milder variants may cause less marked thyroid problems, while more severe variants often cause earlier symptoms and an enlarged thyroid gland.
Treatment
What does that mean for your treatment
Pathogenic variants in the SLC5A5 gene usually mean treatment centers on thyroid hormone replacement, often with levothyroxine, to keep thyroid levels in range. Because iodide uptake is impaired, iodine-based approaches such as radioiodine treatment can be less effective.
Conditions associated with SLC5A5
Gene function
What if the gene works
To make thyroid hormone, your body first needs to get iodine into thyroid cells. The SLC5A5 gene helps make that happen by moving iodine from the bloodstream into the thyroid. This early step supports the steady hormone supply that helps manage how your body uses energy, body temperature, and normal growth.
The SLC5A5 gene helps thyroid cells pull iodine from the bloodstream. It uses the usual flow of sodium into the cell as the driving force for this transport.
Once iodine is inside the thyroid, it can be used to build thyroid hormones. This is how the SLC5A5 gene helps the thyroid use iodine to make hormones your body needs every day.
By concentrating iodine inside thyroid cells, this gene helps keep a ready supply available for routine hormone production. That supports day to day control of how your body uses energy, body temperature, and growth.
What is a variant?
A genetic variant is a small difference in the DNA sequence within a gene. These changes are common and are part of normal human diversity, including differences in appearance, metabolism, or how the body responds to environmental influences. Many variants do not have any noticeable effect and simply represent natural genetic variation. In some cases, though, a variant can more substantially change how a gene functions and may contribute to or cause a genetic condition.
Genetic variants
What if the gene does not work
Variants in the SLC5A5 gene can change the iodide transporter so it folds poorly, reaches the cell membrane less well, or moves iodide less effectively. This helps explain how SLC5A5 gene variants affect iodide transport across a spectrum, from milder changes that leave some activity to more severe variants that nearly abolish transport. That difference in remaining activity can influence whether thyroid features appear later and stay milder or begin earlier and are more noticeable.
How variants are linked to conditions
Pathogenic variants in the SLC5A5 gene cause an inherited thyroid condition called iodide transport defect, which usually leads to congenital hypothyroidism. In practical terms, this means some babies are born with low thyroid hormone levels, and some children or adults may develop an enlarged thyroid gland (goiter). When people look up how SLC5A5 gene variants are linked to conditions, this thyroid-related diagnosis is the main well-established association.
A variant is not necessarily a diagnosis
Gene variants are a routine part of human biology and are common across the general population. Most do not have a direct effect on health and simply reflect natural human diversity. For many genes, carrying a variant associated with a condition indicates a possible link rather than a definite diagnosis, especially when several genes and environmental factors play a role. In some cases, though, a single well-characterized variant in a specific gene is enough to confirm a diagnosis.
Are there things that can increase or change my risk?
For SLC5A5, risk is mainly set by the variants you inherit, especially when changes are present in both copies of the gene. Low iodine intake can make thyroid problems more likely or more noticeable in people living with SLC5A5-related changes, while good iodine intake may help support thyroid health.
Inheritance of SLC5A5 variants
SLC5A5-related conditions are usually inherited in an autosomal recessive pattern. In practice, this means a child inherits one SLC5A5 gene variant from each parent, and both parents are often healthy carriers. When both parents carry a variant, each pregnancy has a 25% chance of being affected, a 50% chance of producing a carrier child, and a 25% chance of producing a child with no familial variant. This inheritance of SLC5A5 gene variants affects sons and daughters equally.
What does my SLC5A5 result mean for my family?
SLC5A5 results linked to this thyroid condition usually matter most for siblings and future children in the family. Parents are often healthy carriers, and brothers or sisters may also be carriers or, less often, have the condition. Close relatives may want to learn whether the same result runs in the family, especially when there is a history of congenital hypothyroidism or goiter.
Genetic information
Genetic testing
How you find out about variants
Genetic testing for SLC5A5 variants usually uses a blood or saliva sample. The lab reads the SLC5A5 gene to look for changes that may help explain congenital hypothyroidism or an iodine transport problem. Results are interpreted alongside symptoms and thyroid test findings.
When should I consider getting a genetic test?
Consider testing the SLC5A5 gene if a baby or child has low thyroid hormone from birth, especially with an enlarged thyroid or a family history of the same problem. Testing can help confirm an inherited cause when the thyroid cannot take up iodine properly.
A genetic result is only one part of your health story
Genetic test results can be helpful, but how much they reveal depends on the condition and the specific type of variant. Many factors, including lifestyle, environment, age, and medical history, also shape how the body functions over time. For some conditions, especially those influenced by many genes, genetic information provides context rather than certainty and is best considered together with other parts of care. In other situations, a genetic result may offer a clear answer. In areas such as medication response, these results can also help put individual experiences into context.
Pharmacogenetics
How variants shape your response to medicine
Genetic variation can affect how people respond to medicines. Small differences in DNA can change how the body absorbs, breaks down, transports, or responds to a drug, so the same treatment may work better for one person than for another. These differences are common and can influence how much benefit someone gets from a medicine or how sensitive they are to side effects.
What is Pharmacogenetics?
Pharmacogenetics examines how differences in genes can affect the way a person responds to medications. By looking at connections between genes and drugs, it helps explain why the same treatment can work differently from one person to another. For many medicines, genes can influence both how strongly a drug works and how the body processes it. This understanding can support treatment decisions that are more informed and more individualized. More detailed information on this topic is available in the LearnHub.
Drugs influenced by the SLC5A5 gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in guiding how medicines are chosen or dosed, so general medication questions are best discussed with your doctor. SLC5A5 has been studied in thyroid care because it helps cells take up iodine, including radioactive iodine, but this research has not led to routine gene-based prescribing guidance.
History
The history of the SLC5A5 gene is closely tied to the long medical use of iodine in thyroid care. In the early 20th century, doctors learned that thyroid tissue takes up iodine, which later made radioactive iodine scans and treatment possible. Initially understood only through visible traits, later recognized as tied to a specific gene, this uptake system was clarified much more precisely in the 1990s. Researchers identified and cloned the SLC5A5 gene in 1996, linking a long used clinical observation to its genetic basis. From these first observations, research expanded steadily. That work helped explain some inherited thyroid conditions and improved the scientific foundation behind thyroid imaging and radioiodine treatment.