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SLC5A5 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

SLC5A5 gene

The SLC5A5 gene provides instructions for making the sodium-iodide symporter, a protein essential for transporting iodide into the thyroid gland to produce thyroid hormones.

Normal Function

The SLC5A5 gene provides instructions for making a protein called sodium (Na)-iodide symporter or NIS. This protein transports iodide, a negatively charged version of iodine, into cells of certain tissues. The NIS protein is found primarily in the thyroid gland, a butterfly-shaped tissue in the lower neck. The thyroid gland produces and releases iodide-containing thyroid hormones that play an important role in regulating growth, brain development, and the rate of chemical reactions in the body (metabolism).

The NIS protein supports an efficient system that ensures iodine from the diet accumulates in the thyroid gland for the production of thyroid hormones. This system depends on the NIS protein being positioned in the cell membrane, so it can transport iodide from the bloodstream into particular thyroid cells called follicular cells.

In addition to the thyroid gland, the NIS protein is found in breast tissue during milk production (lactation), ovaries, salivary glands, certain stomach cells (parietal cells), tear glands (lacrimal glands), and a part of the brain called the choroid plexus. During lactation, the NIS protein transports iodide into the milk to supply breast-fed infants with this critical component of thyroid hormones.

Health Conditions Related to Genetic Changes

Congenital hypothyroidism

Several SLC5A5 gene mutations have been identified in people with congenital hypothyroidism, a condition characterized by abnormally low levels of thyroid hormones starting from birth. About half of these mutations delete part of the SLC5A5 gene or disrupt protein production, resulting in an abnormally small, nonfunctional protein. The remaining mutations change one of the building blocks (amino acids) used to make the NIS protein. Some amino acid substitutions prevent the NIS protein from being positioned in the cell membrane, disabling iodide transport. Other amino acid substitutions do not affect the membrane location of the NIS protein but change the protein's 3-dimensional shape, which impairs its function.

SLC5A5 gene mutations reduce or prevent iodide transport. As a result, the thyroid gland cannot accumulate iodide efficiently, which decreases the production of thyroid hormones. The signs and symptoms of congenital hypothyroidism associated with these gene mutations range from mild to severe depending on the level of hormone production remaining. In many cases, the thyroid gland is enlarged (goiter) in an attempt to compensate for reduced hormone production. Because cases caused by SLC5A5 gene mutations are due to a disruption of thyroid hormone synthesis, they are classified as thyroid dyshormonogenesis.

Other Names for This Gene

  • NIS
  • SC5A5_HUMAN
  • sodium-iodide symporter
  • solute carrier family 5 (sodium/iodide cotransporter), member 5

Frequently Asked Questions

While iodine is essential for thyroid hormone production, the issue in SLC5A5-related congenital hypothyroidism is a defect in the transport of iodide into the thyroid gland, not necessarily a lack of dietary iodine. Therefore, simply increasing iodine intake through diet or supplements usually won't correct the underlying problem. The primary treatment remains thyroid hormone replacement. However, ensuring adequate, but not excessive, iodine intake is still important for overall thyroid health.
Congenital hypothyroidism caused by an SLC5A5 mutation is treated with lifelong thyroid hormone replacement therapy, usually with a synthetic form of thyroxine (levothyroxine). Early diagnosis and consistent treatment are critical for normal brain development and growth. With proper and timely treatment, children can achieve normal physical and intellectual development.
SLC5A5-related congenital hypothyroidism is typically inherited in an autosomal recessive pattern. This means both parents must carry a copy of the mutated gene to pass it on to their child, even if they don't have the condition themselves. If one child is affected, there is a 25% chance with each subsequent pregnancy that another child will inherit two copies of the mutated gene and develop the condition. Genetic counseling can help families understand their specific risks and options for future pregnancies.
Newborns with congenital hypothyroidism often show subtle signs that can be difficult to recognize immediately. These may include prolonged jaundice, poor feeding, lethargy, constipation, a hoarse cry, a large tongue (macroglossia), and a puffy face. Newborn screening programs are crucial for early detection, as untreated congenital hypothyroidism can lead to severe developmental problems.
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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