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

TPO gene

The TPO gene provides instructions for making the thyroid peroxidase enzyme, which is essential for the production of thyroid hormones that regulate growth and metabolism.

Normal Function

The TPO gene provides instructions for making an enzyme called thyroid peroxidase. This enzyme plays a central role in the function of the thyroid gland, a butterfly-shaped tissue in the lower neck. Thyroid peroxidase assists the chemical reaction that adds iodine to a protein called thyroglobulin, a critical step in generating thyroid hormones. Thyroid hormones play an important role in regulating growth, brain development, and the rate of chemical reactions in the body (metabolism).

To function properly, thyroid peroxidase must be located in the cell membrane of certain thyroid cells, called follicular cells. Thyroid peroxidase has several different versions (isoforms), which vary by size and location within the cell. Some versions do not function because they are not located in the cell membrane.

Health Conditions Related to Genetic Changes

Congenital hypothyroidism

TPO gene mutations can cause congenital hypothyroidism, a condition characterized by abnormally low levels of thyroid hormones starting from birth. The TPO gene mutations involved in this condition delete, add, or change DNA building blocks (base pairs) in the TPO gene.

  • Some mutations lead to an abnormally small thyroid peroxidase enzyme that breaks apart before it can be inserted into the cell membrane.
  • Other mutations change the enzyme's 3-dimensional shape, preventing it from functioning properly within the cell membrane.

Without functional thyroid peroxidase, iodine taken up by the thyroid gland is not added to thyroglobulin. As a result, the production of thyroid hormones is absent or reduced, leading to the features of congenital hypothyroidism. In most affected individuals, the thyroid gland is enlarged (goiter) in an attempt to compensate for reduced hormone production. Because cases caused by TPO gene mutations result from a disruption of thyroid hormone synthesis, they are classified as thyroid dyshormonogenesis.

Frequently Asked Questions

TPO antibodies indicate an autoimmune response against the thyroid peroxidase protein and are common in Hashimoto’s thyroiditis and Graves disease. They do not imply a germline TPO gene mutation. Genetic testing for TPO is only relevant when congenital hypothyroidism or a familial thyroid disorder is suspected.
Yes, levothyroxine remains the mainstay of treatment. However, dosing may need close adjustment because some TPO mutations produce unstable enzyme that can lead to fluctuating hormone levels. Regular monitoring of TSH, free T4, and growth parameters is essential, especially during the first years of life.
Heterozygous carriers often have normal thyroid hormone production, but they may be at slightly increased risk for later‑onset autoimmune thyroid disease. Routine genetic testing of asymptomatic children is not required, but periodic thyroid function screening (TSH, free T4) during childhood and adolescence is prudent.
Newborn screening programs measure blood TSH (and sometimes T4) levels within the first few days of life. An abnormal result prompts confirmatory serum testing and thyroid imaging. If congenital hypothyroidism is confirmed, molecular testing for TPO mutations (among other genes) may be performed, especially when the gland appears structurally normal, to determine the underlying cause.
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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