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PAX8 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

PAX8 gene

The PAX8 gene provides instructions for making a transcription factor essential for the development of the thyroid gland and kidneys.

Normal Function

The PAX8 gene belongs to a family of genes that play critical roles in the formation of tissues and organs during embryonic development. PAX genes provide instructions for making proteins that attach to specific areas of DNA to control the activity of particular genes; these proteins are called transcription factors.

During embryonic development, the PAX8 protein activates genes involved in the formation of the kidney and the thyroid gland. The thyroid gland releases hormones that regulate growth, brain development, and metabolism. After birth, the PAX8 protein continues to regulate genes involved in the production of thyroid hormones.

Health Conditions Related to Genetic Changes

Congenital hypothyroidism

At least 15 mutations in this gene cause congenital hypothyroidism, a condition characterized by abnormally low levels of thyroid hormones from birth. Features include:

  • Thyroid dysgenesis: The thyroid gland is unusually small, suggesting that PAX8 mutations disrupt the growth or survival of thyroid cells during development.
  • Reduced function: Nearly all PAX8 mutations prevent the protein from effectively binding to DNA, preventing it from regulating necessary genes.

Tumors

The PAX8 gene is sometimes involved in the formation of thyroid tumors, including follicular adenomas (noncancerous) and follicular carcinomas (cancerous). In some cases, the PAX8 gene on chromosome 2 is fused with the PPARG gene on chromosome 3 due to a chromosomal translocation. This fusion is thought to disrupt the normal control of cell division or trigger activities that promote tumor formation.

Frequently Asked Questions

Certain PAX8 alterations, especially those that create fusion genes (e.g., PAX8‑PPARG), are linked to follicular thyroid adenomas and carcinomas. Adults with a pathogenic PAX8 variant should have an annual neck ultrasound to detect nodules early, and any suspicious nodule should be evaluated with fine‑needle aspiration. Routine thyroid function tests are also advised, as changes may signal tumor activity.
Patients with hypothyroidism due to PAX8 mutations should take levothyroxine on an empty stomach, ideally 30‑60 minutes before breakfast, to ensure optimal absorption. Calcium or iron supplements should be spaced at least 4 hours apart from the hormone. A diet sufficient in iodine is important, but excessive iodine (e.g., from kelp supplements) can interfere with thyroid hormone synthesis and should be avoided. Regular monitoring of thyroid hormone levels guides dose adjustments.
Testing for PAX8 mutations can be offered, especially if thyroid dysgenesis is seen on ultrasound or if there is a family history of thyroid disorders. A positive result confirms a genetic cause but does not change the immediate need for levothyroxine replacement, which is started promptly to prevent neurodevelopmental delay. Knowing the mutation helps with family counseling and may guide monitoring for other renal anomalies that can accompany some PAX8 variants.
Most pathogenic PAX8 variants follow an autosomal dominant pattern, so each first‑degree relative has a 50 % chance of inheriting the mutation. However, penetrance can be variable—some carriers have normal thyroid function while others develop hypothyroidism or structural thyroid anomalies. Genetic testing and baseline thyroid function tests (TSH, free T4) are recommended before conception, and a genetic counselor can discuss reproductive options such as preimplantation genetic testing.
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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