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CYP17A1 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

CYP17A1 gene

The CYP17A1 gene provides instructions for an enzyme essential to the production of steroid hormones, including sex hormones and those that regulate blood pressure and stress responses.

Normal Function

The CYP17A1 gene encodes a member of the cytochrome P450 enzyme family, which is vital for the synthesis of steroid hormones. These hormones include:

  • Sex hormones (testosterone and estrogen), necessary for sexual development and reproduction.
  • Mineralocorticoids, which regulate the body's salt and water balance.
  • Glucocorticoids, which manage blood sugar levels and the body's stress response.

The CYP17A1 enzyme performs two key chemical reactions: 17 alpha-hydroxylase activity (converting pregnenolone and progesterone into precursors for glucocorticoids and sex hormones) and 17,20-lyase activity (converting precursors into DHEA, a critical step in sex hormone production).

Health Conditions Related to Genetic Changes

17 alpha-hydroxylase/17,20-lyase deficiency

Mutations in the CYP17A1 gene can cause 17 alpha-hydroxylase/17,20-lyase deficiency, a condition affecting hormone-producing glands that leads to hypertension and abnormal sexual development.

  • Glucocorticoid impairment: A lack of 17 alpha-hydroxylase activity prevents the production of glucocorticoids, causing the body to produce excess mineralocorticoids, which leads to high blood pressure (hypertension) and low blood potassium (hypokalemia).
  • Sex hormone impairment: A lack of 17,20-lyase activity disrupts sex hormone production. In females, this affects the development of reproductive organs and secondary sex characteristics. In chromosomal males, it leads to abnormal development of external genitalia.

Other disorders

Rare mutations can cause isolated 17,20-lyase deficiency. These mutations specifically affect the enzyme's 17,20-lyase function while leaving 17 alpha-hydroxylase activity intact. Consequently, affected individuals experience abnormal sexual development and delayed or absent puberty without the hypertension or hypokalemia associated with the combined deficiency.

Other Names for This Gene

  • 17-alpha-hydroxyprogesterone aldolase
  • CPT7
  • CYP17
  • CYPXVII
  • cytochrome P450 17A1
  • cytochrome p450 XVIIA1
  • cytochrome P450, family 17, subfamily A, polypeptide 1
  • cytochrome P450, subfamily XVII (steroid 17-alpha-hydroxylase), adrenal hyperplasia
  • cytochrome P450-C17
  • cytochrome P450c17
  • P450C17
  • S17AH
  • steroid 17-alpha-hydroxylase/17,20 lyase precursor
  • steroid 17-alpha-monooxygenase

Frequently Asked Questions

Yes. A low‑sodium diet (<2 g/day) reduces volume overload, while potassium‑rich foods (bananas, spinach, beans) help counteract hypokalemia. Regular blood‑pressure monitoring, avoiding high‑salt snacks, and staying hydrated are practical steps that complement medical therapy.===
In the first weeks of life, parents may notice persistent high blood pressure, low potassium levels, salt craving, and in genetic males, ambiguous genitalia or under‑developed external genitalia. Females may show delayed or absent breast development and lack of pubic hair. These signs prompt early evaluation for the enzyme deficiency.
Diagnosis starts with a hormone panel: low 17‑hydroxyprogesterone, low cortisol, high ACTH, low sex steroids, and elevated mineralocorticoids (aldosterone). A 24‑hour urinary free cortisol and 17‑hydroxyprogesterone can confirm the block. Genetic testing for CYP17A1 mutations is definitive, and adrenal imaging may be done to rule out other causes of hypertension.
Combined deficiency is treated with glucocorticoid replacement (hydrocortisone or prednisone) to suppress ACTH and reduce mineralocorticoid excess, plus antihypertensives and potassium supplementation. Isolated 17,20‑lyase deficiency requires glucocorticoids to control mineralocorticoids and sex‑hormone replacement (estrogen/progesterone for females, testosterone for males) to induce puberty and maintain secondary sexual characteristics.
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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