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CYP21A2 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

CYP21A2 gene

The CYP21A2 gene provides instructions for the 21-hydroxylase enzyme, which is essential for producing hormones that regulate blood sugar, inflammation, and blood pressure.

Normal Function

The CYP21A2 gene provides instructions for making an enzyme called 21-hydroxylase, which is part of the cytochrome P450 family. These enzymes assist with reactions that break down drugs and help produce cholesterol, certain hormones, and fats (lipids).

The 21-hydroxylase enzyme is found in the adrenal glands and plays a role in producing two key hormones:

  • Cortisol: Helps maintain blood sugar (glucose) levels, protects the body from stress, and suppresses inflammation.
  • Aldosterone: Often called the "salt-retaining hormone," it regulates the amount of salt retained by the kidneys, which affects fluid levels and blood pressure.

Health Conditions Related to Genetic Changes

21-hydroxylase deficiency

More than 100 mutations in the CYP21A2 gene have been found to cause 21-hydroxylase deficiency. Some mutations result from an exchange of genetic material between the CYP21A2 gene and a similar but nonfunctional piece of DNA called a pseudogene, a process known as gene conversion. Other mutations involve single amino acid changes or deletions/insertions of DNA.

Researchers have described three forms of 21-hydroxylase deficiency:

  • Salt-wasting type: Mutations result in a completely nonfunctional enzyme.
  • Simple virilizing type: Mutations allow for the production of low levels of functional enzyme.
  • Non-classic type: Mutations result in the production of reduced amounts of the enzyme, but more than the other types.

All types of 21-hydroxylase deficiency interfere with the production of cortisol and aldosterone. The substances that are usually used to form these hormones instead build up in the adrenal glands and are converted to androgens (male sex hormones). This excess production of androgens leads to abnormalities of sexual development.

Frequently Asked Questions

The distinction relies on hormone levels: salt‑wasting shows very low cortisol and aldosterone with high 17‑hydroxyprogesterone and severe electrolyte imbalance; simple virilizing has normal electrolytes but elevated androgens; non‑classic presents with mild enzyme deficiency, normal electrolytes, and often later‑onset symptoms like acne or hirsutism. Genetic testing confirms the specific CYP21A2 mutation and helps predict severity.
dults usually need low‑dose glucocorticoid replacement to suppress excess androgen production, especially during stress or illness. Monitoring hormone levels every 6–12 months, adjusting medication as needed, and counseling on lifestyle factors (e.g., avoiding excessive alcohol) are key. Regular gynecologic or reproductive counseling may be advised for women with menstrual irregularities.
Newborns may exhibit poor feeding, vomiting, dehydration, low blood sugar, or a salt‑crusted rash. In males, ambiguous genitalia or enlarged clitoris may be noted. Early screening with a heel‑stick blood test for 17‑hydroxyprogesterone can detect the condition before severe complications arise.
Couples can undergo carrier testing to confirm both parents’ status. For future pregnancies, options include chorionic villus sampling or amniocentesis for fetal DNA testing, or pre‑implantation genetic testing (PGT‑M) during in‑vitro fertilization to select embryos without the pathogenic variant.===
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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