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CYP27B1 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

CYP27B1 gene

The CYP27B1 gene is responsible for the final activation of vitamin D, and mutations in this gene can lead to weakened bones and rickets.

Normal Function

The CYP27B1 gene provides instructions for making an enzyme that is part of the cytochrome P450 family. This enzyme is found in the mitochondria and carries out the second of two reactions required to convert vitamin D to its active form, calcitriol.

Vitamin D, obtained from food or produced in the skin via sun exposure, is essential for maintaining the proper balance of calcium and phosphate in the blood. These minerals are necessary for the development and strengthening of bones and teeth. The active form of vitamin D regulates the absorption of these minerals from the intestines into the bloodstream.

Health Conditions Related to Genetic Changes

Vitamin D-dependent rickets

Pathogenic variants in the CYP27B1 gene cause a specific form of vitamin D deficiency called vitamin D-dependent rickets type 1A (VDDR1A). This condition results in soft, weak bones that are prone to fracture and misshapen growth.

  • Physical Features: A common feature is abnormally curved (bowed) legs. Affected individuals may also experience enlargement of the skull, the wrists, and the ends of the ribs.
  • Biological Impact: Pathogenic variants produce a non-functional version of the enzyme, which disrupts the conversion of vitamin D to calcitriol. This impairs the intestinal absorption of calcium and phosphate, leading to decreased blood levels of these minerals and subsequent bone weakness.

Genomic Location

The CYP27B1 gene is found on chromosome 12.

Frequently Asked Questions

Yes, VDDR1A is an autosomal recessive condition. Parents who are carriers have one functional copy of the CYP27B1 gene and one mutated copy. Because one functional copy is usually sufficient to produce enough enzyme for normal vitamin D activation, carriers typically do not exhibit any signs of rickets or bone weakness. Genetic testing can confirm carrier status for family planning purposes.
The key difference is that in vitamin D-dependent rickets type 1A (VDDR1A), the body cannot convert vitamin D into its active form, calcitriol, regardless of how much vitamin D is consumed or produced by sun exposure. In nutritional deficiency, the body has the functional enzymes to activate vitamin D but lacks sufficient raw material. Therefore, standard high-dose vitamin D supplementation often fails to correct the bone issues in VDDR1A, whereas it resolves nutritional deficiency.
Treatment requires the direct administration of calcitriol, the active form of vitamin D, because the body cannot produce it. This is distinct from standard vitamin D (cholecalciferol) supplements. Additionally, calcium and phosphate supplements are often necessary to support bone mineralization. This treatment is typically lifelong, as the genetic defect in the CYP27B1 gene is permanent and does not resolve with age.
With early diagnosis and consistent treatment with calcitriol and mineral supplements, the prognosis is generally good. Bone density can normalize, and growth can proceed at a near-normal rate. However, some individuals may still experience mild skeletal abnormalities, such as slightly shorter stature or residual bowing of the legs, depending on how long the condition went untreated before diagnosis. Regular monitoring of bone health and mineral levels is essential to optimize outcomes.
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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