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CYP2R1 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

CYP2R1 gene

The CYP2R1 gene is responsible for producing an enzyme that initiates the conversion of vitamin D into its active form, calcitriol.

Normal Function

The CYP2R1 gene provides instructions for an enzyme in the cytochrome P450 family. This enzyme performs the first of two reactions required to convert vitamin D into its active form, calcitriol. Active vitamin D is essential for maintaining the balance of calcium and phosphate in the blood, which strengthens bones and teeth and regulates the absorption of these minerals from the intestines.

Health Conditions Related to Genetic Changes

Vitamin D-dependent rickets

Pathogenic variants in the CYP2R1 gene cause vitamin D-dependent rickets type 1B (VDDR1B). This condition results in soft, weak bones that are prone to fractures and deformities.

Common features of this disorder include:

  • Abnormally curved (bowed) legs
  • Enlargement of the skull
  • Enlargement of the wrists
  • Enlargement of the ends of the ribs

These variants produce an enzyme that does not function properly, disrupting the conversion of vitamin D to calcitriol. This leads to impaired intestinal absorption of calcium and phosphate, resulting in the weakened bones characteristic of the condition.

Other Names for This Gene

  • vitamin D 25-hydroxylase

Frequently Asked Questions

If Vitamin D-dependent rickets type 1B is left untreated, the persistent inability to absorb calcium and phosphate leads to severe skeletal deformities. In childhood, this manifests as bowed legs, enlarged wrists, and skull abnormalities. If not corrected, these deformities can become permanent, leading to chronic pain, reduced mobility, and a significantly increased risk of fractures throughout life. Additionally, untreated hypocalcemia (low blood calcium) can cause serious neurological complications, including seizures and muscle spasms. Early diagnosis and lifelong management with calcitriol and calcium supplements are critical to preventing these irreversible structural and neurological damages.
Yes, calcium supplements are usually required alongside calcitriol for VDDR1B. Calcitriol increases the body's ability to absorb calcium from the intestines, but if dietary calcium intake is insufficient, the body may still lack the raw material needed to strengthen bones. Your doctor will likely prescribe calcium supplements to ensure adequate levels. Regular monitoring is essential to prevent complications. You will need frequent blood tests to check calcium, phosphate, and parathyroid hormone (PTH) levels. This monitoring helps adjust the calcitriol dose to avoid hypercalcemia (too much calcium), which can damage the kidneys and heart, while ensuring the rickets is effectively treated.
No, standard over-the-counter vitamin D supplements (cholecalciferol or ergocalciferol) are ineffective for treating Vitamin D-dependent rickets type 1B (VDDR1B). This condition is caused by a defect in the CYP2R1 enzyme, which is required to convert vitamin D into its next active stage. Because the enzyme is non-functional, the body cannot process standard vitamin D into a usable form. Patients with VDDR1B require prescription calcitriol (active vitamin D), which bypasses the defective step in the metabolic pathway. Taking high doses of standard vitamin D will not correct the bone issues and may lead to toxicity without providing the necessary active hormone.
The key difference lies in the cause and the treatment response. Nutritional vitamin D deficiency is caused by insufficient intake or sun exposure, and it responds well to standard vitamin D supplements. In contrast, VDDR1B is a genetic disorder where the body cannot process vitamin D due to a faulty CYP2R1 enzyme. A child with VDDR1B may have normal or even high levels of standard vitamin D in their blood but still suffer from rickets because the active form (calcitriol) is missing. Diagnosis typically requires genetic testing or measuring low calcitriol levels despite adequate vitamin D intake, distinguishing it from simple dietary deficiency.
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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