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

CYBB gene

The CYBB gene is responsible for producing the beta chain of the NADPH oxidase enzyme, a vital component of the immune system's defense against infections.

Normal Function

The CYBB gene provides instructions for making the cytochrome b-245, beta chain (also known as p91-phox). This protein serves as a subunit of the NADPH oxidase enzyme complex. It works in tandem with an alpha chain partner (produced from the CYBA gene); both subunits are necessary for the complex to be functional.

NADPH oxidase is primarily active in phagocytes, immune cells that destroy bacteria and fungi. The enzyme also regulates neutrophils to manage the body's inflammatory response. Upon detecting foreign invaders, phagocytes assemble the NADPH oxidase complex, which converts oxygen into reactive oxygen species—such as hydrogen peroxide and hypochlorous acid—to neutralize the threat.

Health Conditions Related to Genetic Changes

Chronic granulomatous disease

More than 650 mutations in the CYBB gene have been linked to chronic granulomatous disease, accounting for approximately 70 percent of all cases of this condition. People with this disorder experience a weakened immune system, leading to recurrent infections and inflammation.

  • Most mutations alter single amino acids or result in an abnormally short, nonfunctional protein.
  • A defective beta chain impairs the function of its alpha chain partner, preventing the NADPH oxidase complex from assembling or functioning correctly.
  • The resulting inability of phagocytes to produce reactive oxygen species leaves individuals vulnerable to persistent infections and excessive inflammation.

Other Names for This Gene

  • CGD91-phox
  • CY24B_HUMAN
  • cytochrome b(558) subunit beta
  • cytochrome b-245 heavy chain
  • cytochrome b-245, beta polypeptide
  • cytochrome b558 subunit beta
  • GP91-1
  • GP91PHOX
  • neutrophil cytochrome b 91 kDa polypeptide
  • p91-PHOX
  • superoxide-generating NADPH oxidase heavy chain subunit

Frequently Asked Questions

The CYBB gene is located on the X chromosome. Males have one X chromosome, so a single pathogenic CYBB mutation results in disease. Females have two X chromosomes; a carrier female usually has one normal copy that compensates, so she is typically asymptomatic but can pass the mutation to 50 % of her children.
Standard prophylaxis includes trimethoprim‑sulfamethoxazole daily to prevent bacterial infections and an oral azole antifungal such as itraconazole or posaconazole to reduce fungal risk. Interferon‑γ injections are sometimes added to boost residual NADPH oxidase activity.
First, a dihydrorhodamine (DHR) flow cytometry test assesses the oxidative burst of neutrophils. If abnormal, next‑step testing is targeted sequencing of the CYBB gene (or a comprehensive CGD panel) to identify the specific mutation.
llogeneic stem cell transplantation is currently the only curative option and has shown high success rates in CYBB‑CGD, especially when performed early. Risks include graft‑versus‑host disease, infection, organ toxicity from conditioning regimens, and transplant‑related mortality, which varies with donor match and patient condition.
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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