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C2 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

C2 gene

The C2 gene provides instructions for making the complement component 2 protein, which is essential for activating the complement system's immune response.

Normal Function

The C2 gene provides instructions for making the complement component 2 protein. This protein helps regulate a part of the body's immune response known as the complement system. The complement system is a group of proteins that work together to destroy foreign invaders (such as bacteria and viruses), trigger inflammation, and remove debris from cells and tissues. When a foreign invader is detected, the complement pathway is turned on (activated) and the complement component 2 protein attaches (binds) to a similar protein called complement component 4. Together, these proteins form a complex called C3 convertase, which triggers further activation of the pathway, allowing the proteins of the complement system to participate in an immune response.

Health Conditions Related to Genetic Changes

Complement component 2 deficiency

At least five mutations in the C2 gene have been found to cause complement component 2 deficiency. This disorder reduces the normal function of the immune system, resulting in an increased risk for infections and autoimmune disorders such as systemic lupus erythematosus (SLE). Autoimmune disorders occur when the immune system malfunctions and attacks the body's tissues and organs.

More than 90 percent of people with complement component 2 deficiency have a mutation that deletes 28 DNA building blocks (nucleotides) from the C2 gene. This mutation prevents the production of any complement component 2 protein. Without this protein to form C3 convertase, activation of the complement system is stalled. As a result, the complement system's ability to fight infections is diminished. It is unclear how complement component 2 deficiency leads to increased susceptibility to autoimmune disorders. Researchers speculate that the dysfunctional complement system is unable to distinguish what it should attack, and it sometimes attacks normal tissues, leading to autoimmunity.

Age-related macular degeneration

MedlinePlus Genetics provides information about Age-related macular degeneration.

Other Names for This Gene

  • ARMD14
  • C3/C5 convertase
  • CO2
  • complement component 2
  • complement component C2

Frequently Asked Questions

clinician orders a serum complement activity assay, usually a CH50 or specific C2 level test. Bring a recent medical history, list of medications, and any recent infections. Fast is not required, but avoid high‑dose steroids or immunosuppressants 48 hours before the test if possible, as they can lower complement levels.
You are especially vulnerable to encapsulated bacteria like Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis. Vaccinations against these organisms (PCV13, PPSV23, Hib, and meningococcal vaccines) are essential. Use prophylactic antibiotics only when prescribed by a clinician, and keep a clean environment to reduce exposure to pathogens.
Patients often notice frequent, recurrent bacterial infections such as sinusitis, pneumonia, or skin abscesses. They may also experience unexplained fevers or swollen lymph nodes that resolve only with antibiotics. If infections recur despite treatment, a blood test for complement levels can confirm a C2 deficiency.
Yes, about 90% of people with C2 deficiency develop autoimmune conditions such as systemic lupus erythematosus (SLE). Regular monitoring for autoimmune symptoms—joint pain, rash, fatigue—helps early detection. If SLE develops, treatment typically involves immunosuppressive medications (e.g., hydroxychloroquine, corticosteroids) guided by a rheumatologist.===
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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