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C2 gene

complement C2

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. Alternatively, the dysfunctional complement system may perform partial attacks on invading molecules, which leaves behind foreign fragments that are difficult to distinguish from the body's tissues, so the complement system sometimes attacks the body's own cells. It is likely that other factors, both genetic and environmental, play a role in the variability of the signs and symptoms of complement component 2 deficiency.

More About This Health Condition

Age-related macular degeneration

MedlinePlus Genetics provides information about Age-related macular degeneration

More About This Health Condition

Other Names for This Gene

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

Additional Information & Resources

Tests Listed in the Genetic Testing Registry

Scientific Articles on PubMed

Catalog of Genes and Diseases from OMIM

Gene and Variant Databases


  • Halili MA, Ruiz-Gomez G, Le GT, Abbenante G, Fairlie DP. Complement component C2, inhibiting a latent serine protease in the classical pathway of complement activation. Biochemistry. 2009 Sep 8;48(35):8466-72. doi: 10.1021/bi900679r. Citation on PubMed
  • Jonsson G, Truedsson L, Sturfelt G, Oxelius VA, Braconier JH, Sjoholm AG. Hereditary C2 deficiency in Sweden: frequent occurrence of invasive infection, atherosclerosis, and rheumatic disease. Medicine (Baltimore). 2005 Jan;84(1):23-34. doi: 10.1097/ Citation on PubMed
  • Krishnan V, Xu Y, Macon K, Volanakis JE, Narayana SV. The structure of C2b, a fragment of complement component C2 produced during C3 convertase formation. Acta Crystallogr D Biol Crystallogr. 2009 Mar;65(Pt 3):266-74. doi: 10.1107/S0907444909000389. Epub 2009 Feb 20. Citation on PubMed or Free article on PubMed Central

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.