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URL of this page: https://medlineplus.gov/genetics/gene/c8a/

C8A gene

complement C8 alpha chain

Normal Function

The C8A gene provides instructions for making one piece, the alpha subunit, of a protein complex called complement component 8. The alpha subunit is linked to another piece of the complex called the gamma subunit (produced from the C8G gene). These two proteins interact with the beta subunit (produced from the C8B gene) to form complement component 8.

Complement component 8 aids in 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, trigger inflammation, and remove debris from cells and tissues. Complement component 8 combines with several other complement proteins to form the membrane attack complex (MAC), which inserts itself in the outer membrane of bacterial cells. This complex creates a hole (pore) in the membrane, which kills the bacterium. This part of the immune response appears to be especially important for fighting infection by bacteria in the Neisseria genus.

Health Conditions Related to Genetic Changes

Complement component 8 deficiency

At least two mutations in the C8A gene have been found to cause complement component 8 deficiency type I. This condition is an immune system disorder, known as an immunodeficiency, in which the immune system is not able to protect the body effectively from foreign invaders such as bacteria. People with complement component 8 deficiency have a significantly increased risk of developing recurrent infections, particularly by Neisseria meningitidis, which causes meningitis, a serious condition that involves inflammation of the membranes surrounding the brain and spinal cord.

Mutations in the C8A gene alter the blueprint for protein production; if produced, the abnormally short alpha subunit is likely broken down quickly. The resulting shortage of this protein impairs formation of complement component 8. Deficiency of this component prevents formation of membrane attack complexes. Without this part of the immune response, affected individuals are prone to infection, particularly by Neisseria bacteria.

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Other Names for This Gene

  • complement component 8 alpha subunit
  • complement component 8 subunit alpha
  • complement component 8, alpha polypeptide
  • complement component C8 alpha chain preproprotein

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

References

  • Bubeck D. The making of a macromolecular machine: assembly of the membrane attack complex. Biochemistry. 2014 Apr 1;53(12):1908-15. doi: 10.1021/bi500157z. Epub 2014 Mar 18. Citation on PubMed
  • Kaufman KM, Snider JV, Spurr NK, Schwartz CE, Sodetz JM. Chromosomal assignment of genes encoding the alpha, beta, and gamma subunits of human complement protein C8: identification of a close physical linkage between the alpha and the beta loci. Genomics. 1989 Oct;5(3):475-80. doi: 10.1016/0888-7543(89)90012-8. Citation on PubMed
  • Kojima T, Horiuchi T, Nishizaka H, Fukumori Y, Amano T, Nagasawa K, Niho Y, Hayashi K. Genetic basis of human complement C8 alpha-gamma deficiency. J Immunol. 1998 Oct 1;161(7):3762-6. Citation on PubMed
  • Merle NS, Noe R, Halbwachs-Mecarelli L, Fremeaux-Bacchi V, Roumenina LT. Complement System Part II: Role in Immunity. Front Immunol. 2015 May 26;6:257. doi: 10.3389/fimmu.2015.00257. eCollection 2015. Citation on PubMed or Free article on PubMed Central
  • Rosa DD, Pasqualotto AC, de Quadros M, Prezzi SH. Deficiency of the eighth component of complement associated with recurrent meningococcal meningitis--case report and literature review. Braz J Infect Dis. 2004 Aug;8(4):328-30. doi: 10.1590/s1413-86702004000400010. Epub 2004 Nov 19. Citation on PubMed

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