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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®

Complement gene family

Reviewed June 2010

What are the complement genes?

Genes in the complement family provide instructions for making proteins involved in the complement system, an essential part of the body's immune response. The complement system is composed of more than 20 proteins that work together to destroy foreign invaders (such as bacteria and viruses), trigger inflammation, and remove debris from cells and tissues. This system must be carefully regulated so it targets only unwanted materials and does not attack the body's healthy cells.

Several diseases have been associated with changes in complement genes. Each of these genetic changes typically results in a shortage (deficiency) of a single complement system protein. These deficiencies disrupt the normal activity or regulation of the complement system, often leading to an increased risk of bacterial infection or recurrent episodes of severe swelling (angioedema). Complement system defects have also been found in autoimmune disorders such as systemic lupus erythematosus. Autoimmune disorders occur when the immune system malfunctions and attacks the body's own tissues and organs.

Which genes are included in the complement gene family?

The HUGO Gene Nomenclature Committee (HGNC) provides an index of gene families ( and their member genes.

Genetics Home Reference summarizes the normal function and health implications of these members of the complement gene family: C2, C3, C8A, C8B, CFH, CFHR5, CFI, and ITGB2.

What conditions are related to genes in the complement gene family?

Genetics Home Reference includes these conditions related to genes in the complement gene family:

  • age-related macular degeneration
  • atypical hemolytic-uremic syndrome
  • C3 glomerulopathy
  • complement component 2 deficiency
  • complement component 8 deficiency
  • complement factor I deficiency
  • leukocyte adhesion deficiency type 1

Where can I find additional information about the complement gene family?

You may find the following resources about the complement gene family helpful.

  • The Merck Manual for Healthcare Professionals (
  • MedlinePlus Encyclopedia: Complement (

What glossary definitions help with understanding the complement gene family?

autoimmune ; bacteria ; cancer ; deficiency ; factor I ; immune response ; immune system ; infection ; inflammation ; innate immunity ; Mb ; protein ; subunit

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


These sources were used to develop the Genetics Home Reference summary for the complement gene family.

  • Immunobiology (fifth edition, 2001): The Complement System and Innate Immunity ( (U.S. National Library of Medicine)
  • Rus H, Cudrici C, Niculescu F. The role of the complement system in innate immunity. Immunol Res. 2005;33(2):103-12. Review. (
  • Thurman JM, Holers VM. The central role of the alternative complement pathway in human disease. J Immunol. 2006 Feb 1;176(3):1305-10. Review. (
  • Chen M, Daha MR, Kallenberg CG. The complement system in systemic autoimmune disease. J Autoimmun. 2010 May;34(3):J276-86. doi: 10.1016/j.jaut.2009.11.014. Epub 2009 Dec 11. Review. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: June 2010
Published: February 1, 2016