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

CYB gene family

Reviewed August 2012

What are the CYB genes?

Genes in the CYB gene family provide instructions for producing a group of proteins called cytochrome b proteins. In humans, the CYB gene family contains six functional genes and six pseudogenes (similar sequences of genetic material that do not provide instructions for making proteins). Cytochrome b proteins are produced in the immune system, brain, liver, and other tissues throughout the body. They play a role in various pathways that form new molecules by transferring negatively charged particles called electrons from one molecule to another. The new molecules that are formed are necessary for the pathway to continue.

The CYB gene family member expressed in the liver is important in the production of hemoglobin, which is the protein in red blood cells that carries oxygen to cells throughout the body. The cytochrome b protein produced in the brain plays a role in transmitting nerve signals between cells. The cytochrome b proteins produced in the immune system help fight off foreign invaders, such as bacteria and fungi.

Diseases caused by mutations in CYB genes usually occur because a key molecule in an important pathway is missing. The inability of the abnormal cytochrome b protein to transfer electrons leads to a shortage of the new molecule. A lack of this molecule disrupts the pathway and prevents it from moving forward. The features of the disease depend on the tissue where the protein is active. For example, mutations in the CYBB gene, which provides instruction for making a cytochrome b protein that is found in immune cells, lead to an immune deficiency disorder called chronic granulomatous disease. This condition results in an increased risk of developing infections caused by bacterial and fungal invaders.

Which genes are included in the CYB 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 CYB gene family: CYBA, CYBB, and MT-CYB.

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

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

  • chronic granulomatous disease
  • mitochondrial complex III deficiency

What glossary definitions help with understanding the CYB gene family?

bacteria ; charged particles ; chronic ; deficiency ; expressed ; gene ; granulomatous ; hemoglobin ; immune system ; molecule ; oxygen ; protein ; tissue

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 CYB gene family.

  • Vargas JD, Herpers B, McKie AT, Gledhill S, McDonnell J, van den Heuvel M, Davies KE, Ponting CP. Stromal cell-derived receptor 2 and cytochrome b561 are functional ferric reductases. Biochim Biophys Acta. 2003 Sep 23;1651(1-2):116-23. (
  • Castresana J. Cytochrome b phylogeny and the taxonomy of great apes and mammals. Mol Biol Evol. 2001 Apr;18(4):465-71. (
  • Sumimoto H. Structure, regulation and evolution of Nox-family NADPH oxidases that produce reactive oxygen species. FEBS J. 2008 Jul;275(13):3249-77. doi: 10.1111/j.1742-4658.2008.06488.x. Epub 2008 May 30. Review. Erratum in: FEBS J. 2008 Aug;275(15):3984. (
  • Deng B, Parthasarathy S, Wang W, Gibney BR, Battaile KP, Lovell S, Benson DR, Zhu H. Study of the individual cytochrome b5 and cytochrome b5 reductase domains of Ncb5or reveals a unique heme pocket and a possible role of the CS domain. J Biol Chem. 2010 Sep 24;285(39):30181-91. doi: 10.1074/jbc.M110.120329. Epub 2010 Jul 14. (
  • Legros F, Chatzoglou E, Frachon P, Ogier De Baulny H, Laforêt P, Jardel C, Godinot C, Lombès A. Functional characterization of novel mutations in the human cytochrome b gene. Eur J Hum Genet. 2001 Jul;9(7):510-8. (


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: August 2012
Published: February 1, 2016