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

CYP gene family

Reviewed March 2008

What are the CYP genes?

Enzymes produced from the cytochrome P450 genes are involved in the formation (synthesis) and breakdown (metabolism) of various molecules and chemicals within cells. Cytochrome P450 enzymes play a role in the synthesis of many molecules including steroid hormones, certain fats (cholesterol and other fatty acids), and acids used to digest fats (bile acids). Additional cytochrome P450 enzymes metabolize external substances, such as medications that are ingested, and internal substances, such as toxins that are formed within cells. There are approximately 60 CYP genes in humans.

Cytochrome P450 enzymes are primarily found in liver cells but are also located in cells throughout the body. Within cells, cytochrome P450 enzymes are located in a structure involved in protein processing and transport (endoplasmic reticulum) and the energy-producing centers of cells (mitochondria). The enzymes found in mitochondria are generally involved in the synthesis and metabolism of internal substances, while enzymes in the endoplasmic reticulum usually metabolize external substances, primarily medications and environmental pollutants.

Common variations (polymorphisms) in cytochrome P450 genes can affect the function of the enzymes. The effects of polymorphisms are most prominently seen in the breakdown of medications. Depending on the gene and the polymorphism, drugs can be metabolized quickly or slowly. If a cytochrome P450 enzyme metabolizes a drug slowly, the drug stays active longer and less is needed to get the desired effect. A drug that is quickly metabolized is broken down sooner and a higher dose might be needed to be effective. Cytochrome P450 enzymes account for 70 percent to 80 percent of enzymes involved in drug metabolism.

Each cytochrome P450 gene is named with CYP, indicating that it is part of the cytochrome P450 gene family. The gene is also given a number associated with a specific group within the gene family, a letter representing the gene's subfamily, and a number assigned to the specific gene within the subfamily. For example, the cytochrome P450 gene that is in group 27, subfamily A, gene 1 is written as CYP27A1.

Diseases caused by mutations in cytochrome P450 genes typically involve the buildup of substances in the body that are harmful in large amounts or that prevent other necessary molecules from being produced.

Which genes are included in the CYP 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 CYP gene family: CYP1B1, CYP2C9, CYP2C19, CYP4V2, CYP11B1, CYP11B2, CYP19A1, CYP21A2, CYP27A1, CYP27B1, and TBXAS1.

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

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

  • 21-hydroxylase deficiency
  • aromatase deficiency
  • aromatase excess syndrome
  • autoimmune Addison disease
  • Bietti crystalline dystrophy
  • breast cancer
  • cerebrotendinous xanthomatosis
  • clopidogrel resistance
  • congenital adrenal hyperplasia due to 11-beta-hydroxylase deficiency
  • corticosterone methyloxidase deficiency
  • early-onset glaucoma
  • familial hyperaldosteronism
  • Ghosal hematodiaphyseal dysplasia
  • multiple sclerosis
  • Peters anomaly
  • vitamin D-dependent rickets
  • warfarin sensitivity

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

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

  • Biochemistry (fifth edition, 2002): The Cytochrome P450 System is Widespread and Performs a Protective Function (
  • Indiana University: Cytochrome P450 Drug-Interaction Table (
  • Human Cytochrome P450 (CYP) Allele Nomenclature Committee (
  • Biochemistry (fifth edition, 2002): Cytochrome P450 Mechanism (

What glossary definitions help with understanding the CYP gene family?

acids ; bile ; breakdown ; cholesterol ; cytochrome P450 ; endoplasmic reticulum ; enzyme ; fatty acids ; gene ; metabolism ; mitochondria ; pharmacogenetics ; polymorphism ; protein ; synthesis

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 CYP gene family.

  • Nebert DW, Russell DW. Clinical importance of the cytochromes P450. Lancet. 2002 Oct 12;360(9340):1155-62. Review. (
  • Wijnen PA, Op den Buijsch RA, Drent M, Kuijpers PM, Neef C, Bast A, Bekers O, Koek GH. Review article: The prevalence and clinical relevance of cytochrome P450 polymorphisms. Aliment Pharmacol Ther. 2007 Dec;26 Suppl 2:211-9. doi: 10.1111/j.1365-2036.2007.03490.x. Review. Erratum in: Aliment Pharmacol Ther. 2009 Feb 1;29(3):350. Kuipers, P M J C [corrected to Kuijpers, P M J C]. (
  • Nelson DR, Zeldin DC, Hoffman SM, Maltais LJ, Wain HM, Nebert DW. Comparison of cytochrome P450 (CYP) genes from the mouse and human genomes, including nomenclature recommendations for genes, pseudogenes and alternative-splice variants. Pharmacogenetics. 2004 Jan;14(1):1-18. Review. (
  • Evaluation of Genomic Applications in Practice and Prevention (EGAPP) Working Group. Recommendations from the EGAPP Working Group: testing for cytochrome P450 polymorphisms in adults with nonpsychotic depression treated with selective serotonin reuptake inhibitors. Genet Med. 2007 Dec;9(12):819-25. (
  • Lynch T, Price A. The effect of cytochrome P450 metabolism on drug response, interactions, and adverse effects. Am Fam Physician. 2007 Aug 1;76(3):391-6. Review. (
  • Ingelman-Sundberg M. The human genome project and novel aspects of cytochrome P450 research. Toxicol Appl Pharmacol. 2005 Sep 1;207(2 Suppl):52-6. Review. (
  • Ingelman-Sundberg M, Sim SC, Gomez A, Rodriguez-Antona C. Influence of cytochrome P450 polymorphisms on drug therapies: pharmacogenetic, pharmacoepigenetic and clinical aspects. Pharmacol Ther. 2007 Dec;116(3):496-526. Epub 2007 Oct 9. Review. (
  • Hannemann F, Bichet A, Ewen KM, Bernhardt R. Cytochrome P450 systems--biological variations of electron transport chains. Biochim Biophys Acta. 2007 Mar;1770(3):330-44. Epub 2006 Aug 2. Review. (
  • Guengerich FP. Cytochrome p450 and chemical toxicology. Chem Res Toxicol. 2008 Jan;21(1):70-83. Epub 2007 Dec 6. Review. (
  • Szczesna-Skorupa E, Kemper B. Influence of protein-protein interactions on the cellular localization of cytochrome P450. Expert Opin Drug Metab Toxicol. 2008 Feb;4(2):123-36. doi: 10.1517/17425255.4.2.123. Review. (
  • Bernhardt R. Cytochromes P450 as versatile biocatalysts. J Biotechnol. 2006 Jun 25;124(1):128-45. Epub 2006 Mar 3. 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: March 2008
Published: February 8, 2016