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


Reviewed April 2014

What is the official name of the CYP19A1 gene?

The official name of this gene is “cytochrome P450 family 19 subfamily A member 1.”

CYP19A1 is the gene's official symbol. The CYP19A1 gene is also known by other names, listed below.

What is the normal function of the CYP19A1 gene?

The CYP19A1 gene provides instructions for making an enzyme called aromatase. This enzyme converts a class of hormones called androgens, which are involved in male sexual development, to different forms of the female sex hormone estrogen.

In cells, aromatase is found in a structure called the endoplasmic reticulum, which is involved in protein production, processing, and transport. The activity (expression) of aromatase varies among different cell types depending on the cells' need for estrogen. In females, aromatase is most active in the ovaries, where it guides sexual development. In males, aromatase is most active in fat (adipose) tissue. In both males and females, estrogen plays a role in regulating bone growth and blood sugar levels. During fetal development, aromatase converts androgens to estrogens in the placenta, which is the link between the mother's blood supply and the fetus. This conversion in the placenta prevents androgens from directing sexual development in female fetuses. After birth, the conversion of androgens to estrogens takes place in multiple tissues.

Does the CYP19A1 gene share characteristics with other genes?

The CYP19A1 gene belongs to a family of genes called CYP (cytochrome P450s).

A gene family is a group of genes that share important characteristics. Classifying individual genes into families helps researchers describe how genes are related to each other. For more information, see What are gene families? ( in the Handbook.

How are changes in the CYP19A1 gene related to health conditions?

aromatase deficiency - caused by mutations in the CYP19A1 gene

More than 20 mutations in the CYP19A1 gene have been found to cause aromatase deficiency. This condition is characterized by reduced levels of estrogen and increased levels of androgens. These abnormal hormone levels lead to impaired sexual development in affected females and unusual bone growth, insulin resistance, and other signs and symptoms in both males and females with the condition. CYP19A1 gene mutations that cause aromatase deficiency decrease or eliminate aromatase activity. A lack of aromatase function results in an inability to convert androgens to estrogens before birth and throughout life. As a result, there is a decrease in estrogen production and an increase in the levels of androgens, including testosterone. In women who are pregnant with an affected fetus, excess androgens in the placenta pass into the woman's bloodstream, and may cause her to have temporary signs and symptoms of aromatase deficiency.

aromatase excess syndrome - caused by mutations in the CYP19A1 gene

More than 10 rearrangements of genetic material involving the CYP19A1 gene have been found to cause aromatase excess syndrome. This condition is characterized by the increased conversion of androgens to estrogen. As a result, affected males have enlarged breasts (gynecomastia) and short stature; affected females can have irregular menstrual periods and short stature.

Several types of genetic rearrangement involving the CYP19A1 gene can cause aromatase excess syndrome. Some genetic rearrangements that cause aromatase excess syndrome duplicate parts of the CYP19A1 gene, doubling some of the instructions used for making the enzyme. As a result, more enzyme than normal is produced. Other genetic rearrangements, called deletions, remove (delete) parts of the CYP19A1 gene and a nearby gene. The remaining DNA is then fused together, creating a fusion gene composed of parts of two different genes. These fusion genes always contain part of the CYP19A1 gene, but can involve a piece of one of several other genes. As a result of these fusion genes, the CYP19A1 gene is active (expressed) in tissues where it is not normally expressed so more aromatase than normal is produced. Another type of rearrangement, called an inversion, occurs when DNA is broken in two places and the resulting piece of DNA is reversed and reinserted into the chromosome. Inversions involving the CYP19A1 gene and a nearby gene also result in the production of a fusion gene. These fusion genes lead to increased aromatase production.

The increase in aromatase production caused by CYP19A1 gene rearrangements leads to increased estrogen production, which results in the signs and symptoms of aromatase excess syndrome.

Where is the CYP19A1 gene located?

Cytogenetic Location: 15q21.1

Molecular Location on chromosome 15: base pairs 51,208,057 to 51,338,598

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBI (

The CYP19A1 gene is located on the long (q) arm of chromosome 15 at position 21.1.

The CYP19A1 gene is located on the long (q) arm of chromosome 15 at position 21.1.

More precisely, the CYP19A1 gene is located from base pair 51,208,057 to base pair 51,338,598 on chromosome 15.

See How do geneticists indicate the location of a gene? ( in the Handbook.

Where can I find additional information about CYP19A1?

You and your healthcare professional may find the following resources about CYP19A1 helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the CYP19A1 gene or gene products?

  • ARO
  • ARO1
  • aromatase
  • CPV1
  • CYAR
  • CYP19
  • cytochrome P450 19A1
  • cytochrome P-450AROM
  • cytochrome P450, family 19, subfamily A, polypeptide 1
  • cytochrome P450, subfamily XIX (aromatization of androgens)
  • estrogen synthase
  • estrogen synthetase
  • flavoprotein-linked monooxygenase
  • microsomal monooxygenase
  • P-450AROM

See How are genetic conditions and genes named? ( in the Handbook.

What glossary definitions help with understanding CYP19A1?

androgens ; cancer ; cell ; chromosome ; class ; cytochrome P450 ; deficiency ; DNA ; endoplasmic reticulum ; enzyme ; expressed ; fetus ; fusion gene ; gene ; gynecomastia ; hormone ; insulin ; insulin resistance ; inversion ; placenta ; protein ; rearrangement ; sex hormone ; short stature ; stature ; syndrome ; testosterone ; tissue

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


  • Belgorosky A, Guercio G, Pepe C, Saraco N, Rivarola MA. Genetic and clinical spectrum of aromatase deficiency in infancy, childhood and adolescence. Horm Res. 2009;72(6):321-30. doi: 10.1159/000249159. Epub 2009 Oct 21. Review. (
  • Belgorosky A, Guercio G, Pepe C, Saraco N, Rivarola MA. Genetic and clinical spectrum of aromatase deficiency in infancy, childhood and adolescence. Horm Res. 2009;72(6):321-30. doi: 10.1159/000249159. Epub 2009 Oct 21. Review. (
  • Bulun SE, Sebastian S, Takayama K, Suzuki T, Sasano H, Shozu M. The human CYP19 (aromatase P450) gene: update on physiologic roles and genomic organization of promoters. J Steroid Biochem Mol Biol. 2003 Sep;86(3-5):219-24. Review. (
  • Czajka-Oraniec I, Simpson ER. Aromatase research and its clinical significance. Endokrynol Pol. 2010 Jan-Feb;61(1):126-34. Review. (
  • Fukami M, Tsuchiya T, Vollbach H, Brown KA, Abe S, Ohtsu S, Wabitsch M, Burger H, Simpson ER, Umezawa A, Shihara D, Nakabayashi K, Bulun SE, Shozu M, Ogata T. Genomic basis of aromatase excess syndrome: recombination- and replication-mediated rearrangements leading to CYP19A1 overexpression. J Clin Endocrinol Metab. 2013 Dec;98(12):E2013-21. doi: 10.1210/jc.2013-2520. Epub 2013 Sep 24. (
  • NCBI Gene (


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: April 2014
Published: February 8, 2016