Aromatase deficiency is a condition characterized by reduced levels of the female sex hormone estrogen and increased levels of the male sex hormone testosterone.

Females with aromatase deficiency have a typical female chromosome pattern (46,XX) but are born with external genitalia that do not appear clearly female or male. These individuals typically have normal internal reproductive organs, but develop ovarian cysts early in childhood, which impair the release of egg cells from the ovaries (ovulation). In adolescence, most affected females do not develop secondary sexual characteristics, such as breast growth and menstrual periods. They tend to develop acne and excessive body hair growth (hirsutism).

Men with this condition have a typical male chromosome pattern (46,XY) and are born with male external genitalia. Some men with this condition have decreased sex drive, abnormal sperm production, or testes that are small or undescended (cryptorchidism).

There are other features associated with aromatase deficiency that can affect both males and females. Affected individuals are abnormally tall because of excessive growth of long bones in the arms and legs. The abnormal bone growth results in slowed mineralization of bones (delayed bone age) and thinning of the bones (osteoporosis), which can lead to bone fractures with little trauma. In affected individuals, the body does not respond correctly to the hormone insulin, so people with aromatase deficiency can have abnormally high blood sugar (glucose), a condition known as hyperglycemia. In addition, people with armoatase deficiency can have excessive weight gain and a fatty liver.

Women who are pregnant with fetuses that have aromatase deficiency often experience mild symptoms of the disorder even though they themselves do not have the disorder. These women may develop hirsutism, acne, an enlarged clitoris (clitoromegaly), and a deep voice. These features can appear as early as 12 weeks of pregnancy and go away soon after delivery.

The prevalence of aromatase deficiency is unknown; approximately 20 cases have been described in the medical literature.

Mutations in the CYP19A1 gene cause aromatase deficiency. 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 estrogen. In females, estrogen guides female sexual development before birth and during puberty. In both males and females, estrogen plays a role in regulating bone growth and blood glucose 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.

CYP19A1 gene mutations that cause aromatase deficiency decrease or eliminate aromatase activity. A shortage of functional aromatase 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 affected individuals, these abnormal hormone levels lead to impaired female sexual development, unusual bone growth, insulin resistance, and other signs and symptoms of aromatase deficiency. In women who are pregnant with an affected fetus, excess androgens in the placenta pass into the woman's bloodstream, which may cause her to have temporary signs and symptoms of aromatase deficiency.

Genetic Testing Information

• Genetic Testing Registry: Aromatase deficiency

Genetic and Rare Diseases Information Center

• Aromatase deficiency

Patient Support and Advocacy Resources

• National Organization for Rare Disorders (NORD)

Catalog of Genes and Diseases from OMIM

• AROMATASE DEFICIENCY

Scientific Articles on PubMed

• PubMed

• Baykan EK, Erdogan M, Ozen S, Darcan S, Saygili LF. Aromatase deficiency, a rare syndrome: case report. J Clin Res Pediatr Endocrinol. 2013;5(2):129-32. doi: 10.4274/Jcrpe.970. Citation on PubMed or Free article on PubMed Central
• 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. Citation on PubMed
• Bulun SE. Aromatase and estrogen receptor alpha deficiency. Fertil Steril. 2014 Feb;101(2):323-9. doi: 10.1016/j.fertnstert.2013.12.022. Citation on PubMed or Free article on PubMed Central
• Ludwikowski B, Heger S, Datz N, Richter-Unruh A, Gonzalez R. Aromatase deficiency: rare cause of virilization. Eur J Pediatr Surg. 2013 Oct;23(5):418-22. doi: 10.1055/s-0032-1324798. Epub 2012 Oct 23. No abstract available. Citation on PubMed
• Rochira V, Carani C. Aromatase deficiency in men: a clinical perspective. Nat Rev Endocrinol. 2009 Oct;5(10):559-68. doi: 10.1038/nrendo.2009.176. Epub 2009 Aug 25. Citation on PubMed