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Causes
By Mayo Clinic staff
The role of chromosomes
The genetic sex of a child is established at conception based on the 23rd pair of chromosomes it inherits. The mother's egg contains an X chromosome, and the father's sperm contains either an X or Y chromosome. A baby who inherits the X chromosome from the father is a genetic female (a pair of X chromosomes). A baby who inherits the Y chromosome from the father is a genetic male (one X and one Y chromosome).
Fetal sexual development
In early fetal development, males and females are indistinguishable. Male and female sex organs develop from the same tissue in the fetus. For example, the same fetal tissue that forms a penis in a male also forms a clitoris in a female. The presence or absence of male hormones controls the development of the sex organs. Normally, male genitalia develop because of male hormones from the fetal testicles. In the female fetus — without the effects of male hormones — the genitalia develop as female.
A deficiency of male hormone in a genetic male fetus results in ambiguous genitalia. In a female fetus, the presence of male hormone during development results in ambiguous genitalia. Although the deficiency or presence of male hormones is the main factor controlling genital development, the exact cause of ambiguous genitalia is often unknown. Many of the disorders seem to happen by chance.
Possible causes in genetic females
Causes of ambiguous genitalia in a genetic female may include:
- Congenital adrenal hyperplasia (CAH). Certain forms of this genetic condition cause the adrenal glands to make excess male hormones (androgens). Congenital adrenal hyperplasia is the most common cause of ambiguous genitalia in newborns.
- Ingestion by the mother of substances with male hormone activity, such as progesterone (taken in the early stages of pregnancy to stop bleeding).
- Tumors in the fetus or the mother that produce male hormones.
Possible causes in genetic males
Causes of ambiguous genitalia in a genetic male may include:
- Impaired testicle development due to genetic abnormalities or unknown causes.
- Leydig cell aplasia, a condition that impairs testosterone production.
- Congenital adrenal hyperplasia. Certain forms of this genetic condition can impair production of male hormones.
- Androgen insensitivity syndrome, a condition in which developing genital tissues are unable to respond to normal male hormone levels.
- 5alpha-reductase deficiency, an enzyme defect that impairs normal male hormone production.
- Ingestion by the mother of substances with female hormone activity, such as estrogens, or anti-androgens. This is unusual, but could occur if a woman taking birth control pills gets pregnant despite taking the pills — then, not knowing she's pregnant, continues taking the pills into pregnancy for several weeks. Also some "nutritional supplements" contain plant estrogens.
