Overview
Clinical Meaning
Androgen insensitivity syndrome (AIS) is an X linked condition in a person with a 46,XY karyotype caused by a pathogenic variant in the androgen receptor (AR) gene at Xq12.
Androgen insensitivity syndrome (AIS) is an X-linked condition in a person with a 46,XY karyotype caused by a pathogenic variant in the androgen receptor (AR) gene at Xq12. The testes produce testosterone and dihydrotestosterone (DHT), but target tissues cannot respond normally to those hormones. The degree of receptor dysfunction determines the phenotype: complete AIS (CAIS), partial AIS (PAIS), or mild AIS (MAIS). The mechanism explains the apparently mixed findings. Testicular anti-Müllerian hormone (AMH) is produced, so Müllerian structures—the uterus, cervix, and upper vagina—do not develop. At the same time, blocked androgen action prevents normal development of Wolffian ducts and typical masculinization of the external genitalia. In CAIS, the external appearance is typically female, the vagina is shortened and blind-ending, and the gonads are testes rather than ovaries. Testosterone can still be aromatized to estrogen. This is why spontaneous breast development is usually normal in CAIS even though androgen action is absent. The same androgen resistance limits pubic and axillary hair growth. The pattern is therefore more informative than any single finding: normal breast development plus absent menses and sparse body...