Androgen Insensitivity Syndrome

Androgen Insensitivity Syndrome (AIS) is a condition in which a person who is genetically male (46,XY karyotype) is unable to respond to androgens (male hormones such as testosterone and dihydrotestosterone). Because the body's cells cannot use these hormones, the person develops with a female or partially female external appearance despite having male chromosomes. The testes produce testosterone normally, but the cells lack functioning androgen receptors, so the masculinizing effects of testosterone do not occur. The testes also produce Müllerian Inhibiting Substance (MIS), which causes the internal female reproductive structures (uterus, fallopian tubes, upper vagina) to regress during fetal development. As a result, individuals with complete AIS are born appearing phenotypically female but have no uterus or fallopian tubes. Undescended testes may be located in the abdomen or inguinal canal and may present as inguinal masses in a phenotypically female newborn.