Androgen insensitivity syndrome is the result of a mutation on the X chromosome of a genetically male (XY) individual that interrupts the formation of the male sex hormone receptors. All other hormone receptors associated with sexual development are intact and functional.
Prenatally, the testes develop normally and secrete hormones (including androgens). Because the androgen receptors are not functional, the epididymis, vas deferens, seminal vesicles, and prostate do not develop. Also, the anti-mullerian hormones (whose receptors are intact) have the normal effect of preventing the development of female internal sex organs (uterus, fimbriae, Fallopian tubes, and the upper portion of the vagina).
At puberty, although the testes (still undescended because they have nowhere to descend to) secrete testosterone as normal for an XY individual, the nonfunctional receptors fail to detect it (testosterone is an androgen). As a result, these individuals develop female secondary sex characteristics. In other words, they look like women, but are genetically male. Because they do not have female internal organs, and cannot produce sperm, people with this syndrome are incapable of having children.
main source: Physiology of Behavior, 6th edition, 1998. Neil R. Carlson