By BSc (embryologist).
Last Update: 01/15/2015

The androgen insensitivity syndrome (AIS), or testicular feminisation syndrome is a type of pseudohermaphroditism in which the individual has the genotype of one sex and the phenotype (appearance) of the other.

This pseudohermaphroditism is linked to the sexual chromosome X. It’s a recessive mutation in which the gen codifies the receptor of the androgens, which provokes an incapacity of the tissues to respond to the stimuli of the hormones. Androgens are male hormones produced mainly in the Leydig cells of the testicles, which stimulate the development of the male sexual characteristics.

Androgen insensitivity syndrome

Female pseudohermaphroditism

In the AIS, the individual is a man by genotype, with a kariotype 46 XY (male) but, as a result of the resistance to the action of the male sexual hormones, the external genitals develop as if the male sexual hormones didn’t exist, with an aspect that is quite similar to that of women.

The syndrome can be mainly divided in two categories:

  • Complete androgen insensitivity syndrome.
  • Incomplete androgen insensitivity syndrome.

Complete AIS prevents the development of penis and other male organs. When the boy is born, he looks like a girl. This manifestation of the syndrome can be found in one out of every 20,000 babies born alive.

The incomplete AIS presents more male characteristics, such as testicles that haven’t descended after birth, and Reifenstein syndrome (presence of micropenis, aperture of the urethra in the inferior part of the penis instead of at the end of it, and cryptorchidism).

Physical appearance

A person with complete Morris syndrome looks like a woman, who tends to be in many occasions tall and attractive. She has external female genitals with few labial folds, short vagina with a blind end, and few genital and armpit hair. During puberty, several female characteristics are developed, such as breasts. Nevertheless, individuals don’t have the period and neither are they fertile, since they lack ovaries, uterus and Fallopian tubes.

In people with incomplete AIS, the physical characteristics may be those of a female or a male. Many of them have the lips of the vagina partially stuck to each other or present an enlargement of the clitoris, a short vagina, amenorrhea, and sterility.

In both cases, they tend to suffer from inguinal hernias, which are testicles that have become atrophied and that can be found in the inner thigh or the lower part of the abdomen, and that can be noticed through a physical exploration.

Vaginal enlargement


The testicles that are located in an inappropriate place can’t be surgically removed until the child develops completely and has got over puberty. In this moment, they can be removed to avoid the risk of cancer, such as in the case of any testicle that hasn’t descended.

They are provided a hormonal treatment that supports their sexual identity, which tends to be feminine, probably due to the lack of prenatal impregnation of the brain by the androgens.

These women can go through a vaginal plastic surgery to enlarge the vagina, in the case that it is too short.

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Authors and contributors

 Laura Rollán Guilén
Laura Rollán Guilén
Bachelor's Degree in Biology from the University of Valencia (UV). Specialist in Human Assisted Reproduction. Writer of scientific contents. More information about Laura Rollán Guilén

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