Androgen Insensitivity Syndrome (AIS)

What Is Androgen Insensitivity Syndrome (AIS)? What Causes Androgen Insensitivity Syndrome?

Androgen insensitivity syndrome is a genetic disorder in which the XY fetus is unresponsive (insensitive) to androgens. Androgens are male hormones, such as testosterone. A baby with androgen insensitivity syndrome is born externally like a normal girl. However, internally they have a short blind-pouch vagina, and no ovaries, fallopian tubes or womb (uterus). The testes are in the inguinal canal or abdomen.

In other words, androgen insensitivity syndrome is a condition in which the development of the genitals and reproductive organs are affected.

Very early on, all unborn babies have identical genitals, regardless of whether they are female or male. A pair of sex chromosomes in the baby - XX or XY - determines whether they develop male (XY) or female (XX) genitals and reproductive organs.

XX and XY sex chromosomes

Sex chromosomes are a pair of DNA molecules, called X or Y, that decide our sexual development.

• A female has two X chromosomes - XX
• A male has one X and one Y chromosome - XY

The Y chromosome stimulates the development of the testes and halts the development of female ovaries. If no Y chromosome is present, the female reproductive system and genitals develop automatically.

Androgen insensitivity syndrome - a baby with androgen insensitivity syndrome is born with an XY set of hormones - so it should develop male genitals and reproductive organs. The testes (testicles), the male reproductive organs, produce androgens (male hormones), which make the human develop male characteristics and sex organs (such as the penis).

If the human is insensitive or ignores the androgen, the testes will stay inside the body (instead of coming down to the scrotum) and genitals will develop along female lines.

There are two forms of androgen insensitivity syndrome:

• Complete androgen insensitivity syndrome (CAIS) - the human is completely insensitive to androgen. External genitals develop along purely female lines. The majority of babies who are born with CAIS are brought up as daughters.
  
• Partial androgen insensitivity syndrome (PAIS) - there is some sensitivity to androgen, but less than normal. How the genitals develop depends on how sensitive that human is to androgen. The individual may look completely male or female, or neither (in between). Some may have a slightly enlarged clitoris while others have a penis which is almost fully formed. Babies born with PAIS may be brought up as sons or daughters, depending on their degree of androgen sensitivity and subsequent genital development.

Intersex conditions versus gender dysphoria

An intersex condition, such as androgen insensitivity syndrome, is when something went wrong in the development of the baby's reproductive organs and genitals because the body was insensitive (unresponsive) to androgen.

In a case of gender dysphoria the reproductive organs and genitals developed normally, but the individual feels their gender is wrong - a person who is physically completely male feels he is female, or vice versa. Gender dysphoria is also known as trans-sexuality or being transgender.

How common is androgen insensitivity syndrome (AIS)?

Approximately 1 in every 20,400 male births has AIS. Complete AIS (CAIS) is believed to be more common than Partial AIS (PAIS). Learn more....