Androgen insensitivity syndrome (AIS) affects the development of the genitals and reproductive organs.
At an early stage of development, all unborn babies, whether they are male or female, have identical genitals. The development of the genitals into either male or female is dictated by which pair of sex chromosomes the baby receives from its parents – XX or XY.
What happens in AIS
A child with AIS is born with a set of genetically male sex chromosomes (XY). The presence of the Y chromosome stops the development of internal female sexual organs and causes the development of testes (two egg-shaped male reproductive organs), which also happens in normal male sexual development. The testes produce male hormones, called androgens, which normally cause male sex organs (such as the penis) to develop.
However, in AIS, the body ignores the androgen or is insensitive to it, so the genitals develop along female lines and the testes usually remain inside the body.
Types of AIS
There are two forms of AIS, which are determined by the level of insensitivity to androgen.
Complete androgen insensitivity syndrome
Complete androgen insensitivity syndrome (CAIS) is where the person is totally insensitive to androgen and develops external genitals that are entirely female. Most children born with CAIS are brought up as girls.
Partial androgen insensitivity syndrome
Partial androgen insensitivity syndrome (PAIS) is where the person has some sensitivity to androgen. The level of sensitivity determines how the genitals develop. The person can look almost entirely male, entirely female, or somewhere in between. Some babies are born with a slightly enlarged clitoris, while others may have an almost fully formed penis.
Children with PAIS can be brought up as girls or boys. The decision is often based on the type of genital development.
Intersex conditions
AIS is a type of intersex condition and should not be confused with gender dysphoria (also known as transsexuality, or being transgender).
Having an intersex condition such as AIS means there has been a problem in the development of the baby’s reproductive organs and genitals due to genetic or hormonal factors (see Androgen Insensitivity Syndrome - Causes for more information). It can result in a mix of male and female characteristics.
Gender dysphoria, on the other hand, is where the reproductive organs and genitals have developed normally, but the person feels that their gender ID (sense of what sex they are) does not match their biological sex.
Who is affected
AIS is thought to affect one in every 20,400 male births, although the exact figures are unknown. CAIS is believed to be more common than PAIS.
Outlook
People with AIS will need hormone therapy and psychological support (see Androgen Insensitivity Syndrome - Treatment for more information). All girls and most boys with AIS will be infertile.
Most people with AIS who have received appropriate care and support come to terms with their condition and live normal lives. AIS does not reduce life expectancy.