Androgen insensitivity syndrome (AIS) affects the development of the genitals and reproductive organs.
A child born with AIS is genetically male, but their genitals may appear female or somewhere between male and female.
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 (see box).
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 the ovaries and womb 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 (see Grading system for AIS for more information).
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.
Disorder of Sex Development
AIS is a Disorder of Sex Development (DSD) which is also sometimes known as intersex. AIS should not be confused with gender dysphoria, which is also known as transsexuality or being transgender.
Gender dysphoria is where the reproductive organs and genitals have developed normally, but the person feels that their gender identity (their sense of what sex they are) does not match their biological sex.
Who is affected
AIS is thought to occur in one in every 20,400 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). Most people 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.
