Androgen insensitivity syndrome (AIS) affects the normal development of a child's genitals and reproductive organs.
A child born with AIS is genetically male, but their genitals may appear to be female or somewhere in between male and female.
AIS is a very rare condition thought to occur in around 1 in every 20,000 births.
At an early stage of development in pregnancy, all unborn babies have identical genitals, regardless of whether they are male or female.
As a baby grows inside the womb, they develop either male or female genitals, depending on many factors including which pair of sex chromosomes they receive from their parents: XX or XY.
Sex chromosomes
Sex chromosomes are a pair of DNA molecules (X or Y) that play a vital role in a baby's sexual development. Females usually have two X chromosomes and males usually have one X and one Y chromosome.
The presence of a Y chromosome is important for the development of testes and prevents ovaries developing. If there is no Y chromosome, the female reproductive system and genitals will develop.
Read more about the male and female sex chromosomes.
What happens in AIS
The testes produce male hormones called androgens, which usually cause male sex organs, such as the penis, to develop. However, in AIS, the body ignores the androgen or is insensitive to it, so genitals develop along female lines and the testes usually remain inside the body.
Read more about the causes of AIS.
Types of AIS
There are two types of AIS, which are determined by the level of insensitivity to androgen. They are:
- complete androgen insensitivity syndrome (CAIS), where there is total insensitivity to androgen and a child develops external genitals that are entirely female; most children born with CAIS are brought up as girls
- partial androgen insensitivity syndrome (PAIS), where there is some sensitivity to androgen; the level of sensitivity will determine how the genitals develop
Depending on a person's level of insensitivity to androgen, they may look almost entirely male, entirely female, or have both male and female characteristics.
Children with PAIS can be brought up either as girls or boys, depending on the results of investigations and discussions with the specialist team after their birth.
Read more about the symptoms and grading system that is used for AIS.
Diagnosing AIS
Partial androgen insensitivity syndrome is usually diagnosed at birth because the genitals appear different.
Diagnosing complete androgen insensitivity syndrome can be more difficult because the genitalia usually look normal for a girl.
Many children with CAIS are diagnosed early in life when their testes cause hernias. When the hernias are operated on, the testes are discovered.
Otherwise the condition may not be diagnosed until puberty, when a girl's periods do not start and she has a lack of pubic and underarm hair. Breast development tends to be normal.
Read more about how AIS is diagnosed.
Treating AIS
A child with AIS should be offered psychological support if they need it.
Counselling is not always needed in young children with AIS because their condition is entirely natural to them. However, counselling will be needed as the child gets older.
It is recommended that children with AIS fully understand their condition before they reach puberty, so that they are aware of the changes they may experience and the differences between them and their friends.
Children with PAIS may need to take hormone supplements. Girls with PAIS who have had their testes removed will need to take oestrogen to encourage female development during puberty and maintain secondary sexual characteristics in adulthood. It is not clear whether androgen supplementation is beneficial.
Boys with PAIS may need to take androgens (male sex hormones) to encourage certain male characteristics, such as the growth of facial hair and the deepening of their voice.
Women with CAIS who have gone through puberty and had their testes removed will need to take oestrogen to prevent them getting menopausal symptoms and developing weak bones (osteoporosis).
Read more about how AIS is treated.
Support
Most people with AIS are able to lead normal lives after receiving the appropriate care and support to help them come to terms with their condition. AIS does not reduce a person's life expectancy.
Support groups, such as the Androgen Insensitivity Syndrome Support Group (AISSG) and Differences of Sex Development (DSD families), provide help and support to young people, adults and families who are affected by AIS.
