Babies with androgen insensitivity syndrome (AIS) will be genetically male, but will either have female genitals or an appearance between male and female genitalia.

There are 2 main types of AIS, which affect people in different ways:

• complete androgen insensitivity (CAIS)
• partial androgen insensitivity (PAIS)

Read more about these 2 types of AIS.

Complete androgen insensitivity syndrome

CAIS isn't usually obvious from birth, as affected babies have female genitals – including a vagina and labia (folds of skin either side of the vaginal opening) – and are raised as girls.

They'll also have undescended testicles, but this will usually go unnoticed unless they cause a hernia (where they push through a weakness in the surrounding tissue) or swelling in the labia.

The first obvious symptoms often don't appear until puberty, which starts at around the age of 11 or 12.

When a girl with CAIS reaches puberty, she will:

• not start having periods
• develop little or no pubic and underarm hair
• develop breasts and have growth spurts as normal, although she may end up slightly taller than usual for a girl

Girls with CAIS don't have a womb or ovaries, so are unable to get pregnant. Their vagina will also be shorter than normal, which may make having sex difficult.

Partial androgen insensitivity syndrome

The development of children with partial androgen insensitivity syndrome (PAIS) can vary.

In many cases, the genitalia are between male and female from birth. For example, affected babies may have:

• a very small penis or an enlarged clitoris (the sexual organ that helps women reach sexual climax)
• partially undescended testicles
• hypospadias – where the hole through which urine passes out of the body is on the underside of the penis, rather than at the end

Children with PAIS are usually raised as boys, although they may experience poor penis development during puberty and develop small breasts. Most children with PAIS raised as boys will be infertile.

Some children with PAIS are raised as girls. Like those with CAIS, girls with PAIS don't have a womb or ovaries and won't be able to get pregnant.

Androgen insensitivity syndrome (AIS) is caused by a genetic fault that means the body can't respond to testosterone properly. The faulty gene is usually passed on to a child by their mother.

Testosterone is the male sex hormone produced by the testicles. It controls the development of the usual changes expected in boys, such as penis growth and the testicles moving into the scrotum.

How babies with AIS develop

In early pregnancy, all unborn babies have identical genitals. As they grow inside the womb, they develop either male or female genitals, depending on the pair of sex chromosomes they receive from their parents and their ability to respond to the sex hormones they make.

Sex chromosomes are bundles of genes – called X or Y – that play a vital role in a baby's sexual development. Females usually have 2 X chromosomes (XX), while males usually have an X and a Y chromosome (XY).

Children with AIS have male (XY) chromosomes, but the genetic fault they inherit prevents their body responding to the testosterone they make.

This means male sexual development doesn't happen as normal. The genitals appear female or between male and female, but a womb and ovaries don't develop internally.

How AIS is passed on

In most cases, the genetic fault is passed on to a child by their mother. The faulty gene is found on the mother's X chromosome.

As the mother has 2 X chromosomes, the normal chromosome is able to make up for the faulty one, so she's a carrier of the faulty gene, but doesn't have AIS and is able to have children.

Any genetically female (XX) children the mother has will also inherit 2 X chromosomes and will be unaffected, although they too may be carriers and be able to pass the genetic fault on to any children they have.

If the mother has a genetically male (XY) child, there's a chance they could pass on the faulty X chromosome, in addition to the Y chromosome the child gets from their father.

If this happens, the Y chromosome won't be able to make up for the faulty X chromosome and the baby will develop AIS.

This means women who carry the faulty X chromosome have a:

• 1 in 4 chance of giving birth to a girl who's unaffected, but can pass on the altered gene to her children
• 1 in 4 chance of having a boy who's unaffected
• 1 in 4 chance of having a girl who's unaffected and doesn't carry the altered gene
• 1 in 4 chance of having a child with AIS

This is known as X-linked inheritance.

Read about genetic inheritance for more information.

Androgen insensitivity syndrome (AIS) is sometimes diagnosed soon after a baby is born, although often it's not noticed until a child reaches puberty.

Doctors may suspect AIS based on a child's appearance and sexual development, but some tests will be needed to confirm the diagnosis.

Appearance and sexual development

Partial androgen insensitivity syndrome (PAIS) is usually spotted soon after birth because the genitals have an unusual appearance.

Complete androgen insensitivity syndrome (CAIS) isn't usually diagnosed at birth because the genitals look normal for a girl, but the condition may be picked up if the child gets a hernia.

Hernias are where an internal part of the body pushes through a weakness in the surrounding tissue. They can occur in babies with CAIS if the testicles fail to move from the tummy into the scrotum.

When the baby has an operation to repair the hernia, the surgeon may find the testicles inside the hernia or in the tummy, and tests may be arranged to check for CAIS.

If a baby with CAIS doesn't develop a hernia, the condition may go undiagnosed until puberty, when she doesn't start having periods and doesn't develop pubic and underarm hair.

Read more about the symptoms of AIS and types of AIS.

Tests and scans

If AIS is suspected, blood tests can be used to:

• check the sex chromosomes – sex chromosomes are bundles of genetic material that determine a person's genetic sex; if their genetic sex is different from their physical appearance, they may have AIS
• check for a genetic fault – AIS is caused by a problem on the X chromosome, the sex chromosome a child with AIS receives from their mother
• measure sex hormone levels – children with AIS tend to have high levels of testosterone (the male sex hormone) in their blood

An ultrasound scan can also be used to confirm the absence of the womb and ovaries. Children with AIS often have female genitals, but no female internal reproductive organs.

If a surgeon thinks they've found testicles in a baby's tummy during a hernia repair operation, a small tissue sample (biopsy) may be taken and analysed to confirm they are testicles and not ovaries.

Testing family members and unborn babies

If someone in your family has AIS and the specific genetic fault causing it has been identified, it may be possible to have a blood test to check if you carry the same fault and are at risk of passing it on to any children you have.

Testing can also be carried out in unborn babies when there's a known family history of AIS.

There are 2 main tests that can be carried out during pregnancy to determine whether a baby has the condition:

• chorionic villus sampling (CVS) – a sample of cells are removed from the afterbirth (placenta) for testing, usually with a needle; this is usually carried out between week 11 and week 14 of pregnancy
• amniocentesis – a needle is used to extract a sample of the fluid surrounding the baby (amniotic fluid) for testing; this is usually carried out between week 15 and week 20 of pregnancy

It can be difficult to decide whether or not to have these tests, so it's a good idea to speak to a genetic counsellor first.

It's also important to be aware that the risk of miscarriage after CVS and amniocentesis is estimated to be about 0.5 to 1%. This means 1 in every 100 to 200 women will have a miscarriage after having CVS or amniocentesis.

Children with androgen insensitivity syndrome (AIS) and their parents will be supported by a team of specialists who can offer ongoing information and care.

Various treatment options are available to someone with AIS, including reconstructive surgery and hormone therapy.

However, psychological support and advice to help you deal with any issues that arise as a result of your child's condition is probably the most important aspect of care.

With appropriate care and support, most people with AIS are able to come to terms with their condition and lead normal lives.

Choosing your child's gender

As a parent of a child with AIS, one of the biggest decisions you'll have to make will be to choose which gender to raise your child as. You'll be given lots of information to help you make this decision. 

Most parents of children with complete androgen insensitivity syndrome (CAIS) choose to raise their child as a girl, as they have female genitals and often ultimately end up identifying with being female.

The decision is more difficult if your child has partial androgen insensitivity syndrome (PAIS), as their genitals may have both male and female aspects. You're entitled to specialist advice about your child's future development and any gender identity issues that could arise later on.

Most children with PAIS stay with the gender they've been raised as. However, some people feel this doesn't represent who they are and decide to switch gender in later life.

Talking to your child about AIS

Parents often wonder when and what they should say to their child about their condition.

Many people feel it's best to explain the basic facts about AIS to the child as soon as possible. They can then be given more detailed information as they get older, as their ability to understand increases.

It's usually recommended that a child fully understands their condition before they reach puberty. This can be a stressful time anyway, but it could be very traumatic if your child starts puberty without knowing about the possible changes they may experience, or the differences between them and their friends.

The situation can be more difficult if a girl with CAIS isn't diagnosed until she has started puberty. The health professionals looking after your child can advise you on how to talk to your child and support you through this process.

Support for parents

If your child is diagnosed with AIS, you should be offered counselling to help you come to terms with your emotions.

A diagnosis of AIS can come as a shock, and feelings of shame, guilt, anger and anxiety are common.

Talking to other parents who have a child with AIS may also help. There are organisations that can put you in touch with other families affected by the condition.

For example, you can call the Contact a Family helpline on 0808 808 3555.

The DSD Families website also provides information and support for families affected by disorders of sex development.

Support for children

Some young children with AIS don't need psychological support because their condition is completely natural to them.

However, as a child gets older, they may need support from a therapist with experience in AIS to help them understand and cope with their condition.

A long-term relationship between the child and therapist is ideal so any new issues can be discussed as the child matures.

Surgery

Children with CAIS and PAIS will sometimes need surgery to help change their body and genitals to be more consistent with the gender they're raised as.

Some procedures may be best carried out while your child is still young, but others can be delayed until they're older.

Hernia repair 

Children with AIS sometimes develop a hernia (where an internal part of the body pushes through a weakness in the surrounding tissue) soon after birth. This is a result of their testicles failing to move from the tummy to the scrotum.

This can be repaired by closing and strengthening the gap created in the surrounding tissues. The testicles may also be removed during another operation.

Removing the testicles

Girls with CAIS will usually have their internal testicles removed, as there's a very small risk they could become cancerous if left in place.

This procedure is often delayed until after puberty because the testicles produce hormones that help girls with CAIS develop a normal female body shape without hormone treatment, and the risk of the testicles becoming cancerous before adulthood is extremely low.

If you decide you'd prefer for your child's testicles to be removed before puberty, hormone treatment will be needed to help them develop a more female body shape.

Moving the testicles and reconstructing the penis

Boys with PAIS may be born with fully or partially undescended testicles. If this happens, an operation can be carried out to move the testicles into the scrotum.

Read more about treating undescended testicles.

Surgery can also be used to straighten the penis and correct hypospadias, where the hole that carries urine out of the body is on the underside of the penis, rather than at the end.

Vaginal surgery

Girls with AIS often have a shorter vagina than normal, which can make having sex difficult. Treatment for this is usually delayed until after puberty, so she can decide if she wants treatment for it and choose what treatment she prefers.

In many cases, surgery isn't necessary because the vagina can be lengthened using a method called dilation. This involves inserting small plastic rods that gradually widen and deepen the vagina.

Alternatively, a procedure to remove skin and tissue from the genital area and use it to reconstruct the vagina can be carried out.

Women with PAIS can also have surgery to reduce the size of their clitoris. This may make it less sensitive, but achieving an orgasm should still be possible.

Male breast reduction

Boys with PAIS will sometimes have some breast development around puberty. If this occurs, an operation can be carried out to remove the breast tissue.

Read more about male breast reductions.

Hormone therapy

If the testicles are removed when a girl with CAIS is a child, treatment with the hormone oestrogen (the female sex hormone) is usually started at the age of 10 or 11, so female development begins at an age consistent with puberty.

This won't cause periods to start, as people with CAIS don't have a womb, but it will help them develop a more female body shape. It will also be continued after puberty to stop them developing menopausal symptoms and weak bones (osteoporosis).

Women with CAIS who had their testicles removed after puberty will also need to take oestrogen to prevent the menopause and osteoporosis.

Children with PAIS may need to take hormone supplements. Girls with PAIS who have their testicles removed may need oestrogen to encourage puberty.

Boys with PAIS may need androgens (male sex hormones) to encourage certain male characteristics, such as facial hair and penis growth, or deepening of the voice.