Male genes with female genitals but some internal male structures
Some people have XY (male) chromosomes, but their external genitals may appear entirely female or atypical. The womb may be present or absent and the testicles may remain in the body or not form properly.
Doctors refer to this condition as 46,XY DSD.
There are several different causes of this condition. One possible cause is androgen insensitivity syndrome (AIS), where the body ignores androgens or is insensitive to them, so external development is female.
This can mean they don't produce enough testosterone, the sex hormone responsible for the development of male characteristics and important for maintaining bone strength, sex drive and fertility in men.
Another type is infertile and their height is shorter than average.
Female with normal genitals but an absent womb
Some females are born with an underdeveloped or absent womb, cervix and upper vagina, but the ovaries and external genitalia are still present and they still develop breasts and pubic hair as they get older.
This is known as Rokitansky syndrome (also called Mayer-Rokitansky-Küster-Hauser or MRKH syndrome). The cause isn't clear, but it's not related to chromosomes because girls and women with it have the normal XX chromosomes.
Often the first sign is that a girl doesn't start having periods. Sex may also be difficult because the vagina is shorter than normal.
As they have no womb, women with Rokitansky syndrome cannot become pregnant, but it's sometimes possible to take eggs from their ovaries, fertilise them, and implant them in another woman (surrogate).
People with this very rare type of DSD have both ovarian and testicular tissue – for example, one ovary and one testis – and their genitals may appear female, male or a mix of both.
Most people with this type of DSD have XX (female) chromosomes. The cause isn't usually clear, but some cases have been linked to genetic material normally found on the Y chromosome being found on the X chromosome.
Doctors refer to this condition as 46,XX ovotesticular DSD.
What happens after birth
Some DSDs are suspected soon after birth because of obvious signs such as undescended testicles or an atypical genital appearance.
A number of tests may be carried out to help confirm the diagnosis and identify any medical problems that may require immediate treatment.
These tests may include a further physical examination of your baby carried out by a specialist, an blood tests to check their genes and hormone levels.
Your care team may advise you to delay registering your child's birth for a few days while these tests are carried out.
Afterwards, the results will be explained to you and you'll have a discussion about whether you'd like to bring your baby up as a boy or a girl.
Emergency treatment is rarely needed, but the team of specialists will also talk to you about your options regarding immediate or delayed treatment with hormone therapy or surgery.
Sometimes a DSD may be diagnosed if an older child doesn't develop normally in puberty. For example, your child may not start the normal puberty changes, or may start puberty but not get periods.
Speak to your GP if you have any concerns about your child's development at puberty. They can refer your child to a specialist, usually a consultant in paediatric endocrinology or an adolescent gynaecologist.
A team of different healthcare professionals will work with you to understand your child's condition, and offer you and your child support and advice.
As your child grows up, they may need hormone therapy and psychological support, and they may eventually decide they want surgery to change their appearance.
With the right care and support, many people with DSDs come to terms with their condition and live happily.
If you think you have a DSD
If you think or know you have a DSD, help and support is available.
Speak to your GP initially, as they'll be able to refer you to a team of specialist healthcare professionals who can offer support and advice.
Most people with a DSD stay with the gender they were assigned as a baby, but if you feel the gender you were assigned doesn't represent who you are, you may wish to change your gender. This will be something you can discuss with your care team.
If you have a DSD, you may be infertile, and may need hormone therapy and psychological support. The right care and support can help you come to terms with your condition and lead a normal life.
If you have a DSD or you're the parent of a child with a DSD, you may find it useful to contact or join a support group.
These groups can often offer more information and advice about living with a DSD, and may be able to put you in contact with others who've been in a similar situation to you.