Klinefelter (XXY) syndrome
Key facts
- Klinefelter syndrome is a congenital (from birth) condition where males are born with one or more extra X chromosomes.
- Young children with Klinefelter syndrome can have motor and language delay, as well as learning and behavioural problems.
- Teens and adults with Klinefelter syndrome may have smaller genitals, less facial and body hair and larger breasts.
- Many people with Klinefelter syndrome don't know they have it and have never received treatment.
- Testosterone therapy is usually started at puberty and can help with many of the features of Klinefelter syndrome.
What is Klinefelter syndrome?
Klinefelter syndrome is a congenital condition (from birth) in which males are born with one or more extra X chromosomes. It is not inherited. Klinefelter syndrome is also called XXY syndrome.
Klinefelter syndrome is common, with 1 or 2 in 1000 males born in Australia diagnosed each year. Most people don't know they have it and have never received treatment.
Males with Klinefelter syndrome are unable to produce enough of the male hormone, testosterone. Low levels of testosterone affect the development of male characteristics. The extra X chromosome also affects the production of sperm. Males with Klinefelter syndrome are usually infertile as they often don't have sperm in their ejaculate. This is sometimes called 'azoospermia'.
What are the symptoms of Klinefelter syndrome?
Most males with Klinefelter syndrome lead normal lives. Some people only have mild symptoms, while for others, it has a major impact on their lives. Most babies with Klinefelter syndrome do not have noticeable signs.
Children with Klinefelter syndrome might have:
- difficulties with walking or talking
- slow language and speech development
- learning or behavioural difficulties
- emotional immaturity and shyness
- poor muscle tone
Sometimes, issues first appear at puberty. People with Klinefelter syndrome don't experience the same rise in testosterone at puberty as other males. This can lead to:
- a small penis and small testes
- less hair on your face and body
- breasts that are a bit bigger than expected
You might also feel a bit different, which can increase your chance of experiencing mental health challenges. You may also be tall for your age.
These symptoms differ in severity between every person with Klinefelter syndrome. You may have some of these symptoms, but you are unlikely to have them all.
Some males don't realise they have Klinefelter syndrome until they experience fertility problems. Some may never find out.
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What causes Klinefelter syndrome?
While Klinefelter syndrome is genetic, it is not inherited from one of your parents.
Most males are born with one X and one Y sex chromosome. Klinefelter syndrome occurs when a male baby is born with one or more extra X chromosomes.
This is the result of a random genetic error that happens during the formation of the egg or the sperm, or it can happen after conception. It is not clear why this happens. If you have a pregnancy affected by Klinefelter syndrome, the likelihood of another affected pregnancy is very low.
When should I see my doctor?
The symptoms of Klinefelter syndrome can be very mild. Many people do not realise that they have the condition. A doctor may diagnose Klinefelter syndrome soon after birth, yet many males only get a diagnosis when they experience fertility problems.
A diagnosis can help your doctors and healthcare professionals provide you with the best medical care.
During childhood, individuals with Klinefelter syndrome may have:
- speech development issues
- attention difficulties
- unusually tall stature
If you notice any combination of these features, speak to your child's doctor.
During puberty, if there is underdevelopment of the genitalia or puberty doesn't continue as expected, see your doctor.
Adult males may only be diagnosed with Klinefelter syndrome after experiencing unexplained infertility. See your doctor if you are experiencing fertility problems.
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How is Klinefelter syndrome diagnosed?
Your doctor can diagnose Klinefelter syndrome with blood tests.
After puberty, your doctor may perform a genital examination. If your testes are smaller than average, your doctor may recommend a genetic test called a karyotype. This is a blood test that looks at your chromosomes. If you have more than one X chromosome in your karyotype, you have Klinefelter syndrome.
If you're pregnant, your health team may offer chromosome testing for Klinefelter syndrome as part of prenatal testing. Non-invasive prenatal testing can check the likelihood that your baby has Klinefelter syndrome. Diagnostic testing can also test the karyotype of your baby.
Talk to your doctor, midwife or genetic counsellor to understand your options for prenatal testing.
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How is Klinefelter syndrome treated?
Klinefelter syndrome has no cure, but treatments are available to help manage symptoms.
Children with Klinefelter syndrome should see their doctor at least every 2 years to check their physical development. Many children with Klinefelter may need specialist help for speech, learning, behaviour or psychiatric issues.
Testosterone therapy can help with the symptoms of Klinefelter syndrome. This treatment should begin at puberty or as soon as possible after puberty begins. Your doctor can check your growth and hormone levels to help you make decisions about testosterone treatment. If you have Klinefelter syndrome and are not receiving testosterone therapy, visit your doctor every 12 months to check your hormone levels.
Plastic surgery is an option for some of the physical features of Klinefelter syndrome, such as surgery to remove extra breast tissue.
If you have Klinefelter syndrome and are experiencing infertility, you may be able to use assisted reproductive technologies (ART), such as new forms of in-vitro fertilisation (IVF). For example, if you have a very low sperm count, a single sperm may be extracted from your testes and injected into an egg (called intra-cytoplasmic sperm injection or ICSI) to increase your chance of conceiving. Speak with your doctor, who may refer you to a fertility expert for support and advice.
Counselling and psychological therapy may also help you cope with emotional difficulties.
Living with Klinefelter syndrome
Most males with Klinefelter syndrome have a normal sex life but are infertile. If you have Klinefelter syndrome, you are at higher risk than other males of developing:
- osteoporosis
- diabetes
- cardiovascular conditions
- some cancers, including breast cancer
- autoimmune diseases such as hypothyroidism
- psychological problems that come about from feeling different
- obesity
There is no cure for Klinefelter syndrome, but a diagnosis allows you to access specialist care to manage your symptoms.
Resources and support
For more information, you should consult your doctor, endocrinologist or health professional. The following organisations can also provide further information and support:
- Australian X and Y Spectrum Support provides a list of professional support networks for each state.
- Healthy Male shares evidence-based, easy-to-understand content on health conditions affecting males.
- Genetics Alliance Australia provides free telehealth genetic counselling and peer support.
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Last reviewed: September 2024
