Klinefelter Syndrome

Klinefelter syndrome is a common genetic condition in which people assigned male at birth (AMAB) have an additional X chromosome. Symptoms may include breast growth, infertility, osteoporosis and learning difficulties. Treatments usually involve physical and emotional therapy, as well as hormone replacement.


What is Klinefelter syndrome?

Klinefelter syndrome is a genetic disorder in which people assigned male at birth (AMAB) have an additional X chromosome in their genetic code. Most people AMAB have 46 chromosomes (packages of DNA). This includes one copy of an X chromosome and one copy of a Y chromosome (46, XY). People with Klinefelter syndrome have a total of 47 chromosomes (47, XXY).

Klinefelter syndrome is a congenital condition. That means you’re born with it. Symptoms vary significantly from person to person. You might receive a diagnosis early in life. But many people don’t even know they have the condition until adulthood, when symptoms like infertility come into play.

How common is Klinefelter syndrome?

Klinefelter syndrome is fairly common, occurring in about 1 in 600 people AMAB. But many people (some experts say 70% to 80%) likely don’t know they have this condition.


Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

Symptoms and Causes

What are the symptoms of Klinefelter syndrome?

The symptoms of Klinefelter syndrome vary in severity. Some people have several symptoms, while others don’t have any obvious ones. There are two general types of symptoms — physical and neurological.

Physical Klinefelter syndrome symptoms

Physical symptoms of Klinefelter syndrome affect your body and how it works. These symptoms may include:

  • A smaller penis.
  • Undescended testicles.
  • Atypical body proportions (like being really tall or having long legs and a short trunk).
  • Flat feet.
  • Radioulnar synostosis (when there’s an abnormal connection between the two main bones in your forearm).
  • Coordination issues.
  • Testicular failure (not making enough testosterone or sperm).
  • Increased breast tissue (gynecomastia) in teen or adult years.
  • Increased risk for blood clots.
  • Weaker bones or higher risk of fractures (called either osteopenia or osteoporosis as an adult).

People with Klinefelter syndrome also commonly experience infertility, meaning they lose the ability to make sperm. If you receive a Klinefelter diagnosis, you should see a fertility specialist (preferably before starting testosterone). If your provider finds sperm, they may be able to collect and freeze it in case you want to have biological children later in life. They can tell you whether fertility preservation is an option for you.

Neurological Klinefelter syndrome symptoms

Neurological symptoms describe things like behavioral issues, learning differences or mental health conditions. These symptoms may include:

What causes Klinefelter syndrome?

Klinefelter syndrome occurs when there’s an extra X chromosome in your genetic code. This change happens before birth and can happen in a few different ways:

  • A sperm cell carries an extra X chromosome.
  • An egg cell holds an extra X chromosome.
  • Cells divide incorrectly during early fetal development. Healthcare providers call this mosaic Klinefelter syndrome. (It occurs when some — but not all — of your cells have an extra X chromosome.)

What are the complications of Klinefelter syndrome?

People with Klinefelter syndrome have a higher risk of developing certain metabolic syndromes like:

Additionally, people with Klinefelter syndrome are more likely to develop:

Diagnosis and Tests

How is Klinefelter syndrome diagnosed?

Healthcare providers may diagnose Klinefelter syndrome during:

  • Fetal development. Providers don’t often test fetuses for Klinefelter syndrome. If they detect the condition, it usually happens when running genetic tests (like chorionic villus sampling or amniocentesis) for other reasons.
  • Childhood or adolescence. A provider may recommend testing if they notice atypical growth or development (related to puberty) during these years.
  • Adulthood. Your provider may test for Klinefelter if you have low testosterone or fertility issues (trouble getting pregnant with your partner).

People with mild cases of Klinefelter syndrome — those without symptoms — may never even know they have the condition. For others, their providers only discover it during infertility testing.

What tests can help diagnose Klinefelter syndrome?

The goal of testing is to detect and identify an extra X chromosome. The most common way to do this is with a karyotype test, which is a blood test that tells your provider the number and types of chromosomes present. Providers can use karyotyping on children, adults and even in fetuses before birth.

Healthcare providers recommend neuropsychological testing for children with Klinefelter syndrome. It’s best to test them at the time of diagnosis and again every few years. This can help identify any learning challenges and guide educators on how to help your child succeed.


Management and Treatment

How do healthcare providers treat Klinefelter syndrome?

People with Klinefelter syndrome are born with it. Because it’s a part of your genetic code, you can’t cure it or get rid of it. But you can manage your symptoms with treatment and guidance from your healthcare provider.

Klinefelter syndrome treatments may include:

  • Hormone replacement.
  • Therapy.
  • Treatment for other medical conditions.
  • Surgery, which is rare for people with this condition.

Hormone replacement

People with Klinefelter syndrome often have less testosterone than those without the condition. Some won’t start puberty at all, while others will start but then stop or regress.

This happens because the testicles usually “fail” in Klinefelter syndrome, which makes them unable to make testosterone and sperm. Replacing the testosterone hormone can help minimize some of the symptoms of the condition.

Healthcare providers usually recommend testosterone injections in children and teens. Adults may receive other types of treatment, including:

The goals of hormone replacement therapy include:

  • Stronger bones.
  • More body and facial hair.
  • A deeper voice.
  • Stronger muscles.
  • Improved mood, self-image and overall mental health.
  • An increased sexual desire.


If you have Klinefelter syndrome, you can benefit from different types of therapy. As part of your treatment, you might see:

Children with Klinefelter syndrome may also need changes in their classrooms or learning environments. If your child has this condition, they may qualify for special help in school to adapt the lessons in a way that works for them.


About half of all teenagers AMAB develop extra breast tissue. But in people with Klinefelter syndrome, the extra breast tissue is more likely to stay. If the excess breast tissue bothers you, your healthcare provider may recommend gynecomastia surgery to remove the extra tissue. Most healthcare providers recommend waiting until adulthood to have this procedure.


Is Klinefelter syndrome preventable?

You can’t prevent Klinefelter syndrome because it’s a random change in your genetic code — and it happens before birth. You can’t pass this condition down to your child. And there’s nothing a parent can do to keep their child from developing Klinefelter syndrome.

Outlook / Prognosis

What can I expect if I have Klinefelter syndrome?

If you or your child has Klinefelter syndrome, it’s important to meet with a genetic counselor as soon as you receive a diagnosis. An endocrinologist can also discuss the timing of initiating testosterone replacement. Because symptoms vary so much from person to person, your treatment might not be the same as another person with the condition. But with help from your healthcare provider, you can come up with a plan that works for you.

How long can a person live with Klinefelter syndrome?

People who have Klinefelter syndrome have a normal life expectancy. Treatment can help people with this condition live full, happy, healthy lives.

Living With

When should I see my healthcare provider?

If you’re a parent, schedule an appointment with your child’s pediatrician if you notice developmental delays. For example, maybe your child took longer than their peers to crawl, walk or talk. If your child is a teen, look for physical symptoms like long legs, a short torso or a taller-than-average stature — or other symptoms like low energy, behavioral issues or learning challenges.

Your child’s healthcare provider can examine your child and ask about their symptoms. They may run tests to determine if your child has Klinefelter syndrome or other genetic conditions.

If you’re an adult with Klinefelter syndrome, let your provider know if you notice new symptoms or changes in existing symptoms. Because people with Klinefelter syndrome are more prone to certain health conditions, it’s important to have routine checkups with your primary care provider.

A note from Cleveland Clinic

It can be scary learning that you or your child has a genetic condition like Klinefelter syndrome. The uncertainty of not knowing exactly how this condition will impact your life can feel overwhelming. Your healthcare providers are here to help. Whether you received your diagnosis in childhood or adulthood, learning about your treatment options can significantly improve your overall quality of life.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 10/09/2023.

Learn more about our editorial process.

Appointments 216.444.6568