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Overview

Klinefelter syndrome is a common condition that results when a person assigned male at birth has an extra copy of the X sex chromosome instead of the typical XY. Klinefelter syndrome is a genetic condition that occurs before birth, but it often isn't diagnosed until adulthood.

Klinefelter syndrome may affect testicular growth. This results in smaller testicles, which can lead to making less of the hormone testosterone. The syndrome also may cause smaller muscle mass, less body and facial hair, and extra breast tissue. The effects of Klinefelter syndrome vary, and not everyone has the same symptoms.

Most people with Klinefelter syndrome produce little or no sperm, but assisted reproductive procedures may make it possible for some people with Klinefelter syndrome to have biological children.

Symptoms

Symptoms of Klinefelter syndrome vary widely. Many children with Klinefelter syndrome show few or only mild symptoms. Most often the condition isn't diagnosed until puberty or adulthood, or it may never be diagnosed. For others, the condition has a noticeable effect on growth or appearance. Klinefelter syndrome may affect development, physical appearance, sexual development and mental health.

Development

• Slow motor development, such as taking longer than average to sit up, crawl and walk.
• Speaking later than other babies of the same age.
• Learning and language problems, such as trouble with reading, writing, spelling or math.

Physical appearance

• Taller than average height.
• Longer legs, shorter body, narrower shoulders, broader hips and extra belly fat compared with other children and adults assigned male at birth.
• After puberty, less muscle mass and less facial and body hair compared with other teens and adults assigned male at birth.
• Extra breast tissue, called gynecomastia.
• Low energy levels.

Sexual development

• Small, firm testicles and a small penis. Babies may be born with testicles that haven't moved from the belly into the scrotum, a condition called undescended testicles.
• Puberty changes that are delayed, that only include some changes or that don't happen at all.
• Low sperm count or no sperm.
• Low sex drive.

Mental health

• Difficulty expressing thoughts and feelings.
• Having a hard time engaging in social activities.

When to see a doctor

Talk to your healthcare professional if you notice:

• Slow development during infancy or childhood. Delays in growth and development can be the first sign of several conditions that need treatment, including Klinefelter syndrome. Though some differences in physical and mental development are expected among children, check with a healthcare professional if you have any concerns.
• Problems with fertility. Problems with fertility aren't often diagnosed in people with Klinefelter syndrome until they realize they're not able to have a biological child.

Causes

Klinefelter syndrome occurs because of a random change in the egg or the sperm that causes a baby assigned male at birth to be born with an extra X sex chromosome. The condition is not passed down in families.

Klinefelter syndrome can be caused by:

• One extra copy of the X sex chromosome in each cell (XXY), the most common cause.
• An extra X sex chromosome in some of the cells. This is called mosaic Klinefelter syndrome and may result in fewer symptoms.
• More than one extra copy of the X sex chromosome, which is rare and results in a severe form of the syndrome.

In people assigned male at birth, extra copies of genes on the X sex chromosome can interfere with sexual development and fertility.

Risk factors

Klinefelter syndrome occurs because of a random genetic change in the sperm or the egg. The risk of Klinefelter syndrome is not raised by anything parents do or don't do. For people carrying a pregnancy after age 35, the risk is higher but only slightly.

Complications

Klinefelter syndrome may raise the risk of:

• Anxiety and depression.
• Social, emotional and behavioral problems, such as low self-esteem.
• Problem with fertility and sexual function.
• Thin and brittle bones, a condition called osteoporosis.
• Heart and blood vessel disease.
• Breast cancer and some other cancers.
• Lung disease.
• Metabolic syndrome, which includes type 2 diabetes, high blood pressure, and high cholesterol and triglycerides.
• Being overweight.
• Autoimmune disorders such as lupus and rheumatoid arthritis.
• Tooth and mouth problems that make dental cavities more likely.
• Autism spectrum disorder.

Some complications caused by Klinefelter syndrome are the result of low testosterone, also called hypogonadism. Hormone therapy lessens the risk of certain health problems, especially when therapy is started at the beginning of puberty.

Diagnosis

To diagnose Klinefelter syndrome, a healthcare professional does a physical exam and asks questions about symptoms and health. This may include looking at the genital area and chest and talking about development and functioning.

Main tests used to diagnose Klinefelter syndrome are:

• Hormone testing. Blood tests can show hormone level changes that are a sign of Klinefelter syndrome.
• Chromosome analysis. Also called a karyotype, this test can confirm a diagnosis of Klinefelter syndrome. A blood sample is sent to the lab to check the shape and number of chromosomes.

Healthcare professionals sometimes diagnose Klinefelter syndrome before birth when testing is done for another reason. The syndrome can be found in pregnancy during a procedure to look at fetal cells taken from the fluid around the baby or from the placenta. These tests may be done for pregnant people who are older than age 35 or have a family history of genetic conditions.

Klinefelter syndrome may be suspected during a noninvasive prenatal screening blood test. This test looks at cell-free DNA in the pregnant person's blood sample. To confirm the diagnosis, more-invasive prenatal testing is needed.

Treatment

If you or your child is diagnosed with Klinefelter syndrome, your healthcare team may include a doctor called an endocrinologist who specializes in conditions involving the body's glands and hormones. Your team also may include a speech therapist, a pediatrician, a physical therapist, a genetic counselor, a reproductive medicine or infertility specialist, and a counselor or psychologist.

Although there's no way to repair the sex chromosome changes due to Klinefelter syndrome, treatments can help lessen its effects. The earlier the condition is diagnosed and treatment is started, the greater the benefits. But it's never too late to get help.

Treatment for Klinefelter syndrome is based on symptoms and may include:

• Testosterone therapy. Starting at the time of the usual onset of puberty, testosterone therapy can be given to help stimulate changes that typically occur at puberty. These changes include a deeper voice, facial and body hair, bigger muscle mass, and sexual desire. Testosterone therapy also can help bone density. It may help mood, focus and attention too. Testosterone therapy does not help with fertility problems.
• Breast tissue removal. If extra breast tissues develops, the tissue can be removed by a plastic surgeon, if desired.
• Therapy. Speech and language therapy can help if there are speech or language problems. Physical therapy can help with motor skills and muscle strength. Occupational therapy can help with social skills and job skills.
• Educational evaluation and support. If learning and socializing are a problem, extra services may help. Talk to your child's teacher, school counselor or school nurse about what kind of support is available.
• Fertility treatment. Most people with Klinefelter syndrome cannot have biological children because few or no sperm are made in the testicles. For some people who make a small amount of sperm, a procedure called intracytoplasmic sperm injection (ICSI) may help. During ICSI, sperm is taken from the testicle with a biopsy needle and injected directly into the egg.
• Mental health support. Having Klinefelter syndrome can be a challenge, especially during puberty and young adulthood. Coping with infertility also can be a challenge. A family therapist, counselor or psychologist can help work through emotional concerns.

Coping and support

Treatment, health education and social support can greatly benefit people with Klinefelter syndrome.

Children and teens with Klinefelter syndrome

If you have a child with Klinefelter syndrome, you can help with healthy mental, physical, emotional and social development.

• Learn about Klinefelter syndrome. Then you can give accurate information, support and encouragement.
• Monitor your child's development. Get help for problems you notice, such as problems with speech or language.
• Keep regular follow-up appointments with medical professionals. This may help prevent future problems.
• Make sports and physical activities available. These activities will help build muscle strength and motor skills.
• Plan social and group activities. These activities can help develop social skills.
• Work closely with your child's school. Teachers, school counselors and administrators who understand your child's needs can make a big difference.
• Learn what support is available. For example, ask about special education services or mental health services, if needed.
• Connect with other parents and families. Klinefelter syndrome is a common condition. Ask your healthcare professional about internet resources and support groups that may help answer questions and provide support.

Adults with Klinefelter syndrome

If you have Klinefelter syndrome, you may benefit from these self-care tips:

• Work with your healthcare professional. Getting treatment can help you keep your physical and mental health and help prevent problems later in life, such as weakened bones that lead to osteoporosis.
• Find out your options for planning a family. You and your partner may want to talk to a healthcare professional about your options.
• Learn about and talk with others who have the condition. Ask your healthcare team about resources that give information about Klinefelter syndrome and that offer the views of others and their partners who cope with the condition. You also may find it helpful to join a support group.

If you have mental health concerns at any age, such as sadness or low self-esteem, talking with a mental health professional can help.

Preparing for an appointment

If you notice symptoms of Klinefelter syndrome in yourself or your child, talk with your healthcare professional. You may be referred to a specialist for testing and diagnosis.

Here's some information to help you get ready for your appointment. If possible, bring a family member or friend with you. This trusted person can help you remember information and offer emotional support.

What you can do

Before the appointment, make a list of:

• Symptoms that concern you.
• Medicines, including vitamins, herbs or other supplements, and the doses.
• Puberty milestones, such as the age at which facial and body hair, growth of the penis, and bigger testicle size began.
• Questions to ask the healthcare professional.

Questions to ask might include:

• Are these symptoms of Klinefelter syndrome?
• What tests are needed to confirm the diagnosis?
• What are other possible causes for the symptoms?
• Is a specialist needed?
• What treatments are needed?
• What are the side effects and expected results of treatment?
• What kind of special therapies do you recommend?
• What kind of support is available?
• How can I learn more about this condition?

Feel free to ask other questions during the appointment.

What to expect from your doctor

Your healthcare professional may ask questions such as:

• What symptoms have you noticed?
• When did you first notice symptoms?
• When were growth and developmental milestones met?
• Do you have problems with fertility?
• Have you had any previous tests or treatments? What were the results?

Being ready for your appointment can give you time to talk about what's most important to you.