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Klinefelter Syndrome (XXY Syndrome)

Klinefelter syndrome is a genetic condition in which a boy is born with an extra X chromosome. Instead of the typical XY chromosomes in men, they have XXY, so this condition is sometimes called XXY syndrome.

Men with Klinefelter usually don't know they have it until they run into problems trying to have a child. There's no cure, but it can be treated.

You get the extra X chromosome by chance. Either the egg or the sperm that came together to create you had an extra X chromosome. Older women have a slightly higher chance of having a boy with XXY syndrome, but the chance is small.

Men with Klinefelter may have:

An extra X chromosome in every cell, which is the most common

An extra X chromosome in only some cells, called mosaic Klinefelter, in which you don't have as many symptoms

More than one extra X chromosome, which is very rare and more severe

Some men show symptoms of Klinefelter as children, but others don't know they have it until puberty or adulthood. Many men never realize that they have it because symptoms aren't always present.

Symptoms of Klinefelter vary with age and include:

Babies: 

Hernia

More quiet than usual

Slower to learn to sit up, crawl, and talk

Testicles that haven't dropped into the scrotum

Weaker muscles

Children: 

A hard time making friends and talking about feelings

Low energy levels

Problems learning to read, write, and do math

Shyness and low confidence

Teenagers: 

Larger breasts than normal

Less facial and body hair, and it comes in later

Less muscle tone and muscles grow slower than usual

Longer arms and legs, wider hips, and a shorter torso than other boys their age

Puberty never comes, comes later, or doesn't quite finish

Small penis and small, firm testicles

Taller than usual for the family

Adults: 

To diagnose Klinefelter syndrome, your doctor will start with a physical exam and questions about your symptoms and general health. They'll probably examine your chest, penis, and testicles and do a few simple tests, such as checking your reflexes.

Your doctor may then run two main tests:

Chromosome analysis. Also called karyotype analysis, this blood test looks at your chromosomes.

Hormone tests. These check hormone levels in your blood or urine.

It's never too late to treat Klinefelter, but the earlier you start, the better.

One common treatment is testosterone replacement therapy. It can start at puberty and can spur typical body changes, such as facial hair and a deeper voice. It can also help with penis size and stronger muscles and bones, but it won't affect testicle size or fertility.

Testosterone replacement therapy throughout your life can help prevent some of the long-term problems that come with Klinefelter.

Other treatments include:

Counseling and support for mental health issues

Fertility treatment (in some cases, using your own sperm to father a child)

Occupational therapy and physical therapy to help with coordination and build muscles

Plastic surgery to reduce breast size

Speech therapy for children

Support in school to help with social skills and learning delays

If your child has Klinefelter, things that might help include:

Playing sports and other physical activities to build muscles

Taking part in group activities to learn social skills

Many problems caused by Klinefelter are because of lower testosterone levels. You may have a slightly higher chance of:

Treatment can help boys and men with Klinefelter live happy, healthy lives. Advances in fertility treatments have made it possible for some to father children. In general, life expectancy is normal. Some research has found that life expectancy for men with the condition may be a year or two less than those without it  because of other health problems linked to Klinefelter.

Klinefelter's Syndrome Directory

Klinefelter's syndrome is a male genetic disorder in which the male body exhibits some female characteristics. These might include enlarged breasts and hips, a higher-pitched voice, and more. Some men, however, do not have any noticeable symptoms. Treatments include testosterone, therapies, and other support. Follow the links below to find WebMD's comprehensive coverage about how Klinefelter's syndrome is caused, diagnosed, treated, and much more.

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X Y Chromosomes

In the imprinted brain theory, everyone's brain is configured somewhere on a spectrum between hypomentalism and hypermentalism. In hypomentalism, the mechanistic, paternal genes are over-expressed, creating a baby with a larger head who demands more from the mother; this child is more likely to have autism. In hypermentalism, the mentalistic, maternal genes are over-expressed; the baby is likely to have a smaller head, demand less from the mother, and develop psychosis. The normal brain falls somewhere between the two extremes, ensuring that the child exhibits neither autism nor psychosis.

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