Klinefelter syndrome is one of the most common genetic conditions affecting males. It usually occurs as the result of an extra copy of the X chromosome in each cell. Klinefelter syndrome affects between one in 500 and one in 1,000 males.

The effects of Klinefelter syndrome vary from person to person. Because the condition can affect testicular growth, boys born with Klinefelter syndrome have low levels of the sex hormone testosterone. This can lead to reduced muscle growth, reduced body and facial hair, and enlarged breast tissue (gynecomastia). In some cases Klinefelter syndrome can cause learning and social problems during childhood and adolescence.

In most cases, Klinefelter syndrome isn't diagnosed until adulthood. But in cases where Klinefelter syndrome is diagnosed with a genetic test before birth or during childhood, treatment can help prevent or treat problems caused by the condition. Most men with Klinefelter syndrome are unable to father children (infertile), though new procedures make it a possibility for some men.

Signs and symptoms of Klinefelter syndrome vary. In some males, the condition has a noticeable impact on growth or appearance. Klinefelter syndrome can also be linked to learning and language problems in some cases. However, many people with Klinefelter syndrome have few noticeable symptoms, and in many cases the condition goes undiagnosed until adulthood.

Klinefelter syndrome symptoms vary by age:

• Babies with Klinefelter syndrome may have no noticeable signs or symptoms at first. As they get older, they may have weak muscles and take longer to sit up and crawl and may walk later than other infants do.
• Boys and teenagers with Klinefelter syndrome may be taller and have longer legs than do other boys. They may reach puberty later than other adolescents do. When they do reach puberty, they may have less muscular bodies and less facial and body hair than other teens do. They also may have testicles that are smaller and firmer than those of other boys. In some cases, low testosterone levels caused by Klinefelter syndrome can lead to enlarged breast tissue (gynecomastia), weaker bones and lower energy levels. Boys with Klinefelter syndrome may be shy and may not be as assertive as other boys are.
• Men with Klinefelter syndrome are usually normal in appearance, though they may be taller than average. Unless they're treated with testosterone, the men are likely to have weak bones (osteoporosis). Most men with Klinefelter syndrome have normal sexual function but cannot father children. Some men with the condition are able to father children with the help of new treatments.

When to see a doctor
You should see a doctor to rule out Klinefelter syndrome or another health condition if you or your son has:

• Slow development during infancy or boyhood. If your son seems to be developing more slowly than other boys are, see your son's doctor. Some variation in physical and mental development is normal among boys. But it's always best to check with a doctor if you have any concerns. Delays in growth and development can be the first sign of a number of conditions that need treatment — including Klinefelter syndrome. If your son does have Klinefelter syndrome, starting testosterone therapy at the time of the usual onset of puberty can help treat or prevent a number of problems caused by the disorder.
• Male infertility. If you haven't been able to get your partner pregnant after a year of regular, unprotected sex, see a doctor. Chances are it's caused by something other than Klinefelter syndrome, but many men aren't diagnosed with the condition until they realize they're unable to father a child. If you do have Klinefelter syndrome, you'll probably never be able to father a child — but you still may need treatment for the condition.

Klinefelter syndrome occurs when a boy inherits an extra sex chromosome from one of his parents during the formation of the embryo. It's a random occurrence and happens entirely by chance. Unlike other chromosomal disorders such as Down syndrome, having a family history of Klinefelter syndrome, or having an older mother at birth doesn't appear to make a person more likely to have the disorder.

Klinefelter syndrome is the result of a random genetic event. The risk of a child being born with Klinefelter syndrome is not increased by what a parent does or doesn't do.

Complications of Klinefelter syndrome vary from person to person. Some complications can be prevented or treated with testosterone therapy. Complications can include:

• Delayed puberty
• Noticeable physical features such as limited facial and body hair, unusually long legs, lack of muscular development, and enlarged breast tissue (gynecomastia)
• Infertility — men with Klinefelter syndrome can rarely father children
• Weak bones (osteoporosis)
• Increased risk of venous ulcers, varicose veins and other problems with blood vessels
• Increased risk of certain health conditions that typically affect women, such as breast cancer
• Increased belly fat, which raises the risk of health problems, including diabetes and heart disease
• Learning or social development issues

A number of complications caused by Klinefelter syndrome are related to low testosterone (hypogonadism). Testosterone replacement therapy reduces the risk of certain health problems, especially when it's started at the beginning of puberty.

When screening for Klinefelter syndrome, the doctor will do a thorough physical examination and ask detailed questions about symptoms and your (or your son's) health. Be prepared to discuss when you, or your son, reached certain puberty milestones, such as the development of pubic and armpit hair, enlargement of the penis, and increased testicle size. The doctor may take blood or urine samples to see whether hormone levels are normal.

Take a few steps to make sure you make the best of the doctor visit:

• Write down detailed notes about any symptoms.
• Make a list of all medications, as well as any vitamins or supplements that you (or your son) are taking.

Your time with the doctor is limited, so preparing a list of questions will help you make the most of your time together. You might want to ask the following questions:

• What tests are needed to confirm my (or my son's) diagnosis or see if the symptoms are caused by something else?
• What treatments are necessary?
• What are the side effects and expected results of treatment?
• Are there any brochures or other printed material that I can take home? What Web sites do you recommend visiting?

In addition to the questions that you've prepared to ask the doctor, don't hesitate to ask questions during your appointment at any time that you don't understand something.

If your son has problems with growth, coordination, strength or learning — or you're an adult male having trouble fathering a child — the doctor may recommend tests to check for Klinefelter syndrome. If you or your child is diagnosed with Klinefelter syndrome, early treatment with teststerone therapy can help prevent problems.

Tests used to diagnose Klinefelter syndrome include:

• A thorough physical examination. This includes carefully examining the genital area and chest and giving tests to check reflexes and mental functioning. The doctor may ask questions about other medical conditions, health problems that run in your family, growth, development and sexual function.
• Hormone testing. Blood or urine samples can reveal abnormal hormone levels that are a sign of Klinefelter syndrome. The doctor may take samples to be evaluated in the lab.
• Chromosome analysis. Also called karyotype analysis, this is the most accurate test used to diagnose Klinefelter syndrome. Results usually aren't available for several weeks. This analysis is necessary to confirm a diagnosis of Klinefelter syndrome. It's usually done by taking a blood sample for laboratory examination to check the shape and number of chromosomes.

Although there's no way to repair the sex chromosome changes due to Klinefelter syndrome, treatments can help minimize its effects.

• Testosterone therapy. Males with Klinefelter syndrome don't produce enough of the male hormone testosterone, and this can have lifelong effects. Starting at the time of the usual onset of puberty, testosterone therapy can help treat or prevent a number of problems caused by the disorder. Testosterone may be given as injections or with a gel or patch on the skin. Testosterone therapy will allow the body changes that normally occur at puberty, such as development of facial and body hair, penis enlargement, and increase in muscle mass. It will also decrease the risk of thinning bones (osteoporosis). It will not result in testicle enlargement or improve infertility.
• Breast tissue removal. Some males develop breasts (gynecomastia) because of the hormonal effects of Klinefelter syndrome. This can be a serious emotional challenge for a teenage boy or a young man. But, treatment can help. Excess breast tissue can be removed by a plastic surgeon, leaving a normal-looking male chest. Testosterone replacement also can help reduce growth of breast tissue.
• Coping with infertility. Nearly all men with Klinefelter syndrome are unable to father children (infertile). For most couples interested in having a child, this can be discouraging. But a number of alternatives exist, including adoption and artificial insemination with donor sperm. One option that may benefit some men with Klinefelter syndrome is a procedure in which sperm is removed from the testicle with a biopsy needle, and injected directly into the female egg. This procedure, known as testicular sperm extraction (TESE) and intracytoplasmic sperm injection (ICSI), is costly and not widely available. But since its introduction in 1996, some men with Klinefelter syndrome have fathered children.
• Psychological counseling. Having Klinefelter can be a challenge, especially during puberty and young adulthood. For men with the disorder, coping with infertility can be difficult. Meeting with a counselor or psychologist to work through these emotional issues can help.
• Educational support. Some boys with Klinefelter syndrome have trouble learning and may benefit from extra assistance. Talk to your child's teacher, school counselor or school nurse about what kind of support might help. Not all boys with Klinefelter syndrome have learning difficulties, but when they do, it's important to monitor their development and seek help.
• Physical and speech therapy. These treatments can help boys with Klinefelter syndrome overcome signs and symptoms such as poor muscle tone and speech and language problems.

Apart from infertility, Klinefelter syndrome may cause minor symptoms for boys or men that are hardly noticeable.

Boys with Klinefelter syndrome
There are a number of steps you can take that can make a big difference in helping your son cope with Klinefelter syndrome and to promote healthy physical and social development through adolescence into young adulthood:

• Monitor your son's development carefully and seek help for any problems you notice, such as trouble with speech or language.
• Encourage participation in sports and physical activities that will help build muscle strength and motor skills.
• Encourage your son to be independent. Be supportive but not overly protective, and provide a home environment with lots of positive feedback and encouragement.
• Cooperate closely with your son's school. Teachers, school counselors and administrators who understand your son's needs can make a big difference.
• Learn what support is available. Boys with Klinefelter syndrome qualify for special programs, including Supplemental Security Income (SSI) benefits.
• Connect with other parents. Klinefelter syndrome is a common condition, and you — or your son — aren't alone. A number of Internet resources and support groups may help answer your questions and alleviate concerns.

Men with Klinefelter syndrome
Men with Klinefelter syndrome can benefit from several self-care measures:

• Work closely with your doctor. Making sure you have the right treatment can help you maintain your current physical and mental health and prevent problems later in life, such as thinning bones (osteoporosis).
• Don't ignore the stress of infertility. You and your partner may both want to talk to a doctor or other health professional about your options.
• Talk with others who have the condition. A number of resources provide information about Klinefelter syndrome and perspectives of other men and their partners who cope with the disorder.