Klinefelter syndrome is a genetic condition that results when a boy is born with an extra copy of the X chromosome. Klinefelter syndrome is a common genetic condition affecting males.
Klinefelter syndrome adversely affects testicular growth, and this can result in smaller than normal testicles. This can lead to lower production of the sex hormone testosterone. Klinefelter syndrome may also cause reduced muscle mass, reduced body and facial hair, and enlarged breast tissue. The effects of Klinefelter syndrome vary, and not everyone with it develops these signs and symptoms.
Klinefelter syndrome often isn't diagnosed until adulthood. Most men with Klinefelter syndrome produce little or no sperm. But assisted reproductive procedures may make it possible for some men with Klinefelter syndrome to father children.
Many boys with Klinefelter syndrome have few noticeable symptoms, and the condition may go undiagnosed until adulthood. For others, the condition has a noticeable effect on growth or appearance. Klinefelter syndrome may also cause speech and learning problems in some boys.
Signs and symptoms of Klinefelter syndrome vary by age and may include:
Boys and teenagers
When to see a doctor
Klinefelter syndrome occurs as a result of a random error that causes a male to be born with an extra sex chromosome. Of the 46 human chromosomes, the two sex chromosomes determine a person's sex. In females, both sex chromosomes are X (written as XX). Males have an X and a Y sex chromosome (XY).
Most often, Klinefelter syndrome occurs because of one extra copy of the X chromosome in each cell (XXY). Extra copies of genes on the X chromosome can interfere with male sexual development and fertility.
Some males with Klinefelter syndrome have the extra X chromosome only in some of their cells (mosaic Klinefelter syndrome). Rarely, a more severe form of Klinefelter can occur if a male has more than one extra copy of the X chromosome.
Klinefelter syndrome isn't an inherited condition. Rather, the additional sex chromosome results from a random error during the formation of the egg or sperm or after conception.
Klinefelter syndrome stems from a random genetic event. The risk of a child being born with Klinefelter syndrome isn't increased by anything a parent does or doesn't do. For older mothers, the risk is higher but only slightly.
Complications of Klinefelter syndrome can include:
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 therapy is started at the beginning of puberty.
Preparing for your appointment
A small percentage of males with Klinefelter syndrome are diagnosed before birth. This might happen if a pregnant woman has a procedure to examine fetal cells drawn from the amniotic fluid (amniocentesis) or placenta (chorionic villus sampling). Most women who have these procedures are older than age 35 or have a family history of genetic conditions.
If you notice symptoms of Klinefelter syndrome in yourself or your son, see a doctor. Your 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, growth of the penis, and increased testicle size.
Take a few steps to make sure you make the best of the doctor visit:
Preparing a list of questions can help make the most of your appointment. You might want to ask the following questions:
In addition to the questions that you've prepared, don't hesitate to ask questions as they occur to you during the appointment.
Tests and diagnosis
As part of a physical examination, your doctor will likely examine your (or your son's) genital area and chest and may do tests to check reflexes and mental functioning.
The main tests used to diagnose Klinefelter syndrome are:
Treatments and drugs
If you or your son is diagnosed with Klinefelter syndrome, early treatment can help minimize problems. You might work with a team of health care providers, including a doctor who specializes in diagnosing and treating disorders involving the body's glands and hormones (endocrinologist), 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 minimize its effects. The earlier a diagnosis is made and treatment is started, the greater the benefits. But it's never too late to get help.
Treatment for Klinefelter syndrome may include:
Coping and support
With treatment and support, men with Klinefelter syndrome can expect to lead a normal life. The condition may cause minor symptoms that are hardly noticeable. Educational and social support can make a positive difference.
Boys with Klinefelter syndrome
Men with Klinefelter syndrome
Last Updated: 2013-06-25
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