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Klinefelter syndrome

Medically reviewed by Drugs.com. Last updated on Sep 11, 2023.

Overview

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 genetic condition affecting males, and it often isn't diagnosed until adulthood.

Klinefelter syndrome may adversely affect testicular growth, resulting in smaller than normal testicles, which can lead to lower production of testosterone. The 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 has the same signs and symptoms.

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.

Symptoms

Signs and symptoms of Klinefelter syndrome vary widely among males with the disorder. Many boys with Klinefelter syndrome show few or only mild signs. The condition may go undiagnosed until adulthood or it may never be diagnosed. For others, the condition has a noticeable effect on growth or appearance.

Signs and symptoms of Klinefelter syndrome also vary by age.

Babies

Signs and symptoms may include:

Boys and teenagers

Signs and symptoms may include:

Men

Signs and symptoms may include:

When to see a doctor

See a doctor if you or your son has:

Causes

Klinefelter syndrome occurs as a result of a random error that causes a male to be born with an extra sex chromosome. It isn't an inherited condition.

Humans have 46 chromosomes, including two sex chromosomes that determine a person's sex. Females have two X sex chromosomes (XX). Males have an X and a Y sex chromosome (XY).

Klinefelter syndrome can be caused by:

Extra copies of genes on the X chromosome can interfere with male sexual development and fertility.

Risk factors

Klinefelter syndrome stems from a random genetic event. The risk of 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

Klinefelter syndrome may increase the risk of:

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.

Diagnosis

Your doctor will likely do a thorough physical exam and ask detailed questions about symptoms and health. This may include examining the genital area and chest, performing tests to check reflexes, and assessing development and functioning.

The main tests used to diagnose Klinefelter syndrome are:

A small percentage of males with Klinefelter syndrome are diagnosed before birth. The syndrome might be identified in pregnancy during a procedure to examine fetal cells drawn from the amniotic fluid (amniocentesis) or placenta for another reason — such as being older than age 35 or having a family history of genetic conditions.

Klinefelter syndrome may be suspected during a noninvasive prenatal screening blood test. To confirm the diagnosis, further invasive prenatal testing such as amniocentesis is required.

Treatment

If you or your son is diagnosed with Klinefelter syndrome, your health care team may include 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 is based on signs and symptoms and may include:

Coping and support

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

Boys with Klinefelter syndrome

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

Men with Klinefelter syndrome

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

Preparing for an appointment

If you notice symptoms of Klinefelter syndrome in yourself or your son, talk to your health care 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. A trusted companion can help you remember information and provide emotional support.

What you can do

Before the appointment, make a list of:

Questions to ask might include:

Don't hesitate to ask other questions during the appointment.

What to expect from your doctor

Your doctor may ask questions such as:

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