Klinefelter Syndrome (xxy syndrome)
Symptoms, Causes, Treatment

Couple getting news from doctor - Klinefelter Syndrome

The Guardian newspaper[1] interviewed several men with Klinefelter syndrome. Most only learned about their condition when they and their partners were experiencing fertility problems. This scenario is far too common, but when Klinefelter syndrome is diagnosed as early as possible, you can get the treatment you need to restore your health and virility. You can also access the help you need to grow your family and cut out years of disappointment and heartbreak.

What is Klinefelter syndrome?

Klinefelter syndrome is a genetic disorder that causes males to have an extra X chromosome. Also called XXY syndrome, the condition interferes with the development and function of your testes and contributes to hypogonadism and low testosterone.

While Klinefelter syndrome increases your risk for a variety of health conditions, it’s not particularly dangerous in itself. In many cases, doctors don’t diagnose the syndrome until you and your partner are struggling to conceive, and you have a sperm analysis as part of your fertility workup.

Approximately 1 in every 650 male babies[2] are born with Klinefelter syndrome. Overall, the condition is rare, although it’s one of the more common sex chromosome abnormalities. 

While it’s possible for the extra X chromosome to be present in every cell of your body, around 10% of men with the chromosomal abnormality[3] have mosaic Klinefelter syndrome when the extra X is only in some of your cells. In very rare cases, other chromosomal abnormalities may be present in your other cells.


You might remember from high school biology that chromosomes[4] are the strands of nucleic acids and proteins that carry your genetic data. Humans usually have 46 chromosomes, which provide the genetic data that control everything from your height and eye color to your hormone production and risk for certain diseases. Your genes even regulate how medications work within your body. 

As a male, your sex chromosomes are 46 XY — women have 46 XX. Klinefelter syndrome occurs when you have an extra X-chromosome, creating a total of 47 chromosomes. The chromosomal expression of your condition is 47 XXY.

Signs of Klinefelter syndrome

The most common signs of Klinefelter syndrome are small, firm testes, a small penis, and little body or facial hair. In most cases, men with Klinefelter syndrome aren’t able to father biological children.

Other signs of Klinefelter syndrome include:

  • Taller than average
  • Longer legs, wider hips, and a shorter torso than average
  • Puberty is delayed, incomplete, or absent
  • Gynecomastia (enlarged breast tissue)
  • Weak bones
  • Low energy
  • Low sperm count
  • Low sex drive
  • Less muscular than other men
  • Increased belly fat

Men and boys with Klinefelter syndrome are often more shy or sensitive than their peers. You might also have trouble expressing your thoughts or feelings and feel awkward socializing with others. 

It’s also common for boys and teenagers with the condition to have difficulty with reading, writing, spelling, or math. You might also struggle with attentiveness and concentration.

Causes of Klinefelter syndrome

Unlike many conditions, Klinefelter syndrome is not inherited from either of your parents. It stems from a random genetic error. Risk factors like parental age or substance abuse that cause other genetic problems and congenital abnormalities don’t influence your risk of developing Klinefelter syndrome. 

When cells divide, your chromosomes distribute your genetic material into the nucleus of every cell. Klinefelter syndrome occurs when a nondisjunction error interferes with X chromosome distribution. Instead of each cell receiving either XX or XY chromosomes, you end up with an extra copy of the X chromosome. 

Potential complications

Klinefelter syndrome can cause health complications. The most common issue is primary hypogonadism and low testosterone. If your testes are underdeveloped, they won’t produce testosterone correctly, which creates a variety of distressing symptoms. 

In addition to fertility problems, you could have decreased muscle mass, a tendency to weight gain, low energy, reduced motivation, and a low to absent sex drive. 

You’re more likely to have mental health conditions like anxiety or depression. It can also contribute to social, behavioral, and emotional problems like low self-esteem, impulsiveness, and emotional immaturity. 

Men with Klinefelter syndrome also have a higher risk of developing:

  • Osteoporosis
  • Heart disease
  • Blood vessel disease
  • Lung disease
  • Dental health problems

Klinefelter syndrome also increases your risk of having autoimmune conditions like rheumatoid arthritis or lupus. You also have an increased chance of having a metabolic disorder like Type 2 diabetes, high cholesterol, or high blood pressure. 


In many cases, men lead healthy lives without ever knowing they have Klinefelter syndrome. If you have severe symptoms or fertility problems, your doctor might recommend additional testing to identify the root cause of your symptoms. 

Your physician might begin with a hormone analysis to determine if you have low testosterone. If your results indicate Klinefelter syndrome, your doctor might order additional genetic testing.

Physicians use karyotype — the clinical term for chromosomal analysis — to confirm your diagnosis. They take a blood sample and separate your white blood cells, which are mixed with a tissue culture and incubated. Lab technicians then examine the sample for chromosomal abnormalities like an extra X chromosome. 

The test usually examines at least 20 cells, which allows the technician to determine if you have full or mosaic Klinefelter syndrome. 

Treatments for Klinefelter syndrome

Testosterone replacement therapy is the most common treatment for Klinefelter syndrome. Your physician can prescribe topical creams or injections to restore and stabilize your testosterone levels. Regulating your hormones often relieves many of your symptoms, restoring your health and vitality. 

When Klinefelter syndrome is diagnosed in boys or adolescents, physicians might recommend educational evaluation, speech therapy, and other counseling services. This can help young men develop the skills they need to cope with their condition. They can learn and practice behaviors that can help them thrive. 

If you’re concerned about low testosterone and conditions like Klinefelter syndrome, don’t feel embarrassed or ashamed. Complete the screening questionnaire and start the process of identifying your condition. Once you and your physician know what is causing your symptoms, you can get the personalized treatment you need to thrive. 

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