What is Klinefelter Syndrome?

Klinefelter Syndrome (kline-fel-ter), also known as 47,XXY, is a genetic condition where you have an extra X chromosome. It’s congenital, which means that you’re born with it.

Klinefelter Syndrome is a common chromosomal disorder, affecting one in 550 men. However, many people with Klinefelter Syndrome are never diagnosed.

What are the symptoms for Klinefelter Syndrome?

Klinefelter Syndrome is the most common cause of hypogonadism, a condition that stops your body from producing sperm and testosterone.

Testosterone is the major androgen (male sex hormone) in your body, as you need it for normal reproductive and sexual function. This means that, if you have Klinefelter Syndrome, it’s likely that you’re infertile.

Small testicles (about the size of a grape) after puberty are a strong indication of Klinefelter Syndrome. Other symptoms of Klinefelter Syndrome, which sometimes but not always occur, include:

  • Taller than average height

  • Reduced facial hair

  • Reduced body hair

  • Reduced muscle strength

  • Breast development (gynecomastia)

  • Osteoporosis

  • Feminine fat distribution (e.g. on thighs)

  • Varicose veins

  • Low energy (lethargy).

What causes Klinefelter Syndrome?

We don’t know why some people have an extra X chromosome. Although Klinefelter Syndrome is a genetic disorder, it’s rare for siblings to have it.

How does diagnosis work?

A diagnosis of Klinefelter Syndrome is confirmed with blood tests.

It can be diagnosed before or immediately after a child is born.  

In other cases, Klinefelter Syndrome is identified during childhood when learning or behavioural difficulties develop, or around the time of puberty when expected physical changes are delayed or don’t happen.

Because the symptoms aren’t always obvious, an adult might not be diagnosed until they seek medical help for infertility, a loss of sex drive, or a bone fracture. The majority of Klinefelter cases are diagnosed in adulthood.

We think that as many as 75% of men with Klinefelter Syndrome are never diagnosed, and remain untreated for life, possibly because doctors don’t routinely check the size of testicles.

What treatment options are there for Klinefelter Syndrome?

Klinefelter Syndrome can’t be cured. Instead, you’ll have lifelong testosterone therapy to help maintain general wellbeing.

In Australia, testosterone therapy is available as injections, gels, creams, patches, and tablets, and works very well for men with testosterone deficiency.

Your doctor or an endocrinologist can supervise testosterone therapy.

Your doctor’s appointment

Questions to ask your doctor

  • Are my children likely to inherit this disorder from me?

  • Will testosterone therapy improve any or all of my symptoms?

Email these questions to yourself to take into your doctor's appointment.

Resources

Klinefelter Syndrome Fact Sheet Image Tile

Fact sheet

Klinefelter syndrome

Klinefelter Syndrome - Hormone and Me Tile Image

Information guide

Klinefelter syndrome - Hormones and me

Video

What is Klinefelter syndrome?