Klinefelter Syndrome

Klinefelter syndrome is the most common genetic disorder in men. An almost certain consequence of having the syndrome is permanent infertility. The syndrome is named after Harry Klinefelter, the endocrinologist who first identified it in 1942. In a nutshell, men with Klinefelter syndrome have an extra X chromosome. Generally, men have one copy of the X chromosome and one copy of the Y chromosome in each of their cells. Women have two X chromosomes. Klinefelter males, on the other hand, have at least one spare X - so the make-up of Klinefelter cells will be XXY.

The Fertility Connection

Klinefelter males are born with the condition. Throughout their development, the syndrome prevents their bodies from producing enough of the male sex hormone testosterone. This can have a direct effect on the growth and development of the testicles. Adult Klinefelter men may have smaller-than-average testes. In almost all cases, these men have can have a normal sex life, but the defect in their testicles makes them infertile. Although some Klinefelter males will exhibit symptoms of the condition from boyhood, many don't realize that they have the condition until they try as adults to become fathers. Then they find that they can't get their partners pregnant.

Klinefelter Symptoms

If you've been trying for over a year, without success, to impregnate your partner, you should see your doctor. The chances of you actually having Klinefelter syndrome are very small (somewhere between 1 in 500 and 1 in 1000 men have the condition).

Men who have Klinefelter's may also be taller than average, have small testicles (as mentioned above), and, possibly, some feminine physical features (lack of facial hair, for example). Of course, no man wants to find out that he has this condition, meaning that he will probably never become a biological father - but it's better to know one way or the other. Osteoporosis (weakening of the bones) is common complication of Klinefelter syndrome. This can be prevented through treatment. Even if a man can't fix his infertility, he can at least protect his own future health.


Klinefelter syndrome is diagnosed by means of a physical exam, blood tests and a chromosome analysis. The physical exam will look for any abnormalities in the genitalia or chest, and check sexual function. The blood tests aim to detect any abnormal levels of certain hormones in the body, which can be an indicator of this genetic condition. Lastly, the definitive diagnosis is made via the chromosome analysis. This involves sending a blood sample off to a DNA laboratory. The results usually take a few weeks to come back. This type of test is called a karyotype analysis.


Treatments are available for some symptoms of Klinefelter syndrome - for example, testosterone therapy can help men who have some feminine features. It can also help them to maintain their bone strength. Unfortunately, the infertility aspect of Klinefelter's is rarely treatable, although some Klinefelter males have become Dads thanks to an assisted reproduction technique called ICSI. See our section on Klinefelter treatment, under Male Infertility: Drugs and Treatment, for more information.

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