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Klinefelter syndrome is the most common cause of male infertility. It is a sex chromosome variation that occurs in 1 in 500 males. Most men do not demonstrate symptoms. Normally, males have one X chromosome in their cells. Males affected by Klinefelter syndrome have one (or more) extra X chromosome in most of their cells.

The extra chromosome impacts their:

Klinefelter Syndrome


Another name for Klinefelter syndrome is XXY syndrome, a very literal description of the chromosome abnormality. It’s worth noting that while Klinefelter is the main cause of infertility in men it does not mean that all Klinefelter sufferers will be infertile. If you have Klinefelter Syndrome, you are not necessarily infertile.



Who discovered the syndrome?

Dr. Harry Klinefelter discovered and defined the XXY syndrome in 1942, while helping male patients at Massachusetts General Hospital (Boston). The actual genetics were worked out by doctors later on, between 1956-1959. their names were: Joe Hin Tjio, Albert Lavan, and Patricia Jacobs.


What causes Klinefelter syndrome?

Klinefelter syndrome develops at the time of conception. After the egg is fertilized, chromosome pairs are meant to separate, so that they join with different daughter cells. Two daughter cells are supposed to receive one chromosome each. Sometimes the pair does not separate and instead both of the chromosomes go to the same daughter cell and the other daughter cell is left on it’s own. This problem is known as meiotic nondisjunction and is more common in older mothers.

This genetic problem causes the baby to develop abnormally, especially in the male/female characteristics. Most common are the abnormal development of the pituitary gland, testicles, and hypothalamus portion of the brain. The boy’s testicles don’t grow properly and as adults, they cannot produce enough sperm.  Clear, glassy collagen fibers, called hyaline, replace the healthy tissue.

Scar tissue (fibrosis) forms in the seminiferous tubules, where the sperm form. Klinefelter boys can also develop feminine breasts durign puberty – this happens in 50% of boys affected by Klinefelters. Often the Klinefelter man will be sterile. As you can see, living with Klinefelters is a struggle but it is manageable. However, all these symptoms and side effects can cause psychosocial issues, especially as the boy becomes a man. The feminizing affects can result in low self-esteem.


Understand more on Klinefelter:

Diagnosing Klinefelter Syndrome

Klinefelter facts & treatment options

Why we need testosterone

The information in this article has been taken with permission from the official Lawley booklet on Understanding Kinefelter Syndrome.