Klinefelter's Syndrome FAQs
What is Klinefelter's Syndrome (KS)?
In 1942 Dr Harry Klinefelter and his co-workers published a study about nine men who had enlarged breasts, sparse facial and body hair and small, firm, infertile testes. By the late 1950s other researchers discovered that men with Klinefelter's Syndrome had an extra sex chromosome giving 47XXY instead of the more usual 46XY.
How many men have KS?
Based on studies in the US in the 1970s it appears that KS is one of the more common genetic abnormalities affecting from 1 in 500 to 1 in 1000 live births.
How does it happen?
Women usually inherit two X chromosomes - one from each parent. Men inherit an X from their mothers and a Y from their fathers. However the cell division process that occurs in the cells destined to become eggs and sperm occasionally gives rise to an egg with two X's or a sperm with both an X and a Y.
This gives two chances to produce an XXY male. Either an XY sperm fertilises an X egg or a Y sperm fertilises an XX egg.
What are all these numbers?
They're the numbers of chromosomes. Human cells have 23 pairs of chromosomes, 46 in total. Men with KS have an extra X making 47. There are other less common variations; for example 48XXXY or 49XXXXY. There is also a mosaic type where some body cells are 46XY.
How does KS affect you?
Boys with or without KS tend to look very similar, but when puberty occurs the testes remain small and this persists into adult life. Infertility is usual and a lack of libido is likely. Some breast development is possible. A KS male may develop a pear-shaped body.
Men with KS tend to be tall but their limbs are disproportionately long compared with their bodies. Many also have big feet and obviously have problems getting clothing to fit.
Body hair may fail to appear and facial hair rarely attains the level that feelings of masculinity may desire.
Boys developing these characteristics are often teased at school and this may give rise to a boy 'turning off' and exhibiting behavioural problems.
Is there any treatment?
Many of these characteristics, but not the height or infertility, may be relieved by Testosterone Replacement Therapy given from puberty onwards. The level should be determined by the Endocrinologist.
Where insufficient testosterone is present, bone density may be reduced when the body fails to lay down sufficient calcium and this may give rise to bone disease such as osteoporosis. For this reason all KS males should request Bone-Density Scans at least every two years.
I think I may have KS. What should I do?
Go to your GP. He or she will probably refer you to an endocrinologist and/or arrange a chromosome test.
Where can I find out more?
- There is more medical information on Medline.
- Klinefelter's Syndrome Association UK
- Klinefelter Syndrome Awareness Day is held in March each year.
We don't currently post comments online but are always keen to hear your feedback.
Date of last review 02/04/14
Date of next review 02/04/17
It’s tough for men to ask for help but if you don’t ask when you need it, things generally only get worse. Especially during a major pandemic like Covid-19. So we’re asking.
Men appear more likely to get Covid-19 and far, far more likely to die from it. The Men's Health Forum are working hard pushing for more action on this from government, from health professionals and from all of us. Why are men more affected and what can we do about it? We need the data. We need the research. We need the action. Currently we're the only UK charity doing this - please help us.
Here’s our fund-raising page - please chip in if you can.