Klinefelter’s Syndrome

Klinefelter syndrome is a genetic disorder that affects males. Klinefelter syndrome occurs when a boy is born with one or more extra X chromosomes. Most males have one Y and one X chromosome. Having extra X chromosomes can cause a male to have some physical traits unusual for males.

Symptoms of Klinefelter syndrome

Klinefelter syndrome doesn’t usually cause any obvious symptoms early in childhood, and even the later symptoms may be difficult to spot. Many boys and men don’t realize they have it.

Possible features, which aren’t always present, may include:

  • In babies and toddlers – learning to sit up, crawl, walk and talk later than usual, being weaker, quieter and more passive than usual
  • in childhood – shyness and low self-confidence, problems with reading, writing, spelling and paying attention, mild dyslexia and/or dyspraxia, low energy levels, difficulty socialising or expressing feelings
  • in teenagers – growing taller than expected for the family (with long arms and legs), broad hips, poor muscle tone and slower than usual muscle growth, reduced facial and body hair that starts growing later than usual, a small penis and testicles, enlarged breasts (gynaecomastia)
  • in adulthood – inability to have children naturally (infertility) and a low sex drive.

Causes of Klinefelter syndrome

Klinefelter syndrome is caused by an additional X chromosome.

This chromosome carries extra copies of genes, which interfere with the development of the testicles and mean they produce less testosterone (male sex hormone) than usual.

The extra genetic information may either be carried in every cell in the body or it may only affect some cells (known as mosaic Klinefelter syndrome).

Klinefelter syndrome isn’t directly inherited – the additional X chromosome occurs as a result of either the mother’s egg or the father’s sperm having the extra X chromosome (an equal chance of this happening in either), so after conception the chromosome pattern is XXY rather than XY.

This change in the egg or sperm seems to happen randomly. If you have a son with the condition, the chances of this happening again are very small.

However, the risk of a woman having a son with Klinefelter syndrome may be slightly higher if the mother is over 35 years of age.

Testing for Klinefelter syndrome

See your GP if you have concerns about your son’s development or you notice any troubling symptoms of Klinefelter syndrome in yourself or your son.

Klinefelter syndrome isn’t necessarily anything serious, but treatment can help reduce some of the symptoms if necessary.

In many cases, it’s only detected if a man with the condition undergoes fertility tests.

Your GP may suspect Klinefelter syndrome after a physical examination and they may suggest sending off a sample of blood to check reproductive hormone levels.

The diagnosis can be confirmed by checking a sample of blood for the presence of the extra X chromosome.