Klinefelter's Sydrome

Also known as

  • XXY Syndrome

Klinefelter's Syndrome (KS) is caused by a common congenital condition which is found in around 1 in 650 live male births and is the result of the presence of one or more additional sex chromosomes. Chromosomes are genetic material and a person's sex is determined by X and Y chromosomes. Generally males have one X and one Y chromosome (XY) and females have two X chromosomes (XX). Klinefelter's Syndrome is characterised by the presence of an additional chromosome (XXY).

Condition details

KS is characterised by a collection of symptoms the presence or absence of which can vary widely. The most common symptoms include: In children: Speech and language development disorders Short attention span, easily distracted Lack of agility and dislike of physical games, especially team games Passive, shy Difficulty with self expression Tall stature with disproportionally long legs and arms (euneuchoidism) Moderate learning difficulties A fear or disproportionate regard of people in authority, to the point of not challenging or questioning instructions Often inappropriate references to subjects in discussions (i.e. reference to partners monthly period problems with a group of strangers) Inappropriate responses to threats; sometimes physical aggression towards people seen as 'enemies.'

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Photos of affected individuals

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  • No baby imageBaby
  • No toddler imageToddler
  • No child 4-10 imageChild 4-10
  • No child 10-18 imageChild 10-18
  • No adult imageAdult

Typical age range of first manifestation

  • Does not manifest in Baby
  • Does not manifest in Toddler
  • Does not manifest in Child 4-10
  • Does not manifest in Child 10-18
  • Can manifest in Adult


Lay terms Clinical terms
  • Delayed language development

Affected genes identified to date

Inheritance patterns

Are carriers affected?

How many are affected?

1 in 650 males

Support groups and organisations

Klinefelter's Syndrome Association (KSA)
Tel 0300 111 4748

Known experts

No experts found

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