Klinefelter’s Syndrome

A chromosomal abnormality in boys, causing tall stature and small genitals

  • Present at birth
  • Affects only boys
  • Due to an extra chromosome
  • Lifestyle is not a significant factor

Klinefelter’s syndrome affects only boys. In the UK, about 1 in every 600 boys has the condition, but it is thought that many cases are never detected. Affected boys have two copies of the X chromosome instead of the usual one. This may lead to insufficient levels of the male sex hormone testosterone and cause infertility and characteristic physical features.

What are the symptoms?

A boy with Klinefelter’s syndrome often appears normal at birth. However, as he reaches puberty, the physical characteristics of the condition become more obvious and include:

  • Tall stature.

  • Long legs.

  • Small penis and testes.

In some cases, breast enlargement also develops (see Gynaecomastia). Men with Klinefelter’s syndrome are infertile because they are unable to produce sperm. A small number of those who have the condition have generalized learning disabilities.

What might be done?

Klinefelter’s syndrome is often suspected from an affected boy’s physical characteristics. The diagnosis is confirmed by a blood test to look for the extra X chromosome. If the condition is diagnosed in childhood, treatment with a testosterone supplement may encourage the development of male characteristics and prevent gynaecomastia. However, if gynaecomastia does occur and causes psychological distress, an operation may be done to reduce breast size. Most boys with Klinefelter’s syndrome lead a normal life, although they will not be able to father children. Genetic counselling is offered to parents of an affected child who plan to have more children.

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

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