Kleinfelter's Syndrome

Klinefelter's syndrome (KS) is one of the commonest chromosomal abnormalities. It affects only males and is caused by the presence of an extra X chromosome in some or all of the cells in the body.

Usually, each cell contains 46 chromosomes arranged in 23 pairs. The 23rd pair are referred to as the sex chromosomes and determine the sex of a person. Women usually have two X chromosomes (XX), whereas men have an X and a Y chromosome (XY). In men with KS, all or some of their cells contain an extra X chromosome. Therefore, they have two X chromosome and one Y (XXY), instead of the usual (XY).

What is a chromosome?

Egg and sperm cells usually only contain 23 chromosomes, one of each pair. Sperm cells contain either an X or a Y chromosome and egg cells contain an X chromosome. In some cases, the eggs and sperm may contain both sex chromosomes due to an error in the way the cells divide. If this occurs, there are two ways in which a child with KS might be conceived. Either a sperm with both an X and a Y chromosome fertilises a normal egg, or an egg with two X chromosomes is fertilised by a normal sperm. The presence of a Y chromosome means that the person is still male but the extra X chromosome leads to certain characteristic changes.

	Characteristics of Kleinfelter's Syndrome

Characteristic features seen in men with KS include breast enlargement, lack of facial and body hair and a pear shaped body. Surgery can reduce breast size and regular injections of testosterone will increase strength and muscle size, and promote the growth of facial and body hair. During childhood, many boys with KS grow faster and have a tendency to be thin with poor muscle development. From the age of 7 there is a tendency to put on fat in about 75% of men with KS and so they are more likely to be overweight. Men with KS also tend to be taller than fathers and brothers. Compared with other men, men with KS have an increased risk of autoimmune disorders, such as type I diabetes, but most of these conditions can be treated with medication.

Learning difficulties and behavioural problems are also associated with KS. Around three-quarters of boys with KS have difficulty learning to read. This problem is caused by a number of factors such as poor memory, short attention span and difficulty in keeping things in order. Boys with KS may also be rather sensitive, passive and shy.

KS may be detected during pregnancy when a CVS or amniocentesis is carried out for other reasons, for example because of a raised risk of Down's syndrome.

However, in many cases boys are not diagnosed with KS until they begin school. KS may be suspected if a boy is delayed in learning to talk, has difficulty with reading and writing and is tall and thin. A few boys may be diagnosed during adolescence, when excessive breast development forces them to seek medical attention.

In other cases, men will only be diagnosed with KS because they are having problems conceiving a child: . Investigations into infertility may reveal that the problem is caused by Klinefelter's syndrome, as XXY males may not produce sufficient sperm. However it should not be assumed that XXY males are infertile without testing, as some men with KS have fathered children.

The majority of people with KS live as men, and are indistinguishable from men with the more usual XY genotype. However, in rare cases, people with KS may not feel comfortable with masculinity. They may choose to live as women, and sometimes have gender reassignment surgery.

Find out more about Kleinfelter's syndrome at the Kleinfelter Syndrome Association UK