Recognising Klinefelter syndrome in children and teenagers

7 min

Klinefelter syndrome is a collection of signs and symptoms caused by an abnormal number of sex chromosomes in the cells of the body and its effects vary between males with the condition. Symptoms of Klinefelter syndrome can be so mild in some individuals that they, their parents, and their doctors may not even realise they have the condition. In many males, it’s picked up when they try to start a family because even for those with mild symptoms, most men with Klinefelter syndrome produce very few or no sperm and are infertile.

However, some boys do show signs and symptoms in childhood and adolescence. Here’s what health professionals can keep an eye out for and what’s next when it comes to management of the condition.

What is Klinefelter syndrome?

People with Klinefelter syndrome can be affected in different ways, but they all share a common genetic characteristic: the cells of their bodies contain a different number of chromosomes than normal.

The collection of chromosomes in an organism’s cells is known as its karyotype. The usual human karyotype is made up of 22 pairs of chromosomes called autosomes (which are the same in males and females) and a pair of sex chromosomes (resulting in a total of 46 chromosomes). Normally, women have 44 autosomes and two X chromosomes (denoted 46, XX) and men have 44 autosomes and one X and one Y chromosome (46, XY).

The most common karyotype associated with Klinefelter syndrome is 47, XXY, which occurs in 80-90% of males with the condition. This is why the condition is sometimes referred to as ‘XXY syndrome’.

How does Klinefelter syndrome occur?

During the development of eggs and sperm, the sex chromosomes might not separate properly, so a sperm or an egg can end up with 22 autosomes and 2 sex chromosomes (either XX from females or XY from males). After fertilisation, this can result in cells that are 47, XXY. People with this genotype have Klinefelter syndrome. Rarely, some people with Klinefelter syndrome have more than 2 X chromosomes (e.g., 48, XY or 49, XY) or more than 1 Y chromosome (e.g., 48, XXYY).

The extra X chromosome in people with Klinefelter syndrome is responsible for effects on development and body function that vary from person to person. The ways in which the extra X chromosome causes these effects are unknown, but it might be because of the extra copies of some genes on the extra X chromosome.

Who does Klinefelter syndrome affect?

Somewhere around 1-2 per 1000 newborn boys is 47, XXY, making it the most common genetic disorder in men. However, only 25-50% of people with Klinefelter system are ever diagnosed, and most of these diagnoses are not made until adulthood[1].

Early detection of Klinefelter syndrome offers the best prospects for managing the condition and preventing complications.

Recognising the signs and symptoms of Klinefelter syndrome is difficult because they’re not the same for everyone.

What to look for and what to do in children with Klinefelter syndrome

What to look for and what to do around the time of puberty

What to look for and what to do in adulthood


[1] Zitzmann et al., 2021. European academy of andrology guidelines on Klinefelter Syndrome Endorsing Organization: European Society of Endocrinology. Andrology


Health practitioners
Klinefelter syndrome

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