Ask an Expert: Is Klinefelter syndrome inherited?

Klinefelter syndrome refers to a collection of characteristics in males that are caused by having two or more X chromosomes. Chromosomes are structures that contain your genes, which is all the information necessary to create you, from your height to your hair colour to your risk of developing certain health conditions. Although Klinefelter syndrome is a genetic condition, Klinefelter syndrome is not inherited from your parents.

Humans have 23 pairs of chromosomes (46 in total), one set comes from your mum and one set comes from your dad. One pair are sex chromosomes, so they differ depending on whether you are male or female (XX for female or XY for male). Usually, males get an X chromosome from their mum and a Y chromosome from their dad. In Klinefelter syndrome, you get either an X and a Y from your dad, or 2 Xs from your mum. There’s about a 50:50 chance of the extra X chromosome coming from your mum or dad.

Although Klinefelter syndrome is a genetic problem it is not inherited; it is a random event that occurs during the formation of eggs or sperm.

The extra X chromosome in men with Klinefelter syndrome leads to them producing very few or no sperm, making they are infertile. However, in some people with Klinefelter syndrome, it’s possible to father biological children with the help of assisted reproductive technology. If you have mosaic Klinefelter there may be very small numbers of sperm in your semen, and it may be possible to use these to fertilise your partner’s eggs as part of an in vitro fertilisation (IVF) treatment called Intracytoplasmic Sperm Injection (ICSI) – the injection of a single sperm into an egg for fertilisation. The genetic risk to the children of men with Klinefelter syndrome is similar to that of other men with non-obstructive azoospermia (zero sperm count).

Scientists are learning new things about Klinefelter syndrome all the time. Recently, a gene mutation was discovered that makes it more likely than normal for sperm to develop with an X and Y chromosome, causing a higher chance of having children with Klinefelter syndrome. A person could inherit this mutation from a parent, which could cause them to have offspring with Klinefelter syndrome. If this happened, the cause of the Klinefelter syndrome would have been inherited.

Klinefelter syndrome is complicated, and there’s still a lot we don’t know about it. Scientists are learning new things about Klinefelter syndrome all the time. If you have questions about Klinefelter syndrome, speak to your doctor or check out our information on the condition or check out organisations like the Association for X and Y Chromosome Variations.