Let’s Talk Klinefelter Syndrome


Klinefelter’s Syndrome is a genetic condition which occurs when a boy is born with an extra X chromosome. Men are typically born with XY chromosomes, whereas women have XX. Men with Klinefelter Syndrome have XXY chromosomes, which is why the condition is sometimes called XXY syndrome. Whilst there is so much mystery and misinformation around the condition, it actually impacts 1 in every 500 men, but the true number could be much higher, as so often symptoms go undetected until adulthood. Some men never even know they have it!

Whether you think you may have the condition or simply want to know more about it, here’s our low down on all things Klinefelter syndrome.

What causes Klinefelter syndrome?

Little is known about the cause of Klinefelter Syndrome – but really it comes down to chance. Essentially, the egg or sperm that created you had an extra X chromosome, and whilst some medical organisations believe this could be more common in older mothers, there’s still a lot more research to be done.
Are there different types of Klinefelter Syndrome? There are a few different types of Klinefelter Syndrome. You could have an extra chromosome in each cell – the most common type – or an extra X chromosome in only some cells. This is called mosaic Klinefelter, and the symptoms tend to be less noticeable. The most extreme kind of Klinefelter is when you have more than one extra X chrome – but this is very rare.

Symptoms of Klinefelter Syndrome

You might think that a condition that runs so deep is full of obvious symptoms. Many men have no idea they have it until they have issues conceiving (but more on that later).

However, there are a few symptoms that can display throughout a man’s lifetime. Some men, following a Klinefelter diagnosis, can reflect back and spot a few subtle symptoms that may have given an indication they had the condition.

Klinefelter in babies


  • Hernias
  • Not very vocal – not much crying or chatting
  • Slower development – particularly in learning to sit up, crawl, and talk
  • Weaker muscles
  • Noticeably small testicles or testicles that haven’t descended into the scrotum

Klinefelter in children


  • Low energy levels – not keen on being active
  • Problems learning to read, write, and do maths
  • Shyness and low confidence
  • Social awkwardness – finding it difficult to make friends and talk about feelings

Klinefelter in teenagers


  • Delayed puberty, or puberty never really happens
  • Less facial and body hair than other boys
  • Tall – often taller than the rest of a family
  • Longer arms and legs and shorter torsos
  • Less muscle tone and muscles grow slower than usual
  • Smaller than average penis and small, firm testicles

Klinefelter in adults


  • Low sex drive
  • Issues with erectile dysfunction
  • Low testosterone – and symptoms associated with that like tiredness and low mood
  • Infertility

What this list of symptoms misses out on is the unique and interesting ‘super powers’ that Klinefelter can also come with. Many men with the syndrome report being highly creative, emotionally intelligent and having an incredible memory! You can hear more about this in our interview with Gareth Landy.

Is there a treatment for Klinefelter Syndrome?

Whilst there is no cure for the syndrome, many symptoms can be improved with testosterone replacement therapy. This is particularly effective if the condition is spotted at a young age, as it can help encourage puberty, development of the penis and bone density. Even later in life testosterone replacement therapy can have huge benefits, especially when it comes to things like mental wellbeing, energy levels and sex drive.

Testosterone Replacement Therapy and Fertility

The one symptom that testosterone replacement therapy won’t help with is infertility. As with anything that artificially increases the amount of testosterone your body naturally produces (like steroids) testosterone replacement therapy could actually make problems with sperm production worse.
If possible, it’s best to start testosterone replacement therapy early – and try to collect and freeze some sperm ahead of time. This might not always be possible, but it gives young boys with Klinefelter Syndrome the best chance of having biological children in the future.


If you receive a diagnosis later in life and want children, talk to your doctor about your options. They may suggest you try assisted fertility treatments before going on to testosterone replacement therapy.

Can men with Klinefelter syndrome have biological children?


The vast majority of men with Klinefelter syndrome will find it impossible to conceive naturally. This is often when a diagnosis happens – as up until then the other signs are pretty subtle (as you can see from the list above).

Infertility in men with Klinefelter syndrome is caused by issues in sperm production – which happens for two reasons. Firstly they often have very low testosterone, a hormone essential for making sperm. They also often have underdeveloped testicles – or testicles that never dropped.

This is a perfect storm for fertility issues but there is a bit of hope. If you have a mild case of Klinefelter (the kind known as ‘mosaic’) there’s a chance you may have sperm cells in your testicles, even if you don’t have enough making their way to your semen.

If this is the case, it is theoretically possible for fertility specialists to extract sperm directly from the testicle and use any healthy sperm in assisted fertility treatments like ICSI. There are different surgical techniques called TESA (testicular sperm aspiration), TESE (testicular sperm extraction and micro-TESE (microdissection testicular sperm extraction) that can extract the sperm. It might not always be successful, but it’s thought that this is possible for around 50% of men with Klinefelter Syndrome to at least extract some sperm through this process.

What are my options if this isn’t successful?


It’s important to remember that, whilst it’s understandable to want biological children, there are many ways to build a family. Even if assisted fertility treatments aren’t possible, many men with Klinefelter Syndrome have wonderful families thanks to donor sperm. This can be a difficult concept to get your head around at first but it opens a whole world of possibilities for men struggling with infertility. You could use sperm from a bank or use a private donor – maybe a family or friend – and figure out a process and approach that works for you.

Once again, check out our interview with Gareth Landy and Sean from Knackered Knackers to hear more about the amazing experience of becoming a father through donor sperm.

A Klinefelter Syndrome diagnosis can be overwhelming at first, but there is no reason you can’t lead a happy, healthy life and become a father. For more information on the condition – head over to our friends at Living with XXY for a bunch of helpful resources and stories.

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