What is Klinefelter syndrome?
Klinefelter syndrome is a common condition in which a male is born with an extra X chromosome.
The collection of chromosomes in your cells is known as its karyotype. The usual human karyotype is 22 pairs of chromosomes called autosomes, which are the same in males and females, and a pair of sex chromosomes. This results in a total of 46 chromosomes. Normally, women have 44 autosomes and two X chromosomes (denoted 46,XX) and men have 44 autosomes, one X and one Y (46,XY).
But with Klinefelter syndrome, a person is born with an X and Y chromosomes and an extra X, which is why the condition is also referred to as 47,XXY. The X chromosome is not a “female” chromosome and boys and men with Klinefelter syndrome are genetically male.
Around one in 500 men have Klinefelter syndrome and for many, it often goes undiagnosed. For some men, Klinefelter syndrome is discovered when they try to start a family. This is because even for those with mild symptoms, most men with Klinefelter syndrome produce very few or no sperm and are infertile.
What are the symptoms of Klinefelter syndrome?
The effects of Klinefelter syndrome can vary quite a bit between different people. Sometimes symptoms of Klinefelter syndrome can be so mild in some individuals that they, their parents, partners, and their doctors may not even realise they have the condition.
Klinefelter syndrome is the most common cause of male hypogonadism, a condition where men are unable to produce enough of the male hormone, testosterone, for the body’s needs. Testosterone is important for the physical changes that happen during male puberty, such as development of the penis and testes, and for the features typical of adult men such as facial and body hair.
Testosterone also acts on cells in the testes to make sperm and is also important for overall good health. It helps the growth of bones and muscles, and it affects mood, libido (sex drive), and certain aspects of mental ability.
If your partner is severely affected by Klinefelter syndrome, they might have been born with:
Symptoms in childhood include:
- Small testes
- Long legs and tall stature
- More body fat than normal
- Difficulties with speaking, learning, behaviour, and socialising.
Boys with Klinefelter syndrome might begin puberty but then it stops, and have signs of low testosterone, such as:
- Reduced growth of the testes and penis
- Reduced masculinisation of their bodies (e.g., reduced development of facial and body hair, reduced muscle, and bone development).
What causes Klinefelter syndrome?
Even though Klinefelter syndrome is a genetic condition, it’s usually not inherited. The symptoms of Klinefelter syndrome are caused by lower-than-normal production of testosterone by the body and the effects on development and function of extra copies of some of the genes on the X chromosomes.
If your partner has Klinefelter syndrome it’s important to get an accurate diagnosis and ongoing specialist treatment managed by their general practitioner. Klinefelter syndrome is associated with several health problems, mainly due to reduced testosterone levels, which are usually successfully treated by testosterone therapy.
People with Klinefelter syndrome are more likely than those without to have psychosexual and social problems, obesity, metabolic disease (e.g., type 2 diabetes), cardiovascular disease, some forms of cancer, autoimmune disease (e.g., multiple sclerosis, lupus), poor vision, dental problems, and blood clots.
Although there is no cure for Klinefelter syndrome, treatment with testosterone to maintain normal levels minimises the risk of health problems1. Therapy provided by a psychologist may help people with Klinefelter syndrome with their emotional stability and self-regulation.
What a person with Klinefelter syndrome could be feeling
Symptoms of Klinefelter syndrome can greatly impact some men’s lives and barely interfere with others. There are useful online resources to help us understand what it’s like to have Klinefelter syndrome but there’s not been a lot of research on the subject. Being diagnosed with Klinefelter syndrome can be a relief (because there’s confirmation that something’s different from normal) but may also raise concerns, particularly related to effects on future health and fertility2.
Helping someone with Klinefelter syndrome to be diagnosed, and to receive long-term care from a coordinated group of health professionals, will probably make a strong contribution to improving their life.
Although the related issues sound severe and a quick Google search offers overwhelmingly negative information, with the right medical care and ongoing support men with Klinefelter syndrome can lead normal, healthy lives.
What you could be feeling
There is no research on how Klinefelter syndrome impacts the partners of those diagnosed. However, associated issues of depression, anxiety, psychosexual problems and social issues can impact loved ones too.
Infertility can also be a cause of distress. It might be possible for people whose fertility is affected by Klinefelter syndrome to have children using assisted reproductive technology (ART). Common alternatives to starting a family include donor sperm with IUI or IVF, adoption, and micro-TESE surgery.
What you can do about Klinefelter syndrome
Men with Klinefelter syndrome must be properly diagnosed, treated, and monitored. Encourage your partner to see their doctor and an endocrinologist, and that they continue to manage their treatment.
If you want to start a family, chat with your GP. If your GP seems unsure of the best course of action, it’s okay to ask for a referral to someone else or to seek a second opinion.
Hearing from or meeting with other men with Klinefelter syndrome could be helpful for you and your partner. Organisations like Living with XXY have a strong community and a range of resources that raise awareness about the condition with a strong focus on the positive.
 Kanakis & Nieschlag, 2018. Klinefelter syndrome: more than hypogonadism. Metabolism
 Hannah et al., 2019. The lived experience of Klinefelter syndrome: a narrative review of the literature. Frontiers in Endocrinology