Common symptoms and effects in children and in adults

KS is a spectrum condition - the severity and frequency of symptoms  varies considerably  from person to person.​

The following symptoms may occur often … but not always.

Physical symptoms and effects

KS/XXY babies are sometimes identified as 'floppy babies'.  Their muscle tone may be poor, causing excessive flexibility of the joints. This can delay physical development. The internal muscles can also be affected causing difficulty sucking, swallowing and constipation.  Physiotherapy may help.

Unilateral and bi-lateral cryptorchidism is common. Sometimes resolves but surgical intervention may be required to avoid risk of  cancer.

Sometimes the penis can be very small.

Infertility is the most common symptom of KS/XXY and many men are diagnosed following infertility investigations. The vast majority are unable to father children normally  because of testicular failure. However, it  is now thought that there may initially be viable sperm but that these die off.  With recent advances in fertility treatment it may be possible to locate and extract viable sperm surgically from the testes. This sperm could be frozen and stored for later use. However, at present success rates are still low, even for younger men. Klinefelter's Syndrome and Infertility

The testes usually do not increase much in size at puberty and sometimes they can be quite firm.

The penis can be small.


KS/XXY adults who do not use testosterone often have little facial and body hair.

Pubic hair has a more feminine distribution pattern.

In common with most KS/XXY symptoms, this isn’t always the case. Some males can have excessive body hair.

Most KS/XXY adults are tall compared to their families.

Generally the legs and arms are long, and the trunk shorter than is usual.

Generally those with KS/XXY do not develop much muscle after puberty. Upper body strength seems to be particularly affected. Regular exercise such as swimming may help to improve this.

Because of the testicular failure, the testicles may be stimulated to make more oestrogen than that is usual for an XY  male. This may  give rise to an increase in breast tissue (gynaecomastia). This can sometimes be made worse by testosterone replacement therapy (TRT) because testosterone  can often also be transformed into oestrogen.

Although there is an increased  risk of breast cancer, it appears to be about  70% lower than for females. Mosaics may have a slightly higher risk than non-mosaics.

It is recommended that all KS/XXY adults should self-examine regularly.

Where there is excessive breast tissue which is causing distress, it may be funded by the NHS. However, this will depend on individual consultants, the area of the country and the individual's overall health.

It is important that the decision to have surgery is the KS/XXY person's decision and not the decision of medics or other adults.

A plastic surgeon with previous experience  should be used rather than a general surgeon.

In some situations a small incision can be made just beneath the breast and the excess tissue removed by liposuction. This can be carried out as a day procedure. However this may not always be suitable.

If liposuction is not possible, then a small incision is made just below the nipple and the excess tissue is removed. This will  leave a small scar which should be unobtrusive.

This should be discussed with your surgeon so that you know what to expect.

Many people who have KS/XXY suffer from sudden, apparently random, bouts of extreme tiredness. Certainly many use a great deal of energy coping with their poor information processing skills. Some also use up a great deal of nervous energy. This tiredness can cause problems in the work place because some may be unable to work full days or a full week.

Testosterone treatment can help but does not seem to cure this problem.

Poor muscle tone is different from muscle strength. Can cause excessive flexibility in hips, elbows and knees.  Can cause clumsiness. Internal muscles also affected. Can cause constipation throughout life and difficulty feeding in babies

Dyspraxia is a common disorder affecting coordination in children and adults.  It can also affect planning, organising and carrying out movements in the right order in everyday situations. Dyspraxia can also affect speech, perception and thought. Difficulties with memory and processing are common.

Handwriting and general dexterity is often affected.

Cognitive symptoms and effects

Those affected by KS/XXY often have a difficulty learning although IQ is usually within the normal range.

Research indicates  that the extra chromosome affects executive function (EF). 

EF encompasses the abilities needed to organise thought and activities, to make plans and carry them out, including  

  • organization of tasks
  • use of one's time
  • setting of goals and priorities
  • assessing the progress

It includes working memory, self monitoring, initiation, emotional control and the ability to shift from task to task. 

Language development disorders are the most common symptom seen in children with KS. This is an invisible disability which is still very common in adults, although many  will have developed coping strategies.

As language is essential for social interaction, many struggle in social situations. There is often difficulty in understanding the nuances of social behaviour as well as the nuances of  language. Literal  interpretation of language can  cause difficulties.

There is often a difficulty with self-expression -  especially when under pressure.

Many of our members report that they feel more comfortable in the company of women, perhaps because the latter are often more empathetic.

It has been recognised that particular areas of the brain may develop differently in a KS person and that could be why short term memory can be poor.

There is often difficulty in processing information - especially if given verbally. As short term memory can also be poor, by the time the second instruction has been understood, the first one may have been  forgotten.

Written  information and  instructions are helpful. Extra time should be allowed  for the processing of information. It is very important to give  time for reflection - excessive pressure will make a situation worse.

Possible brain differences may be the cause of problems with concentration. In addition, those with KS often have enhanced sensory perception and this may affect concentration. Sometimes  particularly acute hearing can make  general noise and bustle very distracting.  Others may be very aware of touch and find chafing clothing labels or texture are an added distraction.

Other common symptoms and effects

Given some of the possible symptoms of KS, it is perhaps not surprising that many of those with the condition are shy and lacking in self esteem.  However many do overcome this, especially with support from family and friends. Testosterone replacement therapy can increase assertiveness.

Libido is often affected because the production of testosterone is poor. Testosterone replacement therapy will usually increase sex drive.

Many of these ‘symptoms’ may be experienced by people who are not KS/XXY. 

As KS/XXY folk often learn strategies to compensate as they get older, many of these symptoms may not be obvious.