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Klinefelter syndrome

Summary

Klinefelter syndrome (or XXY syndrome) is a chromosome disorder that affects males. The affected male has an additional X chromosome, which causes infertility and may cause the development of characteristics such as tall stature and breast development. A number of non-physical features such as problems with language or learning may also be noticed. Treatment may include hormone therapy, cosmetic surgery, speech therapy and counselling.

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Klinefelter syndrome is a chromosome disorder that affects males. Usually, a male has two chromosomes that determine his sex: an X inherited from his mother and a Y inherited from his father. A male with Klinefelter syndrome has an additional X chromosome.

The effects can vary greatly and may include:

  • Infertility – the condition may be diagnosed when fertility problems are being investigated.
  • Reduced testicle size – in all males with Klinefelter syndrome, the testicles do not develop properly and are noticeably smaller from early adolescence.
  • Incomplete puberty – not enough of the male hormone testosterone is produced and puberty may appear to be delayed. These boys may be given testosterone treatment so they develop usual male physical characteristics like facial hair and a deeper voice.
  • Language and learning problems – in many males with Klinefelter syndrome, difficulties with speech, writing, or understanding and processing speech may be noticed.

Klinefelter syndrome occurs in around one in every 450 male babies, which makes it one of the most common variations of the chromosomes. However, only around a quarter of these males have a diagnosis of Klinefelter syndrome, also known as XXY syndrome. The additional X chromosome does not influence sexual orientation.

Signs of Klinefelter syndrome at birth


The condition isn’t usually diagnosed at birth, because the baby boy looks healthy and unaffected. However, certain physical characteristics sometimes associated with Klinefelter syndrome may be apparent, including:
  • Small penis
  • Undescended testicles
  • Hypospadias (the urethra is located on the underside of the penis instead of the tip).

Signs of Klinefelter syndrome at childhood


The appearance of signs of Klinefelter syndrome in childhood can vary greatly and range from mild to those that are more obvious. Many of the signs of Klinefelter syndrome also occur in children with other conditions, or children who do not have an underlying diagnosis, which makes detecting Klinefelter syndrome in childhood difficult.

Furthermore, many boys show no signs of Klinefelter syndrome during childhood. However, for those that do, early intervention provides the opportunity to overcome difficulties and for each boy to reach their individual potential.

Signs that may be apparent in childhood include:
  • Delays in starting to talk or walk
  • Learning difficulties, including trouble listening or concentrating in class
  • Poor motor development or coordination (sometimes leading to shyness or an avoidance of rough sports)
  • Tiredness and fatigue
  • Reduced muscle strength or tone (sometimes leading to other complications such as sleep apnoea or chronic constipation).

Signs of Klinefelter syndrome at puberty


Klinefelter syndrome is often diagnosed at puberty, when the expected physical changes don’t occur. Some of the signs and symptoms of the condition include:
  • Small testicles (hypogonadism) – males with Klinefelter syndrome always have small testicles from puberty
  • Lack of facial, pubic and underarm hair
  • Poor muscle development
  • Breast tissue development (gynaecomastia)
  • Unexplained weight gain, especially on the stomach or trunk
  • Tiredness and fatigue
  • Small penis
  • Disproportionately long arms and legs compared to the length of the body
  • Taller than average height
  • Poor concentration
  • Single crease in the palm (simian crease)
  • Difficulties with sexual functioning
  • Speech and learning difficulties – in some cases this can lead to behavioural problems
  • Sadness, lowered mood or depression.

Boys may become particularly self-conscious in puberty when they notice that their body is not undergoing the same changes as their peers. Testosterone replacement therapy can help the body to undergo these changes.

Most males with Klinefelter syndrome are not diagnosed until they are well into adulthood, when diagnosis can come as a major shock. An earlier diagnosis provides opportunities for the child and his family to access treatments and interventions that can help overcome any difficulties associated with the condition.

Cause of Klinefelter syndrome


While the cause of Klinefelter syndrome is genetic, it is not inherited. Humans have 46 paired chromosomes, made up of two sex chromosomes that determine gender and 44 chromosomes that determine other factors. The mother always passes on an X chromosome. If the father provides an X chromosome, the child will be female, while a Y chromosome makes the child male.

A boy with Klinefelter syndrome has an additional X chromosome. This is thought to be caused by an error within the fertilised egg or the dividing cells as the baby develops. The presence of the Y chromosome ensures male sexual characteristics but, because the testicles are underdeveloped, there may not be enough testosterone production. This is why the penis and testicles may be smaller than average, and why most men with Klinefelter syndrome do not produce sperm. Some researchers suspect that advanced parental age may be a risk factor.

Complications of Klinefelter syndrome


Compared with males in the general population, Klinefelter syndrome is associated with an increased risk of certain diseases and conditions, including:
  • Osteoporosis
  • Diabetes mellitus
  • Lung disease
  • Breast cancer
  • Testicular cancer
  • Anaemia
  • Infertility
  • Depression or other psychiatric conditions
  • Leukaemia
  • Non-Hodgkin’s lymphoma
  • Thyroid disease
  • Sleep apnoea
  • High cholesterol
  • Tooth decay
  • Varicose veins.

It is currently thought that testosterone treatment from puberty, which helps with bone and muscle development among other things, may reduce the risk of many of the above conditions.

Diagnosis of Klinefelter syndrome


Klinefelter syndrome is diagnosed using a number of tests, including:
  • Physical examination – all males with Klinefelter syndrome have small testicles, which can be detected by genital examination
  • Chromosome analysis – will confirm the diagnosis
  • Blood tests – can check for hormone levels
  • Semen examination – checks fertility.

Treatment of Klinefelter syndrome


There is no cure for Klinefelter syndrome. Treatment aims to correct some aspects of the condition and provide emotional support. Options may include:
  • Hormone therapy – such as testosterone, to help bring on the usual changes of puberty. Hormone therapy will need to be lifelong, however it can have a broad range of benefits, including increased energy levels and physical strength
  • Reproductive technologies – such as IVF, to help men with Klinefelter syndrome become fathers. New advances in reproductive technologies mean that up to a quarter of men with Klinefelter syndrome are now able to have their own biological children
  • Educational support if necessary
  • Speech therapy if necessary
  • Physical or occupational therapy – if necessary
  • Cosmetic surgery – to remove enlarged breast tissue
  • Counselling – to help the male come to terms with his condition
  • Frequent screening tests – to ensure the early diagnosis of any associated complications (such as diabetes or breast cancer).

Klinefelter syndrome myths


Because there are some myths associated with Klinefelter syndrome, it is important to remember that:
  • People with Klinefelter syndrome are genetically and physically males because they have a Y chromosome.
  • Males with Klinefelter syndrome are not more likely to be homosexual than the general population.
  • The majority of males with Klinefelter syndrome do not have lowered intelligence or an intellectual disability, but many do have specific problems with language and learning.
  • Males with Klinefelter syndrome do not have increased rates of criminality when compared to the general population.

Where to get help

  • Your doctor
  • Endocrinologist
  • Genetic Support Network Victoria Tel. (03) 8341 6315
  • Andrology Australia Tel. 1300 303 878

Things to remember

  • Klinefelter syndrome is a chromosome disorder that affects males. It is not an inherited disorder.
  • A male with Klinefelter syndrome has an additional X chromosome, which causes infertility, low testosterone and other characteristics such as development of breast tissue.
  • The chromosomes are present in every cell of the body and the extra X chromosome cannot be removed.
  • Treatment includes lifelong testosterone therapy and cosmetic surgery to remove enlarged breast tissue. Options for men with Klinefelter syndrome to have their own children are becoming more widely available.

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This page has been produced in consultation with and approved by:

Victorian Clinical Genetics Services (VCGS) Murdoch Childrens Research Institute

(Logo links to further information)


Victorian Clinical Genetics Services (VCGS)

Last reviewed: February 2014

Content on this website is provided for education and information purposes only. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your doctor or other registered health professional. Content has been prepared for Victorian residents and wider Australian audiences, and was accurate at the time of publication. Readers should note that, over time, currency and completeness of the information may change. All users are urged to always seek advice from a registered health care professional for diagnosis and answers to their medical questions.


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Klinefelter syndrome (or XXY syndrome) is a chromosome disorder that affects males. The affected male has an additional X chromosome, which causes infertility and may cause the development of characteristics such as tall stature and breast development. A number of non-physical features such as problems with language or learning may also be noticed. Treatment may include hormone therapy, cosmetic surgery, speech therapy and counselling.



Content on this website is provided for education and information purposes only. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your qualified health professional. Content has been prepared for Victorian residence and wider Australian audiences, and was accurate at the time of publication. Readers should note that over time currency and completeness of the information may change. All users are urged to always seek advice from a qualified health care professional for diagnosis and answers to their medical questions.

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