Typically a human is considered to have 46 chromosomes and have their 23rd pair either be XX or XY. The 23rd chromosome pair determines the sex in a human: an XX individual is female and an XY is male. However, in approximately 1 out of every 500-1000 births a separate sex is produced. Due to nondisjunction during meiosis, an XXY individual may be produced. The individual is classified as male with an extra X since a female cannot have a Y. While this is overall a random occurrence, woman over 35 who become pregnant are slightly more likely than women younger than them to produce an XXY individual.



It is difficult to determine if an individual has Klinefelter Syndrome since the physical signs can be assumed as a unique aspect of the individual. In most cases, the syndrome is discovered due to infertility in the male. Other symptoms in addition to infertility include: other sexual problems, lack of hair in typical haired areas on males (pubic area, armpits, face, chest), unusually large breasts, atypical proportions, small firm testicles, and taller than average height. Birth defects are also a risk when giving birth to an XXY individual.

Other risks are involved with this syndrome that are not symptoms. A patient most likely will develop taurodontism, a thinning of the teeth surfaces.  ADD, lupis (autoimmune disorder with common joint pain and swelling), rheumatoid arthritis, and Sjogren Syndrome (no production of tears or saliva) are disorders with raised development risk. Breast cancer, lung disease, and depression can develop as well as learning disabilities, osteoporosis, and viscose veins. The likelihood of males developing these complications is comparable to that of adult females.

Sexual development is altered in XXY males. The testes will not function normally and therefore testosterone levels will be low. However, not all patients develop any form of symptoms.

Symptoms by Age – provided by CNN


  • Weak muscles

  • Slow motor development — taking longer than average to sit up, crawl and walk

  • Delay in speaking

  • Quiet, docile personality

  • Problems at birth, such as testicles that haven't descended into the scrotum

Boys and teenagers

  • Taller than average stature

  • Longer legs, shorter torso and broader hips compared with other boys

  • Absent, delayed or incomplete puberty

  • After puberty, less muscular bodies and less facial and body hair compared with other teens

  • Small, firm testicles

  • Small penis

  • Enlarged breast tissue (gynecomastia)

  • Weak bones

  • Low energy levels

  • Shyness

  • Difficulty expressing feelings or socializing

  • Problems with reading, writing, spelling or math

  • Attention problems


  • Infertility

  • Small testicles and penis

  • Taller than average stature

  • Weak bones

  • Decreased facial and body hair

  • Enlarged breast tissue

  • Decreased sex drive or sexual problems 

Male picture


A male suspected of having Klinefelter Syndrome can have confirmation through a variety of tests. The two primary tests are karyotyping and a semen count. A karyotype would show the extra chromosome, while a semen count is for fertility and measures the amount and quality of semen. Blood tests will also be done to ascertain hormone levels of estrogen, testosterone, etc.


Testosterone therapy is used for patients with this syndrome. The therapy will help to reverse the symptoms of the syndrome. This may involve growing of hair, an increase in strength, muscle, energy, sex drive, as well as advances in concentration and mood. With assistive procedures, some men are also able to overcome the fertility issue and father children.

There is no way to repair the sex chromosome error or to have predicted the event. In addition to hormone therapy, educational support and psychiatric counseling is recommended.


Variants of Klinefelter Syndrome are possible. More than one extra chromosome copy may occur and individuals may be XXXY or XXYY. Patients with these variants have severe symptoms. These patients may have intellectual disabilities, poor coordination, and extreme difficulties with speech. Physical appearance may also be altered. Individuals can suffer from skeletal abnormalities and distinct facial features. Births of either of these types of males are rare and occur in approximately 1 in 50,000 male births.

Another possible variant is a mosaic Klinefelter Syndrome individual. This person is XY/XXY meaning they have only some cells that contain the extra X chromosome. This occurrence is due to a random event during cell division in fetal development.

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