Klinefelter syndrome (KS) occurs in some men who have more than one X chromosome (XXY).

Klinefelter Syndrome

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Males usually inherit a single X chromosome from their mother and a single Y chromosome from their father. Males with KS get at least 1 extra X chromosome.

Risk Factors

Women over age 35 may have a slightly increased chance of having a child with KS. There are no other known risk factors for this disorder.


Most men with KS do not have symptoms. When KS does develop, it usually goes undetected until puberty or sometimes much later.

Babies may have lower birth weight, or slower muscle and motor development.

Children or adults may have:

  • Social and learning disabilities
  • Enlarged breasts
  • Inability to produce sperm
  • Small, firm testes
  • Small penis
  • Abnormal body proportions, such as long legs or short trunk
  • Tallness with extra long arms and legs
  • Personality impairment
  • Attention deficit hyperactivity disorder (ADHD)
  • Speech and language problems—Children with KS often learn to speak later than other children do. They may have a difficult time reading and writing.
  • Normal to borderline IQ
  • Lack of facial and body hair
  • Diminished sex drive or sexual dysfunction
  • Men with KS have an increased risk of:

  • Type 2 diabetes
  • Breast cancer
  • Lung cancer
  • Cardiovascular disease
  • Lung disease
  • Osteoporosis
  • Hypothyroidism
  • Dental problems
  • Leg ulcers
  • Diagnosis

    A test called a karyotype is used to diagnose KS. In the case of KS, there are usually 47 chromosomes rather than the normal 46.

    Many men with XXY do not know they have the condition. Diagnosis of KS may be found incidentally. For example:

  • During prenatal amniocentesis
  • In baby boys with undescended testes or very small penis
  • In boys who have persistent learning problems
  • In adolescent boys with delayed puberty or excessive breast development
  • In adult men who have fertility concerns
  • Treatment

    Treatment of KS includes:


    The main treatment is testosterone . When boys with KS are 10-12 years old, their hormone levels are checked yearly. If testosterone levels are low, then treatment may be helpful. Men diagnosed may also benefit from taking the hormone. However, testosterone cannot reverse infertility.

    The benefits of testosterone include:

  • Increased strength
  • More muscular, male appearance
  • Growth of facial and body hair
  • Better self-esteem
  • Modulation of mood
  • Increased energy
  • Increased ability to concentrate
  • Greater sex drive
  • Improved bone density
  • Speech and Language Therapy

    This therapy should begin in early childhood to avoid social and school learning problems. Treatment may involve:

  • Speech therapy
  • Special education services
  • Extra support and help with learning from parents and teachers
  • Social skills training and psychological counseling
  • Prevention

    There are no current guidelines to prevent KS. If you are pregnant, talk to your doctor about prenatal care and screening tests.