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Klinefelter Syndrome

(Klinefelter's Syndrome; XXY)

By

Nina N. Powell-Hamilton

, MD, Sidney Kimmel Medical College at Thomas Jefferson University

Last full review/revision Jul 2020| Content last modified Jul 2020
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Topic Resources
  • Klinefelter syndrome occurs when a boy has one extra X chromosome.

  • Boys may have learning disabilities, long arms and legs, small testes, and infertility.

  • The diagnosis is suspected at puberty when most of the symptoms develop.

  • Treatment with testosterone may be of benefit to some people.

The sex chromosomes Sex chromosomes Genes are segments of deoxyribonucleic acid (DNA) that contain the code for a specific protein that functions in one or more types of cells in the body. Chromosomes are structures within cells... read more Sex chromosomes determine whether a fetus becomes male or female. A pair of X and Y chromosomes (XY) results in a male, and a pair of X and X chromosomes (XX) results in a female.

Klinefelter syndrome is the most common sex chromosome disorder and occurs in about 1 in every 500 live male births. Most boys inherit the extra X chromosome from their mother.

Symptoms of Klinefelter Syndrome

Most boys with Klinefelter syndrome have normal or slightly decreased intelligence. Many have speech and reading disabilities and difficulties with planning. Most have problems with language skills. Lack of insight, poor judgment, and impaired ability to learn from previous mistakes often cause these children to get into trouble. Although their physical characteristics can vary greatly, most are tall with long arms and legs. They may also have wider hips but otherwise have a relatively normal appearance.

Puberty usually occurs at the normal time, but the testes remain small. At puberty, growth of facial hair is often sparse, and the breasts may enlarge somewhat (gynecomastia Breast enlargement in men Breast disorders occur infrequently in men. Breast disorders include Breast enlargement Breast cancer Breast enlargement in males is called either gynecomastia or pseudogynecomastia. Gynecomastia... read more ). Males with the syndrome are usually infertile, but sometimes the testes develop enough to produce sperm. Men with Klinefelter syndrome tend to develop diabetes mellitus Complications of Diabetes Mellitus People with diabetes mellitus have many serious long-term complications that affect many areas of the body, particularly the blood vessels, nerves, eyes, and kidneys. (See also Diabetes Mellitus... read more Complications of Diabetes Mellitus , chronic lung disease, varicose veins Varicose Veins Varicose veins are abnormally enlarged superficial veins in the legs. Varicose veins may ache or cause itching or a sensation of tiredness. Doctors can detect varicose veins by examining the... read more Varicose Veins , hypothyroidism Hypothyroidism Hypothyroidism is underactivity of the thyroid gland that leads to inadequate production of thyroid hormones and a slowing of vital body functions. Facial expressions become dull, the voice... read more Hypothyroidism , and breast cancer Breast cancer in men Breast disorders occur infrequently in men. Breast disorders include Breast enlargement Breast cancer Breast enlargement in males is called either gynecomastia or pseudogynecomastia. Gynecomastia... read more more often than other men.

Some affected boys have 3, 4, and even 5 X chromosomes along with the Y. As the number of X chromosomes increases, the severity of intellectual disability and physical abnormalities also increases. Each extra X is associated with a 15- to 16-point reduction in intelligence quotient (IQ), with language most affected, particularly expressive language skills.

Diagnosis of Klinefelter Syndrome

  • Before birth, testing of the mother

  • After birth, blood test

After birth, the syndrome is usually first suspected at puberty, when most of the symptoms develop. Analysis of the chromosomes using a blood test confirms the diagnosis of Klinefelter syndrome. However, many men are diagnosed only during an infertility assessment.

Treatment of Klinefelter Syndrome

  • For children, speech and language therapy

  • For adolescents, testosterone therapy for life

Boys with Klinefelter syndrome usually benefit from speech and language therapy and eventually can do well in school.

Males with Klinefelter syndrome may require supplemental testosterone beginning at puberty. The hormone improves bone density, making fractures less likely, and stimulates development of a more masculine appearance. Hormone replacement therapy may help lessen some behavior and developmental problems.

More recently, fertility preservation counseling has become an important part of the care of adolescents with Klinefelter syndrome. Obtaining and preserving sperm cells from males who produce them can give them the opportunity to father biological children.

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