Klinefelter's syndrome is a relatively common genetic abnormality that results from an extra X chromosome. It affects only males and usually becomes apparent at puberty, when the secondary sex characteristics develop; the testicles fail to mature, and degenerative testicular changes begin that eventually result in irreversible infertility. It commonly causes gynecomastia and is also associated with a tendency toward learning disabilities.
Klinefelter's syndrome is unlike Turner's syndrome, which results from the loss of an X chromosome. (See Turner's syndrome, page 36.)
Klinefelter's syndrome, probably the most common cause of hypogonadism, appears in approximately 1 in every 500 males. This disorder usually results from one extra X chromosome, giving such patients a 47,XXY complement instead of the normal 46,XY. (See Fertilization in Klinefelter's syndrome, page 36.) In the rare mosaic form of this syndrome, some cells contain the extra X chromosomes, whereas others contain the normal XY complement.
The extra chromosome responsible for Klinefelter's syndrome probably results from either meiotic nondisjunction during parental gametogenesis or from meiotic nondisjunction in the zygote. The incidence of meiotic nondisjunction increases with maternal age.
Klinefelter's syndrome may not be apparent until puberty or later in mild cases. Because many of these patients aren't mentally retarded, behavioral problems in adolescence or infertility may be the only presenting features initially.
The syndrome's characteristic features include a small penis and prostate gland, small testicles, sparse facial and abdominal hair, feminine distribution of pubic hair (triangular shape), sexual dysfunction (impotence, lack of libido) and, in fewer than 50% of patients, gynecomastia. Aspermatogenesis and infertility result from progressive sclerosis and hyalinization of the seminiferous tubules in the testicles and from testicular fibrosis during and after puberty. In the mosaic form of Klinefelter's syndrome, such pathologic changes and resulting infertility may be delayed.
Klinefelter's syndrome may also be associated with osteoporosis, abnormal body build (long legs with short, obese trunk), tall stature, learning disabilities characterized by poor verbal skills and, in some individuals, behavioral problems beginning in adolescence. It's also associated with an increased incidence of pulmonary disease and varicose veins and a significantly increased rate of breast cancer because of the extra X chromosome.
Characteristically, Klinefelter's syndrome decreases urinary 17-ketosteroid levels, increases the excretion of follicle-stimulating hormone, and decreases the levels of plasma testosterone after puberty.
Depending on the severity of symptoms, treatment may include mastectomy in patients with persistent gynecomastia and supplemental testosterone to induce secondary sexual characteristics of puberty.
❑ Psychological counseling may be indicated for body image problems or emotional maladjustment due to sexual dysfunction.
❑ Genetic counseling is essential for patients with the mosaic form of the syndrome who are fertile; they may transmit this chromosomal abnormality as well as others.
❑ Encourage patients to discuss feelings of confusion and rejection that may arise, and try to reinforce their male identity.
❑ Improve compliance with hormone replacement therapy by making sure patients understand the potential benefits and adverse effects of testosterone administration.
Review other book chapters online related to Klinefelter syndrome:
Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Professional Guide to Diseases (Eighth Edition) Authors: Springhouse Publisher: Lippincott Williams & Wilkins Copyright: 2005 ISBN: 1-58255-370-X 
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