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Home > Wellness > Health Library > Klinefelter Syndrome
genetic disorder that affects males. Klinefelter
syndrome occurs when a boy is born with one or more extra X
chromosomes. Most males have one Y and one X
chromosome. Having extra X chromosomes can cause a male to have some physical
traits unusual for males.
Many men with an extra X chromosome are
not aware that they have it, and they lead normal lives. Males who have Klinefelter
syndrome may be described as XXY males or males with XXY syndrome. Klinefelter
syndrome occurs in about 1 out of 1,000 males.
The presence of
an extra X chromosome in males most often occurs when the genetic material in the eggs splits unevenly. But it can also occur when the genetic material in the
sperm splits unevenly.
Many men who have Klinefelter
syndrome do not have obvious symptoms. Others have sparse body hair, enlarged
breasts, and wide hips. In almost all men the testicles remain small. In some
men the penis does not reach adult size. Their voices may not be as deep. They
usually cannot father children. But they can have a normal sex life.
Some boys with Klinefelter syndrome have language and learning
See a picture of a
male with Klinefelter syndrome.
syndrome usually is not diagnosed until the time of
puberty. At this point, the boy's testicles fail to
grow normally and you may start to notice other symptoms.
out if your son has Klinefelter syndrome, your doctor will ask questions about
his past health, do a physical exam, and order a chromosome test called a
Klinefelter syndrome can be detected before birth (prenatally) through
genetic tests on cells collected from amniocentesis or
chorionic villus sampling (CVS). But this is not
In adult men, lab tests in addition to a karotype may be done, such as hormone tests or a
semen analysis, if Klinefelter syndrome is
Males with Klinefelter syndrome
can be given
testosterone, a hormone needed for sexual development.
If treatment is started around the age of puberty, it can help a boy have more
normal body development.
Testosterone is given by injection or
through a skin patch or gel. The treatment usually continues
throughout a man's life but does not help
Speech therapy and educational support
can help boys who have language or learning problems.
If your son has been
diagnosed with Klinefelter syndrome:
Learning about Klinefelter syndrome:
The American Association for Klinefelter Syndrome
Information and Support (AAKSIS) is a national volunteer association with the
mission of education, support, research, and understanding of 47 XXY and its
variants, collectively known as Klinefelter syndrome.
The Hormone Foundation is a nonprofit organization
started by the Endocrine Society. The organization promotes the prevention,
treatment, and cure of hormone-related conditions through public outreach and
KS&A is focused on Knowledge,
Support, and Action. It's a nonprofit education and
support organization for people who have Klinefelter syndrome or other
conditions caused by extra X and/or Y chromosomes.
The March of Dimes tries to improve the health of babies
by preventing birth defects, premature birth, and early death. March of Dimes
supports research, community services, education, and advocacy to save babies'
lives. The organization's website has information on premature birth, birth
defects, birth defects testing, pregnancy, and prenatal care.
The National Institute of Child Health and Human
Development (NICHD) is part of the U.S. National Institutes of Health. The
NICHD conducts and supports research related to the health of children, adults,
and families. NICHD has information on its Web site about many health topics.
And you can send specific requests to information specialists.
Other Works Consulted
Bojesen A, et al. (2003). Prenatal and postnatal
prevalence of Klinefelter syndrome: A national registry study. Journal of Clinical Endocrinology and Metabolism, 88(2):
Braunstein GD (2007). Klinefelter's syndrome (XXY
seminiferous tubule dysgenesis) section of Testes. In DG Gardner, D Shoback,
eds., Greenspan's Basic and Clinical Endocrinology, 8th
ed., pp. 482–484. New York: McGraw-Hill.
Styne DM, Grumbach MM (2008). Klinefelter's syndrome
and its variants section of Puberty: Ontogeny, neuroendocrinology, physiology,
and disorders. In HM Kronenberg et al, eds., Williams Textbook of Endocrinology, 11th ed., pp. 1051–1053. Philadelphia: Saunders
Tsai A C-H, et al. (2011). Klinefelter syndrome (XXY)
section of Genetics and dysmorphology. In WW Hay et al., eds., Current Diagnosis and Treatment: Pediatrics, 20th ed., p.
1039. New York: McGraw-Hill Medical.
February 7, 2011
Susan C. Kim, MD - Pediatrics & Stephen LaFranchi, MD - Pediatrics, Pediatric Endocrinology
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