Klinefelter syndrome

Not to be confused with XYY syndrome or XXX syndrome. For the Lucía Puenzo film, see XXY (film). Klinefelter's syndrome, 47, XXY or XXY syndrome is a condition caused by a chromosome aneuploidy. Affected males have an extra X sex chromosome. The principal effect is small testes development and reduced fertility. A variety of other physical and behavioral differences and problems are common, though severity varies and many boys and men with the condition have few detectable symptoms. It is the second most common extra chromosome condition, and is named after Dr. Harry Klinefelter, an endocrinologist at Massachusetts General Hospital, Boston, Massachusetts, who first described it in 1942. The condition exists in roughly 1 out of every 500 to 1,000 males.
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Klinefelter syndrome is a chromosomal disorder that affects only males. [more]Klinefelter syndrome - Community and Resources

Noun
1. syndrome in males that is characterized by small testes and long legs and enlarged breasts and reduced sperm production and mental retardation; a genetic defect in which an extra X chromosome (XXY) is present in the male
(synonym) Klinefelter's syndrome, XXY-syndrome
(hypernym) syndrome

The most common single cause of hypogonadism (underfunction of the gonads) and infertility in men, Klinefelter syndrome is due to a chromosome abnormality with XXY (plus additional X or Y chromosomes). It affects about 1 in 500 males and results in small testes (hypogenitalism), underproduction of testosterone and infertility (hypogonadism), and a long-limbed, long-trunked, relatively tall, slim build. Klinefelter boys tend to have learning and/or behavioral problems. At adolescence there is little growth of facial hair and a third of boys develop gynecomastia (enlargement of the male breast). Named for the physician Harry Klinefelter who with E.C. Reifenstein, Jr. and Fuller Albright (the founder of modern endocrinology) described the condition in 1942 long before its chromosomal basis became known.

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Sex=Male
Chromosome karyotype
47,XXY
(or XXYY)
There is an extra X chromosome or an extra X and Y chromosome
Incidence and risks
1:1000 births (more in sons of older mothers)
Clinical features:
*Decreased crown-pubis:pubis-heel ratio
*eunuchoid testicular atrophy
*Infertility
*Gynaecomastia
*Learning defficulties(20%;related to numbers of X chromosomes)