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Klinefelter syndrome

Klinefelter syndrome is a chromosomal abnormality affecting around 1 in 600 newborn boys, in which the boy is born with an extra X chromosome (XXY). It is not usually diagnosed before the expected onset of puberty, although some boys will be born with undescended testicles. Males with Klinefelter syndrome may not produce sufficient testosterone to develop secondary male characteristics, and in adulthood, fertility may be affected because the testicles will produce little or no sperm.

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