Definition of Klinefelter syndrome
1. Noun. 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.
Medical Definition of Klinefelter syndrome
1.
A genetic syndrome observed in many mammals caused by the presence of an extra X chromosome in the male karyotype.
The normal male is XY but in this disorder the chromosomal abnormality is XXY, and affects only males. Infertility is common. In humans, the infant appears normal at birth, but the defect usually becomes apparent in puberty when secondary sex characteristics fail to develop along with female escutcheon, gynaecomastia, tall stature, small testes, aspermatogonia and Leydig cell hyperplasia.
It is characterised by small testes, feminine appearance, sterility (except in the case of genetic mosaics) and there is no effect on performance IQ but the verbal IQ can be affected.
The genetic abnormality can be detected in 0.003% of spontaneous abortions and is associated with nondisjunction in paternal meiosis I (53%), maternal meiosis I (34%) and maternal meiosis II (9%). In a large number of patients the karyotype shows a 47,XXY constitution and in 10% of the cases there is mosaicism and some of these mosaics can be fertile. Patients with mosaic karyotypes that include 48,XXXY and 49,XXXXY can show short stature, mental retardation, hypogonadism and other abnormalities.
Incidence: 1 in 1000 to 1 in 2000 newborn males.
(17 Dec 1997)
Lexicographical Neighbors of Klinefelter Syndrome
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