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Chromosomal disorder that occurs in one out of 500 males. With an extra X chromosome in each cell (XXY), patients look male, with firm, small testes, but they produce no sperm and may have enlarged breasts and buttocks and very long legs. Testosterone is low and pituitary reproductive hormones high. Intelligence is usually normal, but social adjustment can be difficult. Rarer variants cause additional abnormalities, including intellectual disability. In the XX male syndrome, Y chromosome material has been transferred to another chromosome, causing changes typical of Klinefelter syndrome. All variants are treated with androgens.
This entry comes from Encyclopædia Britannica Concise. For the full entry on Klinefelter syndrome, visit Britannica.com.