Klinefelter syndrome (KS), also known as 47,XXY, is a syndrome where a male has an additional copy of the X chromosome. The primary features are infertility and small, poorly functioning testicles. Usually, symptoms are subtle and subjects do not realize they are affected. Sometimes, symptoms are more evident and may include weaker muscles, greater height, poor motor coordination, less body hair, breast growth, and less interest in sex. Often, these symptoms are noticed only at puberty. Intelligence is usually normal, but reading difficulties and problems with speech are more common.Klinefelter syndrome occurs randomly. The extra X chromosome comes from the father and mother nearly equally. An older mother may have a slightly increased risk of a child with KS. The syndrome is defined  by the presence  of at least one extra X chromosome in addition to a Y chromosome yielding a total of 47 or more chromosomes rather than the usual 46. KS is diagnosed by the genetic test known as a karyotype.While no cure is known, a number of treatments may help. Physical therapy, occupational therapy, speech and language therapy, counselling, and adjustments of teaching methods may be useful. Testosterone replacement may be used in those who have significantly lower levels. Enlarged breasts may be removed by surgery. About half of affected males have a chance of fathering children with the help of assisted reproductive technology, but this is expensive and not risk free.
The account given by Klinefelter came to be known as Klinefelter syndrome as his name appeared first on the published paper, and seminiferous tubule dysgenesis was no longer used. Considering the names of all three researchers, it is sometimes also called Klinefelter–Reifenstein–Albright syndrome. In 1956, Klinefelter syndrome was found to result from an extra chromosome. Plunkett and Barr found the sex chromatin body in cell nuclei of the body. This was further clarified as XXY in 1959 by Patricia Jacobs and John Anderson Strong. The first published report of a man with a 47,XXY karyotype was by Patricia Jacobs and John Strong at Western General Hospital in Edinburgh, Scotland, in 1959. This karyotype was found in a 24-year-old man who had signs of KS. Jacobs described her discovery of this first reported human or mammalian chromosome aneuploidy in her 1981 William Allan Memorial Award address.In August 2022, a team of scientists published a study of a skeleton found at Torre Velha, Municipality of Bragança in north-eastern Portugal. The male was buried in a cut grave around 1,000CE, and found from DNA tests to be the earliest known person with this syndrome. See also
Aneuploidy
Intersex
Turner syndrome
XYY syndrome
XXYY syndrome
Taurodontism
Trisomy X

References
Further reading
Virginia Isaacs Cover (2012). Living with Klinefelter Syndrome, Trisomy X and 47,XYY: A Guide for Families and Individuals Affected by Extra X and Y Chromosomes. ISBN 978-0-615-57400-4. External links

Klinefelter syndrome at Curlie