Klinefelter syndrome (KS) or 47,XXY syndrome is a variation of intersex affecting approximately 1/500 AMAB/CTM individuals, making it one of the most common chromosomal variations of intersex. It results from having two or more X chromosomes and one Y chromosome (XXY) rather than just XY.
Symptoms may include greater height, poor coordination, less body hair, broader hips, decreased ability to gain muscle, breast growth, lower sex drive (unless they are already on the ace-spectrum and/or not sex-favorable), a micropenis and/or microorchidism, reduced chance at fertility, and possibly AMAB hypogonadism. Symptoms are typically not noticed until puberty. Often, symptoms may be subtle and many individuals do not realize they are affected because of this.
Those with this variation have a higher risk of experiencing autoimmune disorders, breast cancer, venous thromboembolic disease, and osteoporosis.
The syndrome was first discovered from and named after American endocrinologist Harry Klinefelter. This took place in 1942, within Massachusetts General Hospital in Boston and was first described it in the same year. The account given by Klinefelter came to be known as Klinefelter syndrome as his name appeared first on the published paper. Considering the names of all three researchers, it is sometimes also called Klinefelter–Reifenstein–Albright syndrome.
In 1956, it was discovered that Klinefelter syndrome resulted 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. Lili Elbe, one of the early recipients of sex reassignment surgery, may have had Klinefelter Syndrome. John Randolph of Roanoke had a genetic variation, possibly Klinefelter syndrome, that left him beardless and with a soprano prepubescent voice throughout his life.
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