KS&A | XYY syndrome

The following sections of this site specifically address 47,XYY -

Brief Introduction to 47,XYY

In 1956, Drs. Joe Hin Tjio and Albert Lavan confirmed that there were 23 pairs of chromosomes in humans. Up until that time, it had been thought that there were 48 chromosomes. However, using a more advanced experimental technique, Tjio and Lavan were able to confirm that there are typically, in fact, only 46 chromosomes. (1) Because men commonly have 22 pairs of autosomes, plus one X and one Y sex-determining chromosome, men are referred to as 46,XY; and because women commonly have the same 22 pairs of automsomes plus two X chromosomes, they are referred to by geneticists as 46,XX. The discovery by Tjio and Lavan is generally considered to be the beginning of modern “cytogenetics,” which is the study of chromosomes and the diseases caused by either numerical and/or structural abnormalities in them.

Three years following this discovery, in 1959, a young English researcher named Patricia Jacobs and her associate described the first chromosmal abnormality in man, the extra X chromosome that is found in an estimated 80% of the men with Klinefelter syndrome; and later that year, Dr. Jacobs identified the extra X in Trisomy X (47,XXX). (2, 3) Approximately two years later, in 1961, Dr. Avery Sandberg and his associates published a paper in the medical journal Lancet reporting the first man to be discovered with an extra Y chromosome in his cells. (4)

According to the latest estimates, the incidence level of 47,XYY is approximately 1 out of 900 live birth males. (5)

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Other Resources for Individuals and Families Dealing with 47,XYY

Information on this website is updated regularly, including based on the input of other individuals and families dealing this same condition. Accordingly, users are encouraged to check back often and to consider participating in any of the following free support services -

KS&A’s Online Discussion Groups
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(1) Joe Hin Tjio and Albert Levan, “The Chromosome Number of Man,” American Journal of Obstetrics and Gynecology, 1956, 130:723-724.

(2) Patricia A. Jacobs and J. A. Strong, “A Case of Human Intersexuality Having a Possible XXY Sex-determining Mechanism,” Nature, 1959, 183: 302-303.

(3) Patricia A. Jacobs, et. al., “Evidence for the Existence of the Human “Super Female,” Lancet, September 26, 1959, 2:423-5.

(4) Avery A Sandberg, et. al., “An XYY Human Male,” Lancet, August 26, 1961, 2: 488-9. This was an incidental finding in a normal 44-year-old, 6 foot tall man of average intelligence.

(5) [Cite]

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