Associated with karyotype formula 47,XYY. Occurs in about 1 in 1000 men. Affected males are often somewhat taller than the norm for their genetic group, and may tend toward aggression, but intelligence is unaffected and behavioral issues are the exception, not the norm as may be suggested elsewhere.

I'm XYY. I'm taller than average, inclined toward aggression and have the metabolism from hell. I heal approximately three times more quickly than anyone else i know. Apart from that, i believe that's all there is to it as it certainly hasn't made me different in any other ways.

XYY syndrome: a condition identified by a supernumerary Y-chromosomal anomaly in morphologic males who are typically over 6 feet (183 cm) in height, and are likely to have one or more of a varied assortment of congenital physical anomalies, including sterility in some cases. The basic genetic defect is an extra sex chromosome with a total count of 47,XYY, although other variants also occur, e.g. 48XXYY; 48,XYYY. In behavioral development, there is an increased risk of impulsiveness, including antisocial and lawbreaking impulsiveness.

Dictionary of Sexology Project: Main Index

At one time, it was thought that men with the XYY karyotype were more prone to violence, aberrent behavior, and criminal activity. There was even a study published that claimed that XYY men were 25-60 times more likely to perform criminal acts, and Richard Speck actually tried to use (falsely) the XYY karyotype as an excuse for committing 8 murders.

Another study claimed that more prison inmates were XYY than were XY.

It was later found, after a random sampling among the civilian population, that the prison population fairly closely mimicked the general population.**

And, being the Devil's Advocate that I am, I'd like to see some proof comparing the heights, acne problems, and behaviours of XYY men to their normal brothers. It seems to me that at least some of these cases presented may actually be exceptions to the norm, and that many men may be XYY and not even know it.

Or, maybe I'm too difficult to convince.

** - The best source I can find for anything related to this is Beckwith & King, New Scientist, 1974, pp. 474-76, but I could only get access to the abstract thus far.
