The 47,XYY syndrome, 50 years of certainties and doubts: A systematic review

• Full review of the literature of the last 50 years.
• Analysis of the most significant and frequent phenotypic expressions of the 47,XYY syndrome, including somatic, psychic and behavioral ones.
• Evaluation of a possible connection between 47,XYY and deviance.
• The analysis of all the studies proves that there are no statistical evidence that a 47,XYY man is predisposed to aggressive and deviant behavior.
• The presence of an extra Y can be considered only a genetic substrate, which cannot be the only cause of deviant behaviors.

The Jacobs’ syndrome consists in the presence of a Y chromosome in excess. The prevalence of XYY sex chromosome abnormalities in newborns is as high as 1:1000, but they are often unidentified because they are not necessarily associated with gross physical or cognitive impairments, and so they may never come to medical attention. The only common and obvious features are high stature and a strong build. During the 1960s and the 1970s, some studies postulated that the Jacobs’ syndrome could lead to aggressive behavior, but the statistical certainty was questioned. More recent developments in genetics and neuroimaging have led to new publications on the relationship between the presence of an extra Y chromosome and social function, trying to explain the possible increasing tendency to commit a crime and to search for a biological nature of human behavior and deviant conducts. The authors conduct a review of the literature of the last 50 years concerning this chromosome trisomy, focusing on a possible connection between 47,XYY and deviance. According to the results of these studies, the authors conclude that there is no noteworthy evidence that a person affected by Jacobs’ syndrome has to necessarily turn into an antisocial or deviant individual.