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High androgen activity linked to violent criminal behavior

A gene variant that affects the activity of androgens (male hormones) may play a role in violent criminal behavior, according to a new study.

The androgen receptor (AR) gene codes for a protein that allows cells to respond to androgens. One segment of this gene (CAG) varies in length depending on the number of “repeats” it contains. A shorter CAG region leads to increased androgen activity, while a longer CAG region results in lower activity.

Singh Rajender and colleagues took blood samples from 374 male prisoners convicted of antisocial acts. Of the group, 241 were convicted of rape, 107 of murder, and 26 of both rape and murder. Forensic evidence had confirmed the guilt of each of the men. The researchers compared the violent prisoners, who ranged in age from 16 to 58 years at the times of their crimes and came from three major population groups, to a control group of non-criminal men of similar ages and ethnicities.

Analysis showed that murderers and rapists had significantly shorter CAG repeats than control subjects. Criminals convicted of both rape and murder had far shorter repeats in comparison to either controls or men who committed only one of these crimes.

“In short,” the researchers say, “our study suggests that the reduced CAG repeats in the AR gene are associated with criminal behavior.” They note that while theirs is the first study to analyze CAG length in rapists, previous research suggests a correlation between increased signaling through androgen receptors and a higher risk for antisocial or criminal behavior.


“Reduced CAG repeats length in androgen receptor gene is associated with violent criminal behavior,” Singh Rajender, Guguluth Pandu, J. D. Sharma, K. P. C. Gandhi, Lalji Singh, and Kumarasamy Thangaraj, International Journal of Legal Medicine, March 26, 2008 (epub ahead of print publication). Address: Kumarasamy Thangaraj,