Vol. 8, No. 4, 2002 Page 1&2
Many people who are abused or neglected as children grow up to be criminals or abusers themselves. Many others, however, go on to become highly successful, and never exhibit aggressive tendencies. A new study suggests that the difference between the two groups lies in their genetic makeup.
Avshalom Caspi and colleagues analyzed data from 442 New Zealand male adults involved in a long-term study. The researchers identified 154 subjects who were abused or maltreated as children, including 33 who were severely abused.
The researchers then evaluated the influence of a particular gene on the abused children's outcomes as adults. A "low activity" variant of this gene—which affects levels of monoamine oxidase A (MAOA), an enzyme that metabolizes the brain chemicals serotonin, dopamine, and norepinephrine—has previously been linked to abnormal aggression (see related article, Crime Times, 1995, Vol. 1, No. 3, Page 1).
Caspi et al. discovered that 85 percent of severely abused subjects with the low-activity variant of the MAOA gene developed some form of antisocial behavior. In contrast, study participants with the high-activity variant only rarely exhibited aggressive or criminal behavior in adulthood even if they had been severely abused as children.
"Although individuals having the combination of low-activity MAOA genotype and maltreatment were only 12 percent of the male birth cohort," the researchers say, "they accounted for 44 percent of the cohort's violent convictions."
Says study co-leader Terrie Moffitt, "The combination of the low- activity MAOA genotype and maltreatment predicts antisocial behaviors as well as high cholesterol predicts heart disease." Richie Poulton, also a study co-author, says, "These findings may explain why not all victims of maltreatment grow up to victimize others. It is possible that some genes may promote resistance to stress and trauma."
Poulton also notes that the MAOA gene investigated in their study is found on the X chromosome, and that females have two copies of this chromosome while males have only one. Thus, women are much more likely to carry at least one copy of the protective variant of the MAOA gene. "This might help explain," Poulton says, "why severe antisocial behavior is more common among men than women."
"Role of genotype in the cycle of violence in maltreated children," A. Caspi, J. McClay, T. E. Moffitt, J. Mill, J. Martin, I. W. Craig, A. Taylor, and R. Poulton, Science, Vol. 297, No. 5582, August 2002, 851- 4. Address: Terrie Moffitt, Medical Research Council, Social, Genetic, and Developmental Psychiatry Research Centre, Institute of Psychiatry, King's College, London SE5 8AF, UK
"Criminality linked to early abuse and genes," New Scientist, August 1, 2002.
"Gene that prevents male violence discovered by Otago researchers," press release, University of Otago, August 2, 2002.
"Violent effects of abuse tied to gene," Daily inScight, August 1, 2002.