PITTSBURGH — The same genetic variation that has been associated with aggressive behaviors in certain psychiatric and criminal populations may predict confrontational and antagonistic behavior among men, Stephen B. Manuck, Ph.D., reported at the International Congress of Neuroendocrinology.
Men who reported a history of fights, conflicts with authority figures, or breaking objects in bouts of anger are more likely to carry the 3-repeat or “low-activity” monoamine oxidase A (MAOA) allele, Dr. Manuck and his colleagues found. MAOA is an enzyme that inactivates serotonin, a neurotransmitter thought to exert largely inhibitory effects.
Most white men possess either the 3-repeat or 4-repeat (high-activity) allele, at a frequency of about 35% and 60%, respectively. But this does not mean that all men with the 3-repeat allele are genetically wired to be aggressive.
The allele appears to be predictive of aggression only among men who have generally cynical and hostile attitudes, whose fathers never completed high school, and who report unaffectionate parenting in childhood, said Dr. Manuck of the department of psychology, University of Pittsburgh.
The study involved 531 white men of European ancestry in good general health who were selected from the university's Adult Health and Behavior registry. Their mean age was 44 years (range 30–54 years); 67% were married; and 86% were employed either full or part time. They were well educated, with a mean of 16.2 years of education. Incomes varied across a range from less than $25,000 to more than $80,000 per year. DNA available on registry participants was used for genotyping. The Life History of Aggression interview and personality measurements with multiple informants were used to assess behavioral attributes.
Overall, 188 men had a high lifetime history of aggression, and 192 had a low history of aggression. Forty-three percent of men in the high-aggressive group carried the 3-repeat allele, compared with 32% in the low-aggressive group. The 3-repeat allele was associated with lifetime histories of aggressive and antisocial behavior in the overall sample—even when excluding the most aggressive 20% of the study participants and after adjusting for variation in socioeconomic indicators, Dr. Manuck said at the meeting, which was sponsored by the University of Pittsburgh and the American Neuroendocrine Society.
Socioeconomic status in childhood did not significantly differ between more and less aggressive men. But both educational attainment and income among high-aggressive men were significantly lower than in their less-aggressive counterparts.
Men with the 3-repeat allele who had a less-hostile disposition and those whose fathers had attained a higher level of education were no more aggressive than were men carrying the 4-repeat allele. Among men with the 4-repeat allele, hostile attitudes and a low level of parental education were unrelated to histories of aggression.
“These findings suggest that MAOA variation is associated with expressed aggression, but only in individuals whose beliefs and attitudes give license to such behavior,” Dr. Manuck said.