A distressingly large number of children suffer physical or sexual abuse. A new study adds a genetic twist to the much-noted tendency of maltreated kids to become violent, law-breaking adults.
Abused boys who inherited a highly active version of one gene crucial in brain chemistry later had far fewer behavioral problems and arrests for violent crimes than did abused boys who were born with a sluggish version of the same gene, say psychologist Avshalom Caspi of King’s College in London and his colleagues.
“There’s an interplay between two variations of this gene and the experience of childhood maltreatment,” remarks King’s College psychologist Terrie Moffitt, a study coauthor. “One genetic variation may protect abused boys from converting their stressful experiences into antisocial behavior toward others.”
Individual differences in the gene for monoamine oxidase A, or MAOA, proved critical for maltreated boys tracked up to age 26, the scientists report in the Aug. 2 Science. Situated on the X chromosome, the MAOA gene yields an enzyme that lowers brain concentrations of chemical messengers such as norepinephrine, serotonin, and dopamine.
Earlier studies had linked genetic deficiencies in MAOA production to extreme aggression in mice and in men of a Dutch family.
Caspi’s team probed the molecular structure of MAOA genes in 442 young men in New Zealand who had been studied since age 3 (SN: 4/15/95, p. 232). By age 11,
36 percent of the boys had experienced some form of maltreatment, including physical and sexual abuse and frequent shuttling from one caretaker to another.
Although only 12 percent of maltreated boys possessed the low-activity MAOA gene, Caspi found, they account for nearly half of all later convictions for physical assault and other violent crimes.
Moreover, 85 percent of severely maltreated boys with the low-activity MAOA gene developed antisocial behavior by young adulthood. Antisocial behavior includes persistent fighting, bullying, stealing, and law breaking with no sign of remorse.
In contrast, antisocial behavior and criminal arrests occurred in only a minority of maltreated males who had inherited the highly active MAOA gene. High MAOA activity may promote “trauma resistance,” even though the boost doesn’t make all maltreated boys solid citizens, Moffitt contends.
Compared with the males, females in the same study showed a significant but less dramatic effect of the MAOA gene on the linkage between childhood maltreatment and later antisocial behavior. One reason that females engaged in less of such behavior than males did may be that, by having two X chromosomes, girls more often inherited at least one copy of the high-activity MAOA gene, Moffitt theorizes.
The new findings open the door to identifying biological mechanisms that connect childhood maltreatment to ensuing behavior problems, comments psychologist Seth D. Pollak of the University of Wisconsin–Madison. “And when you have a mechanism, you can begin to design effective treatments,” he says.