June 28, 2006

Why are some men more aggressive than others?

By Charnicia Huggins

NEW YORK (Reuters Health) - Why are some men
confrontational or break objects in fits of anger, while others
appear to be more in control under similar circumstances? New
study findings suggest the answer may involve genetic
differences in combination with the men's early environment.

A variation in a gene involved in the activity of the brain
chemical serotonin, which is known to play an important role in
regulating emotions and impulses, may cause some men to have
problems controlling their anger. Yet, this appears to be true
only for men raised in certain environments, in particular
under adverse circumstances.

"The take-home message is not to change the genes or the
brain, but the environment in which the brain matures or
develops," study author Dr. Stephen B. Manuck, of the
University of Pittsburgh, told Reuters Health.

Studies have shown that some people with psychiatric
disorders and those imprisoned for an impulse-related crime are
either deficient in serotonin or exhibit poor regulation of the
brain chemical.

In previous studies, researchers also found that men
carrying one form of the monoamine oxidase-A (MAOA) gene
responsible for inactivating serotonin were more likely to be
violent and antisocial than men with a different form of the
gene. However, the negative behavior was seen only among men
who were abused in childhood.

Manuck investigated if this was also the case among men who
exhibited less dramatic aggression. He studied 531 healthy,
white men from the general population and found that the same
form of the MAOA gene found in violent criminals was also more
common in study subjects who reported a history of
confrontational and antagonistic behavior, such as fighting,
having temper tantrums or breaking objects in fits of anger.

This form of the MAOA gene, referred to as "low activity,"
was associated with aggressive behavior only in men who were
cynical and hostile toward others and among those with poorly
educated fathers. In contrast, men with the low activity MAOA
gene who were not cynical or hostile or whose fathers had at
least graduated from high school were no more likely to exhibit
aggressive behavior than those with the high-activity form of
the gene, study findings indicate.

In other findings, differences in the serotonin 2A
receptor, another serotonin gene, were also associated with a
higher level of aggressiveness in men. Again, increased
aggression was only apparent among men whose fathers had not
completed high school. The subjects' educational level did not
appear to be related to their behavior.

In another study, Dr. Stephen Suomi, of the National
Institute of Child Health and Human Development, studied the
association of genetics, the environment and aggression in

Up to 10 percent of wild rhesus monkeys exhibit impulsive
behavior or extreme aggression under mild stress conditions.
Researchers have found that these monkeys are also deficient in
the breakdown and use of serotonin.

Suomi found that laboratory monkeys with a gene that blocks
serotonin were also more impulsive and aggressive, but only
those who failed to develop secure attachment relationships
with their mothers. In contrast, monkeys that experienced
"maternal buffering" via secure attachment relationships did
not exhibit these characteristics.

The study findings imply that even though a child may have
a genetically related increased susceptibility for conduct
problems, affectionate and loving parents can negate this
increased susceptibility, Manuck said. "We can't change our
genes, but perhaps we can change our rearing environment."

The findings were presented last week at the Sixth
International Congress of Neuroendocrinology in Pittsburgh,