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January 4, 2011

Violence Gene

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We all get angry sometimes. But some people turn that anger into violence... and scientists are discovering that may be partly due to genetics. This ScienCentral News video explains.

Genetically Wired Brains

With swelling prison populations, researchers are trying to understand the biology behind aggressive behavior. National Institute of Mental Health scientist Andreas Meyer-Lindenberg is looking for clues to how genes wire our brains early in life.

He's focusing on a specific gene that was previously linked to impulsive violence in certain populations of people. A study in 2002 found that subjects with a particular form of a gene had a significantly higher risk of violence only if they were abused as children. While this gene-environment interaction is important in understanding this behavior, Meyer-Lindenberg wanted to focus on the genetic facets of violence.

The study also found that a variation in this gene, called the L version of MAO-A, disproportionately affects men, because this gene is located on the X chromosome, which determines sex. Since men only have one X chromosome, they are more prone to the effects of the gene. Women have two X chromosomes, but the chances of having the gene variation on both chromosomes is very rare.

"One of the most fascinating things," Meyer-Lindenberg says, about this field of science called psychiatric genetics, "is how it is possible that genes [can] encode for molecules that affect something as complex as behavior, even psychiatric illness such as depression and social behavior."

Genes direct the production of proteins, which are the building blocks of living systems. Meyer-Lindenberg is investigating a gene that directs the creation of a special type of protein, an enzyme, that breaks down a chemical in the brain called serotonin.

Serotonin is a chemical messenger in the brain that affects how brain cells communicate with each another. Meyer-Lindenberg says that different forms of the gene can affect the brain's wiring and, "will then presumably contribute to behaviors and emotions such as fear or aggression."

To isolate how this gene variation might affect the brain, Meyer-Lindenberg took MRI brain scans of more than 100 healthy volunteers. Since this genetic variation is common in our population, some of the volunteers had this genetic variation, and some didn't.

He showed them pictures of angry and fearful faces, and other disturbing images, like those of an angry dog or of a gun pointed towards the screen.

The study volunteers looked at angry and scared faces.
image: NIMH/NIH
As he wrote in Proceedings of the National Academy of Sciences those with the aggression-related form of the gene responded to the pictures with increased activity in the amygdala — the brain area that detects danger, but less activity in the cingulate cortex — the brain region which controls aggression.

These brain patterns have been linked to impulsive violence, but Meyer-Lindenberg cautions in his paper, " ...because our sample was psychiatrically normal, the variation observed is clearly compatible with normal mental health and does not imply or suggest increased risk for violence in our sample."

There are many possible factors at work, he says, and violence is an extremely complex behavior. "Whether or not any given person in any given situation will become violent is known to be almost impossible to predict," he explains.

So while this gene may contribute to aggressive behavior, that doesn't mean we're chained to our genetic makeup.

Meyer-Lindenberg's research was published in the online edition of the Proceedings of the National Academy of Sciences on March 28, 2006 and was funded by the National Institutes of Health.

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