Genes for Aggression?


A new study by researchers at the National Institute of Mental Health has combined genomics with functional nuclear resonance imaging (fMRI) of brains to look for the roots of aggression. As I reported in my 2002 column "Born To Be Wild?," researchers found that children (especially boys) with a low activity version of the gene for monoamine oxydase-A (MAO-A) who were abused in childhood were more prone to violence. Boys with the high activity version of the MAO-A gene, even if abused, were much less violent and less likely to get into trouble with the law. MAO-A is an enzyme that breaks down serotonin in the brain.

The new research using fMRI looks at the brains of people who carry the two different versions of the gene. The researchers found:

A version of a gene previously linked to impulsive violence appears to weaken brain circuits that regulate impulses, emotional memory and thinking in humans, researchers at the National Institutes of Health's (NIH) National Institute of Mental Health (NIMH) have found. Brain scans revealed that people with this version–especially males–tended to have relatively smaller emotion-related brain structures, a hyperactive alarm center and under-active impulse control circuitry. The study identifies neural mechanisms by which this gene likely contributes to risk for violent and impulsive behavior through effects on the developing brain.

Males are more vulnerable because MAO-A genes are carried on the X chromosome. This means that men who get one X along with a Y chromosome receive only one version of the gene whereas women get two X chromosomes which gives them a much higher chance of inheriting at least one high activity (low violence) MAO-A gene.

Genes are not destiny, especially if we choose to counteract their possible negative effects. For instance, people with genes that predispose them to produce "bad" LDL cholesterol can thwart heart disease by exercising, eating a low fat diet and/or taking statin drugs. Similarly, people who find that they have inherited a low activity version of the MAO-A gene may some day choose to take a drug (which does not currently exist) that boosts the gene's activity in order to lower their chances of engaging in inappropriate violent behavior.