A mutated gene may predispose a person to severe impulsive behaviors, scientists announced in Nature last week.
Impulsivity, the authors say, describes action without foresight, decreased inhibitory control and a lack of consideration of consequences. It’s also an important feature of several psychiatric diseases and a long list of behavioral manifestations like suicide, violence and attention deficit hyperactivity disorder (ADHD).
Not that having the mutation necessarily results in these. “These disorders are often difficult to disentangle at the causal level, but by studying traits, we can find genes that contribute to important aspects of them,” says David Goldman from the National Institute on Alcohol Abuse and Alcoholism who led the international team of researchers.
They discovered a mutation on the gene HTR2B, after sequencing and comparing DNA from 96 ‘severely impulsive’ criminal offenders with 96 men free of psychiatric diagnoses.
The mutation occurred three times more frequently in the violent offenders and arsonists. According to the study, the crimes occurred as disproportionate reactions to minor irritations and were unpremeditated, without potential for financial gain and recurrent. And because of the extreme nature of their crimes, they underwent inpatient forensic psychiatric examination at the time of their initial incarceration.
All the participants are Finnish and male, and according to the researchers, the mutation is apparently exclusive to Finns.
The mutation prevents the production of receptors for serotonin and dopamine. Not having enough receptors for those neurotransmitters in a certain part of the brain called the nucleus accumbens might lead to a lack of restraint and foresight into the consequences of actions.
(Previous research showed that ecstasy stimulates the release of serotonin and dopamine by activating HTR2B.)
The researchers caution that genetics is just one of the many factors that predispose a person to act impulsively.
"There were two triggers in people with the genetic mutation: the male sex and alcohol," Goldman says. The men who carry this gene and committed the crimes were intoxicated.
People with the gene, he adds, “behave as if they have a very short fuse, and it becomes even shorter when they're disinhibited by alcohol."
Although impulsivity can be an adaptive dimension of personality, they say, the intolerance for delay, disinhibition and the inappropriate weighting of contingencies are maladaptive. That has sometimes led to violent criminality, antisocial personality disorder, borderline personality disorder, intermittent explosive disorder, kleptomania and even trichotillomania, the compulsion to pull out your own hair.
But the team cautions against screening for the gene to identify potentially violent and impulsive individuals, because only a fraction of carriers turn to violence. "The vast majority of carriers are normal behaviorally and cognitively, so population screening would not be justified," Goldman says.
Additionally, mice who don’t have the gene act impulsively.
Image: Nucleus accumbens via Wikimedia Commons