Dec. 22, 2010— -- In a discovery that could help scientists further understand impulsivity in humans, researchers announced that they found a genetic variant that may contribute to spontaneous violent behavior.
In a new study released in the journal Nature, a multinational research team examined the genes of 96 violent criminal offenders in Finland with behavioral disorders and compared it with DNA from a control group of 96 people in the country who had no such psychiatric diagnoses.
The offenders had been diagnosed with antisocial personality disorder, borderline personality disorder or intermittent explosive disorder, all conditions with symptoms of impulsive aggression.
The mutation was found to affect the brain's levels of serotonin, a neurotransmitter that affects mood, appetite, sleep and impulsive behavior.
"Impulsivity is a normal dimension of behavior, but it also plays a role in many psychiatric disorders, including alcoholism and suicidalism," said Dr. David Goldman, chief of the Laboratory of Neurogenetics at the National Institute on Alcohol Abuse and Alcoholism, in Bethesda, Md., and senior author of the study. "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."
Researchers specifically conducted the study in Finland because of its unique population and medical genetics. Goldman said modern Finns descend from a relatively small number of original settlers, which increased the chance of finding specific genes that influence impulsive behavior.
"Finns have the same degree of genetic diversity as people from other cultures, but their genetic disease diversity is reduced," said Goldman. "Genetic heterogeneity tends to be reduced in Finland because of its unique population, which was founded by two major waves of migration."
Alcohol and Impulsive Behavior
"There were two triggers in people with the genetic mutation: the male sex and alcohol," continued Goldman. "Everyone who carried this gene and committed a violent crime was intoxicated, and this is an important interactive factor to note."
Dr. Jason Jerry, a psychiatrist at the Alcohol and Drug Recovery Center at Cleveland Clinic, was struck by the overlap between serotonin levels, alcohol and impulsive behavior.
"This is important to look at because serotonin is one of the main neurotransmitters that have been looked at across the board, from alcoholism to suicide," said Jerry. "And in this study, it wasn't just the variant of the gene. The variant had to be coupled with intoxication."
But doctors note that violent and severely impulsive behavior is never cut and dry. The traits can be attributed to a host of nature and nurture characteristics, unique to each person.
Impulsivity is defined as action without foresight. It is the center point of many psychiatric behaviors including suicide, aggression and alcoholism. Other conditions that feature highly impulsive behavior include kleptomania, pyromania, intermittent explosive disorder and trichotillomania (the compulsion to pull one's own hair out).
While the study's authors noted the correlation between the gene variant and impulsivity, there are approximately more than 100,000 Finns who have this mutation. Just because people carry the genetic variant does not mean that they will act in an impulsive or criminal way.
Dr. Igor Galynker, associate chairman of psychiatry at Beth Israel Medical Center in New York, pointed out that, although this specific genetic mutation relates to only people of Finnish descent, other genetic mutations have been found to cause impulsive behavior.
"As most things in behavior, it is a multigenetic thing," said Galynker. "There are likely a lot of genes that relate to impulsivity."
In a 2006 study published in the Proceedings of the National Academy of Sciences, researchers found that a variant of the MAOA gene, found in many Americans, was associated with an increased risk of impulsive aggression in humans. And carriers of the gene who had been abused as children were even more likely to be violent later in life.
DNA & Individualized Medicine
So how can these findings help medicine in the future, especially for those who suffer from severe impulsivity?
While personalized care has become the face of new medicine, Dr. David Beversdorf, a neurologist in the departments of radiology, neurology and psychological sciences at University of Missouri Health Care, said that scientists still must take caution when assuming the identification of genes will result in individualized treatment.
"[It] has been tricky," said Beversdorf. "Some positive findings have been confirmed in follow-up research. However, a large number of studies that showed tremendous promise for identifying a gene that might affect treatment in initial research have not panned out in further studies."
But still, doctors remain hopeful.
Jerry said, "Studies like these can hold the hope and promise of someday directing treatment where we can ask, Is there a way we can intervene from a medical standpoint to decrease impulsive behavior?"