Scientists have discovered the genetic variant of a brain receptor molecule that leads to violently impulsive behavior when people who carry it are under the influence of alcohol.
The multinational research team was led by scientists at the U.S. National Institutes of Health. A report of the findings, which include human genetic analyses and gene knockout studies in animals, appears in the December 23 issue of Nature.
“Impulsivity, or action without foresight, is a factor in many pathological behaviors including suicide, aggression, and addiction,” explained senior author David Goldman. M.D. Goldman, chief of the Laboratory of Neurogenetics at the NIH National Institute on Alcohol Abuse and Alcoholism (NIAAA), added that it is “also a trait that can be of value if a quick decision must be made or in situations where risk-taking is favored.”
Goldman and researchers in Finland and France studied a sample of violent criminal offenders in Finland. The hallmark of the violent crimes committed by the individuals in the study sample, he said, was that they were spontaneous and purposeless.
“We conducted this study in Finland because of its unique population history and medical genetics,” Goldman explained. “Modern Finns are descended from a relatively small number of original settlers, which has reduced the genetic complexity of diseases in that country.”
The researchers sequenced
HTR2B encodes one type of serotonin receptor in the brain. Serotonin is a neurotransmitter – a brain chemical – known to influence many behaviors, including impulsivity.
However, the genetic variant alone did not account for the violent impulsivity, Goldman added. “Carriers of the HTR2B variant who had committed impulsive crimes were male, and all had become violent only while drunk with alcohol, which itself leads to behavioral disinhibition.”
The researchers then conducted studies in mice and found that when the equivalent HTR2B gene is knocked out or turned off, mice also become more impulsive. Studies of any alcohol interaction in the knockout mice are ongoing.
The findings may lead to a better understanding of some aspects of impulsivity, and ultimately to strategies for diagnosis and treatment of clinical conditions. The researchers cautioned, however, that impulsivity is a complex trait with multiple genetic and environmental causes. “Although relatively common in Finland, the genetic variant we identified in this study is unlikely to explain a large fraction of the overall variance in impulsive behaviors, as there are likely to be many pathways to impulsivity in its various manifestations,” Goldman said.
The findings are likely to make headlines in the field of addictions and among scientists dealing with attention deficit hyperactivity disorder, or ADHD.
The research carries particular implications for ADHD adults who drink, especially those who are diagnosed with the impulsive-hyperactive subtype.
Adolescents and young adults with ADHD – which affects up to 10 percent of school children worldwide -- are at a statistically significant higher risk of abusing alcohol and illicit drugs than their peers in the general population, according to numerous studies.
ADHD teens who do not receive timely treatment are also at statistically higher risk of getting into motor vehicle accidents, dropping out of high school and juvenile deliquency.