The monoamine oxidase A (MAOA) gene is an outer membrane mitochondrial enzyme that breaks down monoamines such as serotonin, noradrenalin and dopamine. A common polymorphism in MAOA results in high- or low-activity MAOA, and both genotypes have been linked to aggression and violence. A Finnish study has found that drinking and high-activity MAOA can predict the risk of impulsive violence, while aging may decrease this risk.
Results will be published in the March issue of Alcoholism: Clinical & Experimental Research and are currently available at Early View.
"Alcoholism, alcohol consumption and violence are clearly related," said Roope Tikkanen, a researcher in the department of psychiatry at Helsinki University Central Hospital and corresponding author for the study. He noted that crime statistics show that most impulsive homicides occur among adolescent and middle-aged groups rather than among the elderly, and habitually violent-impulsive offenders are often expected to "grow out of their difficulties" with increasing age. "Surprisingly little accurate information, however, is available on this aging-impulsive aggression issue," he said.
Tikkanen and his colleagues decided to look at the MAOA gene, alcohol consumption and aging as predictors for recidivism in impulsive violent behavior among a sample of 174 Finnish alcoholic male offenders originally recruited between 1990 and 1998. Each offender was given a psychiatric assessment; in addition, their alcohol consumption was measured, their violent behavior was assessed, and they were genotyped for polymorphisms of MAOA.
"Increased alcohol consumption and aging seem to predict violence," said Tikkanen, "although these risk factors 'work' in opposite directions, and only concern individuals who have been given by nature a high-activity variant of MAOA." On the other hand, he added, additional research has suggested that individuals with low-activity MAOA seem to be at risk for criminality and violence after exposure to severe childhood maltreatment.
"People react quite differently to acute alcohol exposure," Tikkanen continued. "Most individuals become relaxed and talkative, while some – particularly persons who are introverted while sober – become expansively extroverted and aggressive. A dramatic change from a normally introverted personality to extroverted aggressiveness and uncontrolled behaviors under the influence of alcohol was formerly called 'pathological intoxication' in Finland."
Regarding the decline in impulsive-aggressive behavior with aging among high-activity MAOA offenders, Tikkanen hypothesized that it may be due to a correction of low central serotonin levels in the central nervous system.
Tikkanen cautioned against genetic testing for individuals who may be worried for one reason or another about their risk. "Even though whole genome scans will one day be affordable, the average person probably has very many factors that differ from the violent offenders in the study," he said. "For instance, the average Finnish consumption is two drinks a day or 10 kg pure alcohol per year, whereas the upper 10 percent of violent offenders drink approximately one 0.75 liter bottle of liquor a day or around 100 kg pure alcohol a year."
Tikkanen and his co-authors suggest that high-activity MAOA offenders may be helped to control their violent behaviors by coaching to maintain alcohol abstinence, and possibly by psychopharmacological treatment to increase central serotonin levels.
"In some countries, prison sentences may be very long – even a lifetime or more – and the reason for the sentence may be an accumulation of minor convictions committed in a drunken state," said Tikkanen. "In such cases, it could perhaps benefit all parties to decrease the length of the sentence. Our results suggest that the risk for new violent crimes decreases by 150 percent when high-activity MAOA individuals become 20 years older. Perhaps we could increase the efficacy of addiction rehabilitation by focusing resources particularly on younger heavy-drinking high-activity MAOA individuals."
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