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TUESDAY, Oct. 28, 2014 (HealthDay News) -- In a cutting-edge look at the biology of crime, a team of Swedish investigators has identified two specific genetic mutations that appear to be linked to a higher risk for extremely violent behavior.
"Our study suggests that up to 10 percent of violent crimes might be explained by the aforementioned two genes," said study lead author Dr. Jari Tiihonen, a professor in the department of clinical neuroscience with the Karolinska Institute in Stockholm, Sweden.
One of the mutations involves a version of gene called MAOA. This genetic mutation appears to short circuit the usual way the hormone dopamine is processed and controlled. Prior research has suggested that an excess of dopamine can promote aggressive behavior, particularly when mixed with drugs or alcohol, according to background information in the study.
The other mutation involves a gene known as CDH13. This mutation seems to impede the development of normal neural connections and undermine impulse control. It has previously been linked to the onset of Attention Deficit and Hyperactivity Disorder (ADHD), according to the study.
"[But] I think that it is important to realize that there are probably many more genes that [also] contribute to violent behavior," he added, and noted that simply carrying the mutations does not mean a person is inevitably destined for a life of violence.
In fact, Tiihonen pointed out that although carriers of the MAOA and CDH13 mutations are 13 times more likely to commit a violent crime, "the vast majority [of] high-risk genotype individuals do not commit severe violent crimes." The researchers only found an association between violent crime and gene mutations; the study didn't prove the mutations were the cause of such behavior.
Tiihonen and his colleagues discussed their findings in the Oct. 28 online issue of Molecular Psychiatry.
To explore the potential genetic underpinnings of criminal behavior, the authors conducted a genetic analysis involving nearly 800 Finnish citizens.
All had been convicted of a crime, and were incarcerated in one of 19 Finnish prisons, the study noted. Some crimes involved nonviolent behavior, including property theft and drug-dealing. Others, however, had been found guilty of repeatedly engaging in extremely violent offenses, including at least 10 acts of murder and/or assault.
In all, 215 participants were classified as "nonviolent offenders," while 538 were deemed "violent" (with at least one conviction). A subgroup of the violent offender group included 84 people who were deemed "extremely violent" (with 10 or more convictions), according to the study.
DNA samples from the criminals were compared to the DNA of more than 2,000 non-incarcerated Finnish citizens who'd given DNA samples for a previous study.
Based on these genetic analyses, the researchers found that having the MAOA mutation was associated with a higher risk for being a "violent offender." They also found that the gene was strongly linked with "extremely violent" crime. Similarly, having the CDH13 mutation was also linked to extremely violent behavior, the researchers noted.
Neither mutation was found to be associated with nonviolent crime, according to the study.
Could these findings lead to a futuristic world of policing, in which some citizens are genetically pegged as trouble long before a crime has even been committed?
"The sensitivity and specificity of the findings are too low for any screening [for] prevention purposes," Tiihonen cautioned. "According to the basic principles of forensic psychiatry, any risk factors, such as genotype or brain injury in car accident, must not have any effect per se on convictions or prison sentences. The mental capacity to understand the nature and consequences of one's deeds, and ability to control one's behavior, are the only things that matter."
That said, Tiihonen argued that the findings could be used to help some offenders break their cycle of repetitive violence. This, he noted, would be particularly applicable to MAOA mutation carriers, because their aggression is often fueled by sky-high dopamine surges that occur whenever they consume drugs or alcohol.
"One way to prevent... [repeat] offending would be a combination sentence," he suggested. "The offender might get slightly shorter prison sentence, if he/she would accept to take [the dopamine depressant] disulfiram two to three times a week under strict supervision. This would make it impossible for him/her to use alcohol anymore," he noted, given the medication's ability to make drinking unpleasant and distasteful.
Kevin Beaver, a professor with the College of Criminology and Criminal Justice at Florida State University in Tallahassee, said that "much remains unknown about which genes are involved [in violent behavior], and how they ultimately may predispose to different types of criminal behaviors."
"The findings from this study are extremely important," he noted, "as they provide some newer insight into the genetic architecture to extreme forms of violent behavior among offenders from Finland."
"It would be interesting," Beaver added, "for future research to address the issue of how this genetic information could be used to increase rehabilitation and treatment program effectiveness. It would also be interesting to examine what role environmental factors play in exacerbating or dampening the effects of these genes on violent criminal behavior."
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SOURCES: Jari Tiihonen, M.D., Ph.D., professor, department of clinical neuroscience, Karolinska Institute, Stockholm, Sweden; Kevin M. Beaver, Ph.D,, professor; College of Criminology and Criminal Justice; Florida State University, Tallahassee; Oct. 28, 2014, Molecular Psychiatry