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Are we genetically programmed to be timid or violent? Earlier this week a study was published in Molecular Psychiatry titled “Genetic background of extreme violent behavior.” Two groups of Finnish prisoners had their genes tested, and in a brute force hack comparing behavior and genotype called a genome-wide association study, it turns out that the most violent offenders were considerably more likely to have combinations of certain variants of the MAOA and CDH13 genes.
The MAOA gene variant known as the “warrior” gene is actually a variant for the promoter region of the gene, coding for a less active MAOA enzyme. Since this enzyme hangs out inside cells and breaks down neurotransmitters, having less active MAOA means more neurotransmitters (dopamine, norepinephrine, epinephrine, and dopamine) are available, which might be protective against depression (the results are mixed), but it is also possible it could lead to more impulsive and violent behavior. Over the years, controversy around the “warrior gene” has popped up, as to whether it, in combination with maltreatment as a child, leads to sociopathy in adults (again, results are mixed)(1)(2)
The CDH13 gene (snp is rs11649622, the risk allele A if you happen to have your genome) codes for a neuronal membrane adhesion protein. It has a questionable link to alcoholism.
Anyway, the authors were especially interested in the most violent offenders, defined in this study as having committed more than 10 seriously violent crimes. According to the paper, “the majority of violent crime is committed by a relatively small group of antisocial…offenders” who commit crimes over and over again. While links between the above genes and the general prison population were iffy, those prisoners who had a combination of the less active MAOA and the risk allele for CDH13 were way more likely to be in that small group of super violent repeat offenders. The calculated odds ratio of having both in this group was 13.45. Usually, an odds ratio of more than 2 makes you sit up and take notice that a finding could be something very interesting. It is possible that a combination of the less active MAOA enzyme and a genetic issue with neuronal membranes puts someone at higher risk for becoming violent.
So is this finding the beginning of genetic testing for all and a Gattaca-like pruning of people into genetic haves and have-nots? Not so fast. A large portion of the population has the so-called “warrior” gene (depending on race, around 40-50%). Most of the extremely violent offenders didn’t have the highly risky combo of genes found in the study. Human behavior is explained by a combination of environment and a complex interaction of multiple genes. It will likely never be accurate to say there is a particular gene for violence or any other specific behavior. Figuring out the physiology and phenotype defined by the genotype is certainly interesting, but it's way too early to start planning a kid’s career based on her results from 23andMe.
Image credit: Wikimedia Commons
Copyright Emily Deans MD
