Can the genes make you criminal?

Two gene variants often appear in violent repetitive tribes

Is there a biological cause for violent crime? © freeimages
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Researchers have discovered two gene variants that are particularly common in convicted violent criminals. These genes promote aggression and weaken impulse control, both traits that are particularly common to repeat offenders. However, the researchers emphasize that the mere presence of these gene variants in the genome does not automatically make anyone a violent criminal.

Linking crime with genetic factors is tricky: it can quickly lead to unjustified discrimination of the carriers. It also arouses bad memories of Nazi practice of classifying criminals and mental patients as genetically inferior and subjecting them to compulsory sterilization. For a long time the idea of ​​a genetic component was considered politically incorrect.

Indications for a biological component

Recently, however, there is increasing evidence that in certain cases, not only social or psychological circumstances, but also biology plays a role. For example, a Swedish study showed that children of criminal parents are more likely to become criminal even if they have already been adopted as infants. Another study found that boys who were abused as children were more likely to be convicted for violent crime even if they carried a particular gene variant. However, a later repetition of this study with a larger number of participants could not confirm this.

To clarify matters, Jari Tiihonen from the Karolinska Institute in Stockholm and his colleagues carried out a study with 794 Finnish prison inmates. Of these, 538 had been convicted of violent crime, and 84 had committed more than ten such crimes. Using DNA samples from the participants, the researchers performed a genome-wide association analysis. With this they examined whether certain gene variants were more common in violence and the 84 extreme repeat offenders than the average of the population.

The enzyme monoamine oxidase A plays an important role in the neurotransmitters serotonin and dopamine © in the public domain

Gene variants weaken the impulse control

The result: at two loci, researchers actually found a signal that was more common among violent criminals. One of them belonged to the gene variant in the MOA-A gene, which had already been noticed in the study with the abused boys. It leads to the fact that the enzyme monoamine oxidase in the brain of its carriers is not produced or reduced. This deficiency in turn affects the activity of two major brain messengers, serotonin and dopamine. display

"That could lead to an increased impulsive aggression, " explain the researchers. Especially if alcohol or drugs are also involved. According to their estimates, around nine percent of serious violent crime in Finland could be traced back to T ter with this MAO A genotype.

A second gene variant, which is frequently found in the criminal scene, concerns the CDH13 gene, which also plays a role in ADHD, as the researchers report. It has long been known that this variant can lead to problems in impulse control. "Therefore, it is plausible that there is a link between the CDH13 genotype and impulsive violence, " say Tiihonen and his colleagues.

The criminal is not there

According to the researchers, these results suggest that there are people who, due to their genetic makeup, have less favorable conditions for controlling their aggressive impulses under adverse circumstances or under the influence of drugs. Nevertheless, Tiihonen and his colleagues emphatically stress that these gene variants alone do not make anyone a criminal.

"Criminal behavior is a complex phenomenon characterized by both genetic and environmental factors, " they explain. Whether or not someone carries the genetic risk factors does not say anything about whether he will ever commit an act of violence. "Potential risk factors such as the genotype therefore do not play a role in convictions and they are not suitable for preventive screening either." (Molecular Psychiatry, 2014; doi: 10.1038 / MP.2014.130)

(Nature Group, 29.10.2014 - NPO)