What does criminal disposition mean

Criminal by the genes?

When it comes to murder, robbery or other violent crimes, the question arises again and again what drives people to such acts. The social and psychological circumstances obviously play a major role. But there are also indications that genetic predisposition is also involved. An international team of researchers has now investigated this for the first time in convicted violent criminals in Finland. In fact, they came across two gene variants that are more common in violent repeat offenders. However, this does not mean that anyone who wears these variants automatically becomes a criminal, the scientists emphasize.

Linking crime with genetic factors is tricky: this can quickly lead to unjustified discrimination against the carrier. It also brings back bad memories of the Nazis' practice of classifying criminals and the mentally ill as genetically inferior and therefore subjecting them to forced sterilization. For a long time, therefore, the idea of ​​a genetic component was considered politically incorrect.

Recently, however, there has been increasing evidence that in certain cases not only social or psychological circumstances but also biology play a role. A recent Swedish study showed that children of criminal parents are more likely to become criminals themselves even if given up for adoption as infants and adopted by other, non-criminal parents. Another study found that boys who were abused as children were particularly likely to be convicted of violent crimes if they carried a certain gene variant, as reported by Jari Tiihonen of the Karolinska Institute in Stockholm and his colleagues. A later repetition of this study with a larger number of participants could not confirm this, however. The role of this gene variant therefore remains controversial, the researchers explain.

In order to create more clarity, they now carried out a study with 794 Finnish prison inmates for the first time. Of these, 538 had been convicted of violent crimes, 84 participants had even committed more than ten such crimes. Using DNA samples from the participants, the researchers carried out a genome-wide association analysis. They used this to test whether certain gene variants occurred more frequently in violent offenders and the 84 extreme repeat offenders than in the average for the population.

Abnormalities in two gene locations

The result: the researchers actually found a signal that was more common among violent criminals at two gene locations. One of them belonged to the gene variant in the MOA-A gene that was already noticed in the study with the abused boys. It means that the enzyme monoamine oxidase is not produced in the brain of its carrier or is produced to a reduced extent. This deficiency in turn influences the activity of two brain neurotransmitters that are important for behavior, serotonin and dopamine. “This could lead to increased impulsive aggression,” explain the researchers. Especially when alcohol or drugs are also involved. They estimate that around nine percent of serious violent crimes in Finland could be attributed to perpetrators with this MAO-A genotype. A second gene variant that is conspicuously often represented among offenders 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 with impulse control. “It is therefore plausible that there is a connection between the CDH13 genotype and impulsive acts of violence,” say Tiihonen and his colleagues.

These results suggest that there are people who, due to their genetic makeup, have less favorable conditions to control their aggressive impulses under adverse circumstances or under the influence of drugs. Nevertheless, the researchers emphatically emphasize that these gene variants alone do not turn anyone into a criminal. “Criminal behavior is a complex phenomenon that is shaped by both genetic and environmental factors,” they explain. Whether or not someone carries the genetic risk factors therefore does not say anything about whether they will actually ever commit an act of violence. "Potential risk factors such as genotype therefore play no role in convictions either - and they are also not suitable for preventive screening."


© Wissenschaft.de - Nadja Podbregar
October 28, 2014