Why do certain individuals partake  in criminal behaviour? This question has no simple, straightforward answer, because there may be several complex and multifactorial causes. Social factors, such as the environment one grows up in or their socio-economic status, as well as psychological factors, have been extensively studied. However,  genetics may also contribute to criminality, as observed in  several other studies.

Sibling and twin studies, which compare incidences of specific traits between family members, indicate clusters of criminality within families. This suggests that a genetic component may be present.

Several genes have been studied for the potential link to criminal activity. These genes can be tested for, using ‘next generation genetic sequencing’. The MAOA-L gene is a variant of the normal gene, which encodes an enzyme that degrades neurotransmitters such as noradrenaline and dopamine. Such neurotransmitters have a wide range of functions, including but not limited to mood regulation, emotions and sympathetic system activation. In this variant gene, the activity of the enzyme is less than normal. This gene has also been called the ‘warrior gene’, since it has been linked to violent crime and antisocial behaviour.

Yet, several studies have yielded mixed results regarding the MAOA-L gene. Only when childhood maltreatment is  present in combination with the MAOA-L gene, is there a significant increase in violent behaviour and, possibly, crime. This shows the complex relationship between criminality and genetics. Moreover, different types of the warrior gene have been shown to be relatively common in certain populations.

Another gene which has been studied is the cadherin 13 (CDH13) gene. It has been associated with attention-deficit/hyperactivity disorder (ADHD) as well as substance abuse. A recent study in Finland has shown that when these two genes were present, an individual was 13 times more likely to have a history of repeat violent activity. However, the presence of such genes does not mean that the individual will necessarily become a criminal, it just indicates a higher risk. As such, genetic profiling cannot be used as a predictive factor alone. Numerous other genes are currently being studied for their  relation to crime, most prominently COMT and HTR2B serotonin receptor gene.

In addition, the presence of certain genes may also raise the co-occurrence of alcoholism and violent behaviours. This adds yet another way by which the genetic makeup of an individual may increase the risk of criminality.

Furthermore, several genetic syndromes have also been linked with criminality. These include Jacob’s syndrome, also known as XYY syndrome, and Klinefelter syndrome. Both are associated with increased rate of serious criminal convictions.

The genetics of individuals on trial have recently been used in criminal courts. The possible influence of genetics on criminality raises an issue with crime sentencing. This is so since it may be seen that the individual who committed a crime is not accountable for their genes. Thereby, should such criminals be held responsible for their actions to the same extent as an individual who does not have these genes? Different countries address this issue differently. However, further research and clarification of the local legal framework is needed to better handle such cases.

In conclusion, several genes have been attributed to criminal behaviour such as violence and substance abuse. However, further research is necessary in order to further elucidate this complex relationship.

Robert Pisani, Radiographer practitioner, medical student, University of Malta