Children exposed to such media violence are in turn more likely to show ADHD-related behaviours; but the findings also suggest that this correlation is true for children who do not carry the studied gene variant.
'Our results indicate that children's violent media use is partly influenced by genetic factors. This could mean that children with this gene variant are more likely to seek out stimulating activities, such as violent television viewing and video game playing', commented Sanne Nikkelen, the first author of the study, from the University of Amsterdam.
However, it is possible that children with ADHD are simply more likely to use violent media, as the study only checked for correlation between these two factors without determining which factor influences the other. In addition, no direct effects on ADHD behaviour patterns were observed due to the studied gene variant; it only acted indirectly by enhancing the children's use of violent media.
It has previously been shown that ADHD-related behaviours as well as media use are heritable. This study is the first to suggest that use of violent media can be thought of as an intermediate step between genetic disposition and ADHD. A variant of the 5-HTT gene, previously linked to ADHD behaviour patterns in context of interaction between children's genes and their home environment, was chosen to test this hypothesis.
The 5-HTT gene is involved in regulation of serotonin in the brain, which in turn is important for control of human emotions and impulses. Several variants of the 5-HTT gene are known; the specific ADHD-linked variant, evaluated in this study, was the long variant 5-HTTLPR.
The research was conducted on a sample of 1612 children of Dutch origin, aged five to nine years. The children's health was frequently examined by physicians at health centres, their DNA was tested, and surveys on their use of violent media were filled out by their parents. Correlations between the 5-HTTLPR gene variant and use of violent media were determined.
In addition to the 5-HTT gene, several other genes have been linked to ADHD. In the study, the scientists also tested their hypotheses on a variant of another ADHD-related gene, the DRD4, but found no correlations. The authors concluded that more research is needed to answer questions about relationships between genes, environment, such as exposure to media violence, and complex behaviours, such as ADHD.
The study was published in the Journal of Communication.