A study published on 24 September in Translational Psychiatry, a peer-reviewed medical journal, suggests that environmentally-induced epigenetic changes may have an important impact on intelligence. The research, led by Dr Jakob Kaminski and Prof Andreas Heinz from the Department of Psychiatry and Psychotherapy of Charité Universitätsmedizin Berlin, has shown that modifications in the structure of a specific gene can have a negative impact on an individual’s test performance. Thus, the findings demonstrate a clear link between differences in intelligence and the activity of certain genes.
The authors suggest that one possible reason for what they refer to as “intelligence malleability” is the modification of gene expression via epigenetic mechanisms like DNA methylation, owing to environmental factors such as changes in the educational system, overall exposure to stress, traumatic experiences, nutrition, and poverty. The considerable increase in test results for average intelligence within one generation in the second half of the last century cannot be explained by genetics alone, which is where epigenetics comes in.
Epigenetics are heritable changes in gene expression rather than changes in the underlying DNA structure itself that are typically associated with evolution. Changes in DNA sequences can take millions of years to appear, whereas epigenetic changes happen much faster and can occur within one generation. When DNA is passed along to the next generation of cells, the epigenetic information can also be passed along, which can dictate the environmental conditions for which a particular gene is activated. In other words, the environment can have an impact on how DNA is read and which proteins are produced, which can have both positive and negative repercussions.
In the study, a regression model to assess the influence of various genetic and epigenetic predictors on IQ based on associations between cognitive capacity (gIQ) and polygenic scores ― a measure of genetic risk based on genetic variations ― as well epigenetic markers of the dopaminergic system, gray matter density in striatum, and striatal activation during reward processing in almost 1500 healthy adolescents.
The researchers focused on genes that are involved in dopamine-based neurotransmission ― the process of sending chemical signals between neurons ― since dopamine is known to play an important role in the brain’s reward system, thereby modulating drive and motivation. The findings show a link between the epigenetic changes in dopamine neurotransmission and an individual’s IQ test performance. Epigenetic modifications can silence the dopamine receptor gene leading to reduced signal transmission and fewer dopamine receptors being activated. This, in turn, was associated with lower IQ test results. The authors admit the study size was too small for genetic and epigenetic studies to obtain conclusive results and suggest a more comprehensive DNA methylation analysis would likely identify more epigenetic loci associated with IQ score.
Stress and dopamine production have both previously been linked to cognitive performance. Now, environmentally-induced gene activity can be added to the list of factors known to influence IQ scores.
(1) Kaminski, J.A. et al. Epigenetic variance in dopamine D2 receptor: a marker of IQ malleability? Translational Psychiatry (2018). DOI: 10.1038/s41398-018-0222-7