Are the monoamines involved in shaping conduct ...(impulsiveness and sensation seeking. Hig...)

With regard to the association between platelet MAO-B and personality, experimental results make us hypothesise that part of the explanation is to be found in the regulation of the activity of genes. Regardless of individual variants in the structure of genes, their activity is also regulated by activators or inhibitors (transcription factors), which bind to a specific part, the regulatory or promoter part, of the gene. There is reason to believe that the gene producing MAO-B and a number of genes producing proteins that constitute important parts of the brain monoamine systems are regulated by the same transcription factors.

One candidate for being such a common transcription factor is AP2 (Nilsson et al., 2009). A low transcriptional activation of both the gene responsible for the production of platelet MAO-B and for a number of genes responsible for building up brain monoamine pathways could in this way explain how a low activity (or level) of platelet MAO-B protein is mirroring a weak or low capacity of the monoamine systems in the brain. These would in turn constitute the biological basis for personality traits such as impulsiveness and sensation seeking.

Clinical implications

• Our gene-environment interaction findings, as well as those of others in this field, show a way of understanding biological mechanisms underlying the individual's degree of dependence on the environment for the development of e.g. substance abuse, antisocial behaviour, suicidal behaviour, etc.

• Thus, individuals with one set of MAO gene variants seem to be virtually independent of environment for the risk of e.g. antisocial behaviour, and in this way could explain resilience towards an unfavourable environment, while those with another set of
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