Is Monoamine Oxidase A (MAOA) Really The ‘Killer’ Gene?
“Violence is behaviour involving physical force, intended to hurt, damage, or kill someone or something.”- WHO.
Whilst we all have ability to become violent, many can control these impulses. A debate over the last 20 years argues that violence may be due to genetic predisposition, particularly MAOA, rather than social factors.
A Brief History
American murderer Stephen Mobley’s trial (1994) was the first to request a test for a mutation of MAOA gene. His lawyers argued that this mutation was the cause of Mobley’s violent murder, thus exonerating the college student. Nevertheless, due to the lack of scientific evidence, the courts had rejected the request.
The first study of MAOA was by Brunner et al (1993), who conducted a genetic analysis on a Dutch family where several males exhibited destructive behavior, such as rape and aggression. A rare point mutation was found on each male’s chromosome X, region p11-12- an exon of MAOA. Enzyme MAOA catalyzes metabolism of several neurotransmitters in the brain such as dopamine (Figure 2). Furthermore Brunner et al found high concentrations of non-metabolized neurotransmitters in urine tests, concluding that low MAOA (L-MAOA) activity causes impulsive violence. Multiple studies have supported this conclusion.
A Recent Update
Tiihonen et al (2014) performed a genetic analysis of 895 Finnish offenders, committing non-violent to extremely violent crimes. They also found an association of MAOA with violent offenders. However a variant of gene Cadherin 13 (CDH13), involved in neuronal membranes, was identified to alter impulse control of violent offenders. They conclude that low recycling of dopamine (associated with MAOA) and neuronal membrane dysfunction (CDH13 allele) are major factors in ~10% of violent crime in Finland.
Brunner suggested that L-MAOA causes a build-up of neurotransmitters, resulting in nerve over-excitation during stressful situation. Though drugs that block MAOA to treat depression have yet to cause violent outbursts in patients. Serotonin accumulation has also been shown to depress individuals, rather than trigger violence. Moreover anatomical differences of the prefrontal cortexes, of L-MAOA male carriers, may be behind exaggerated/violent responses to provocation.
Lastly, L-MAOA alleles may predispose violence by interacting with environmental factors such as mistreatment, abuse of substances and so on. There is the need for a larger scale study to identify these factors and determine their impact on violence. Therefore MAOA may not be the sole cause of violence, as suggested.
Huffington Post Canada, (2014). Cover Photo. [image] Available at: http://www.huffingtonpost.ca/2014/01/06/alberta-reserve-gang-violence_n_4550232.html
Nemeroff, C., Preskorn, S. and DeVane, L. (2007). Normal Function of MAOA. [image] Available at: http://www.cnsspectrums.com/aspx/articledetail.aspx?articleid=1085
Moosajee, M. (2003). Violence–a noxious cocktail of genes and the environment. JRSM, 96(5), pp.211-214.
Smith, P. (2014). Domestic Violence Words. [image] Available at: http://www.poppysmith.com/research-domestic-violence/
Stetler, D., Davis, C., Leavitt, K., Schriger, I., Benson, K., Bhakta, S., Wang, L., Oben, C., Watters, M., Haghnegahdar, T. and Bortolato, M. (2014). Association of low-activity MAOA allelic variants with violent crime in incarcerated offenders. Journal of Psychiatric Research, 58, pp.69-75.
Tiihonen, J., Rautiainen, M., Ollila, H., Repo-Tiihonen, E., Virkkunen, M., Palotie, A., Pietiläinen, O., Kristiansson, K., Joukamaa, M., Lauerma, H., Saarela, J., Tyni, S., Vartiainen, H., Paananen, J., Goldman, D. and Paunio, T. (2014). Genetic background of extreme violent behavior. Molecular Psychiatry.
Pritpal Kaur Klear
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