The Genetics of Aggression- Brunner Syndrome and Ethical Nightmares

 I’ve decided to do a very controversial medico-ethical issue this week. Although it’s not an issue that frequently comes up, I chose it because it’s a good example of when scientific research has started to threaten our ethical principles.

  Hans Brunner et al.¹ identified a rare genetic disorder in a large farming family. Certain males in the family displayed mild impairment of cognitive functions and abnormal impulsive aggressive behaviour such as arson, rape and violence. Brunner showed that in the affected males there was a mutation in the gene for the enzyme monoamine oxidase A (MAOA). The enzyme deactivates the hormones and neurotransmitters epinephrine and norepinephrine, more commonly known as noradrenaline and adrenaline. (The terms are effectively interchangeable, adrenaline and noradrenaline come from Latin and epinephrine and norepinephrine from Greek. Despite the Latin terms being the most commonly used they are known medically by the Greek terms to avoid confusion with a pharmaceutical drug marketed as the annoyingly similar adrenalin.)

Epinephrine

Norepinephrine

 Both epinephrine and norepinephrine are part of the body’s “fight or flight” response (80% of the hormones released are epinephrine and 20% norepinephrine). This is the body’s response to dangerous or unexpected situations. The effect is the dilatation of the blood vessels to the muscles, the stopping of digestion and the increase in heart and breathing rate. This prepares the body for persistent muscles contraction in life-threatening situations. In this hyper-excitable state there is increased male aggression.

 Sufferers of Brunner syndrome have lower amounts of the MAOA enzyme so deactivate epinephrine and norepinephrine much more slowly. After getting provoked or startled they could remain in the aggressive, excitable state for hours or days after the initial trigger. The effect was also demonstrated in MAOA-mutant mice (which bit the experimenter more than non-mutant mice) and in the relative number of fights between macaque monkeys.

  The link however between genetics and violence however is fraught with difficulties. All sort of environmental and genetic factors combine to form behaviour as complex as aggression. Of the 14 MAOA-mutant men Brunner found 5 were arsonists, 5 were convicted of rape or attempted murders but the remaining 4 showed no obvious signs of excessive aggression whatsoever.

Worryingly a different mutation in the MAOA gene (which became known as the ‘Warrior gene’ in the flood of research following Brunner’s paper) was found to be roughly 10 times as common in African-American men than white American men.³ It has been suggested this a reason why African Americans commit five times as many violent crimes per capita as white Americans.³ (although personally I think social and economic factors are probably more likely). For some this line of thinking leads to a Nazi-style eugenics nightmare.

  The problem of how the law should deal with individuals with a genetic disposition towards aggression is a thorny ethical issue. Law and order relies on people being responsible for the bad things they do. If science is throwing doubt on this principle of moral responsibility then what are we to do? As yet no one have been found innocent due to a genetic predisposition to violence although an argument based on child abuse and a mutation in the MAOA gene was successful in down grading the punishment of first-degree murder from the death penalty to 32 years in prison in a 2009 criminal trial. Although it appears we have some time to debate this issue it appears that the advance of genetic science will inevitably continue to threaten our moral beliefs.

1. Brunner HG, Nelen MR, van Zandvoort P, Abeling NGGM, van Gennip AH, Wolters EC, Kuiper MA, Ropers HH, van Oost BA. “X-linked borderline mental retardation with prominent behavioral disturbance: phenotype, genetic localization, and evidence for disturbed monoamine metabolism.” American Journal of Human Genetics. 52: 1032-1039, 1993.

2. Beaver KM, Sak A, Vaske J, Nilsson J. “Genetic risk, parent-child relations, and antisocial phenotypes in a sample of African-American males.” Psychiatry Research. 175: 160-164, 2010.

3. http://www2.fbi.gov/ucr/cius2009/data/table_49.html