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Did you know the warrior gene is linked to aggression?

Taming the inner beast - MAOA, neurotransmitter breakdown and aggression

When the brilliant nuclear physicist Bruce Banner was caught in a blast of gamma radiation, his physiology changed. Ever since, when he’s stressed Bruce turns from a mild mannered scientist into a green destruction machine, known as the Incredible Hulk. Marvel’s backstory on the Hulk may be too far fetched to be real. However, the premise behind his transformation – the imbalance of neurotransmitters (chemical messengers) in the brain – is not at all fictional. There are men among us who are actually predisposed to aggression. These men inherit genetic variants that influence their neurotransmitter levels, and the MAOA variants known as the “warrior” gene are the primary culprit.

The MAOA gene gives instructions for the monoamine oxidase A enzyme. This enzyme is responsible for the breakdown of three important neurotransmitters – norepinephrine, dopamine and serotonin . Norepinephrine is involved in the “fight or flight response” influencing blood pressure and alertness. Both dopamine and serotonin affect mood and alertness, and are linked to psychiatric disorders.

Changes in the MAOA gene were first discovered in a study of a Dutch family with a history of violence. A concerned woman contacted clinical geneticists, because within just the last five generations, 14 men in her family had displayed abnormal behaviour. They each had a history of impulsive aggression, with some even involved in arson, exhibitionism, and attempted rape. The underlying cause of this violence appeared to be genetic, and she was concerned that she too might carry this nasty genetic change, and could pass it onto her children.

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Analyses of the five affected men still living today showed a complete lack of monoamine oxidase A activity, so the geneticists focused their attention on the MAOA gene. They soon identified the same genetic mutation in all five affected men. This mutation prevented the complete “reading” of the MAOA gene, so there were no instructions to make monoamine oxidase A. These men lacked the ability to efficiently break down their neurotransmitters, and this accumulation is thought to explain their impulsive aggression.

Since the initial study, many different versions of the MAOA gene have been identified. All warrior versions of MAOA (aka MAOA-L) result in lower monoamine oxidase A levels. This impairs the breakdown of neurotransmitters and can lead to behavioural changes.

One study analyzed aggression following provocation in men either with normal MAOA or the warrior version of MAOA. Men with the warrior gene were more likely to ‘punish’ their opponents with hot sauce, when they believed that the opponent had taken 80% of their earnings. Men with the warrior gene are also at higher risk for becoming gang members and using weapons in a fight. Other negative behaviours, such as alcoholism, panic disorders, pathological gambling and antisocial behaviour, are also associated with the warrior gene.

In case you are left wondering why the studies all focused on men, the explanation is simple. MAOA is located on the X chromosome. Men only inherit one X chromosome, which means they only have one version of MAOA. So if a man inherits the warrior gene, he can only produce low levels of monoamine oxidase A, and is at risk of the behavioural changes associated with the warrior gene. If a woman inherits the warrior gene, there is a good chance that her second copy of MAOA is normal, so she can still produce plenty of monoamine oxidase A. However, she can still pass the warrior gene to her children, so there is a 50% chance that a son will be affected by the warrior gene.

Inheriting the warrior gene does not mean that a man will definitely be aggressive, as there are environmental factors involved as well. For example, maltreated children with normal MAOA are less likely to develop antisocial problems, unlike their counterparts with the warrior gene.

MAOA was back in the spotlight recently when a judge in Italy reduced the sentence of a murderer because he had the MAOA gene. This was not the first time, nor will it be the last time, that lawyers use genetic predisposition to violence and MAOA status as evidence to defend violent crimes.

Trying to explain behaviour based on a single gene is tricky, and it is further complicated by the fact that our environment also influences our genes. But science has shown that there is definitely an association between the warrior gene and increased aggression. A simple genetic test can tell you whether you may be predisposed to aggression, and encourage you to learn how to manage and control any aggressive tendencies in stressful situations.

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