The psycho gene (from National Library of Medicine 2010)

While the idea of a ‘criminal gene’ is nonsense, there is growing evidence that some psychopathic behaviour might indeed be grounded in genes

Using structural MRI scanning, the study identified that people with MAOA-L were more likely to have a smaller limbic system—the hippocampus, amygdala, anterior thalamic nuclei and limbic cortex—which participates in emotion, behaviour and long-term memory. The team then applied functional MRI, which measures changes in blood flow, and discovered that the MAOA-L group also showed hyperresponsiveness of the amygdala during tasks such as copying facial expressions. The amygdala is associated with emotional processing and the MAOA-L group was less able to inhibit strong emotional impulses.

But some trigger is still needed to tip MAOA-L people towards violence. An earlier study suggested that this trigger could be persistent maltreatment during childhood (). At first sight, this suggests that nearly half the human population are predisposed to violence given these triggers, but the situation is not quite that bad—it is merely nearly half of men. Women are protected in two ways: the MAOA gene is linked to the X chromosome so that women with the MAOA-L variety on one chromosome usually have a normal allele on the other; and there is circumstantial evidence that women are also protected by other genes from being disposed to violence.

[T]he MAOA-L allele is just one of several genes—most of which are still not identified—that increase risk of violent or antisocial behaviour.

But the whole story takes a rather different turn in the case of psychopathy, which is now widely regarded as a congenital state characterized by lack of empathy or moral compass and defined at least partly by genes, in contrast to other forms of sociopathy or antisocial personality disorder (APD), in which environmental factors make a major contribution ().

As there is no genetic or clinical test as yet, psychopathy is still diagnosed in terms of behaviour, but taking account of various factors in combination. Robert Hare, who led the UK study and is now at the Department of Psychology of the University of British Columbia in Vancouver, Canada, has designed a test known as the ‘Psychopathy Checklist—Revised’ of about 20 symptoms that he uses to diagnose psychopathy. These include pathological lying, superficial charm, lack of empathy and guilt, proneness to boredom and sexual promiscuity.

[P]sychopathy seems to be more common in men than women, which could have two possible explanations. First, it might be true at the genetic and neurological level, in particular if some of the relevant genes are linked to the X chromosome. Yet, this is speculative as few genes have been identified that contribute specifically to psychopathy, with most of the evidence for its heritability being statistical. There is the case of the X-linked MAOA gene, but that has only been associated with general antisocial tendencies.

Source: The psycho gene – PMC

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