Professor Bruce McEwen describes how the interplay between life events and genes can lead to behavioral problems.

I think you cannot separate the genes and environmental factors, or even the intermediate epigenetic factors. I’ll give you an example: the studies of Avshalom Caspi and his colleagues, which are also quite well known, in Dunedin, New Zealand. It’s a longitudinal study where they took genetic information; they have very careful behavioral analysis. There are, in one of their now classic papers that was published in Science, if you have certain alleles of the monoamine oxidase gene, if you have a certain allele and you happen to be abused in one of these chaotic home situations, the person is more likely to themselves become an abuser, if you will, an antisocial personality. But if the person has not had a chaotic home life, then you’ll never see these traits emerge, I mean you won’t see them, it’s a probabilistic argument. One of their other studies involves the serotonin transporter. There’s an allele that results in less expression of the serotonin transporter, and there’s another that results in a greater expression. People who have the short form [of the serotonin transporter allele] are more vulnerable to anxiety, depression, alcoholism, a whole bunch of things like that. But again, it’s conditional, dependent on the kind of life experiences they have, whether it’s tolerable or toxic stress, if you will. Because if it’s tolerable and they have good support systems, they may not become depressed as frequently as people with the short allele who had a tough life. So, I don’t think you can really separate out the genetic from the environmental, and in both cases, as I was saying, the idea of resilience or lack of resilience in the brain is very important. If the brain cannot bounce back on its own, then you may have to treat with a drug, and it may be that these certain gene characteristics – these alleles – may make the brain less likely to be resilient.

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