Читать книгу Lifespan Development - Tara L. Kuther - Страница 121

Not all children exposed to adversity experience negative outcomes. Genes, such as MAOA, influence children’s sensitivity to maltreatment.

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Children who are maltreated or abused by their parents are at risk for developing many problems, including aggression and violent tendencies. Yet not all children who are maltreated become violent adolescents and adults. Why? A classic study examined this question.

Caspi and colleagues (2002) followed a sample of males from birth until adulthood and observed that not all maltreated boys developed problems with violence. Only boys who carried a certain type of gene were at risk for becoming violent after experiencing maltreatment. Specifically, there are two versions of a gene that controls monoamine oxidase A (MAOA), an enzyme that regulates specific chemicals in the brain; one produces high levels of the enzyme, and the other produces low levels. Boys who experienced abuse and other traumatic experiences were about twice as likely to develop problems with aggression, violence, and to even be convicted of a violent crim—but only if they carried the low-MAOA gene. Maltreated boys who carried the high-MAOA gene were no more likely to become violent than nonmaltreated boys. In addition, the presence of the low-MAOA gene itself was not associated with violence. The low-MAOA gene predicted violence only for boys who experience abuse early in life. These findings have been replicated in another 30-year longitudinal study of boys (Fergusson, Boden, Horwood, Miller, & Kennedy, 2011) as well as a meta-analysis of 27 studies (Byrd & Manuck, 2014).

Similar findings of a MAOA gene × environment interaction in which low MAOA, but not high MAOA, predicts negative outcomes in response to childhood adversity has been extended to include other mental health outcomes such as antisocial personality disorder and depression (Beach et al., 2010; Cicchetti, Rogosch, & Sturge-Apple, 2007; Manuck & McCaffery, 2014; Nikulina, Widom, & Brzustowicz, 2012). Many of these studies have examined only males. Females show a more mixed pattern, with some studies showing that girls display the MAOA gene × environment interaction but to a much lesser extent than boys, whereas other studies suggest no relationship (Byrd & Manuck, 2014).

In addition, some genes might increase our sensitivity to, and the effectiveness of, environmental interventions (Bakermans-Kranenburg & van IJzendoorn, 2015; Chhangur et al., 2017). Just as we may adjust contextual factors to contribute to successful developmental outcomes and resilience, in the future we might learn how to “turn on” protective genes and “turn off” those that contribute to risk.