they reported that a functional polymorphism in the gene encoding the neurotransmitter-metabolizing enzyme monoamine oxidase A (MAOA) moderated the effect of maltreatment: Males who carried the genotype conferring high levels of MAOA expression were less likely to develop antisocial problems when exposed to maltreatment (Caspi et al. 2002). In the 2003 paper, they reported that a functional polymorphism in the promoter region of the serotonin transporter gene (5-HTT) was found to moderate the influence of stressful life events on depression. Individuals carrying the short allele of the 5-HTT promoter polymorphism exhibited more depressive symptoms, diagnosable depression, and suicidality in relation to stressful life events than did individuals homozygous for the long allele (Caspi et al. 2003). Both studies were significant in demonstrating that genetic variation can moderate individuals’ sensitivity to environmental events. These studies sparked a multitude of reports that aimed to replicate, or to further extend and explore, the findings of the original papers, resulting in huge literatures surrounding each reported gene-environment interaction in the years since the original publications (e.g., Edwards et al. 2009, Enoch et al. 2010, Frazzetto et al. 2007, Kim-Cohen et al. 2006, McDermott et al. 2009, Prom-Wormley et al. 2009, Vanyukov et al. 2007,
