All of the analyses discussed thus far use latent, unmeasured indices of genetic influence to detect the possible presence of gene-environment interaction. This is largely because it was possible to test for the presence of latent genetic influence in humans (via comparisons of correlations between relatives with different degrees of genetic sharing) long before molecular genetics yielded the techniques necessary to identify specific genes influencing complex psychological disorders. However, recent advances have made the collection of deoxyribonucleic acid (DNA) and resultant genotyping relatively cheap and straightforward. Additionally, the publication of high-profile papers brought gene-environment interaction to the forefront of mainstream psychology. In a pair of papers published in Science in 2002 and 2003, respectively, Caspi and colleagues analyzed data from a prospective, longitudinal sample from a birth cohort from New Zealand, followed from birth through adulthood. In the 2002 paper, 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
