Environments for which there are latent G × E effects offer promising avenues for follow-up with cG × E studies. In a few examples of this, findings coming out of the twin G × E literature were used to develop hypotheses about how the association between GABRA2 genotype and externalizing behavior might change as a function of parental monitoring and peer deviance. The logic of this approach is that if a significant G × E effect is detected using twin methodology, it must indicate that the environmental factor changes the association between most genetic variants and the outcome (assuming the outcome is influenced by a large number of small genetic effects). Consistent with what would be expected given the latent G × E literature, adolescents with more copies of the major allele for SNPs in the risk-increasing GABRA2 haplotype block were more likely to exhibit an elevated persistent trajectory of externalizing behavior if they also experienced less parental monitoring (Dick et al., 2009). Similarly, the association between GABRA2 genotype and externalizing behavior was stronger under conditions of high peer deviance
