et al., 2009; Belsky & Pluess, 2009). The best evidence for differential susceptibility—in which individuals who carry a particular genotype are both most likely to develop problems under adverse conditions and most likely to benefit from advantaged conditions—comes from studies that use randomized controlled trials to study how behavioral interventions may have different consequences for individuals who carry different variants of certain genes (Bakermans-Kranenburg & van Ijzendoorn, 2011; van IJzendoorn et al., 2011; Brody et al., 2013). To date, this approach has been used primarily to study discrete, short running interventions, including literacy support programs for preschoolers (Kegel, Bus, & van IJzendoorn, 2011) and positive parenting interventions (Bakermans-Kranenburg et al., 2008). An example of GxI research with a broader focus is the genetic analysis of the Strong African American Families intervention, a 7-week, family-based youth risk-behavior prevention program for rural African-Americans (Brody et al., 2009). Here, we apply this now established method to study genetic heterogeneity in the effects of a much longer-running trial, the 10-year Fast Track intervention, which aimed to prevent high-risk kindergarteners from developing persistent externalizing psychopathology.
