The present study was also designed to address questions about the mechanisms through which G×E prevention effects operate. Recently, Brody and colleagues (in press) extended the G×E and the differential susceptibility perspectives to include a focus on mediators or intermediate phenotypes. That study focused on a cohort of rural African American emerging adults who were 17 years old at the first assessment and 20 years old at a third assessment. A DRD4 × life stress interaction forecast substance use, with carriers of at least one l allele evincing increases in use. DRD4 × life stress interaction effects on two intermediate phenotypes—increases in vulnerability cognitions for substance use and increases in affiliations with substance-using peers—accounted for this finding. Carriers of at least one l allele of DRD4 who experienced high levels of life stress evinced increases in both intermediate phenotypes. Carriers of two s alleles of DRD4 who experienced high levels of life stress did not evince increases in substance use or in either intermediate phenotype. Similarly, the present study demonstrated that G×E effects on the intermediate phenotype of protective parenting
