To rule out caregiver genotype as a source of passive genetic effects in response to intervention, the analysis of change in youth past-month substance use was repeated using caregiver rather than youth genotype as both a main effect and a moderator of intervention effects. Because there was no effect for youth genotype at 5HTT, parent genotype at 5HTT was not included in the analysis. All parents who provided genetic material and could be assigned to either the 7-repeat allele or the two 4-repeat allele group were included in the analyses (N = 344); the results are presented in Table 3. In this model, the effect of caregiver genotype on youth past-month substance use was not significant as a main effect (γ g = -.03, NS) or in interaction with intervention (γS×G = -.13, NS). Thus, youths’ own genetic variation at DRD4 and not genetic similarity to the caregiver was responsible for the observed intervention × genotype interaction.
