in the intervention reduced age-related increases in past-month substance use. The net result was greater differential change in the predicted direction between intervention and control youth for those with the 7-repeat allele relative to those with two 4-repeat alleles. In the context of the susceptibility hypothesis, the results indicated that SAAF interacted with presence of the 7-repeat polymorphism in DRD4 to change a potentially deleterious genetic factor into a potentially positive one. It is important to note, however, that the results are based on youth self-reported substance use and are not corroborated by biological tests. In addition, in other exploratory analyses, we found no evidence of similar moderation by DRD4 for parent-reported delinquency outcomes, suggesting that genetic moderation of the effect of DRD4 is specific to increases in substance use or that parent report may yield a different pattern of results.
