Recent research on G × E interaction involving the 7-repeat allele of the dopamine receptor gene, DRD4, which meta-analysis reveals to be reliably associated with ADHD,1 also provides support for the claim that the so-called vulnerability genes may be better conceptualized as plasticity genes. What makes the first two studies to be considered especially important is that the predictor variable, parenting, ranges from quite limited to very competent, thus meaning that a supportive environment is not just the one in which adverse experiences are absent. In a longitudinal investigation of 47 infants, greater maternal insensitivity observed when children were 10 months predicted greater externalizing problems reported by the mother more than 2 years later, but only for children carrying the 7-repeat DRD4 allele.41 Moreover, although children with the 7-repeat DRD4 allele displayed, consistent with a diathesis–stress model, the most externalizing behavior of all children when mothers were judged insensitive, they also manifested the least externalizing behavior when mothers were highly sensitive (but see, for contradictory results, Propper et al.42). Similar results emerged in a cross-sectional investigation of sensation seeking involving
