Experimental intervention research involving the enhancement of parenting also documents a moderating effect of the 7-repeat allele; once again, then, this G × E work does not simply define the ‘good' environment in terms of the absence of adversity. Thus, when Bakermans-Kranenburg et al.44 looked at the change over time in parenting—from before to well after a video-feedback parenting intervention was provided on a random basis to 157 mothers of 1–3-year-olds who scored high on externalizing problems—they not only found that the intervention succeeded in promoting more sensitive parenting and positive discipline, but that experimental effects extended to improvements in child behavior. This proved to be the case, however, only for those children carrying the DRD4 7-repeat allele, with most of the experimental effect being carried by these genotypically susceptible children whose mothers showed the most improvement in their parenting. Much the same was the case when, at post-treatment follow up, stress reactivity was measured by means of change in salivary cortisol before and after administration of an experimental stressor (that is, area under the curve44). Indeed, DRD4 7-repeat children
