Since gene × gene and gene × environment interactions may be important in the development of psychiatric disorders, exploratory analyses investigating previously reported interactions in the impulsive behavior literature were also conducted. For example, DRD2 A1-allele × DRD4 7-repeat allele interaction has been reported for impulsivity [25], sensation seeking [28], and antisocial behavior [29], and DRD4 VNTR × DAT1 VNTR interaction has been reported for behavioral inhibition [30]. Also, environmental risk and protective factors, such as maternal insensitivity or intervention promoting positive parenting, were shown to interact with the DRD4 7-repeat allele on child externalizing (oppositional, aggressive) behavior [31,32].
