DRD4 and attention deficit-hyperactivity disorder: Cross-sectional studies indicated gene–environment (G × E) interactions between the 7-repeat allele of the dopamineD4receptor gene (DRD4) and parenting factors (e.g., consistent parenting, sensitive maternal care) in association with ADHD or externalizing symptoms, for better or for worse (i.e., positive parenting in those with the 7-repeat allele was associated with fewer symptoms and negative parenting with more symptoms [21, 22]).