DRD4 and attention deficit-hyperactivity disorder: Although a majority of studies investigating ADHD have focused on catecholamine dysregulation and dopamine‐related genes (e.g., dopamine receptor D4 [DRD4]) that are related to attentional processes (Gizer, Ficks, & Waldman, 2009), copy number variation and genome‐wide association studies (GWAS) have identified several neurodevelopmental genes as possible candidate genes involved in ADHD (Li, Chang, Zhang, Gao, & Wang, 2014; Poelmans, Pauls, Buitelaar, & Franke, 2011).