Besides reported associations between the DRD4 exon III polymorphism and various phenotypes related to decision making behavior like impulsivity, novelty seeking, gambling behavior and attention-deficit hyperactivity disorder (ADHD) the functionality of this polymorphism has been demonstrated (Ebstein et al., 1996; Strobel et al., 1999; Eisenegger et al., 2010; Nikolaidis and Gray, 2010). Here, DRD4 is linked to attention deficit-hyperactivity disorder.