There is evidence that cortical dopamine, norepinephrine and serotonin play the central role in the pathology of the disorder [14,67,68], while recent findings suggest that the paradoxical calming effect of psychostimulants in ADHD, as well as in DAT-KO mice, is mediated predominantly by dopamine [13]. This evidence concerns the gene SLC6A3 and attention deficit-hyperactivity disorder.