Specifically, dysregulation of dopamine (DA) has been hypothesized in ADHD based on the potent efficacy of indirect dopaminergic agonists, such as methylphenidate, supported by in vivo evidence that methylphenidate effects are related to striatal occupancy of the dopamine transporter (DAT), by increasing extracellular dopamine levels in the striatum [2]. This evidence concerns the gene SLC6A3 and attention deficit-hyperactivity disorder.