DRD4 and attention deficit-hyperactivity disorder: Among various polymorphic sites of the DRD4 gene, perhaps associations with the DRD4 VNTR is the most controversial: The 7 repeat form was referred to as the”adventure gene” because of its associations with novelty seeking (e.g. [21], opioid-dependence [22] and attention deficit, hyperactivity disorder [23, 24].