Eighty-five patients were assessed overall, and the presence of the T allele (C/T and T/T) of DRD2 c.957C > T polymorphism was found to be significantly associated with the occurrence of defiant and oppositional problems and with attention and hyperactivity problems.
DAT1 intron8 was associated with parent-rated hyperactivity (ηp(2)=.045) and both DAT1 9/10 VNTR (ηp(2)=.105) and DRD2rs2283265 (ηp(2)=.069) were associated with teacher-rated inattention.
Furthermore, flies treated with bromocriptine, an agonist of Drosophila dopamine D2 receptor (dD2R), exhibited nocturnal locomotor hyperactivity in a dose-dependent manner and this effect was inhibited in dD2R knockdown flies.
For example, the hypoactive alleles of DRD2 and the hyperactive alleles of COMT, which degrade the dopamine in the synaptic cleft, are associated with schizophrenia.