DRD4 and attention deficit-hyperactivity disorder: Recently, only two resting-state fMRI studies implicated that DRD4 2-repeat may also alter the local brain functional activity of the parietal or prefrontal regions in children with ADHD and have found that these abnormalities would be related to dysfunction in a sustained and divided attention test (Kim et al., 2018; Qian et al., 2018).