Among ADHD boys, serum prolactin levels were negatively correlated with oppositional symptoms rated by parents (r = −0.266, p = 0.012), hyperactivity/impulsivity symptoms rated by teachers (r = −0.279, p = 0.008), and oppositional symptoms rated by teachers (r = −0.328, p = 0.002). The gene discussed is PRL; the disease is attention deficit-hyperactivity disorder.