Firstly, Park and Waldman (2014) studied the influence of COMT (Val158Met) genotype status not in healthy participants (our study) but in a clinically selected sample consisting of children with a diagnosis of either ADHD, conduct disorder, or oppositional defiant disorder, and their healthy (not fulfilling the criteria for diagnosis) siblings and twins. This evidence concerns the gene COMT and Oppositional defiant disorder.