COMT and attention deficit-hyperactivity disorder: In order to test this hypothesis, we used three measures of executive function: the WCST [47], a measure of set-shifting ability capable of differentiating between ADHD children and controls [18] and associated with the COMT polymorphism in normal [36,37] and schizophrenic adults [39-41]; the Tower of London (TOL) [48], a measure of planning ability, which consistently differentiates ADHD children from controls [18], and the Self-Ordered Pointing Task (SOPT) [49], a measure of working memory also capable of differentiating between ADHD children and controls [18].