0.15). Studies utilizing dimensional measures of ADHD tended to result in higher rates of positive findings than those using categorical diagnoses (X(2) = 5.6, P = 0.018), and case-control studies tended to result in higher rates of positive findings than family-based studies (X(2) = 18.8, P < 0.001). However, for either dichotomy, no significant difference remained when analyzing only studies using both methods within the same population and polymorphism. Evidence for association exists for four genes in ADHD: the dopamine D4 and D5 receptors, and the dopamine and serotonin transporters; others are promising but need further replication, including the dopamine D2 and serotonin 2A receptors. All candidate gene approaches continue to face the problem of relatively low power, given modest odds ratios for even the best replicated genes.
(Copyright 2004 Wiley-Liss, Inc.)