DAO and attention deficit-hyperactivity disorder: Given that our sample was composed of patients with a primary diagnosis of ADHD, that most of them displayed at least one AOC1 variant related to DAO deficiency, and that some medications approved for the treatment of ADHD (i.e., lisdexamfetamine dimesylate) may improve DAO activity [43], thus helping to decrease blood histamine levels, we may conclude that some medications for ADHD may help to reduce both ADHD and HIT symptoms by killing two birds with one shot [14].