Although highly heritable, genetic correlates of attention-deficit/hyperactivity disorder (ADHD) have been difficult to pinpoint. In 2009, researchers at CAG identified copy number variations as a potential cause of the disorder. CNVs are relatively large segments of chromosomes where the DNA has been deleted, duplicated, or rearranged. We found 222 CNVs that were more common in individuals with ADHD than in unrelated healthy individuals. These CNVs tended to concentrate in areas that had previously been associated with other neurodevelopmental disorders including autism, schizophrenia and Tourette syndrome. They also tended to occur at or near genes known to be important for learning, synapse transmission, and nervous system development. This paper was one of the first to pinpoint CNVs as a genetic cause of ADHD and was important in identifying previously unassociated genes. This paper was published in Molecular Psychiatry.