the Long Version of Conners’ Parent and Teacher Rating Scales, as well as the parent and teacher version of the Strength and Difficulties Questionnaires (SDQ) (Conners 2003). A standardized algorithm was applied to PACS to derive each of the 18 DSM-IV ADHD items, and, taking into account a number of Conners items, a clinical diagnosis was made. Exclusion criteria included a low IQ (<70), autism, epilepsy, and brain or genetic disorders known to mimic ADHD symptoms. In GAIN, 958 family triads from IMAGE, including the proband and his/her parents were analyzed (http://www.ncbi.nlm.nih.gov/projects/gap/cgi-bin/study.cgi?study_id=phs000016.v1.p1). DNA was isolated from blood by Rutgers Cell and DNA Repository (http://www.rucdr.org/). The samples were analyzed by Perlegen Sciences on a microarray specially designed for GAIN. The array investigates approximately 600,000 SNPs able to capture information of close to 100% of the common genetic variation in Caucasians (Neale et al. 2008a). Data cleaning of the genotyping results was performed through the National Centre for Biotechnology Information (NCBI), leaving 438,784 SNPs for analysis.
