Families were ascertained at Massachusetts General Hospital (MGH, N=309 trios), Washington University at St Louis (WASH-U, N=272 trios), and University of California at Los Angeles (UCLA, N=156 trios). Children were 6–17 years of age at initial assessment and met criteria for DSM-IV-TR attention-deficit hyperactivity disorder. All study procedures were reviewed and approved by the subcommittee for human subjects of each respective institution. All subjects’ parents or guardians signed written informed consent forms and children older than 7 years of age signed written assent forms.
