Susan E. Young1, M. C. Stallings1, R. P. Corley1, J. K. Hewitt1, & D. W. Fulker1
The substantial comorbidity between the symptoms of attention deficit hyperactivity disorder (ADHD) and conduct disorder (CD) has been well-documented in both clinical and community samples. However, the etiological processes underlying this relationship are not clear. Examining this association by clustering ADHD symptoms into the subtypes proposed by DSM-IV (American Psychiatric Association, 1994, Washington, D.C.), (1) inattention and (2) hyperactivity-impulsivity, may help to illuminate these links. In the current study, the phenotypic and familial associations between ADHD cluster scores and CD was investigated in siblings drawn from the Adolescent Substance Abuse (ASA) study, including both selected families identified through male patient probands, and matched control families. Severity measures of CD and ADHD were computed using a count of DSM-III-R (APA, 1987, Washington, D.C.) criteria assessed by structured psychiatric interviews. Phenotypic correlations between cluster scores for inattention and hyperactivity-impulsivity were substantial in each sample, ranging from r=.65 to .71 in the control and clinical samples. These ADHD scores were also significantly associated with the symptoms of CD, ranging from r=.28 to .41. Patterns of sibling correlations suggested that ADHD and CD are influenced by similar family (genetic + shared environmental) factors.
Address: Institute for Behavioral Genetics, Campus Box 447, University of Colorado, Boulder, CO 80309, PH: (303) 492-1235, FAX: (303) 492-8063, Susan.Young@Colorado.edu.
1Institute for Behavioral Genetics, University of Colorado, Boulder, CO 80309 2Supported by NIDA DA-05131, DA-10540, DA-11015, and NICHD HD-07289.