Attention deficit disorder and conduct disorder: Longitudinal evidence for a familial subtype

Background. An obstacle to the successful classification of attention deficit hyperactivity disorder (ADHD) is the frequently reported co-morbidity between ADHD and conduct disorder (CD). Prior work suggested that from a familial perspective, ADHD children with CD may be aetiologically distinct from those without CD. Methods. Using family study methodology and three longitudinal assessments over 4 years, we tested hypotheses about patterns of familial association between ADHD, CD, oppositional defiant disorder (ODD) and adult antisocial personality disorder (ASPD). Results. At the 4-year follow-up, there were 34 children with lifetime diagnoses of ADHD + CD, 59 with ADHD +ODD and 33 with ADHD only. These were compared with 92 non-ADHD, non-CD, non-ODD control probands. Familial risk analysis revealed the following: (1) relatives of each ADHD proband subgroup were at significantly greater risk for ADHD and ODD than relatives of normal controls; (2) rates of CD and ASPD were elevated among relatives of ADHD + CD probands only; (3) the co-aggregation of ADHD and the antisocial disorders could not be accounted for by marriages between ADHD and antisocial spouses; and (4) both ADHD and antisocial disorders occurred in the same relatives more often than expected by chance alone. Conclusions. These findings suggest that ADHD with and without antisocial disorders may be aetiologically distinct disorders and provide evidence for the nosologic validity of ICD-10 hyperkinetic conduct disorder.