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.