To determine whether children with attention deficit hyperactivity disorder (ADHD) and mild intellectual disability (ID) are a clinically distinct ADHD subgroup.
Study design
This was a cross-sectional study comparing clinical characteristics (ADHD subtypes, total number of symptoms, and rates of common comorbidities) between children with ADHD and mild ID and those with ADHD and IQ test scores >70, and also between children with ADHD and ID and a general population sample of children with ID alone. The sample comprised a clinical sample of children with ADHD with ID (n = 97) and without ID (n = 874) and a general population sample of children with ID and without ADHD (n = 58).
Results
After correcting for multiple statistical tests, no differences were found between the 2 ADHD groups on any measure except the presence of conduct disorder (CD) symptoms and diagnoses. Children with ADHD and ID had higher rates of both (OR, 2.38; 95% CI, 1.71-3.32 and OR, 2.69; 95% CI, 1.69-4.28, respectively). Furthermore, children with ADHD and ID had significantly higher rates of oppositional defiant disorder (OR, 5.54; 95% CI, 2.86-10.75) and CD (OR, 13.66; 95% CI, 3.25-57.42) symptoms and a higher incidence of oppositional defiant disorder diagnoses (OR, 30.99; 95% CI, 6.38-150.39) compared with children with ID without ADHD.
Conclusion
Children with ADHD and mild ID appear to be clinically typical of children with ADHD except for more conduct problems. This finding has implications for clinicians treating these children in terms of acknowledging the presence and impact of ADHD symptoms above and beyond ID and dealing with a comorbid CD.
ADHD
Attention deficit hyperactivity disorder
ALSPAC
Avon Longitudinal Study of Parents and Children
ASD
Autism spectrum disorder
CAPA
Child and Adolescent Psychiatry Assessment
CD
Conduct disorder
CNV
Copy number variant
DSM-III-R
Diagnostic and Statistical Manual of Mental Disorders, 3rd edition revised
DSM-IV
Diagnostic and Statistical Manual of Mental Disorders, 4th edition
Clinical ADHD sample was funded by the Baily Thomas Charitable Trust, Action Medical Research, and the Wellcome Trust. The ALSPAC sample was funded by the UK Medical Research Council, the Wellcome Trust (092731), and the University of Bristol. The authors declare no conflicts of interest.