Objective: Because ADHD is heterogeneous with respect to psychiatric comorbidity, familiality, and learning disabilities, it was hypothesized that such features might influence the severity and pattern of neuropsychological function in ADHD.
Method: Subjects were 9- to 20-year-old males with DSM-III-R ADHD (n = 65) and normal controls (n = 45). Information on neuropsychological performance was obtained in a standardized manner, blind to the proband's clinical status.
Results: ADHD probands were significantly impaired on neuropsychological functions compared with controls irrespective of composite psychiatric comorbidity status, and those with a family history of ADHD were most impaired. ADHD probands with learning disabilities showed a pattern suggestive of reduced motor dominance and extremely slow reading speed.
Conclusions: These results indicate that neuropsychological performance in ADHD is significantly affected by familial status and presence of learning disabilities. The similarity of findings between ADHD children with and without comorbid psychiatric disorders suggests that the neuropsychological impairments in our sample were associated with ADHD. These findings raise the possibility of alterations of cerebral dominance and of frontal networks in ADHD. Further research is needed to replicate these findings in larger samples, to clarify the role of specific comorbid psychiatric disorders, and to assess directly cerebral functioning in subjects with ADHD.