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Abstract:
Attention Deficit Hyperactivity Disorder (ADHD) and reading
disability (RD) are comorbid disorders, and recent research has
shown that they may be influenced by common genetic factors.
Another way to explore relations between these disorders is to
examine their neuropsychological correlates. Using multiple
measures, we assessed executive functions and phonological
awareness (PA) in a sample of twins (ages 8-18) classified into
four groups: RD (N=128), ADHD (N=66), RD + ADHD (N=68), and
controls (N=175). Four composite variables, working memory, set
shifting, inhibition, and PA, were created based on a factor
analysis. A 2x2 factorial ANCOVA, covarying full scale IQ, was used
to compare groups across these domains. Results indicated that
children with ADHD were significantly impaired on inhibition tasks,
but not on working memory, set shifting, or phonological tasks.
Children with RD, in contrast, were impaired only on PA and working
memory tasks. There was no RD x ADHD interaction on any of the
variables, indicating additive rather than synergistic effects in
the comorbid group. Further, an ADHD x Age interaction was found,
whereby inhibition scores in ADHD did not improve with age,
contrary to other groups. These results indicate that executive
function deficits in ADHD may be limited to the inhibition domain,
whereas children with RD exhibit PA as well as working memory
deficits.
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