A comparison of the cognitive deficits in reading disability and attention-deficit/hyperactivity disorder

This study used a nonreferred sample of twins to contrast the performance o f individuals with reading disability (RD; n = 93), attention-deficit/hyper activity disorder (ADHD; n = 52), RD and ADHD (n = 48), and neither RD nor ADHD (n = 121) on measures of phoneme awareness (PA) and executive function ing (EF), Exploratory factor analysis of the EF measures yielded underlying factors of working memory, inhibition, and set shifting. Results revealed that ADHD was associated with inhibition deficits, whereas RD was associate d with significant deficits on measures of PA and verbal working memory. Th e RD + ADHD group was most impaired on virtually all measures, providing ev idence against the phenocopy hypothesis as an explanation for comorbidity b etween RD and ADHD.