ABSTRACT
This study used a nonreferred sample of twins to contrast the performance of individuals with reading disability (RD; n = 93), attention-deficit/hyperactivity disorder (ADHD; n = 52), RD and ADHD (n = 48), and neither RD nor ADHD (n = 121) on measures of phoneme awareness (PA) and executive functioning (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 associated with significant deficits on measures of PA and verbal working memory. The RD + ADHD group was most impaired on virtually all measures, providing evidence against the phenocopy hypothesis as an explanation for comorbidity between RD and ADHD.
Subject(s)
Attention Deficit Disorder with Hyperactivity/psychology , Cognition , Dyslexia/psychology , Reading , Adolescent , Attention Deficit Disorder with Hyperactivity/complications , Child , Dyslexia/complications , Female , Genetic Predisposition to Disease , Humans , Inhibition, Psychological , Male , Neuropsychological Tests , PhoneticsABSTRACT
OBJECTIVE: To test the external validity of the dimensions and subtypes of DSM-IV attention-deficit/hyperactivity disorder (ADHD) by assessing the prevalence of psychiatric comorbidity. METHOD: Eight- to 18-year-old twins with ADHD (n = 105) and without ADHD (n = 95) were recruited through local school districts. Comorbid disorders were assessed by structured diagnostic interviews with the parent and child and by a behavioral rating scale completed by the child's classroom teacher. RESULTS: Symptoms of inattention were associated with lower intelligence and higher levels of depression, whereas symptoms of hyperactivity-impulsivity were associated more strongly with symptoms of oppositional defiant disorder (ODD) and conduct disorder (CD). All DSM-IV subtypes were associated with higher rates of ODD and CD in comparison with controls, and the combined type was associated with more disruptive behavior disorder symptoms than the other 2 subtypes. The combined type and predominantly inattentive type were associated with more symptoms of depression than controls or the predominantly hyperactive-impulsive type. CONCLUSIONS: These results provide support for the discriminant validity of the dimensions and subtypes of DSM-IV ADHD and suggest that clinicians should carefully screen for comorbid disorders as part of a comprehensive assessment of ADHD.
