title: Twin study of the etiology of comorbidity between reading disability and attention-deficit/hyperactivity disorder.
abstract: This study utilized a sample of 313 eight- to sixteen-year-old same-sex twin pairs (183 monozygotic, 130 dizygotic) to assess the etiology of comorbidity between reading disability (RD) and attention-deficit/hyperactivity disorder (ADHD). RD was assessed by a discriminant function score based on the Peabody Individual Achievement Test, a standardized measure of academic achievement. The DSM-III version of the Diagnostic Interview for Children and Adolescents was used to assess symptoms of ADHD, and separate factor scores were computed for inattention and hyperactivity/impulsivity (hyp/imp). Individuals with RD were significantly more likely than individuals without RD to exhibit elevations on both symptom dimensions, but the difference was larger for inattention than hyp/imp. Behavior genetic analyses indicated that the bivariate heritability of RD and inattention was significant (h(2)(g(RD/Inatt)) = 0.39), whereas the bivariate heritability of RD and hyp/imp was minimal and nonsignificant (h(2)(g(RD/Hyp)) = 0.05). Approximately 95% of the phenotypic covariance between RD and symptoms of inattention was attributable to common genetic influences, whereas only 21% of the phenotypic overlap between RD and hyp/imp was due to the same genetic factors.
authors.affiliation: University of Colorado at Boulder, 80309, USA. willcutt@Colorado.edu
authors.forename: E G
authors.initials: EG
authors.lastname: Willcutt
authors.forename: B F
authors.initials: BF
authors.lastname: Pennington
authors.forename: J C
authors.initials: JC
authors.lastname: DeFries
mesh_terms: D000293:Adolescent; D001289:Attention Deficit Disorder with Hyperactivity / Q000150:complications* / Q000235:genetics; D002648:Child; D015897:Comorbidity; D004200:Diseases in Twins; D004410:Dyslexia / Q000150:complications* / Q000235:genetics; D005260:Female; D005838:Genotype; D006801:Humans; D008297:Male; D012044:Regression Analysis; D013223:Statistics as Topic; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic