title: Contrast effects and sex influence maternal and self-report dimensional measures of attention-deficit hyperactivity disorder.
abstract: The heritability of attention-deficit/hyperactivity disorder (ADHD) is higher for children than adults. This may be due to increasing importance of environment in symptom variation, measurement inaccuracy when two raters report behavior of a twin-pair, a contrast effect resulting from parental comparison of siblings and/or dimensionality of measures. We examine rater contrast and sex effects in ADHD subtypes using a dimensional scale and compare the aetiology of self, versus maternal-report. Data were collected using the Strengths and Weaknesses of ADHD and Normal Behaviour Scale (SWAN): maternal-report for 3,223 twins and siblings (mean age 21.2, SD = 6.3) and self-report for 1,617 twins and siblings (mean age 25.5, SD = 3.2). Contrast effects and magnitude of genetic and environmental contributions to variance of ADHD phenotypes (inattention, hyperactivity-impulsivity, combined behaviours) were examined using structural equation modeling. Contrast effects were evident for maternal-report hyperactivity-impulsivity (b = -0.04) and self-report inattention (-0.09) and combined ADHD (-0.08). Dominant genetic effects were shared by raters for inattention, hyperactivity-impulsivity and combined ADHD. Broad-sense heritability was equal across sex for maternal-report inattention, hyperactivity-impulsivity and combined ADHD (0.72, 0.83, 0.80). Heritability for corresponding subtypes in self-reported data were best represented by sex (0.46, 0.30, 0.39 for males; 0.69, 0.41, 0.65 for females). Heritability difference between maternal and self-report ADHD was due to greater variance of male specific environment in self-report data. Self-reported ADHD differed across sex by magnitude of specific environment and genetic effects.
authors.affiliation: Environmental and Rural Sciences, University of New England, Armidale, NSW, Australia, ebejer.j@gmail.com.
authors.forename: J L
authors.initials: JL
authors.lastname: Ebejer
authors.forename: S E
authors.initials: SE
authors.lastname: Medland
authors.forename: J
authors.initials: J
authors.lastname: van der Werf
authors.forename: M
authors.initials: M
authors.lastname: J Wright
authors.forename: A K
authors.initials: AK
authors.lastname: Henders
authors.forename: N A
authors.initials: NA
authors.lastname: Gillespie
authors.forename: I B
authors.initials: IB
authors.lastname: Hickie
authors.forename: N G
authors.initials: NG
authors.lastname: Martin
authors.forename: D L
authors.initials: DL
authors.lastname: Duffy
mesh_terms: D000293:Adolescent; D000328:Adult; D001289:Attention Deficit Disorder with Hyperactivity / Q000453:epidemiology / Q000235:genetics*; D002648:Child; D003625:Data Collection; D004200:Diseases in Twins; D005260:Female; D005799:Genes, Dominant; D006801:Humans; D007175:Impulsive Behavior; D008297:Male; D008425:Maternal Behavior; D008875:Middle Aged; D009035:Mothers; D010641:Phenotype; D012189:Retrospective Studies; D012737:Sex Factors; D035781:Siblings; D055815:Young Adult