Does the definition of ADHD affect heritability?
OBJECTIVE
A twin study design was used to examine the genetic validity of attention-deficit hyperactivity disorder (ADHD)-related phenotypes.


METHODS
Questionnaires covering ADHD symptoms were sent to the families of 2,846 school-age twins. Parent-rated symptoms were obtained for 2,082 twin pairs and teacher-rated symptoms were available for 1,470 twin pairs.


RESULTS
Broadly defined parent-rated, teacher-rated, and "pervasive" (both parent- and teacher-rated) ADHD categories were found to be highly heritable. Significant shared environmental effects were also detected for teacher-rated ADHD. A common genetic factor was found to have a modest influence on both parent- and teacher-rated symptom scores and categories, but additional genetic and environmental influences were also found forteacher-rated ADHD. Consistent with previous findings, ADHD symptom scores were again found to be highly heritable. Maternal contrast effects were found for the Rutter A scale items but could not be detected for the DuPaul ADHD rating scale.


CONCLUSIONS
Broadly defined pervasive ADHD appears to be as heritable as ADHD behaviors defined by maternal reports alone. A common genetic factor influences maternally rated and teacher-rated ADHD but does not account for all of the genetic variance for teacher-rated ADHD. ADHD symptom scores are highly heritable, and maternal contrast effects appear to vary for different measures.
Thapar
A
A
Department of Psychological Medicine, University of Wales College of Medicine, Cardiff, UK. Thapar@cardiff.ac.uk
Harrington
R
R
Ross
K
K
McGuffin
P
P
D000293:Adolescent; D001289:Attention Deficit Disorder with Hyperactivity / Q000453:epidemiology / Q000235:genetics*; D002648:Child; D002675:Child, Preschool; D004739:England / Q000453:epidemiology; D005260:Female; D018740:Genetic Heterogeneity; D006801:Humans; D008297:Male; D008957:Models, Genetic; D015999:Multivariate Analysis