The genetic and environmental contributions to attention deficit hyperactivity disorder as measured by the Conners' Rating Scales--Revised.
OBJECTIVE
The majority of published reports on twin studies of attention deficit hyperactivity disorder (ADHD) have indicated robust additive genetic influences and unique environmental influences. These studies typically used DSM ADHD symptoms collected by telephone or interviews with mothers. The purpose of this study was to test the genetic architecture of ADHD by using the ADHD index from Conners' Rating Scales-Revised.


METHODS
From the Conners' scale forms, data for the ADHD index were collected from the mothers of 1,595 7-year-old twin pairs from the Netherlands Twin Registry. Rates of ADHD diagnoses were computed by using Conners' gender- and age-specific cutoff points. Contributions from additive, dominant, unique environmental, interaction, and gender effects were computed by using gender-genetic models.


RESULTS
The prevalence of ADHD across the sample of 7-year-old twin pairs was about 4% according to the mothers' reports, consistent with other reported rates of ADHD. However, using the gender norms provided with the ADHD index, the authors found slightly higher rates of ADHD in girls than previously reported. Genetic analyses yielded a model that includes genetic dominance (48%), additive genetic factors (30%), and unique environmental factors (22%).


CONCLUSIONS
The ADHD index from Conners' Rating Scales-Revised identified an appropriate percentage of children across this epidemiologic twin sample as being at risk for ADHD. The results of the genetic analyses are consistent with prior reports that ADHD is predominantly influenced by genetic factors that are both dominant and additive.
Hudziak
James J
JJ
Division of Behavioral Genetics, Department of Psychiatry, University of Vermont, Given B229, Burlington, VT 05405, USA. jhudziak@zoo.uvm.edu
Derks
Eske M
EM
Althoff
Robert R
RR
Rettew
David C
DC
Boomsma
Dorret I
DI
D001289:Attention Deficit Disorder with Hyperactivity / Q000145:classification / Q000453:epidemiology / Q000235:genetics*; D002648:Child; D039721:Diagnostic and Statistical Manual of Mental Disorders; D004200:Diseases in Twins / Q000145:classification / Q000453:epidemiology / Q000235:genetics*; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics; D006801:Humans; D008297:Male; D008957:Models, Genetic; D015233:Models, Statistical; D009035:Mothers / Q000523:psychology; D009426:Netherlands; D010555:Personality Inventory; D011569:Psychiatric Status Rating Scales / Q000706:statistics & numerical data*; D012042:Registries / Q000706:statistics & numerical data; D012737:Sex Factors; D012931:Social Environment; D011795:Surveys and Questionnaires