Genetic support for the dual nature of attention deficit hyperactivity disorder: substantial genetic overlap between the inattentive and hyperactive-impulsive components.
OBJECTIVE
Attention deficit hyperactivity disorder (ADHD) is a common, complex and highly heritable disorder, characterised by inattentive, impulsive and overactive behaviour. Evidence for the heritability of ADHD measures in twin population samples has come from the analysis of total scores that combine inattentive and hyperactive-impulsive symptoms subscales. This study investigated, in a community sample, the aetiology of ADHD-like traits and the aetiological overlap between the two dimensions that define the ADHD disorder.


METHODS
Parents of 6,222 approximately 8-year-old twin pairs from the Twins Early Development Study (TEDS) population sample completed the two subscales of the Conners' 18-item DSMIV checklist, a screening instrument for ADHD symptoms.


RESULTS
Both subscales were highly heritable (hyperactive-impulsive: 88%; inattentive: 79%). Bivariate genetic modelling indicated substantial genetic overlap between the two components; however, there were significant independent genetic effects.


CONCLUSIONS
These findings suggest that many genes associated with the hyperactivity-impulsivity dimension will also be associated with the inattentive dimension but that there is significant genetic heterogeneity as well. These results provide genetic support for combining the two behavioural dimensions that define ADHD, but also suggest that some symptom-specific genes will also be identified.
McLoughlin
Gráinne
G
MRC Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, King's College London, De Crespigny Park, London, UK. g.mcloughlin@iop.kcl.ac.uk
Ronald
Angelica
A
Kuntsi
Jonna
J
Asherson
Philip
P
Plomin
Robert
R
D001288:Attention; D001289:Attention Deficit Disorder with Hyperactivity / Q000175:diagnosis / Q000235:genetics* / Q000523:psychology; D002648:Child; D002652:Child Behavior / Q000523:psychology; D015331:Cohort Studies; D004739:England; D005163:Factor Analysis, Statistical; D005260:Female; D006801:Humans; D007175:Impulsive Behavior / Q000175:diagnosis / Q000235:genetics* / Q000523:psychology; D008297:Male; D010290:Parents / Q000523:psychology; D011569:Psychiatric Status Rating Scales / Q000706:statistics & numerical data; D012737:Sex Factors; D014427:Twins / Q000523:psychology; D014852:Wales
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