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BACKGROUND: A twin study design was used to assess the degree to which additive genetic variance influences ADHD symptom scores across two ages during infancy. A further objective in the study was to observe whether genetic association with a number of candidate markers reflects results from the quantitative genetic analysis. METHOD: We have studied 312 twin pairs at two time-points, age 2 and age 3. A composite measure of ADHD symptoms from two parent-rating scales: The Child Behavior Checklist/1.5 - 5 years (CBCL) hyperactivity scale and the Revised Rutter Parent Scale for Preschool Children (RRPSPC) was used for both quantitative and molecular genetic analyses. RESULTS: At ages 2 and 3 ADHD symptoms are highly heritable (h2 = 0.79 and 0.78, respectively) with a high level of genetic stability across these ages. However, we also observe a significant level of genetic change from age 2 to age 3. There are modest influences of non-shared environment at each age independently (e2 = 0.22 and 0.21, respectively), with these influences being largely age-specific. In addition, we find modest association signals in DAT1 and NET1 at both ages, along with suggestive specific effects of 5-HTT and DRD4 at age 3. CONCLUSIONS: ADHD symptoms are heritable at ages 2 and 3. Additive genetic variance is largely shared across these ages, although there are significant new effects emerging at age 3. Results from our genetic association analysis reflect these levels of stability and change and, more generally, suggest a requirement for consideration of age-specific genotypic effects in future molecular studies.

Original publication

DOI

10.1186/1471-244X-10-102

Type

Journal article

Journal

BMC Psychiatry

Publication Date

01/12/2010

Volume

10

Keywords

Age Factors, Attention Deficit Disorder with Hyperactivity, Attention Deficit and Disruptive Behavior Disorders, Child, Preschool, Diseases in Twins, Female, Genetic Markers, Genetic Variation, Genome-Wide Association Study, Genotype, Humans, Male, Models, Genetic, Parents, Psychiatric Status Rating Scales, Social Environment, Surveys and Questionnaires, Twins, Dizygotic, Twins, Monozygotic