GENETIC-EFFECTS ON ADHD SYMPTOMATOLOGY IN 7-YEAR-OLD TO 13-YEAR-OLD TWINS - RESULTS FROM A TELEPHONE SURVEY

The magnitude of genetic and environmental factors and the influence o f contrast effects on attention-deficit hyperactivity disorder (ADHD) symptomatology were examined on a sample of 900 twin pairs, aged 7-13, participating in the Virginia Twin Study of Adolescent Behavioral Dev elopment (VTSABD). In addition, the genetic and environmental correlat ions between ADHD and oppositional-defiant disorder/conduct disorder ( ODD/CD) symptomatology were estimated. A series of structural models w as applied to maternal ratings from a telephone survey, designed to sc reen for the three dimensions of ADHD symptomatology (hyperactivity, i mpulsivity, and inattention) and ODD/CD symptomatology. Model-fitting results suggested that ADHD symptomatology is highly heritable and inf luenced mostly by additive genetic, specific environmental, and contra st effects. However, this analysis could not exclude with statistical significance additional effects from dominance. The results of the bes t-fitting bivariate model suggested that the genetic correlation betwe en the two traits is 50% and replicated previous findings of a common genetic factor influencing the comorbidity of ADHD and ODD/CD symptoma tologies.