CHILDHOOD HYPERACTIVITY SCORES ARE HIGHLY HERITABLE AND SHOW SIBLING COMPETITION EFFECTS - TWIN STUDY EVIDENCE

Hyperactivity has consistently been shown to be familial. Until recent ly however, due to a lack of systematic twin evidence, it has remained uncertain to what extent familial transmission can be explained by ge netic factors. We used a systematically ascertained population-based s ample of twin pairs aged between 8 and 16 years old to explore the rol e of genetic influences on maternally rated hyperactivity scores. Hype ractivity scores were found to be substantially heritable. The data we re best explained by a model which incorporated sibling competitive ef fects as well as additive genetic factors. These findings suggest not only that hyperactivity scores are influenced by genetic factors but t hat sibling interaction effects are also of importance.