Clumsiness and psychopathology: Causation or shared etiology? A twin study with the CBCL 6–18 questionnaire in a general school-age population sample

In a sample of 398 twin pairs aged 8–17 belonging to the Italian Twin Registry we explored the extent to which physical clumsiness/motor problems covary with a broad spectrum of behavioral problems identified by the Child Behavior Checklist 6–18/DSM oriented scales, and the causes of such covariation. Only Anxiety and Attention Deficit Hyperactivity (ADH) Problems maintained significant correlation with Clumsiness after partialling out the effects of the other problem scales. By the co-twin control method we found no indication of clear, direct causal effect of Clumsiness upon Anxiety or ADH Problems, or vice versa. Twin bivariate analyses showed that the co-occurrence of motor problems and Anxiety/ADH Problems is best explained by genetic factors shared between Clumsiness and the behavioral problems phenotypes.