The nature of covariation between autistic traits and clumsiness: a twin study in a general population sample.

While social impairment, difficulties with communication, and restricted repetitive behaviors are central features of Autism Spectrum Disorders, physical clumsiness is a commonly co-occuring feature. In a sample of 398 twin pairs (aged 8-17 years) from the Italian Twin Registry we investigated the nature of the co-variation between a psychometric index of Clumsiness and the Child Behavior Checklist (CBCL) Autistic scale. Bivariate twin analyses showed that a genetic etiological overlap, rather than direct causation, is a plausible explanation for the association between clumsiness and autistic-like traits, as measured by indices derived from the parent-rated CBCL scale. Additive genetic influences that impinge upon clumsiness/motor problem and autistic-like traits coincided remarkably, with a genetic correlation of 0.63.