Background: The present study sought to examine the specificity, developmental correlates, nature and pervasiveness of imitation deficits very early in the development of autism.

Methods: Subjects were 24 children with autism (mean age 34 months), 18 children with fragile X syndrome, 20 children with other developmental disorders, and 15 typically-developing children. Tasks included manual, oral-facial, and object oriented imitations, developmental measures, joint attention ability, and motor abilities.

Results: Children with autism were found to be significantly more impaired in overall imitation abilities, oral-facial imitation, and imitations of actions on objects than children in all of the other groups. Imitation skills of young children with fragile X syndrome were strongly influenced by the absence or presence of symptoms of autism. For children with autism, imitation skills were strongly correlated with autistic symptoms and joint attention, even when controlling for developmental level. For comparison groups, imitation was related to other developmental abilities including play, language, and visual spatial skills. Neither motor functioning nor social responsivity accounted for a significant amount of variance in imitation scores, when controlling for overall developmental level, which accounted for much of the variation in imitation ability.

Conclusions: Simple imitation skills were differentially impaired in young children with autism, and lack of social cooperation did not account for their poor performance. In autism, imitation skills clustered with dyadic and triadic social interactions and overall developmental level, but were not related to play or language development. For comparison children, all these areas were inter-related. Hypotheses about a specific dyspraxic deficit underlying the imitation performance in autism were not supported.