The linguistic and cognitive profile of Down syndrome: evidence from a comparison with fragile X syndrome.

In this paper, we report on the results of our research, which is designed to address two broad questions about the cognitive and linguistic profile of Down syndrome: (1) Which domains of functioning are especially impaired in individuals with Down syndrome? and (2) Which aspects of the language and cognitive profile of Down syndrome are syndrome specific? To address these questions, we focused on three dimensions of the Down syndrome profile--receptive language, expressive language, and theory of mind--and made comparisons to individuals with fragile X syndrome, which is an X-linked form of intellectual disability. We identified Down syndrome impairments on all three dimensions that were substantially greater than those seen in nonverbal cognition and that were not shared by individuals with fragile X syndrome. Clinical implications of these findings are considered.