Language acquisition in special populations: a comparison between Down and Williams syndrome

To investigate the relationship between language acquisition and
cognition, we evaluated linguistic abilities in twelve Italian-speaking
children with Williams (WS) and twelve with Down syndrome (DS) of
comparable global cognitive level. Another control group included twelve
typically developing children, matched for mental age. Linguistic measures
included a parent questionnaire to assess vocabulary, a verbal
comprehension test, a sentence repetition test and MLU calculated on
spontaneous production. No dissociation was evident between lexical and
cognitive abilities, but specific morphosyntactic difficulties emerged
both in comprehension and production in children with DS. Individuals with
WS, albeit less compromised than DS, also had difficulty in the phrase
repetition task and, particularly, using content words. Our results
demonstrate that the linguistic abilities of infants with WS are not above
their cognitive level and that language development in these special
populations is not only delayed, but follows a different developmental
trajectory.