Lexical and syntactic development in Italian children with Down's syndrome

Although children with Down's syndrome show some delays in each area of language development, their morphosyntactic competence appears to be more severely compromised than their lexical skills and, therefore, they are frequently mentioned as an example of dissociation between grammar and lexicon.

The principal aim of the present study was to compare the lexical and syntactic development of Italian children with Down's syndrome with that of typically developing children, considering their spontaneous production. Particular attention was given to the relationships between these linguistic areas and the transition from single-word utterances to multiword combinations (that is, transitional forms).

Twenty-four children participated in the study: twelve with Down's syndrome and twelve typically developing children. On average, the children with Down's syndrome participating in the study had a vocabulary size of about 450 words; and their mean chronological age was 54 months, whereas their mean developmental age was 30 months. The criteria for inclusion in the typically developing children group were a mean vocabulary size similar to that of the participants with Down's syndrome and a mean chronological age equivalent to the mean developmental age of the children with Down's syndrome. Each child's spontaneous verbal production was assessed during a parent-child play session. Data analyses focused on both lexical variables (type and tokens, vocabulary composition) and syntactic variables (frequency and types of transitional forms, frequency of utterances with different degree of complexity, and argument structure of verbs).

The vocabulary composition of the children with Down's syndrome appeared to be simpler than that of the typically developing children at the same lexical size. Children with Down's syndrome used a higher number of transitional forms, but their production of multi-word utterances was less frequent; they were able to use word combinations, but they produced a low number of morphologically complete sentences. In addition, a significant relationship emerged between the development of the lexicon and the production of multi-word utterances.

Children with Down's syndrome seem to have greater difficulties in expressing sentences in a grammatically correct form, though they are able to combine words. The theoretical relevance of the study lies in the fact that individuating a significant relationship between lexical and syntactic skills supports the hypothesis of interdependence between these two language domains; the practical relevance of the results lies in the fact that intervening on lexical abilities could have a beneficial effect on syntactic skills.