Difference in Language Profiles of Children With Autism Spectrum Disorder and Down Syndrome Is Not Driven by Non‐Verbal Cognition

BACKGROUND: Autism Spectrum Disorder (ASD) and Down syndrome (DS) are among the most common types of neurodevelopmental conditions that have co-occurring language impairments. Usually, non-verbal IQ has been reported as one of the main predictors of language functioning in children with these conditions. Although language abilities of children with ASD and DS have been described in the previous studies, there is still a lack of direct comparisons of language profiles in the non-verbal IQ-matched groups of children with these disorders, and, therefore, it is largely unexplored whether language difficulties in these populations are of similar or different origins. AIMS: The study provided a direct comparison of language profiles in non-verbal IQ-matched children with ASD and DS at different linguistic levels (phonology, vocabulary and morphosyntax) in both production and comprehension and explored the influence of different psycholinguistic variables on accuracy. Also, the study assessed whether non-language factors (non-verbal IQ and age) influence language skills in both groups of children. METHODS AND PROCEDURES: In total, 60 children participated in the study: 20 children with ASD, 20 children with DS and 20 typically developing controls (7-11 years old; all groups were age-matched). The language testing included seven tests from the Russian Child Language Assessment Battery, assessing expressive and receptive language skills at phonological, lexical and morphosyntactic levels. OUTCOMES AND RESULTS: Overall, we revealed both similarities and differences in language profiles between children with ASD and DS. At the group performance level, children with ASD and DS were comparable in vocabulary and syntax but differed in phonological processing, on which children with ASD had higher accuracy. Some psycholinguistic variables that influenced accuracy in language test performance were present uniquely in the ASD group: for example, autistic children struggled more with verbs than nouns in naming or comprehended sentences with canonical SVO word order more accurately than sentences with noncanonical OVS word order. In comparison to children with DS, in the ASD group, non-verbal IQ was related to language skills in three out of seven tests, with evidence of a positive association between them. CONCLUSIONS AND IMPLICATIONS: This study provided new insights on the differences in language profiles of non-verbal IQ-matched children with ASD and DS and identified specific impairments related to linguistic levels and structural language characteristics in each group. These findings contributed to speech and language therapy strategies, as they highlighted specific 'linguistic deficits' that should be targeted during intervention and therapy. WHAT THIS PAPER ADDS: What is already known on this subject Language profiles of children with Autism Spectrum Disorder (ASD) and Down syndrome (DS) have been described in previous studies on different languages. Usually, non-verbal IQ has been reported as one of the main predictors of language functioning in these groups of individuals with neurodevelopmental disorders. However, there is a lack of direct comparisons of language profiles at different linguistic levels in these groups, matched by non-verbal IQ and using standardized language assessment tools to understand whether the nature of language impairments is common or different in ASD and DS regardless of non-verbal cognition. What this study adds to the existing knowledge This study provided a direct comparison of language profiles at different linguistic levels in children with ASD and DS matched by non-verbal IQ. This identified similarities and differences in language functioning at different linguistic levels in children with ASD and DS as well as revealed non-language factors that were associated with language abilities. What are the potential or actual clinical implications of this work? The study showed the differences in language profiles of children with ASD and DS regardless of non-verbal IQ and identified specific impairments related to linguistic levels and structural language characteristics. This knowledge contributes to speech and language therapy strategies, as it elucidates specific 'linguistic deficits' that should be targeted during intervention and therapy.

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