Vocabulary and Syntactic Development in Japanese Children With Autism Spectrum Disorder and Down Syndrome Accompanied by Intellectual Disability.

Researchers studied how Japanese children with autism and Down syndrome develop language skills compared to other children of similar mental ability. While these children learned vocabulary (word knowledge) at expected levels, they had much more difficulty with grammar and sentence structure. This suggests children with autism and Down syndrome may need extra support specifically focused on grammar skills, not just vocabulary building.

This study compared vocabulary and syntactic development in Japanese children with autism spectrum disorder (ASD, n=14) and Down syndrome (DS, n=19) against typically developing children (n=28), controlling for mental age. Children with ASD and DS aged 9-17 years with mental age over 4 years were matched to 5-year-old typically developing children. While vocabulary comprehension and expression were similar across groups, children with ASD and DS showed significantly impaired syntactic comprehension and expression compared to mental age-matched peers. Both groups particularly struggled with grammatical morphemes and grammatical knowledge, suggesting syntax develops differently than vocabulary in these populations despite similar mental ages.

Results suggest vocabulary and syntactic development follow different trajectories in ASD and DS. Clinical and educational interventions should specifically target grammatical morphology and syntax rather than assuming vocabulary gains will translate to syntactic improvements. Mental age matching may not be sufficient for predicting syntactic abilities.

Small sample sizes (14 ASD, 19 DS participants). Limited to Japanese language which may affect generalizability to other languages. Cross-sectional design prevents understanding of developmental trajectories over time. Study type not specified in metadata.

Children with intellectual disability (ID) have significantly delayed morphological and syntactic development. This study aimed to establish the link between vocabulary and syntactic development in children with autism spectrum disorder (ASD) and Down syndrome (DS) compared with children with typical development (TD), controlling for mental age (MA) as defined by the Tanaka-Binet Intelligence Scale V. Participants comprised children with ID (N = 33), including 14 with ASD and 19 with DS; chronological age (CA) ranged from 9 to 17 years, with an MA of over 4 years. Children with TD (N = 28) had a CA of 5 years.

Participants were assessed on vocabulary comprehension, vocabulary expression, syntactic comprehension and syntactic expression. We examined both group differences and within-group associations between vocabulary and syntax. Although we witnessed no significant differences in vocabulary comprehension or expression, children with ASD and DS performed significantly lower on syntactic comprehension and expression tasks than MA-matched children with TD. Both groups demonstrated difficulty with grammatical items requiring understanding of grammatical morphemes and grammatical knowledge.

Both groups exhibited vocabulary development similar to that of children with TD; however, their syntactic development was lower than expected considering their MA and vocabulary development. Building and examining approaches focusing on syntax, particularly grammatical morphology, is important in educational and clinical practice for Japanese children with ASD and DS.