Paediatrics (RCH) - Theses
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ItemLanguage development in autism spectrum disorder: longitudinal comparison with a community cohort of children with language impairment and typical development( 2016)Background: Autism spectrum disorder (ASD) is a lifelong developmental disability that affects more than 1 in 50 children in Australia. Language difficulties are common in ASD with up to 30% of children unable to communicate using words. Despite a substantial number of studies examining language outcomes in individuals with ASD, it is difficult for families and clinicians to interpret study findings. This is because many studies use; selected clinical samples that may not generalise to the broader population, heterogeneous methodology, and the quality of studies varies. Rarely do studies use standardised language-specific tools. In addition, few studies have compared development in children with ASD to children without ASD, which means it is difficult to place differences in children with ASD within a developmental context. As a consequence, we do not yet fully understand how language develops in children with ASD and we are not able to accurately predict language outcomes. Parents and clinicians need evidence about language trajectories in ASD to inform decision-making and understand prognosis. Service providers and policy makers also require information for appropriate resource allocation for current and future needs. Aims: The overall aim of this thesis was to examine trajectories of language development in individuals diagnosed with ASD. To achieve this aim, three main studies were conducted. Study 1 systematically reviewed and synthesised the extant literature on language outcomes in individuals with ASD. Studies 2 and 3 examined individual and mean trajectories of language development in children with ASD from 1 to 2 years and 4 to 7 years, respectively, and compared these trajectories to large samples of children with language impairment (LI) and typical language development (TD). Study 3 described language trajectories for children with ASD and investigated predictors of language outcomes from 4 to 7 years in children with and without ASD. Method: Children in studies 2 and 3 were recruited from a prospective longitudinal community-based study of 1910 children in Victoria (the Early Language in Victoria Study; ELVS). Individual and mean trajectories were mapped from 1 to 2 years (ASD; n=41, LI: n=119, TD: n=861) and 4 to 7 years (ASD; n=27, LI n=110, TD: n=831). In Study 2, individual and mean communication trajectories were mapped using scores from two parent checklists, namely the Communication Symbolic Behaviour Scales Infant Toddler Checklist and the MacArthur Bates Communicative Development Inventories. We compared the proportion of children who lost specific communication skills between the three groups (ASD, LI, TD) and the spread of loss across different communication domains. In Study 3 we used the Clinical Evaluation of Language Fundamentals data collected in ELVS (preschool second edition and fourth edition) to map individual and mean language trajectories from 4 to 7 years. The proportion of children who had declined, remained stable or accelerated in language skills was compared across groups. Putative predictors of language outcomes were also investigated. Results: Language ability was heterogeneous, however, mean scores for children with ASD and LI were lower than scores for children with TD and reference norms, in all studies included in the systematic review and Studies 2 and 3 in the community sample. From 1 to 2 years, the gap between children with ASD and TD/LI grew larger in all communication domains except in the areas of speech and expressive vocabulary, which was similar for children with LI and ASD. From 4-7 years, despite having lower language ability on average compared with the typically developing group, most children with ASD were developing language at the same pace as the LI and TD children. A diagnosis of ASD did not predict a greater gap between receptive and expressive language ability. The child’s early language ability and IQ were most important in predicting language ability at a later age. Conclusion: Systematic review and synthesis of existing studies showed that children with ASD in all studies (with one exception) had lower scores at baseline when compared with reference norms but children tracked in parallel to reference norms. The limited amount of data available from studies investigating children over 9 years made it difficult to draw accurate conclusions on trajectories beyond this age, however the few studies that had presented data suggest rate of language progress may slow from around 10 years. In Studies 2 and 3 that utilised the ELVS, children with ASD demonstrated communication abilities that were not significantly different to other children at12 months of age in most areas. However, on average their language and social communication progressed at a slower rate than other children from around 12 months to 2 years in most areas of communication. Findings from children in the ELVS aged 4 to 7 years were consistent with the systematic review findings. In Study 3 children with ASD who were verbal and had IQ in the normal range demonstrated lower language scores at baseline and follow up on average, but tracked in parallel to reference norms over time. The knowledge gained from this thesis will help guide prognostic information to be provided to parents. It will also assist with planning for future support needs of individuals with ASD.