Atypical language development is a key feature of autism spectrum disorders (ASD), with language delay common in the subgroup of children with core autism diagnoses. Delays and differences in the acquisition of both receptive and expressive vocabularies have been demonstrated, with preschoolers with autism often failing to show the usual developmental pattern of comprehension significantly in advance of production.
The current study extended existing findings of atypical receptive and expressive vocabulary profiles in children with ASD by exploring these in toddlers at high genetic risk for ASD (based on having an older sibling with a diagnosis) along with low-risk controls where there is no such family history. The aim was to identify the period in development at which developmental trajectories of vocabulary acquisition began to emerge.
Participants were 50 toddlers at high-risk for ASD recruited through the British Autism Study of Infant Siblings (BASIS), and 50 low-risk controls. Profiles of receptive and expressive vocabulary growth were evaluated using the MacArthur Communicative Development Inventory, completed by parents at multiple visits, when children were aged around 6, 12, 24 and 36 months. Diagnostic outcomes of the high-risk group were determined at the final visit, permitting comparison of three groups of children: low-risk controls, children at high-risk with no ASD outcome, and children developing ASD.
Preliminary analysis comparing all children at high-risk with all low-risk controls suggests a different trajectory for both receptive and expressive vocabulary growth. Overall, vocabulary growth was slower in children at high-risk for ASD compared to low-risk controls. However, growth in receptive vocabulary appeared to slow at an earlier age, with expressive growth initially maintaining typical levels and showing signs of slowing only later. Additional analyses are planned to evaluate these data with respect to final outcome diagnosis of the high-risk group.
These results expand upon previous research around receptive and expressive vocabulary and language patterns in individuals with diagnosed ASD, to prospectively examine vocabulary growth in a high-risk cohort followed longitudinally. Further results including diagnostic outcomes at 3 years of age will address the specificity of language atypicalities in receptive vs. expressive domains and the developmental period at which ASD-characteristic profiles emerge.
*The BASIS Team in alphabetical order: S. Baron-Cohena, P. Boltonb, K. Daviesc, J. Fernandesc, H. Garwoodc, L. Tuckerc, A. Voleinc
aUniversity of Cambridge, bInstitute of Psychiatry, cBirkbeck, University of London
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