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Rethinking the idea of late autism spectrum disorder onset

Published online by Cambridge University Press:  14 August 2017

Elizabeth C. Bacon*
Affiliation:
University of California, San Diego
Eric Courchesne
Affiliation:
University of California, San Diego
Cynthia Carter Barnes
Affiliation:
University of California, San Diego
Debra Cha
Affiliation:
University of California, San Diego
Sunny Pence
Affiliation:
University of California, San Diego
Laura Schreibman
Affiliation:
University of California, San Diego
Aubyn C. Stahmer
Affiliation:
University of California, Davis
Karen Pierce
Affiliation:
University of California, San Diego
*
Address correspondence and reprint requests to: Elizabeth Bacon, Department of Neurosciences, Autism Center of Excellence, University of California, San Diego, 8110 La Jolla Shores Drive, La Jolla, CA, 92037; E-mail: ebacon@ucsd.edu.

Abstract

A common theory of autism spectrum disorder (ASD) symptom onset includes toddlers who do not display symptoms until well after age 2, which are termed late-onset ASD cases. Objectives were to analyze differences in clinical phenotype between toddlers identified as ASD at initial evaluations (early diagnosed) versus those initially considered nonspectrum, then later identified as ASD (late diagnosed). Two hundred seventy-three toddlers recruited from the general population based on a failed developmental screening form or parent or physician concerns were followed longitudinally from 12 months and identified as early- and late-diagnosed cases of ASD, language delayed, or typically developing. Toddlers completed common standardized assessments and experimental eye-tracking and observational measures every 9–12 months until age 3. Longitudinal performance on standardized assessments and experimental tests from initial evaluations were compared. Delay in social communication skills was seen in both ASD groups at early-age initial assessment, including increased preference for nonsocial stimuli, increased stereotypic play, reduced exploration, and use of gestures. On standardized psychometric assessments, early-diagnosed toddlers showed more impairment initially while late-diagnosed toddlers showed a slowing in language acquisition. Similar social communication impairments were present at very early ages in both early-detected ASD and so-called late-onset ASD. Data indicate ASD is present whether detected or not by current methods, and development of more sensitive tools is needed.

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Type
Regular Articles
Copyright
Copyright © Cambridge University Press 2017 

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