Does Age of ASD Diagnosis Produce Differential Outcomes in Middle Childhood

Background: To date, no other studies have investigated the development pathways of children with an ASD prospectively ascertained from a community sample. Research that has studied children with an ASD from infancy to school age, has relied on high-risk and infant sibling cohorts (Landa et al., 2013; Landa & Garrett-Mayer, 2006). Further, although it is considered best practice to diagnose ASDs by 2 years of age where possible, the average age of diagnosis in Australia remains between 4 and 6 years of age (Bent, 2015). Research is yet to investigate the impact age of diagnosis has on later outcomes (cognitive and behavioural). Specifically, this study is interested in whether children who receive an earlier diagnosis (at 24 months) experience more positive develpmental outcomes in middle childhood, relative to those who were detected later.

Objectives:  The primary focus in this investigation is to assess the developmental progress at school age, of children diagnosed with an ASD at 24 months, first identified through the SACS study. A longitudinal design is employed here. A secondary objective is to compare the outcomes of the SACS cohort at school age, to those children who were formally diagnosed with an ASD after 3 years of age, using a cross sectional design

Methods: All children were involved in a throrough developmental assessment at school age. Cognition was assessed using the Wechsler Abbreviated Scale of Intelligence (WASI) while the Autism Diagnostic Observation Schedule (ADOS) was administered to assess social communication development and autism severity at school age.

Results: Children in the SACS cohort made significant gains in cognition from toddlerhood to school age, with only few meeting criteria for an ID at outcome (7%). Despite changes in severity of autism symptoms, diagnoses of ASD were highly stable over time with 73% of children retaining their early ASD diangosis from toddlerhood to middle childhood. Preliminary between group comparisons reveal that children diagnosed early are demonstrating higher Full Scale IQ (FSIQ) and Verbal IQ (VIQ) and lower ASD severity at school age, relative to children diagnosed later. However, at this stage, these between group differences are not significant.

Conclusions:  This research illustrates the cognitive and behavioural trajectories of children at school age, who were identified and diagnosed with an ASD at 24 months as part of the Social Attention and Communication Study (SACS; Barbaro & Dissanayake, 2009). Further, these findings, although preliminary at this stage, will highlight the importance of age of ASD diagnosis and will identify whether the timing of diagnosis contributes to differential developmental outcomes in middle childhood.