Developmental Differences Associated with Early Diagnosis: A Comparison of Toddlers Diagnosed with ASD at Age 2 Versus Age 3

Background: Early identification of children with Autism Spectrum Disorders (ASD) and thus early intervention are consensually regarded as critical for improving lifetime outcomes of individuals affected by ASD (Warren et al., 2011; Zwaigenbaum et al., 2013). Though ASD can reliably be diagnosed by 24 months of age, the average age of diagnosis in the US is currently 4.5 years (CDC, 2014), after the window of opportunity afforded by early intervention (Dawson et al., 2012). The question remains as to what the quantitative impact is of earlier diagnosis.

Objectives: The goal of the current study was to examine the effect of early diagnosis on cognitive, language, and adaptive functioning one year following an ASD diagnosis. Specifically, this study compared developmental and adaptive profiles of 3-year-old children at initial diagnosis to 3-year-old children with a previous diagnosis.

Methods: Participants included 25 clinically-referred toddlers, who were initially evaluated around age 2 (M=22.89 months, SD=4.38) and again between 36 and 42 months (M=38.2 months, SD=2.3) and 81 clinically-referred toddlers, who were initially evaluated between 33 and 41 months (M=37 months, SD=2.1). All were diagnosed with ASD. A comparison was made between two groups: Children at age 3 who were previously diagnosed around age 2 and children at age 3 with no prior diagnosis. 87% of children diagnosed at 2 years received some type of intervention prior to 3 years of age.

Evaluations included assessment of cognitive/developmental abilities using the Mullen Scales of Early Learning, Bayley Scales of Infant and Toddler Development- 3^rd  Edition, or Differential Abilities Scales-2^nd Edition; adaptive abilities using the Vineland Adaptive Behavior Scales, 2^ndEdition, Survey Form; and autism symptomatology using the Autism Diagnostic Observation Schedule. Developmental and adaptive scores were converted to standard scores to compare group means.

Results: Groups did not differ for gender and cognitive/developmental profiles at first diagnosis. Significant differences were found between groups for nonverbal IQ, (t(30)=-2.61, p=.014), verbal IQ, (t(92)=-3.16, p=.002) and adaptive communication skills (t(79(=-4.59, p<.001). Specifically, 3-year-olds who were diagnosed a year previously had higher mean nonverbal IQ scores, verbal IQ scores and adaptive communication skills  compared to those receiving a first time diagnosis at age 3.

Conclusions: Data from the current study suggests that receiving a diagnosis earlier is associated with greater nonverbal problem solving, verbal reasoning, and adaptive communication skills at age 3. Standard scores on measures of nonverbal problem solving and adaptive communication were more than one standard deviation higher for children who received an earlier diagnosis, while verbal reasoning scores were 14 points higher.  These gains suggest that early diagnosis has a meaningful effect on development. However, groups did not show differences in the areas of adaptive daily living, social, and motor skills, suggesting that the earlier interventions are not impacting these areas of early development. A limitation of this study is racial disparity, which needs to be further examined. In addition, future research should examine the developmental trajectory of children diagnosed at various ages controlling for varying levels and types of early intervention, race, ethnicity, and socio-economic status.