Comparison of the Clinical Profiles of 1-Year Olds and 2-Year Olds with Autism Spectrum Disorders

Background: Accurate, stable diagnosis of ASD may be possible within community settings during the second year of life for some children (Corsello et al., 2012; Guthrie et al., 2012), and young children with ASD receiving early behavioral intervention demonstrate substantial gains in functioning (Dawson et al., 2010, 2012; Warren et al., 2011). Numerous screening initiatives (AAP, CDC Act Early) have pushed for identification prior to age two. However, CDC figures suggest a majority of individuals with ASD are not diagnosed until after age 3. To date, few studies outside of high-risk sibling protocols have characterized the developmental profiles of toddlers with ASD in the 1 and 2-year age range. It remains unclear whether children identified before age two evidence more concerning clinical profiles (e.g., lower cognitive abilities, severe impairments of adaptive functioning, higher levels of ASD symptoms) than children identified at later ages. Understanding such differences has implications for programs targeting universal screening and very early diagnosis.

Objectives: This project explored the developmental profiles of toddlers diagnosed with ASD in the 2^nd year of life in comparison to children diagnosed in the 3^rd year of life in a well-characterized university clinical research database. We examined whether younger children evidenced profiles of more significant delays and impairments.

Methods: Participants included children seen through university-affiliated developmental clinics as well as children participating in a variety of research protocols (e.g., genetic collections, infant sibling studies, intervention protocols). 488 children below the age of 36 months (n = 63 <24 months; n = 425 between 24 and 35 months) were included in the sample. All children were newly diagnosed with ASD. Diagnostic measures included the MSEL, ADOS, and VABS. Child demographics including gender, rural/urban setting, and sibling status via caregiver report were also utilized. 

Results: A series of preliminary independent samples t-tests were conducted to compare differences in developmental profiles for children below 24 months of age and children between 24-35 months of age. There was a statistically significant difference in overall performance of the MSEL composite for children with ASD diagnosed before 24 months of age (M = 61.4, SD = 13.1) compared to those diagnosed between 24-35 months of age (M =57.7, SD =14.8) scores, t(475) = 2.00,  p <.05. No differences were obtained for the VABS Composite scores; however, differences were observed within the VABS Socialization domain between the below 24 months group (M = 73.4, SD = 6.42) and the 24-35 months group (M = 68.8, SD = 8.43), t(471) = 2.31,  p <.05. No differences were observed in ADOS Comparison scores between the two groups.

Conclusions: Preliminary results suggest that children identified before 24 months of age do not evidence patterns of more pronounced delay than children diagnosed after two.  In fact, children identified before 2 demonstrated higher cognitive and adaptive behavior scores. This finding suggests that early identification efforts aimed at identifying very young children are not simply identifying children with more severe delays.