Emergence of Social Deficits During the Second Year of Life in Infants with ASD

Background:  By 24 months, children with autism spectrum disorder (ASD) have marked social deficits in initiating interactions and responding to bids for attention. These impairments and their precursors have been seen in infants as young as 12 months, with recent prospective studies showing that infants later diagnosed with ASD often have deficits in eye contact, responding to their name, showing, imitating, and engaging in play-based activities (Landa, 2007; Macari, 2012; Nadig, 2007; Rozga, 2011).  However, further research is needed to explore the emergence and progression of these social deficits within the second year for infants later diagnosed with ASD, with atypical features and delays (ATYP) and typically developing children (TD).

Objectives:  1) To compare specific social deficits at 12, 18, and 24 months in infants later diagnosed with ASD, ATYP, and TD;  2) To explore when these deficits emerge as unique characteristics of ASD.

Methods:  105 infants at high (n=64) and low (n=41) risk for ASD were assessed at 12, 18, and 24 months using the ADOS–Toddler Module. Children were assigned a clinical best estimate diagnosis of ASD (n= 18), ATYP (n=32) or TD (n=55) at 36 months. Social behaviors were quantified based on 4 ADOS items: Level of Engagement (B17), Response to Name (B7), Ignore (B8), and Showing (B12). The items were recoded into 0/1 categories with 0 denoting robust social behavior and 1 capturing any atypicalities or deficits. Chi-squared analyses identified significant group differences at each time point.

Results:  Level of engagement exhibited by the toddlers with ASD was significantly limited compared to the TD toddlers at all three time points: 12 months (p=.022), 18 months (p<.001), 24 months (p<.001) and compared to the ATYP toddlers at 18 (p=.027) and 24 months (p=.001).  The toddlers with ASD responded significantly less to their name than their ATYP (p=.024) and TD (p=.002) peers at 18 months and their TD peers at 24 months (p=.042). There was also a marginally significant difference at 12 months (ASD to TD: p=.057).  The toddlers with ASD were less likely to request a bid for attention when ignored than the ATYP and TD groups at 24 months (ATYP: p=.004, TD: p<.001). Both the ASD and ATYP groups engaged in significantly less showing than the TD group at 12 months (ASD: p=.014, ATYP: p=.011).  By 18 and 24 months, the toddlers with ASD showed significantly less than both the ATYP and TD groups (all significant at p<.01).

Conclusions:  Marked deficits in level of engagement, showing and response to name uniquely characterized the ASD group at 18 months.  Inconsistent patterns of group differences at 12 months reflect both heterogeneity in onset of ASD symptoms and variability in the skills of the infants in the ATYP group. By 18 months, however, toddlers with ASD presented with clear deficits in these critical social behaviors and seem to plateau developmentally, while their peers with delays experienced gains in these areas.  The group differences emerging between 12 and 18 months suggest a critical period for developing important social behaviors.