A Longitudinal Analysis of Early Social Anxiety Risk Factors in Siblings of Children with Autism Spectrum Disorder

Background: Siblings (ASIBs) of children with autism spectrum disorder (ASD) are at elevated risk for a variety of suboptimal developmental outcomes, including anxiety disorders. Childhood anxiety can have detrimental long-term effects that carry into adulthood and impact quality of life. However, early intervention for anxiety has been shown to ameliorate these long-term impacts. In neurotypical (NT) infants and toddlers, several early risk markers for social anxiety have been identified. These include high and stable expression of behavioral inhibition, a temperament profile characterized by excessive fear in response to novelty, and reduced physiological reactivity, as indexed by blunted respiratory sinus arrhythmia (RSA) responses. Identifying early risk markers of social anxiety in ASIBs can provide important insight into the emergence and trajectories of prodromal anxiety features in this high-risk population.

Objectives: To examine the developmental trajectory of early social anxiety risk markers in non-ASD ASIBs and low-risk controls (LRCs) in the first two years of life.

Methods: Participants included 32 later-born siblings of children with ASD who were not diagnosed themselves with ASD at >=24 months (non-ASD ASIBs) utilizing standard clinical best estimate procedures including the ADOS-2. Low-risk controls (n=42) with no personal or family history of ASD or related disorders were included. Participants were assessed at several timepoints from 7 to 28 months of age, for a total of 214 observations (ASIB: n = 90; LRC: n = 124) Behavioral inhibition was measured via the Fear subscales from the IBQ-R (< 18 months) and ECBQ (>=18 months) (Gartstein & Rothbart, 2003; Putnam, Gartstein, & Rothbart, 2006). Physiological reactivity was measured through heart activity recorded during a baseline period and the Stranger Approach paradigm (Goldsmith & Rothbart, 1996), which is designed to elicit behavioral inhibition in response to a novel adult. Reactivity was defined as Baseline RSA – Stranger RSA.

Results: Multi-level growth models were employed, with age, group, and age by group interaction entered as predictors. For parent-rated behavioral inhibition, significant main effects of age (b = -0.03, p < .01) and group (b = 0.39, p < .05) were revealed, with a non-significant interaction effect (b = -0.03, p = .11) (Figure 1). For physiological reactivity, the age by group interaction was significant, (b = -0.07, p < .05) (Figure 2), indicating that physiological regulation in ASIBs becomes more blunted with age.

Conclusions: Results suggest that non-ASD ASIBs exhibit elevated behavioral inhibition throughout the first two years of life, though by the age of 2, they are approaching normative levels. Conversely, physiological reactivity in response to a novel stranger becomes more atypical as non-ASD ASIBs age. These patterns of behavioral inhibition and blunted physiological reactivity are early risk markers for social anxiety in neurotypical infants. Thus, it appears that even ASIBs without ASD themselves are showing atypical social responsivity and may be at elevated risk for later social anxiety symptoms and diagnoses.