Physiological Responses to Social and Object Fear in Children with Autism Spectrum Disorder and Fragile X Syndrome

Background: Children with autism spectrum disorder (ASD) and children with fragile X syndrome (FXS) are often diagnosed with comorbid anxiety. Anxiety is associated with long-term impairment; however, with early intervention, anxiety symptomology can be mitigated. Increased fear during novel social situations is associated with later social anxiety, whereas heightened fear to novel or frightening objects could be linked to specific phobia or generalized anxiety later in development. Previous research has shown that children with anxiety also have atypical physiological regulation (e.g., respiratory sinus arrhythmia, RSA), exhibiting less suppression of RSA during challenge tasks. No studies have compared physiological responses to social and object fear-inducing stimuli in children with ASD and FXS.

Objectives: The current study uses RSA to evaluate group differences between children with ASD, FXS, and typically developing (TD) controls during presses meant to evoke social fear (i.e., fear in response to a novel person) and object fear (i.e., fear in response to a novel object). Additionally, the study investigates the relationship between RSA and ASD and anxiety symptom severity.

Methods: Participants included 81 males between the ages of 3 and 6 years old: 29 ASD (chronological age M = 45.57, SD = 8.92), 26 FXS (chronological age M = 50.93, SD = 11.66), and 26 TD (chronological age M = 47.52, SD = 13.29). RSA was measured during a baseline period as well as during the Stranger Approach and Scary Spider presses of the Laboratory Temperament Assessment Battery (Lab-TAB). RSA suppression was calculated by subtracting RSA during the Stranger or Spider press from RSA during the baseline period. ASD symptom severity was assessed using the Autism Diagnostic Observation Schedule (ADOS-2). Parent-reported anxiety was determined using the Anxiety Depression and Mood Scale (ADAMS). Cognitive abilities were measured using the Early Learning Composite (ELC) of the Mullen Scales of Early Learning (MSEL).

Results: Analyses of covariance (ANCOVA, covarying for chronological age) with Bonferroni-adjusted post-hoc comparisons were used to determine group differences in RSA suppression for both tasks. For the Stranger Approach press, a main effect of group emerged, F(2,75) = 3.51, p = .035, in that TD children displayed greater RSA suppression than children with ASD, p = .045. The effect of group was non-significant for the Scary Spider press, F(2,76) = 0.05, p = .956. RSA suppression during the Stranger Approach press was correlated with ASD severity scores on the ADOS-2, r = -0.31, p = .007. Mullen ELC scores significantly differed between TD children and children with ASD and FXS, F(2,73) = 83.71, p = .00; however, scores did not significantly differ between the children with ASD and FXS, p = .403.

Conclusions: Results indicate that TD children exhibit greater RSA suppression than children with ASD during challenges involving social, but not non-social fear. However, correlations suggest that blunted RSA suppression is related to ASD symptomology rather than anxiety. Future work should explore the relationship between physiological risk markers and behavior as well as investigate other biomarkers.