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Respiratory Sinus Arrhythmia Predicts Fear Longitudinally in Infants and Children with FXS, ASD, and Typical Development
Fragile X syndrome (FXS) is a neurodevelopmental disorder characterized by intellectual disability, inattention, and increased likelihood of maladaptive behaviors (Bailey et al., 2008). Further, it is the most common genetic cause of autism spectrum disorder (ASD; Cohen et al., 2005). Both FXS and ASD have high rates of comorbid anxiety disorders which often are not diagnosed until later in life (Cordeiro et al., 2010; Kessler et al., 2005). However, prodromal signs of anxiety can be observed in infants and young children across typical and atypical development. In typically developing (TD) children, atypical respiratory sinus arrhythmia (RSA), an index of parasympathetic nervous system function, and elevated fear are known to predict later anxiety (Viana et al., 2017). The relationship between early RSA and fear has not been examined in young children with FXS or ASD despite the high risk for anxiety in both groups.
Objectives:
The objective of the current study is to examine whether baseline RSA predicts fear across infancy and early childhood in FXS and ASD as well as TD controls. Further, we aim to determine whether the relationship between RSA and fear is different across groups.
Methods:
Participants included 36 children with FXS (10 [27.8%] female), 28 children with ASD (2 [6.9%] female), and 37 TD children (7 [18.9%] female). Participants were tested several times between 4 and 117 months of age, for a total of 276 observations (FXS n=116; ASD n=29; TDn=131). Baseline RSA was extracted using CardioBatch (University of Illinois at Chicago). Fear was measured via parent-report temperament questionnaires; specifically, the Fear subscales from the Infant Behavior Questionnaire-Revised (<18 months), Early Childhood Behavior Questionnaire (18-36 months), and the Childhood Behavior Questionnaire (>36 months) (Gartstein & Rothbart, 2003; Putnam, Gartstein, & Rothbart, 2006; Rothbart, et al., 2001; respectively).
Results: Univariate analysis of covariance controlling for age and sex revealed no difference between groups for fear (F(1,276) = 0.249, p = .780) and baseline RSA (F(1,276) = 2.187, p = .114). To examine the relationship between RSA and fear across early childhood, a linear mixed model was employed with baseline RSA, age, group, and an RSA by group interaction entered as predictors of fear. There were significant main effects of age (F(1,271) = 14.386, B= -0.014, p < .001) and baseline RSA (F(1,271) = 7.975, B= -0.23, p = .005). The main effect of group (F(1,271) = 3.516, B = -0.839, p = .062) and the interaction of group by RSA (F(1,171) = 2.888, B= 0.137,p = .090) were both non-significant.
Conclusions: Results indicate that higher baseline RSA is related to lower fear across all groups, suggesting that the physiological mechanisms associated with fear may be similar across typical and atypical development. Early physiological dysregulation and temperamental fear are risk markers for later anxiety in TD children, so interventions targeting the physiological dysregulation and/or temperamental fear may be effective in prevention. Given similar relationships between physiology and fear across groups, interventions known to be effective in TD groups could potentially be applied to both FXS and ASD.