Examining Underlying Mechanisms of Emotional Regulation in Toddlers with Fragile X Syndrome

Background: Frustration, an emotional response to the interruption of a task or the blocking of a goal, begins to develop during infancy. An individual’s ability to react to and recover from frustrating situations is mediated by behavioral and physiological responses to emotional arousal via the autonomic nervous system. An inability to effectively regulate responses to frustration during infancy has been associated with later behavioral problems, anxiety, and attentional difficulties. Children with fragile X syndrome (FXS), a neurodevelopmental disorder associated with autism, often exhibit atypical autonomic regulation as well as anxiety, ADHD, and challenging behaviors.

Objectives: This longitudinal study aimed to investigate frustration regulation in toddlers with FXS and typically-developing (TD) toddlers between the ages of 12 and 36 months. Furthermore, the study investigated the relationship between frustration regulation and autism symptom severity at 36 months.

Methods: Participants included 136 toddlers assessed at 12, 24, and 36 months (FXS: n = 84, Mage = 27.81; TD: n = 52, Mage = 24.95), for a total of 240 observations. Physiological responses to a frustration-inducing task were evaluated by measuring respiratory sinus arrhythmia (RSA) during the Arm Restraint or End of the Line paradigm of the Laboratory Temperament Assessment Battery. Both paradigms consisted of three conditions: baseline (toy play), frustration reactivity (toy retraction), and frustration recovery (toy return). Parent-reported frustration reactivity and frustration recovery were assessed using age-appropriate Rothbart temperament questionnaires. Furthermore, autism symptom severity was calculated using the Autism Diagnostic Observation Schedule – Second Edition calibrated severity score (ADOS-2 CSS).

Results: Linear mixed models employed to investigate how physiological regulation changes across age revealed a significant main effect of age, F(2, 59) = 7.50, p = .001, and a marginally significant effect of condition, F(2, 129) = 2.53, p = .083. The main effect of group and the interaction effects were non-significant, Fs < 1.45, ps > .238. For parent-reported frustration reactivity, the main effect of age was significant, F(1, 82) = 18.47, p < 0.001. No main effect of group or group-by-age interaction was observed, Fs(1, 82) < 2.83, ps > 0.10. For parent-reported frustration recovery, the main effect of group, F(1, 125) = 14.33, p < .001, and age, F(1, 86) = 6.92, p = .010, were significant, whereas the group-by-age interaction was marginally significant, F(1, 86) = 3.48, p = .065. Pearson correlations were conducted to assess the relation of reactivity and recovery to ADOS-2 CSS at 36 months. Parent-reported frustration recovery correlated with ADOS-2 CSS, r = -0.61, p < 0.001, and RSA suppression, r = -0.58, p = 0.003. No other significant correlations were found.

Conclusions: Findings indicate that toddlers with FXS and TD toddlers show similar changes in physiological regulation in response to frustration between 12 and 36 months. However, parents of toddlers with FXS reported poorer frustration recovery than parents of TD toddlers. Furthermore, at 36 months, poorer parent-reported frustration recovery was associated with higher autism symptom severity and attenuated physiological reactivity, suggesting a link between ASD features and difficulties with frustration regulation in FXS.