Date of Award

Summer 2023

Document Type

Open Access Dissertation



First Advisor

Jane Roberts


Fragile X syndrome (FXS) is a monogenic neurodevelopmental disorder characterized by elevated rates of intellectual disability, autism, and anxiety. Social anxiety affects approximately 60 percent of individuals with FXS and is cited as one of the most impairing comorbid disorders in FXS; however, little is understood about the developmental patterns of social anxiety markers in young children with FXS. The current study investigates cardiac and behavioral markers of social anxiety across the first five years of life and tests the predictive utility of these variables on social anxiety symptomatology. Participants included 80 children with FXS and 50 neurotypical controls. Participants were tested multiple times between 3 and 60 months of age, resulting in 417 observations. Cardiac indices were measured at baseline and in response to a novel person. Behavioral measures were measured via parent report and direct observation. Our findings reflect complex relationships among and between physiological and behavioral indices of later-emerging social anxiety across early development in FXS. Results demonstrated that social behavioral inhibition was related to autonomic nervous system functioning in both groups. Additionally, baseline RSA was lower, and parent-reported social behavioral inhibition was higher by the third year of life in the FXS group compared to controls. The initial level and increasing rate of parent-reported social behavioral inhibition across age predicted social anxiety symptoms at preschool age. In contrast, RSA reactivity to a social challenge did not differ across groups and was not a predictor of social anxiety symptoms. These findings have important clinical implications suggesting that early and repeated measurement of behavioral inhibition may aid in identifying social anxiety in young children with FXS as it has for neurotypical children. Given the elevated rate of social anxiety and its negative effect on the quality of life for children and adults with FXS, early identification and treatment of initial symptoms could result in the prevention of social anxiety later in life or reduced symptom severity.


© 2023, Conner James Black