Related Experiment Video
Updated: May 23, 2026
TMS: Using the Theta-Burst Protocol to Explore Mechanism of Plasticity in Individuals with Fragile X Syndrome and Autism
Published on: December 28, 2010
Heart activity and autistic behavior in infants and toddlers with fragile X syndrome
Jane E Roberts1, Bridgette Tonnsen, Ashley Robinson
1University of South Carolina.
Insights
Infants with fragile X syndrome exhibit atypical physiological arousal, including shorter interbeat intervals (IBIs) and lower vagal tone (VT). These early physiological markers predict later autism severity in fragile X syndrome.
Area of Science:
- Neurodevelopmental disorders
- Autism Spectrum Disorder research
- Pediatric physiology
Background:
- Fragile X syndrome (FXS) is a genetic disorder associated with intellectual disability and increased risk for autism spectrum disorder (ASD).
- Early identification of ASD in FXS is crucial for timely intervention.
- Understanding the developmental trajectory of physiological regulation in young children with FXS is essential.
Purpose of the Study:
- To compare physiological arousal in infants and toddlers with FXS to typically developing controls.
- To investigate early physiological predictors of later autism severity in FXS.
- To explore the relationship between physiological measures and autistic behaviors in young children with FXS.
Main Methods:
- Included 31 males with FXS (8-40 months) and 25 age-matched controls.
- Assessed physiological arousal using interbeat intervals (IBIs) and vagal tone (VT).
- Examined linear and nonlinear associations between physiological measures and autism severity.
Main Results:
- Infants and toddlers with FXS demonstrated shorter IBIs, lower VT, and reduced IBI modulation compared to controls.
- A nonlinear relationship was observed between IBI and autistic behavior.
- A linear relationship emerged between VT and autistic behavior, indicating VT predicts autism severity.
Conclusions:
- Atypical physiological arousal is present early in development in children with FXS.
- Early physiological measures, particularly vagal tone, can predict the severity of autistic behaviors.
- These findings highlight the complex interplay between physiological regulation, brain function, and behavioral outcomes in FXS, informing early identification and intervention strategies.
Abstract:
The present study contrasted physiological arousal in infants and toddlers with fragile X syndrome to typically developing control participants and examined physiological predictors early in development to autism severity later in development in fragile X syndrome. Thirty-one males with fragile X syndrome (ages 8-40 months) and 25 age-matched control participants were included. The group with fragile X syndrome showed shorter interbeat intervals (IBIs), lower vagal tone (VT), and less modulation of IBI. Data suggested a nonlinear effect with IBI and autistic behavior; however, a linear effect with VT and autistic behavior emerged. These findings suggest that atypical physiological arousal emerges within the first year and predicts severity of autistic behavior in fragile X syndrome. These relationships are complex and dynamic, likely reflecting endogenous factors assumed to reflect atypical brain function secondary to reduced fragile X mental retardation protein. This research has important implications for the early identification and treatment of autistic behaviors in young children with fragile X syndrome.
