This research study “Emergence, Stability and Predictors of Anxiety in Fragile X Syndrome” is the first longitudinal developmental study of early features and predictors of anxiety in individuals with Fragile X Syndrome (FXS) as contrasted to individuals with Autism Spectrum Disorder (ASD) and intellectual disabilities in addition to typically developing individuals.  One intent of the study is to identify mechanistic factors underlying anxiety etiology in subgroups which have increased risk for anxiety. The need for in depth analysis of early indicators is critical, for co-morbidity of anxiety in persons with intellectual disabilities reduces function across multiple domains.  Our emphasis is on the trajectory of anxiety symptomology on a continuum, which reflects both behaviors (rating scales, eye tracking, direct observation) and biomarkers (heart activity, cortisol) to highlight the diverse aspects of anxiety as a composite. Furthermore, we will Identify the predictors of anxiety symptoms in 3-to-5-year-old boys with FXS by analyzing developmental level, ASD symptom severity, ADHD and externalizing symptomology as well as genetic and environmental factors such as FMR1 protein, maternal anxiety, mood disorders, and parenting stress. The results from this study will expand knowledge in the field of developmental psychology for populations with increased risk for psychiatric disorders, and will highlight the interaction of genetic and environmental factors that influence mental health and treatment.  Our findings have the potential to assist individuals with psychiatric disorders to predict and seek interventions which could aide in putting them on a trajectory leading to better health and wellbeing. The study is also led by Co- Investigator, Kim Hills and Co- Investigator Amanda Fairchild, both of the University of South Carolina.