Author

Erin Hunt

Date of Award

Spring 2022

Document Type

Open Access Thesis

Department

Psychology

First Advisor

Jane Roberts

Abstract

Inhibitory control (IC), the ability to suppress inappropriate responses, emerges late in the first year of life and improves across typical development, concurrent with brain maturation. The development of IC is critical to various social-emotional and behavioral functions, with IC deficits being linked to numerous psychiatric conditions, including attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). Fragile X syndrome (FXS) is a single-gene disorder characterized by IC deficits, and elevated rates of ADHD and ASD, making it a useful model for understanding the early development and consequences of IC. In this longitudinal study, we characterized IC trajectories across multiple time points between 16 and 71 months of age in young males with FXS (n=80) relative to neurotypical controls (n=49). To explore the association between psychiatric features and IC, we identified a subsample of 48 children with longitudinal IC data and an outcome assessment for ADHD and ASD symptoms at age 5 (FXS: n=26, neurotypical: n=22). Results indicated that, compared to their neurotypical peers, young males with FXS exhibit IC deficits as early as 18 months, with group differences increasing through age 5. Additionally, we determined that lower IC levels at 18 months were associated with later ADHD symptoms and attenuated growth in IC over time was associated with later ASD symptoms in male children with FXS. These findings help refine early developmental phenotypes of FXS and highlight IC as a potential target for early detection and intervention of ASD and ADHD symptoms in male children with FXS.

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