Date of Award

Summer 2021

Document Type

Open Access Dissertation



First Advisor

Jane Roberts


Autism spectrum disorder (ASD) is a highly prevalent neurodevelopmental disorder characterized by the presence of social-communication deficits and restricted and repetitive interests and behaviors (American Psychiatric Association, 2013b; Baio et al., 2018). It is characterized by high genotypic and phenotypic heterogeneity, which complicates both diagnosis and treatment efforts (Jeste & Geschwind, 2014; Kim, Macari, Koller, & Chawarska, 2016). Well-studied sources of heterogeneity in ASD include age, sex, intellectual ability, temperament, physiological arousal, social attention, and the presence of genetic syndromes that are highly penetrant with ASD (Campbell, Shic, Macari, & Chawarska, 2014; Harris et al., 2008; Klusek, Roberts, & Losh, 2015; Macari, Koller, Campbell, & Chawarska, 2017).

Symptoms of ASD can resemble those of other diagnoses, especially social anxiety and intellectual disability (ID; Kerns & Kendall, 2012; Roberts et al., 2018; Thurm, Farmer, Salzman, Lord, & Bishop, 2019). These phenotypic overlaps greatly complicate the diagnostic process in children with neurodevelopmental disorders. As a result, researchers have begun to use biobehavioral measurement markers to support the differentiation of social anxiety and ASD in children with neurodevelopmental disorders. A biobehavioral framework integrates behavioral observations and biological data as indicators of complex characteristics or processes. By so doing, it has the potential to supplement current diagnostic procedures by providing quantifiable information about a child’s overall functioning that takes into account a variety of developmental systems.

Towards this end, this dissertation employed biobehavioral measurement procedures to inform our understanding of the ASD phenotype across preschoolers with varied genetic risk for ASD and social anxiety.

Although ASD in itself is highly heterogeneous, it can also occur concomitantly with additional disorders and psychological problems. One of the most common genetic disorders associated with ASD is fragile X syndrome (FXS). Fragile X syndrome is a rare monogenic disorder caused by expansions of a CGG repeat on the FMR1 gene (R. Hagerman, Turk, Schneider, & Hagerman, 2014). This mutation leads to an underexpression of fragile X mental retardation protein (FMRP) and results in several associated physical features and psychological characteristics, including ASD symptoms, social anxiety, and intellectual disability (Bailey, Raspa, Olmsted, & Holiday, 2008).

Given the complicated nature of heterogeneity in ASD, robust phenotypic characterization of ASD is critical to adequately assessing the various profiles of this disorder for both diagnostic and treatment purposes. In particular, much work needs to be done to understand which features are potentially indicative of comorbid disorders and which are part of the ASD phenotype. The proposed dissertation furthers our understanding of heterogeneity in ASD through a series of two studies aimed at cataloging phenotypic profiles among children with etiologically distinct (e.g., syndromic versus non-syndromic) risk factors for ASD.

The first study seeks to understand how two biological mechanisms, temperamental negative affect and baseline physiological arousal inform our understanding of ASD and other comorbid clinical symptoms. It addresses the following research questions: how do physiological regulation and temperamental negative affect vi differ in preschoolers with non-syndromic ASD (nsASD), FXS, and typical development (Research Question 1); and do physiological regulation and temperamental negative affect predict ASD symptomology and social anxiety symptoms within all groups (Research Question 2)? The second study aimed to clarify how social attention impairments manifest in nsASD, FXS, and TD and how social attention, a neurally-based biobehavioral process, relates to clinical symptoms. This study asks: how do preschoolers with nsASD, FXS, and typical development differ in their allocation of attention to faces in response to social and non-social scenes? (Research Question 1); and how does attention to faces during social scenes relate to developmental ability, ASD symptom severity, and social anxiety within groups? (Research Question 2)?

Taken together, these studies leverage biobehavioral methods to understand the influence of genetics, biology, and behavior on the presentation of ASD and related comorbidities. Results will address critical gaps in our understanding of the entire spectrum of ASD and have the potential to inform more targeted intervention techniques.