Quantitative Analysis of Language Development in Autism Spectrum Disorder and Related Genetic Disorders

Developmental delay is characterized by a lag in attainment of developmental milestones, while developmental d(fference, sometimes called developmental deviance, refers to nonsequential acquisition of skills within a developmental domain. Developmental difference has been associated with autism spectrum disorder (ASD), particularly in skills obtained throughout language development. This has primarily been evaluated through qualitative observations of atypical traits such as echolalia, jargon, and other semantic and syntactic error patterns that do not fit the classic model of developmental delay. Developmental difference in other domains such as cognition, motor skills, or reading development remains largely unexplored. In clinical practice, standard scoring metrics on standardized psychometric assessments are primarily intended to identify developmental delay and not designed to capture inconsistencies in response patterns, known as within-task variability, that are indicative of developmental difference. In 2019, Hare-Harris et al. published the first study of its kind to use a quantitative metric, the Response Dispersion Index (ROI), to capture within-task variability on standardized language assessments administered to individuals with ASD. The ROI demonstrated an increase in within-task variability among individuals with ASD, was correlated with severity of ASD-associated traits, and was a robust predictor of ASD diagnostic status. In this thesis, we replicated the results of this pilot study and expanded our evaluation of developmental difference to a similar developmental domain: reading development. Our findings further validate the utility of the ROI as a measure of within-task variability and a significant predictor of ASD diagnosis in both language and reading development. In addition, we provide rationale for further investigation of developmental difference in genetic disorders related to ASD. We believe the results of the following studies have implications for personalized interventions in ASD, and set precedent for larger scale replication of these analyses in individuals with ASD and related genetic disorders across language, reading, and other developmental domains.