Disaggregating Core Feature Domains in 12-Month-Old Infants at High Likelihood for Developing Autism Spectrum Disorder

Objective: Behavioral traits that define autism spectrum disorder (ASD) map onto two primary symptom domains: social communication (SC) and restricted and repetitive behavior (RRB). This study assessed the psychometrics and utility of disaggregating the Autism Observation Scale for Infants (AOSI) into SC and RRB+ (RRB plus other relevant infant behavior) subscores for 12-month-old infants. Methods: We analyzed data from the 12-month visit of two cohorts of the Infant Brain Imaging Study (IBIS): IBIS (N = 387, 40% female, mean age = 12.6 months [range 11.4 to 15.9 months]) and IBIS-Early Prediction (IBIS-EP; N = 152, 51% female, mean age = 12.7 months [range 11.2 to 14.3 months]). Confirmatory factor analyses (CFAs) evaluated the psychometric fit of disaggregating SC and RRB+ subscores. Regression analyses were used to determine convergent and discriminant validity, leveraging parent-report measures as well as structural brain development data derived from MRI.Results: CFAs supported a two-factor model of the AOSI. The SC and RRB+ subscores showed convergent and discriminant validity with concurrent parent report measures. The SC subscore – not the RRB+ subscore or overall AOSI score – correlated with amygdala volume at 12 months and amygdala growth from 6 to 12 months. Conclusion: The presence of separable SC and RRB+ domains in the AOSI was supported by the analyses. The disaggregation of domains also allowed for detection of a brain-behavior association that was obscured when considering only overall AOSI score. These findings underscore the importance of taking a multi-domain approach to measures of ASD-related behavioral traits in infancy.