LATENT STRUCTURE AND BEHAVIOURAL HETEROGENEITY OF RESTRICTED AND REPETITIVE BEHAVIOURS IN AUTISM USING ORDINAL ADI-R DATA

Autism Spectrum Disorder (ASD) is a neurodevelopmental condition characterised by social and communication differences alongside restricted and repetitive behaviours (RRBs). RRBs are a core domain consisting of a range of cognitive and motoric features. Despite their clinical relevance, the underlying mechanisms and genetic underpinnings of these behaviours remain incompletely understood. Based on prior evidence suggesting two broad RRB domains, this study aimed to identify the latent structure of RRBs using behavioural data extracted from the Autism Genetic Resource Exchange (AGRE). Eight subscales from the Autism Diagnostic Interview-Revised (ADI-R) containing RRBs were analysed in 2636 ASD-affected individuals. Descriptive statistics and non-parametric analyses assessed ranked severity across ordinal subscales (scored 0-3). Friedman tests were used to assess differences across subscales, and Spearman correlation analysis was used to measure interrelationships between subscales. Exploratory and confirmatory factor analysis (EFA/CFA) was used to examine latent dimensions, and subgroup identification was completed using latent class analysis (LCA). Subscales differed significantly in ranked severity (Friedman p < 0.001) and showed modest positive intercorrelations (ρ ≈ 0.1–0.3). EFA supported two domains consistent with cognitive rigidity and motoric/object-focused behaviours, which were confirmed by CFA. LCA identified four behavioural profiles, including mild, high global RRB, motor-focused, and intermediate presentations. Together, these findings demonstrate the heterogeneous and multidimensional nature of RRBs in ASD and support a reproducible two-domain model. This behavioural stratification framework may improve interpretability and power in future genotype–phenotype analyses of RRB variation.