To plot longitudinal trajectories of autism spectrum disorder (ASD) severity from early childhood to early adolescence. In line with reported trajectories in toddlers, we hypothesize that a substantial minority of children will show marked changes in ASD severity over time, with “Improvers” demonstrating the highest mean baseline and rate of growth in verbal IQ (VIQ).
Patients included 345 clinic referrals and research participants with best-estimate clinical diagnoses of ASD at 1 or more time points, and repeated Autism Diagnostic Observation Schedule (ADOS), VIQ, and nonverbal IQ scores. Standardized ADOS severity scores were applied to 1026 assessments collected longitudinally between the ages of 2 and 15 (VIQ at most recent assessment: mean = 58, SD = 35). Scores were fitted for latent severity trajectory classes with and without covariates. Adaptive behavior and VIQ trajectories over time were modeled within each of the best-fit latent classes.
A 4-class model best represented the observed data. Over 80% of participants were assigned to persistent (stable) high or moderately severe classes; 2 small classes respectively increased or decreased in severity over time. Age, gender, race, and nonverbal IQ did not predict class membership; VIQ was a significant predictor. Baseline VIQ was highest in the improving and worsening classes; it increased at the greatest rate in the improving class. Adaptive behavior declined in all but the improving class, with consistent impairment in all classes.
If replicated, identified trajectory classes of ADOS severity may contribute to clinical prognosis and to subtyping samples for neurobiological and genetic research.