Development of Restricted and Repetitive Behaviors from 2-19: Stability and Change in Repetitive Sensorimotor, Insistence on Sameness, and Verbal Behaviors in a Longitudinal Study of Autism.

This study examined trajectories of repetitive sensorimotor (RSM), insistence on sameness (IS), and verbal RRBs from ages 2-19 in a well-characterized longitudinal cohort. We also tested the factor structure of the ADI-R restricted and repetitive behavior (RRB) domain at age 19 and the inclusion of a verbal RRBs factor, in addition to previously identified RSM and IS factors, at ages 9 and 19. The ADI-R was administered to 193 participants at five timepoints from 2 to 19. Confirmatory factor analysis (CFA) was used to examine the factor structure of ADI-R RRB data. Change in RRB subtypes was examined using group-based trajectory modeling and multilevel modeling. RSM and IS behaviors generally decreased from 2 to 19, with some participants experiencing increases from ages 2-9. 46.46% of participants experienced increasing verbal RRBs from 2 to 9, followed by a plateau from 9 to 19. The remaining participants had few to no verbal RRBs throughout development. Multilevel modeling indicated ADOS CSS scores were associated with change in RSM trajectories only. Child IQ was not associated with change in any RRB trajectories. CFA indicated previously-derived RSM and IS factors fit age 19 ADI-R data well. The inclusion of a third factor, verbal RRBs, worsened goodness-of-fit statistics and was ultimately omitted. Our findings suggest the RRB factor structure of the ADI remains consistent into early adulthood and illustrate developmental continuity and change in RRBs. For autistic individuals with fluent speech, RRB presentation may be influenced by verbal ability in ways that are highly variable, but clinically meaningful.