Development of Restricted and Repetitive Behaviors from 2-19 and Internalizing Symptom Outcomes in a Longitudinal Study of Autism

Using data from a well-characterized longitudinal cohort, this study examined trajectories of restricted and repetitive behaviors (RRBs), specifically repetitive sensorimotor (RSM), insistence on sameness (IS), and verbal RRBs, as measured by the Autism Diagnostic Interview, Revised (ADI-R) from ages 2 to 19. Additionally, this study investigated relationships between RSM and IS trajectories and parent- and self-report depression and anxiety symptoms in early adulthood. Group-based trajectory modeling and multilevel modeling were used to investigate change in RRB subtypes. RSM and IS behaviors generally decreased from 2 to 19, though some participants experienced increases in these RRB subtypes from ages 2 to 9. 65% of this sample had sufficient verbal ability prior to age 19 to calculate trajectories of verbal RRBs. Of this subset, 49% had few to no verbal RRBs throughout development; in contrast, the remaining 51% experienced increasing verbal RRBs from 2 to 9, followed by a plateau in verbal RRBs from 9-19. Higher ADOS Social Affect (SA) CSS scores in early childhood were linked with more RSM symptoms across development, but not related to the IS and Verbal trajectories. Non-verbal IQ from early childhood was not connected to change in any of the identified RRB trajectories. There were no associations between IS trajectories and internalizing symptom in early adulthood. However, preliminary data suggests that a Moderate-Decreasing pattern of RSM development may be linked to anxiety in early adulthood. These findings illustrate continuity and change in a core ASD symptom domain, RRBs, from early childhood to early adulthood.