Developmental Trajectories of Repetitive Behaviors in Preschoolers with and without Autism
Objectives: 1) Characterize trajectories of repetitive behavior from ages 12 to 36-48 months in infant siblings at high familial risk for ASD and a low-risk control sample; and 2) examine repetitive behavior trajectories in relation to key cognitive and behavioral outcomes.
Methods: Prospective, longitudinal parent-report repetitive behavior data (RBS-R; Repetitive Behavior Scale - Revised) were collected for 202 toddlers at high-risk for ASD and 53 low-risk controls (LR-Neg) at 12, 24, and 36 months of age. Fifty-two high-risk toddlers were classified with ASD at age 36 months based on clinical best estimate (HR-ASD). Longitudinal profiles of RRB across 5 subtypes were compared using generalized estimating equations. Relations of RRB to key cognitive and behavioral variables (i.e. IQ, adaptive behavior, and ASD symptom severity) were examined using nonparametric correlations.
Results: Longitudinal profiles for children with ASD differed significantly between groups on RBS-R composite and all subtype measures of repetitive behavior, p ≤ .001. The HR-ASD group showed significantly higher rates of repetitive behavior across all RRB subtypes at the 12 month time point, with trajectories significantly diverging thereafter. Groups markedly differed across RRB subtypes by preschool age, with ritualistic and sameness behaviors showing the most dramatic change over time. Trajectories for high-risk children without ASD (HR-Neg) were intermediate to low-risk and ASD positive counterparts. Intercept, but not slope, of composite RBS-R scores were significantly associated with social skills (F = 28.1, p < .001) and communication scores (F = 17.3, p < .001) at age 36-48 months. Consistent with findings from age 24 months, RRBs were not associated with motor ability (F = 3.6, p = .06) or overall IQ (F = 3.8, p = .051).
Conclusions: These results build upon previous findings by demonstrating that subtypes of RRB develop in dynamic fashion over early childhood. For those diagnosed with ASD at age 36 months, RRBs were elevated at age 12 months, with developmental trajectories diverging sharply from non-ASD groups thereafter. These results further suggest that higher rates of RRB reported in preschoolers with ASD may be preceded by subtle but steady changes in behavior from later infancy and early toddlerhood.
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