Emerging Patterns of Repetitive Behavior Linked to Clinical and Behavioral Outcomes in High-Risk Infant Siblings

Background: Restricted and repetitive behaviors associated with autism spectrum disorder (ASD) were once believed to manifest after core social-communication symptoms. However, recent evidence suggests that such behaviors may be early manifestations of the disorder, emerging during a prodromal period in qualitatively different fashion than similar behaviors associated with typical development. How different forms of repetitive behaviors unfold during this early interval, particularly among toddlers at high familial risk for ASD, remains unclear.

Objectives: 1) Characterize early longitudinal profiles of repetitive behavior in a large, prospective study of infants at high familial risk for ASD (by virtue of having an older sibling with the disorder) and low-risk controls; and 2) Examine how early repetitive behaviors relate to key cognitive and behavioral outcomes.

Methods: Prospective, longitudinal parent-report repetitive behavior data (Repetitive Behavior Scales-Revised) were collected for 184 toddlers at high-risk for ASD and 59 low-risk controls at 12 and 24 months of age. Forty-two high-risk toddlers were classified with ASD at age 2 based on clinical best estimate by experienced, licensed clinicians. Longitudinal profiles of repetitive behavior across 5 subtypes were compared between groups using generalized estimating equations. The relationship of repetitive behaviors to cognitive and behavioral variables (e.g. ratio IQ, adaptive behavior, 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 < .0001. High-risk toddlers without ASD were intermediate to low-risk and ASD positive counterparts. Cross-sectionally, toddlers who went on to meet diagnostic criteria for ASD showed significantly higher rates of repetitive behavior across repetitive behavior subtypes at the 12 month time point. Repetitive behaviors at 12 months predicted social communication scores and symptom severity at 24 months, and 12-month-olds with 3 or more forms of repetitive behavior were at four-fold risk for meeting diagnostic criteria at age 2. In children with ASD, repetitive behaviors were significantly negatively correlated with adaptive socialization scores. In contrast to findings from studies of older children with ASD, repetitive behaviors were unrelated to general cognitive ability in our sample of toddlers. 

Conclusions: These findings suggest that as early as 12 months age, a broad range of repetitive behaviors are highly elevated in children who go on to develop ASD relative to both low-risk children and, importantly, high-risk counterparts who do not develop the disorder. While some degree of repetitive behavior is expected in typical early development, the nature and extent of these behaviors among toddlers who develop ASD appears highly atypical.