Characterizing Restricted and Repetitive Behaviors: Exploring the Influence of Age on Rrb Phenotype Clusters

Background: Restricted and repetitive behaviors (RRBs) are a complex and heterogeneous phenotype of autism spectrum disorders (ASD). Despite being half of the diagnostic criteria dyad, the relationship between specific RRB subdomains and other individual characteristics such as age remains unclear.

Objectives: The purpose of this study was to explore 1) the factor structure of RRB symptoms 2) identify RRB phenotype clusters in a large sample of youth with autism spectrum disorder and 3) determine if phenotypic clusters differ for children as compared to adolescents.

Methods:  Participants included 2,757 individuals from Simons Simplex Collection, Simons Ancillary and Simons VIP datasets between the ages of 4 and 18 years old (M= 9.2 years) diagnosed with ASD. An exploratory factor analysis (EFA) was conducted to determine the factor structure of the Repetitive Behavior Scale-Revised (RBS-R). After visual inspection of RRB subtypes identified by EFA, participants were dichotomized into two groups - participants 4 to 14 years old and participants 14 to 18 years old. A K-means cluster analysis was run on both age groups to determine RRB phenotype clusters and descriptive statistics were calculated for each group.

Results: The EFA resulted in five RRB subdomains, which included hand/body mannerisms (H/B), self-injurious behaviors (SI), compulsivity (C), rigidity (R), and perseverative interests (PI). Results from the cluster analysis indicated that for both age groups there was a cluster of individuals that had elevated scores in all RRB domains as well as a group who exhibit reduced frequency across all RRB domains. The younger group produced a cluster with elevated compulsivity, rigidity and perseverative behaviors and low levels of self-injury and hand/body mannerisms. Additionally, the remaining cluster endorsed H/B mannerisms the most, with moderate scores of self-injury and perseverative interests, with compulsivity and rigidity having the lowest endorsement. Older participants’ mixed clusters exhibited a pattern of more complex RRBs (perseverative interests, rigidity and compulsivity) manifested comparably across clusters, with the lower RRBs (hand/body mannerisms and self-injury) exhibiting a similar pattern.

Conclusions: The present study shows that a simplified representation of RRB presentation would not account for the incredible variability that exists among individuals with ASD. The cluster differences between age groups implies that RRBs do not manifest in the same way across individuals with ASD; which poses complications when the measurement of RRBs is inconsistent across studies. Further, results suggest that the more complex RRB phenotypes (e.g. perseverative interests) may not be as strongly linked in younger children, as they are in 14-18 year olds. These findings have important implications for future research exploring intervention targets for RRBs. It is possible that interventions for RRBs must be domain-specific given the varied RRB subdomain combinations manifested across individuals. Further, researchers should continue exploring the various ways RRBs are manifested across individuals with ASD and across ages to inform appropriate and useful intervention approaches.