From Subtypes to Phenotypes: Discovering the Clinical Predictors of RRB Profiles in ASD

Autism spectrum disorders (ASD) are defined by impairments in social communication skills and the presence of restricted and repetitive behaviors (RRBs). Research has primarily focused on the measurement and influence of social communication deficits, despite the impact RRBs can have on daily functioning for individuals with ASD and their families. To date, age and cognitive functioning have been the focus of examination relating RRBs to individual characteristics. There is a gap in our understanding and consistency of measurement tools, conceptualization of RRB subtypes and understanding of the relationship between individual characteristics and RRBs in individuals with ASD. In the current study, parent reported rates of RRBs in 2,856 individuals with ASD ranging in age from 4 to 18 were examined in order to both characterize the RRB types measured and for co-occurrence of other factors, such as coping skills, anxiety and hyperactivity. Using a standardized parent report of RRBs, factor analytic results indicate that there are 5 distinct RRB types captured which include, hand/body mannerisms, rigidity, perseverative interests, compulsivity, and self-injurious behaviors. Next, a cluster analysis revealed 5 distinct phenotypic cluster profiles of RRB presentation, with each cluster encompassing various intensities of each of the 5 RRB subtypes. Lastly, a multinomial logistic regression analysis (MLR) was run with age, IQ, severity of ASD symptoms as well as standardized values of hyperactivity, anxiety and coping skills as predictors of phenotypic profile membership. Most notably, ASD symptom severity scores and nonverbal IQ did not significantly predict profile membership; rather hyperactivity, anxiety and coping skills were the significant predictors of RRB profile membership. In particular, anxiety was the strongest predictor of membership when comparing the optimal "All Low" RRB profile to each of the other phenotypic profiles. Results from this study have uniquely exhibited the limitations of using an individuals' IQ, ASD symptom severity scores or age as the only characteristics in adequately predicting RRB presentation profile; contrary to most literature on the topic. This discrepancy across studies highlights the importance of using a standardized measure to define and quantify RRBs across studies. Further, results of the current study expand our understanding of the potential characteristics and developmental domains that have the most influence on RRB presentation. Although beyond the scope of the current study, these findings have significant implications in understanding potential underlying mechanisms related to RRB presentation and the functions they may serve for individuals with ASD, which may lead to improved treatment approaches to indirectly influence RRBs