The Concordance of Repetitive Behaviors in Multiplex Autism Families

Background: Repetitive and restricted behaviors (RRBs) have received comparatively little attention in the study of children with autism. Furthermore, relatively few researchers have considered RRBs in families with more than one child affected by autism (“multiplex families”). Previous studies of RRBs in multiplex families using the Autism Diagnostic Interview (ADI) have indicated that multiplex siblings tend to be more similar to each other in areas such as circumscribed interests, preoccupations with part-objects, and inflexible language and behavior than are unrelated children (Kolevzon et al., 2004; Georgiades et al., 2007). No known studies of RRBs in multiplex families have used the more detailed Repetitive Behavior Scale – Revised (RBS-R; Bodfish et al., 1999) to assess RRBs. Use of the RBS-R may reveal more detailed information on the concordance of specific RRBs within multiplex families. Objectives: To investigate the familiality of restricted and repetitive behaviors in multiplex autism sibling pairs using the RBS-R. Methods: Thirty-eight pairs of multiplex siblings affected by an autism spectrum disorder (ASD) were evaluated as part of a larger study on the early detection of autism in toddlers. Pairs consisted of non-twin siblings only. The younger siblings of children already diagnosed with an ASD were ascertained on the basis of screening positive on the Modified Checklist for Autism in Toddlers (M-CHAT). Their older siblings were evaluated to confirm their previous diagnoses. Evaluations included a battery of diagnostic, cognitive, and adaptive tests. Diagnoses were assigned based on the DSM-IV symptom checklist, completed using information from testing and clinical judgment. All children in this sample received a diagnosis of Autistic Disorder, Pervasive Developmental Disorder – Not Otherwise Specified (PDD-NOS), or Asperger's Disorder. Parents completed the RBS-R for both children in the sibling pair. The RBS-R consists of 43 items (scored on a Likert scale) across six subscales: Stereotyped Behavior, Self-Injurious Behavior, Compulsive Behavior, Ritualistic Behavior, Sameness Behavior, and Restricted Behavior. Results: Intraclass correlations (ICCs) conducted between older and younger siblings in a pair indicate that multiplex siblings were more similar to each other on several domains of RRB than were unrelated children. Significantly large ICCs between related siblings were found for all subscales except for the Ritualistic Behavior and Restricted Behavior subscales. Conclusions: Analysis of multiplex siblings' scores on the RBS-R indicates that related siblings were more similar to each other in several RRB areas compared with children who are unrelated. Previous studies have found multiplex siblings to be more similar to each other than to unrelated children on behaviors such as preoccupation with part-objects. These results did not replicate this finding, as the ICC for the RBS-R's Restricted Behavior subscale (which included items related to preoccupation with part-objects) was not significant. Other previous findings were replicated, however, including the familiality of inflexible behavior (the RBS-R's Sameness Subscale). These preliminary results suggest that prior research assessing RRBs with the ADI may not have fully described the familiality of RRBs given the limited range of the ADI's RRB questions.