Characterization of Restricted and Repetitive Behavior and Interests in Autism Spectrum Disorders within and beyond the ADI-R Using the Simons Simplex Collection

Background: Restrictive repetitive behavior and interests (RRB) represent a core domain of autism spectrum disorders (ASDs), which are assessed on the Autism Diagnostic Interview-Revised (ADI-R).  Recent analysis identified three factors of RRB on the ADI-R: Insistence on Sameness, Repetitive Motor Behaviors, and Circumscribed Interests (Lam, Bodfish, & Aman, 2008).  Similar factors are among the five produced on the Repetitive Behavior Scale-Revised (RBS-R), which was created as an independent measure of the severity of RRB.  It is unknown whether the measurement of RRB on these instruments relates, whether they are both useful for characterizing phenotypes, and how their characterizations of RRB relate to common non-core behavior including aggression, anxiety, and hyperactivity.

Objectives: The goals of this study are: 1) to identify the prevalence, severity, and patterns of RRB in a large ASD population, and how these vary by sex, age, cognitive ability, and language use, 2) to investigate the relation between RRB factors derived from the ADI-R and the RBS-R, 3) to test whether RRB as captured by these instruments relates to non-ASD behaviors. 

Methods: Individuals participating in the Simons Simplex Collection, a North American multiple site, university-based research study of the genetics of ASDs that includes approximately 420 families with only one child with an ASD, completed an extensive battery of diagnostic measures.  All study probands were 4 to 17 years of age and met criteria for a research diagnosis of an ASD (Risi et al., 2006) based on the ADI-R, the Autism Diagnostic Observation Schedule (ADOS), and clinical consensus.  Primary ineligibility criteria included a diagnosis of an ASD in the proband’s first or second degree relatives or cousins.  Approximately 25% of the families in the SSC have one child with an ASD but no other children.  Parents completed several measures about their children including the ADI-R, RBS-R, the Child Behavior Checklist (CBCL), and the Aberrant Behavior Checklist (ABC).  Descriptive analysis of item level data will show the prevalence and severity of individual behaviors.  Independent factor analysis of the RRB items on the ADI-R and all items on RBS-R will be conducted.  Correlations between factor scores from each analysis, age, and IQ will be calculated, and factor scores will be compared across language use and sex.  A combined analysis of these instruments incorporating age, sex, IQ, and language use will be produced.  The derived measures of RRB will be used to assess the relation between RRB and behavior problems on the CBCL and ABC.

Results: The most prevalent and frequently endorsed aspects of RRB in this sample will be identified.  Three sets of RRB factors will be derived in the analyses.  The relation between individual factor scores will show whether the ADI-R and RBS-R capture similar components of RRB.

Conclusions: These analyses will be put in context of previous research trying to identify subtypes of RRB which may be useful phenotypes for genetic and treatment studies of ASDs.