International Meeting for Autism Research (May 7 - 9, 2009): Developmental Trajectories of Repetitive Behaviors in Young Children with Autism Spectrum Disorders

Thursday, May 7, 2009

Northwest Hall (Chicago Hilton)

11:00 AM

P. Mirenda , Educational and Counseling Psychology and Special Education, University of British Columbia, Vancouver, BC, Canada

I. M. Smith , Pediatrics & Psychology, Dalhousie University & IWK Health Centre, Halifax, NS, Canada

P. Szatmari , The Offord Centre for Child Studies, McMaster University, Hamilton, ON, Canada

S. E. Bryson , Pediatrics and Psychology, Dalhousie University/IWK Health Centre, Halifax, NS, Canada

E. Fombonne , Head, Division of Child Psychiatry, McGill University, Montreal, QC, Canada

W. Roberts , Department of Pediatrics, Hospital for Sick Children & Bloorview Kids Rehab, University of Toronto, Toronto, ON, Canada

T. Vaillancourt , University of Ottawa, Ottawa, ON, Canada

J. Volden , Speech Language Pathology, University of Alberta, Edmonton, AB, Canada

C. Waddell , Simon Fraser University

L. Zwaigenbaum , Department of Pediatrics, University of Alberta, Edmonton, AB, Canada

S. Georgiades , The Offord Centre for Child Studies, McMaster University, Hamilton, ON, Canada

A. P. Thompson , The Offord Centre for Child Studies, McMaster University, Hamilton, ON, Canada

E. Duku , Offord Centre for Child Studies, McMaster University, Hamilton, ON, Canada

.. Pathways in ASD Study Team , Offord Centre for Child Studies & McMaster University, Hamilton, ON, Canada

Background: Recent research suggests that the restricted and repetitive behaviors (RRB) domain is composed of at least two symptom dimensions in young children with autism spectrum disorders (ASDs). However, to date most studies of RRB have been descriptive or cross-sectional rather than longitudinal in nature, which limits our understanding of how these behaviors are related to other developmental factors over time. In addition, most studies have been done with samples across a wide age range and have been based on a single measure, the ADI-R, which is designed to identify the presence/absence of symptoms rather than to quantify symptom severity.

Objectives: To confirm the factor structure of RRB in a large sample of preschool children with ASD, using the Repetitive Behavior Scale-Revised (RBS-R), an instrument specifically designed to measure this domain; and to examine trajectories and correlates of the resulting factors over a 12-month period.

Methods: The RBS-R was completed by parents of newly-diagnosed 2-to-5-year olds with ASD, participating in a Canadian longitudinal study (Pathways in ASD). Our sample consisted of 283 children (241 males; mean CA=39.5 months; mean MA=22.9 months; 71.7% Caucasian). Exploratory and confirmatory factor analyses were conducted to examine the structure of the RBS-R in this sample. Semi-parametric modeling was used to examine trajectories of the resulting factors over a 12-month period. Spearman's rank order correlations were calculated to examine relationships between the derived factors and adaptive behavior, cognitive functioning, and other ASD symptoms.

Results: A three-factor solution explaining 40% of the variance was selected, using scree plot and goodness-of-fit criteria. The three factors were: Compulsive Ritualistic Sameness Behaviour (CRSB), Self Injurious Behaviour (SIB), and Stereotyped Restricted Behaviour (SRB). Two distinct flat trajectories were found for the total RBS-R score and the CRSB factors, one with higher scores and the other with lower scores. Children with higher CRSB scores were significantly older (r=.19), showed more severe ASD symptoms in the communication and social domains of the ADI-R (r= .61), and had poorer adaptive behavior (Vineland II composite score, r=-.18). Two distinct trajectories were also found for the SIB factor, one of which consisted of a small group of children whose risk for serious SIB persisted across a 12-month period. Children with higher SIB scores were younger (r=-.15) and had lower cognitive ability (Merrill-Palmer-Revised, r=-.16). Finally, we found three groups for the SRB factor, with the highest and lowest trajectories declining over time and the middle trajectory remaining flat. Children with high scores on SRB were younger (r=-.15), had more severe autism (ADI-R, r=.17), and were more impaired on both cognitive (Merrill-Palmer-Revised) and adaptive (Vineland II) skills (r=-.16 to -.21).

Conclusions: Results of the factor analyses confirm the results of studies of RRB in a more homogeneous sample with a different instrument than usually used. The results also indicate that distinct developmental trajectories exist in this independent domain. In general, children with more severe autism, lower cognitive ability, and poorer adaptive behavior had higher rates of RRB across all three factors.

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