title: Evidence for three subtypes of repetitive behavior in autism that differ in familiality and association with other symptoms.
abstract: BACKGROUND
  Restricted repetitive behaviors (RRBs) are a core feature of autism and consist of a variety of behaviors, ranging from motor stereotypies to complex circumscribed interests. The objective of the current study was to examine the structure of RRBs in autism using relevant items from the Autism Diagnostic Interview-Revised in a sample of 316 individuals with autistic disorder.
  
  
  RESULTS
  Using exploratory factor analysis, three distinct factors were identified: Repetitive Motor Behaviors (RMB), Insistence on Sameness (IS), and Circumscribed Interests (CI). RMB were found to be associated with a variety of subject characteristics such as IQ, age, social/communication impairments, and the presence of regression. IS was associated with social and communication impairments whereas CI appeared to be independent of subject characteristics, suggesting CI may be particularly useful in subsetting samples. Based on sib-pair correlations, IS and CI (but not RMB) appear to be familial. Analysis of the data at the case level suggests that the presence of multiple forms of RRB in an individual is associated with more impairment in the social and communication domains, suggesting a more severe presentation of autistic disorder.
  
  
  CONCLUSIONS
  There appears to be considerable structure within repetitive behavior in autism. The finding that these behaviors are differentially related to subject characteristics and familiality adds to their validity.
authors.affiliation: Neurodevelopmental Disorders Research Center, University of North Carolina-Chapel Hill, NC 27599-3367, USA. kristen_lam@med.unc.edu
authors.forename: Kristen S L
authors.initials: KS
authors.lastname: Lam
authors.forename: James W
authors.initials: JW
authors.lastname: Bodfish
authors.forename: Joseph
authors.initials: J
authors.lastname: Piven
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D001321:Autistic Disorder / Q000145:classification* / Q000453:epidemiology / Q000235:genetics* / Q000523:psychology; D002648:Child; D002675:Child, Preschool; D005163:Factor Analysis, Statistical; D005260:Female; D020022:Genetic Predisposition to Disease / Q000453:epidemiology / Q000235:genetics / Q000523:psychology; D006801:Humans; D007223:Infant; D007360:Intelligence; D007406:Interview, Psychological / Q000379:methods; D007806:Language Disorders / Q000453:epidemiology / Q000523:psychology; D008297:Male; D009657:North Carolina / Q000453:epidemiology; D012720:Severity of Illness Index; D012919:Social Behavior; D019956:Stereotypic Movement Disorder / Q000453:epidemiology* / Q000235:genetics* / Q000523:psychology; D055815:Young Adult