title: Rapid video-referenced ratings of reciprocal social behavior in toddlers: a twin study.
abstract: BACKGROUND
  Reciprocal social behavior (RSB) is a developmental prerequisite for social competency, and deficits in RSB constitute a core feature of autism spectrum disorder (ASD). Although clinical screeners categorically ascertain risk of ASD in early childhood, rapid methods for quantitative measurement of RSB in toddlers are not yet established. Such measurements are critical for tracking developmental trajectories and incremental responses to intervention.
  
  
  METHODS
  We developed and validated a 20-min video-referenced rating scale, the video-referenced rating of reciprocal social behavior (vrRSB), for untrained caregivers to provide standardized ratings of quantitative variation in RSB. Parents of 252 toddler twins [Monozygotic (MZ) = 31 pairs, Dizygotic (DZ) = 95 pairs] ascertained through birth records, rated their twins' RSB at two time points, on average 6 months apart, and completed two developmental measures, the Modified Checklist for Autism in Toddlers (M-CHAT) and the MacArthur Communicative Development Inventory Short Form (MCDI-s).
  
  
  RESULTS
  Scores on the vrRSB were fully continuously distributed, with excellent 6-month test-retest reliability ([intraclass correlation coefficient] ICC = 0.704, p < .000). MZ twins displayed markedly greater trait concordance than DZ twins, (MZ ICC = 0.863, p < .000, DZ ICC = 0.231, p < .012). VrRSB score distributions were highly distinct for children passing versus failing the M-CHAT (t = -8.588, df = 31, p < .000), incrementally improved from 18-24 months, and were inversely correlated with receptive and expressive vocabulary on the MCDI-s.
  
  
  CONCLUSIONS
  Like quantitative autistic trait ratings in school-aged children and adults, toddler scores on the vrRSB are continuously distributed and appear highly heritable. These ratings exhibited minimal measurement error, high inter-individual stability, and developmental progression in RSB as children matured from 18-24 months, supporting their potential utility for serially quantifying the severity of early autistic syndromes over time and in response to intervention. In addition, these findings inform the genetic-environmental structure of RSB in early typical development.
authors: Department of Psychiatry, Washington University, St. Louis, MO, USA.
authors: Natasha
authors: N
authors: Marrus
authors: Department of Psychiatry, Washington University, St. Louis, MO, USA.
authors: Anne L
authors: AL
authors: Glowinski
authors: Department of Psychology, Palo Alto University, Palo Alto, CA, USA.
authors: Theodore
authors: T
authors: Jacob
authors: Marcus Autism Center, Children's Healthcare of Atlanta, Atlanta, GA, USA.|Division of Autism & Related Disabilities, Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA.|Center for Translational Social Neuroscience, Emory University, Atlanta, GA, USA.
authors: Ami
authors: A
authors: Klin
authors: Marcus Autism Center, Children's Healthcare of Atlanta, Atlanta, GA, USA.|Division of Autism & Related Disabilities, Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA.|Center for Translational Social Neuroscience, Emory University, Atlanta, GA, USA.
authors: Warren
authors: W
authors: Jones
authors: Department of Psychiatry, Washington University, St. Louis, MO, USA.|Department of Neurology, Washington University, St. Louis, MO, USA.
authors: Caroline E
authors: CE
authors: Drain
authors: Department of Psychiatry, Washington University, St. Louis, MO, USA.
authors: Kieran E
authors: KE
authors: Holzhauer
authors: Department of Psychiatry, Washington University, St. Louis, MO, USA.
authors: Vaishnavi
authors: V
authors: Hariprasad
authors: Department of Psychiatry, Washington University, St. Louis, MO, USA.
authors: Robert T
authors: RT
authors: Fitzgerald
authors: Department of Psychiatry, Washington University, St. Louis, MO, USA.
authors: Erika L
authors: EL
authors: Mortenson
authors: Department of Psychiatry, Washington University, St. Louis, MO, USA.
authors: Sayli M
authors: SM
authors: Sant
authors: Department of Psychiatry, Washington University, St. Louis, MO, USA.
authors: Lyndsey
authors: L
authors: Cole
authors: Department of Psychiatry, Washington University, St. Louis, MO, USA.
authors: Satchel A
authors: SA
authors: Siegel
authors: Department of Psychiatry, Washington University, St. Louis, MO, USA.
authors: Yi
authors: Y
authors: Zhang
authors: Department of Psychiatry, Washington University, St. Louis, MO, USA.
authors: Arpana
authors: A
authors: Agrawal
authors: Department of Psychiatry, Washington University, St. Louis, MO, USA.
authors: Andrew C
authors: AC
authors: Heath
authors: Department of Psychiatry, Washington University, St. Louis, MO, USA.
authors: John N
authors: JN
authors: Constantino
mesh_terms: D002652:Child Behavior / Q000502:physiology*; D002657:Child Development / Q000502:physiology*; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D009483:Neuropsychological Tests / Q000592:standards*; D011594:Psychometrics / Q000295:instrumentation*; D012919:Social Behavior
keywords: Autism; reciprocal social behavior; toddlers; twins; video