Psychometric Properties of a New Video-Referenced Rating of Quantitative Autistic Traits in Toddlers

Background:  The ability to quantify and track autistic traits in early development has significant implications for improving early identification of autism spectrum disorders (ASDs), elucidating developmental mechanisms, and allowing measurement of incremental responses to intervention.  Deficits in reciprocal social behavior (RSB) characterize core features of ASD, emerge early in development, and serve as an ASD endophenotype. Previously, we quantified RSB in an epidemiological sample of toddler twins using a video-referenced rating of Reciprocal Social Behavior (vr-RSB), a novel measure in which children are rated by a caregiver on a subset of items in comparison to a socially competent toddler presented on a brief video clip. 

Objectives:  To investigate: 1) the vrRSB’s ability to distinguish typically developing toddlers from those with ASD or suspected ASD, 2) heritability of early social communication (SC) and restricted repetitive behaviors (RRB), the two core ASD symptom domains, 3) sex differences in RSB in toddlers, and 4) developmental course of RSB, SC, and RRB between 18 and 24 months.

Methods:  Parents of 252 epidemiologically representative twins [monozygotic (MZ)=31 pairs, dizygotic (DZ)=95 pairs] rated their twins on the vrRSB at 18 and 24 months. This sample included a second wave of enrollment enriched for female twins and parents without college degrees, under-represented groups in the first wave. Parents of an initial contrast sample of toddlers with ASD or suspected ASD (by virtue of parental concern for social delays), aged 18-33 months (n=11), also provided vrRSB ratings. Items on the vrRSB were reviewed and classified as SC or RRB items.

Results:  vrRSB scores in this enlarged sample recapitulated a continuous, unimodal distribution and excellent 6-month test-retest reliability (ICC=0.704, p=0.000). Children with ASD/suspected ASD had elevated scores vs. twins in the general population (video-referenced: t=-2.454, df=10, p=.034; RSB Total: t=-4.055, df=10, p=.002). MZ vs. DZ concordances suggested significantly more heritability for SC compared to RRB (Table 1). Males had higher vrRSB scores than females (video-referenced: t=2.815, df=124, p<.006; RSB Total: t=3.348, df=124, p<.001). Scores on the vrRSB and SC items decreased between 18 and 24 months, whereas RRB scores showed no change. Item level analyses demonstrated that questions with the greatest improvement involved parent-child interaction, pretend play, ability to cooperate, verbal understanding, and initiation of interactions.

Conclusions:  An initial sample of toddlers with ASD or suspected ASD displayed lower RSB on both the video-referenced items and full-length vrRSB. RSB and SC appear strongly heritable at the toddler stage, in contrast to RRB. Males have lower RSB than females, paralleling RSB later in life and supporting the vrRSB as a measure of RSB.  Maturation of RSB occurred between 18 and 24 months and was attributable to improved SC but not RRB. These results highlight the vrRSB’s potential clinical utility, in terms of promoting earlier identification of ASD and tracking response to early intervention, as well as its scientific utility for elucidating behavioral mechanisms of ASD in relation to sexual dimorphisms and distinct contributions of SC and RRB to the development of ASD.