Variation in Social Visual Engagement - a Putative Autism Endophenotype - Reflects Stringent Genetic Control in Early Childhood

Saturday, May 13, 2017: 12:00 PM-1:40 PM
Golden Gate Ballroom (Marriott Marquis Hotel)
S. Kennon-McGill1, N. Marrus2,3, C. Weichselbaum4, A. Klin5,6,7, W. Jones6,7,8 and J. N. Constantino2,3,9, (1)Department of Psychiatry, Washington University School of Medicine, St. Louis, MO, (2)Washington University in St. Louis, St. Louis, MO, (3)Intellectual and Developmental Disabilities Research Center, Washington University, St. Louis, MO, (4)Psychiatry and Genetics, Washington University School of Medicine, St. Louis, MO, (5)Marcus Autism Center, Children's Healthcare of Atlanta & Emory University School of Medicine, Atlanta, GA, (6)Center for Translational Social Neuroscience, Emory University, Atlanta, GA, (7)Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, (8)Marcus Autism Center, Children's Healthcare of Atlanta and Emory University School of Medicine, Atlanta, GA, (9)Department of Pediatrics, Washington University School of Medicine, St. Louis, MO
Background:  Diminished eye contact—and more specifically, atypical development of social visual engagement (SVE)—has been shown to predict autism spectrum disorder (ASD) by as early as 6 months-of-age among infants at elevated familial risk for ASD. Deviations in visual orientation to socially-salient cues in the course of moment-to-moment life experience are a target of early intervention for ASD, but the nature of causal influence on variation in SVE in early childhood , as well as the genetic structure, is unknown.

Objectives:  This study aims to examine the genetic structure of early SVE in an epidemiologically-ascertained sample of normal, like-sex toddler twins.

Methods:  We examined patterns of concordance in how children visually engage a caregiver's face and how they observe and seek information in the actions and reactions of peers. By collecting eye-tracking data from 338 toddlers, we first examined pairwise concordance in social visual engagement as a function of genetic and environmental variation in 82 monozygotic twins (MZ, 41 pairs), 84 dizygotic twins (DZ, 42 pairs), and 84 non-biologically-related toddlers (42 randomized pairs, matched by age and sex). Our experiments measured both macro-level indices of SVE (e.g. percentage of time spent looking at eye regions), as well as micro-level indices (e.g. timing of individual eye movements, direction of eye movements, etc.).

Results:  For concordance in eye- and mouth-looking, MZ twin-twin intraclass correlations (ICCs) were remarkably high: 0.91 for eyes (95% CI: 0.85-0.95) and 0.86 for mouth (95% CI: 0.76-0.92). This markedly contrasted with correlations for DZ twins: eyes, 0.35 (95% CI: 0.07-0.59) and mouth, 0.44 (95% CI: 0.16-0.65). We also found similar striking concordance among MZ twins compared to DZ twins for micro-level, moment-by-moment SVE. MZ twins demonstrated greater probability of moving their eyes at the same times: for each movement made by twin 1, within 350 milliseconds, there was an 18.6% increase in twin 2’s probability of also making an eye movement. When analyses were restricted to moments of motor initiationof the saccade, we observed a 21.1% increase in probability of time-locked eye movements: within +/-16.7 msec, MZ twins, but not DZ twins, initiated saccades at the same moments.

Conclusions:  MZ twins exhibit strikingly high concordance in overall levels of eye-looking; greater probability of shifting their eyes at the same moments in time; greater probability of shifting their eyes in the same subsequent directions; and greater probability of contemporaneously fixating on the same semantic content. These high levels of MZ concordance, observed at both macro- and micro-levels, indicate strong biological basis for variation in social visual engagement, with a substantial amount of that variation accounted for by genetic influence.