Abstract

Although autism spectrum disorder (ASD) is heritable, the mechanisms through which genes contribute to symptom emergence remain unclear. Investigating candidate intermediate phenotypes such as the pupillary light reflex (PLR) prospectively from early in development could bridge genotype and behavioural phenotype. Using eye tracking, we longitudinally measured the PLR at 9, 14 and 24months in a sample of infants (N=264) enriched for a family history of ASD; 27 infants received an ASD diagnosis at 3years. We examined the 9- to 24-month developmental trajectories of PLR constriction latency (onset; ms) and amplitude (%) and explored their relation to categorical 3-year ASD outcome, polygenic liability for ASD and dimensional 3-year social affect (SA) and repetitive/restrictive behaviour (RRB) traits. Polygenic scores for ASD (PGSASD ) were calculated for 190 infants. While infants showed a decrease in latency between 9 and 14months, higher PGSASD was associated with a smaller decrease in latency in the first year (β=-.16, 95% CI=-0.31, -0.002); infants with later ASD showed a significantly steeper decrease in latency (a putative 'catch-up') between 14 and 24months relative to those with other outcomes (typical: β=.54, 95% CI=0.08, 0.99; other: β=.53, 95% CI=0.02, 1.04). Latency development did not associate with later dimensional variation in ASD-related traits. In contrast, change in amplitude was not related to categorical ASD or genetics, but decreasing 9- to 14-month amplitude was associated with higher SA (β=.08, 95% CI=0.01, 0.14) and RRB (β=.05, 95% CI=0.004, 0.11) traits. These findings corroborate PLR development as possible intermediate phenotypes being linked to both genetic liability and phenotypic outcomes. Future work should incorporate alternative measures (e.g. functionally informed structural and genetic measures) to test whether distinct neural mechanisms underpin PLR alterations.

Highlights

  • Autism spectrum disorder (ASD) is a neurodevelopmental condition characterised by social communication impairments, repetitive/restricted behaviours, and sensory anomalies (American Psychiatric Association, 2013)

  • The present study demonstrates pupillary light reflex (PLR) development associates with later ASD, with PLR latency development relating to ASD polygenic liability

  • PLR atypicalities varied over developmental time, reiterating the importance of longitudinal investigations in early development

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Summary

Introduction

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterised by social communication impairments, repetitive/restricted behaviours, and sensory anomalies (American Psychiatric Association, 2013). Elsabbagh et al, 2013; Jones & Klin, 2013) Both PLR latency and amplitude change over early development, with Kercher et al (2020) reporting latency decreased (becomes faster) from 6 to 24 months while amplitude increased (becomes stronger); ASD family history did not alter these developmental trajectories. Nystro€m et al (2018) demonstrated amplitude increased from 9 to 14 months in infants with typical development but decreased in those with later ASD – no analysis was reported on latency development These findings highlight PLR development as potentially fruitful in understanding early ASD development. We examined the 9- to 24-month developmental trajectories of PLR constriction latency (onset; ms) and amplitude (%) and explored their relation to categorical 3-year ASD outcome, polygenic liability for ASD and dimensional 3-year social affect (SA) and repetitive/restrictive behaviour (RRB) traits.

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