Behavioural Risk Markers for Autism in Early and Later Infancy: A Prospective Study of High-Risk Siblings Using the Autism Observation Scale for Infants

Background: The British Autism Study of Infant Siblings (BASIS) is a longitudinal study involving participants with older siblings with a diagnosis of ASD (high-risk sibs) and controls with older siblings with no family history of ASD. Participants are assessed at four points between 6 and 36 months, using a range of observational, experimental and questionnaire measures. The Autism Observation Scale for Infants (AOSI) is an experimenter-led, standardized assessment of 19 putative early risk markers for ASD, developmentally appropriate for infants aged between 6 and 18 months. Item codes can be summed to yield a Total Score, or non-zero codes counted to yield a Number of Markers.

Objectives: To assess whether individual items, total AOSI scores or cumulative AOSI scores (summed across two time points) differ between risk or outcome groups.

Methods: Fifty-four high-risk infants and 50 low-risk controls took part in the study. The AOSI was administered at two visits when infants were aged around 7 months (M = 7.4, SD = 1.26), and 14 months (M= 13.8, SD = 1.46).  Based on information from later assessments at around 24 and 36 months, high-risk infants were assigned to one of three outcome groups: Sibs-ASD (n=17) who received a best-estimate clinical diagnosis of ASD; Sibs-AT (n = 12) who were considered not to be to be typically developing, but who did not meet criteria for ASD; Sibs-TD (n=24) who were considered to be typically developing.

Results: After controlling for IQ, higher AOSI Number of Markers but not Total Score differentiated high-risk sibs from low-risk controls at both the 7 and 14 month visits. Higher cumulative scores on both measures differentiated the high-risk group from controls, irrespective of IQ. Both Number of Markers and Total Score were significantly higher in the Sibs-ASD group compared to controls at the 14 month visit, but not the 7 month visit, although these differences did not remain significant after controlling for IQ. Higher Cumulative Number of Markers differentiated Sibs-ASD from controls irrespective of IQ. At the 7 month visit higher scores on Social Referencing differentiated Sibs-ASD from controls and two further items (Visual Tracking and Motor Control and Behaviour) differentiated Sibs-AT from controls. Cumulative item scores yielded more significant item-level differences than scores from either single visit.

Conclusions: Findings contribute towards the validation of the use of the AOSI to detect risk of ASD and provide some evidence of behavioural differences from as early as 7 months. Summing scores from multiple time points across infancy improves the capacity of the AOSI to identify those at highest risk and appears to provide a more robust measure, consistently differentiating risk and outcome groups irrespective of IQ.