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

Friday, 3 May 2013: 15:30
Meeting Room 1-2 (Kursaal Centre)
I. Gammer1, K. R. Davies2, H. Ribeiro3, L. A. Tucker2, A. Volein2, H. Garwood2, M. Elsabbagh4, G. Pasco1, M. H. Johnson3, T. Charman1 and .. The BASIS Team5, (1)Centre for Research in Autism & Education, Institute of Education, London, United Kingdom, (2)Birkbeck, University of London, London, United Kingdom, (3)Centre for Brain & Cognitive Development, Birkbeck, University of London, London, United Kingdom, (4)Department of Psychiatry, McGill University, Montreal, QC, Canada, (5)BASIS, London, United Kingdom
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.

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