Repetitive behavior with objects in infants developing autism predicts diagnosis and later social behavior as early as 9 months.

We evaluated repetitive behavior with objects in infants at risk for autism spectrum disorder (ASD) from 9 to 36 months of age, and associations between early repetitive behavior and social engagement. Infant siblings of children with ASD (high-risk) or typical development (low-risk) were administered a task eliciting repetitive object use at 9, 12, 15, 18, 24, and 36 months of age. Infants (n = 147) were classified into 1 of 3 outcome groups at 36 months: Low-Risk Non-ASD (n = 58), High-Risk Non-ASD (n = 72), and ASD (n = 17). Behavior was coded from video for frequencies of unusual visual inspection, spinning, and rotating behaviors. Differences in unusual visual inspection were most prominent, consistent, and present earliest: At 9 months, the ASD group engaged in this behavior more frequently than both other groups, persisting through 36 months. Differences in frequencies of spinning and rotating were later-appearing, more time-limited, and/or related to familial ASD risk rather than ultimate diagnosis. Sensitivity and specificity estimates for the presence of unusual visual inspection at 9 months of age were in the moderate range (.60 and .68, respectively) for ASD versus Low-Risk Non-ASD comparisons, generally increasing over time. Unusual visual inspection at 9 months predicted 12-month social behavior controlling for 9-month social behavior, but not vice versa, with no evidence of moderation by ASD diagnosis. In summary, unusual visual inspection of objects is present and stable by 9 months of age in infants developing ASD and predicts reduced social engagement three-months later. Close monitoring of this behavior may aid early detection. (PsycInfo Database Record (c) 2021 APA, all rights reserved).