The Emergence of Autism Symptoms Prior to 18 Months of Age: A Systematic Literature Review.
Amy Tanner, Katerina Dounavi
PMID 32734422WHAT IT FOUND
Infants later diagnosed with autism showed subtle deficits in gaze, smiling, gestures and motor skills from 6 to 12 months, before full symptoms appeared.
These early signs were often less frequent typical behaviors rather than unusual excesses, making them hard to spot without careful monitoring.
Key findings
01No single early sign reliably predicts autism; risk increases cumulatively as more subtle deficits appear.
02Prospective tracking using dimensional ratings identified regression in 88% of high-risk infants who later had ASD, whereas retrospective categorical questions only identified it in 29-30%.
03Early markers are predominantly deficits in the frequency of typical behaviors, such as less smiling, fewer gestures and slower motor growth, rather than the presence of atypical excesses.
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTsWhat it means for SLPs
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What it does not show
Most included studies (23 of 26) used high-risk samples (siblings of children with ASD), so findings may not generalize to low-risk infants. Only two studies separated results by gender, despite evidence that autism presents differently in girls. The review excluded studies using eye-tracking or other technology, limiting the scope to behaviors visible in routine clinical or home settings. Quality assessment showed that many studies lacked blinding of assessors to risk status, which could introduce bias.
The easy way to misread this
Do not assume that the absence of obvious atypical behaviors means an infant is not at risk. The review found that early signs are often subtle deficits in the frequency of normal behaviors, which are easily missed without systematic prospective tracking.