Early Warning Signs of Autism: A Systematic Review of Nonverbal Behavioral Markers and Early Developmental Red Flags...

Area of Science:

• Developmental Psychology
• Neurodevelopmental Disorders
• Clinical Psychology

Background:

• Early identification of autism spectrum disorder (ASD) is critical for timely intervention, but current diagnostic timelines often miss the earliest developmental windows.
• Early behavioral signs of ASD can be subtle and vary significantly among children, complicating diagnosis.
• Nonverbal behavioral markers assessed before 36 months are key targets for improving early ASD risk identification.

Purpose of the Study:

• To systematically review evidence on early nonverbal behavioral markers (before 36 months) associated with later autism spectrum disorder (ASD) diagnosis.
• To synthesize findings on the predictive performance of these markers and identify patterns in early ASD-related signals.
• To inform strategies for improving early risk identification through longitudinal surveillance.

Main Methods:

• A PRISMA-aligned systematic search was conducted for studies assessing nonverbal markers before age three with later ASD outcomes.
• Data extraction included study design, population, marker domains, assessment methods, and predictive performance.
• Risk of bias was assessed, and findings were synthesized narratively due to heterogeneity in study designs and outcome definitions.

Main Results:

• Early ASD signals often manifest as developmental changes over time, not static abnormalities.
• Consistent evidence points to differences in social visual engagement and attention flexibility in the first year.
• More pronounced differences emerge from late infancy to the second year, including attention disengagement, repetitive/sensory behaviors, and motor/postural development.

Conclusions:

• Single nonverbal markers have limited predictive performance for ASD.
• Combinations of markers across domains and multimodal approaches show greater promise but require external validation and transparent reporting.
• Longitudinal surveillance combining multiple early behavioral domains is supported for enhancing early ASD risk identification.