Can autism spectrum disorder (ASD) develop in toddlerhood?

Evidence for Autism Development in Toddlerhood

Yes, there is strong evidence that autism spectrum disorder (ASD) can develop and be detected during toddlerhood, with reliable diagnosis possible as early as 14 months of age. 1

Early Signs and Development of ASD

• Reduced levels of social attention and social communication, along with increased repetitive behavior with objects, are established early markers of ASD between 12 and 24 months of age 2
• Additional potential markers include abnormal body movements and temperament dysregulation during this developmental period 2
• By age 12 months, significant differences can be observed between children who will later be diagnosed with ASD and typically developing children, with slower growth in language skills becoming apparent 2
• Some children with ASD show behavioral differences from the earliest months of life, while others present with speech delay in the second year, and some are described as becoming withdrawn and losing skills after a period of relatively typical development into the second year 2

Diagnostic Stability in Toddlerhood

• The diagnostic stability of ASD in toddlers as young as 14 months is high (0.79), increasing to 0.83 by 16 months of age 1
• By age 2, developmental precursors of autism symptoms can be used to diagnose children reliably, and by age 3, the diagnosis is thought to be relatively stable 3
• Research shows that only 1.8% of toddlers initially diagnosed with ASD transition to a final diagnosis of typical development 1
• A 2023 study found that approximately 37.1% of children diagnosed with ASD between 12-36 months did not continue to meet diagnostic criteria at school age (5-7 years), with higher baseline adaptive skills and female sex associated with non-persistence 4

Developmental Trajectories and Early Detection

• The second year of life is a particularly critical developmental period for children with ASD for several reasons:

  • It is a dynamic period of brain growth during which increases in brain volume and atypical connectivity associated with ASD first emerge 2
  • It is a time of substantial neural plasticity providing greater potential to alter developmental course 2
  • A proportion of children with ASD reportedly regress during this period 2

• Declining trajectories of social communication behavior and loss of skills are observed in most infants with later ASD diagnosis 2

• By 18 months, significant differences in development are noted between children with ASD and typically developing children 2

Screening and Early Identification

• The Modified Checklist for Autism in Toddlers (M-CHAT) shows lower positive predictive value in younger children (16-23 months) compared to older toddlers (24-30 months) 2
• Despite lower specificity for autism at 18 months, the positive predictive value for any diagnosable developmental disorder is high 2
• Universal screening at 18 months may identify toddlers with ASD when their symptoms are milder and more amenable to intervention, while repeated screening at 24 months can detect children who may be more severely affected 5

Clinical Implications

• Early detection and screening aim to ensure that children with ASD can access evidence-based interventions to provide the best opportunity for optimal development and outcomes 2
• Interventions during the second year may counter the developmental cascade that contributes to progressive symptom development 2
• Children diagnosed later in development (between 25-41 months) are often more impaired on measures of cognitive, adaptive, and social functioning than those diagnosed earlier 5

Common Early Signs in First Two Years

• No response to name when called 6
• No or limited use of gestures in communication 6
• Lack of imaginative play 6
• Failure to respond to name at 12 months is highly suggestive of developmental abnormality 2
• Fewer nonverbal behaviors to initiate shared experiences 2
• Significant differences in initiation of joint attention 2
• Less frequent eye contact 2

The evidence clearly demonstrates that ASD can develop and be detected during toddlerhood, with reliable diagnosis possible from 14 months onward. Early identification is crucial for timely intervention that may significantly impact developmental outcomes.