The emergence of autism symptoms in childhood is variable, with some children showing signs of autism spectrum disorder very early, and others not being identified until much later. Although most children in the United States are not diagnosed with autism spectrum disorder until preschool, at ages 3-4 years, symptoms can be reliably detected at 14 months. It is less certain how those toddlers diagnosed with autism spectrum disorder earlier versus later differ from each other clinically. This study revealed that young children diagnosed later in development, between ages 25 and 41 months, are more impaired on measures of cognitive, adaptive, and social functioning than their counterparts who are diagnosed with autism spectrum disorder earlier. All young children with autism spectrum disorder are impaired in communication to a similar degree, however. Universal autism screening at 18 months may identify toddlers with autism spectrum disorder when their symptoms are milder and more readily amenable to intervention. Repeated screening at 24 months is supported to detect those children missed by an earlier screening, who may be more severely affected. Caregivers should be encouraged to pursue diagnostic evaluation at an initial positive screening result to ensure timely diagnosis and treatment.
Keywords: autism spectrum disorder; early diagnosis; early identification; later diagnosis; symptom onset.