Abstract
Later diagnoses of autism spectrum disorder (ASD) represent a theoretical challenge for researchers, including myself, who have conceived of ASD as a very early arising developmental disorder that affects learning and behavior from infancy onward.(1) Such diagnoses also are a concern because of disparities in access to early intervention, which we know are associated with ethnic minority status and less parental education.(2) If we believe that early intervention makes a difference, then finding children with ASD who cannot be identified until early school age is problematic. Three recent studies, before the present study by Ozonoff et al.,(3) found relatively small, but not insignificant, numbers of children who were not diagnosed until after 6 years of age.(4-6) The present study by Ozonoff et al.(3) uses the opportunity provided by a unique prospective dataset of younger siblings of children with autism (often referred to as the Baby Siblings Research Consortium) to describe 14 children who had not been identified as having ASD at 3 years of age, despite detailed early assessments by a skilled research team, out of 113 children who received ASD diagnoses in middle childhood.