II Ongoing Debates About Case Definitions
DIAGNOSTIC BOUNDARY ISSUES
Using Developmental Trajectories to Validate Diagnostic Categories Comparing and Contrasting Asperger’s Syndrome and Autism
Autism spectrum disorder (ASD) is a neurodevelopmental disorder of childhood characterized by impairments in social communication and a preference for repetitive, stereotyped behaviors and activities. The diagnosis and classification of the condition has been the subject of much debate over the years. In particular, the clinical heterogeneity of ASD has generated much discussion and even controversy, with many suggestions proposed for different subtypes or subgroups. Asperger’s syndrome (AS) is a subtype of ASD that was incorporated into DSM-IV but was removed in DSM-5 on the basis of evidence suggesting that it lacked “diagnostic validity.” The objective of this chapter is to review the evidence on the usefulness of the current criteria for “diagnostic validity” of AS and autism, thus illustrating the debate with data from longitudinal studies of developmental trajectories of these two subtypes of ASD. We conclude that a close study of developmental trajectories is not only an extremely useful way of providing evidence on diagnostic validity but also is more pertinent than the etiological studies that currently dominate the field.