PDD-NOS Symptoms in Adults with Intellectual Disability: Toward an Empirically Oriented Diagnostic Model

PDD-NOS has been an illusive diagnostic category in Autism Spectrum Disorders (ASD). It is a frequently occurring ASD, but it has typically been defined by what it is not—autism. This latter condition has received the bulk of the attention in the development of diagnostic methods, while PDD-NOS has largely been ignored from a diagnostic standpoint. The symptoms that characterize PDD-NOS in adults with intellectual disability (ID), beyond the extrapolation of a few child studies, are largely unknown. This study is an attempt to provide systematic empirical data to describe the condition of PDD-NOS in adults with ID. The implication of these data for diagnosis and future research are discussed.