Copyright @ 2007 American Academy of Child and Adolescent Psychiatry. Unauthorized reproduction of this article is prohibited. Structure of the Autism Symptom Phenotype: A Proposed Multidimensional Model

Background: The main objective of this study was to develop a comprehensive, empirical model that will allow the reorganization of the structure of the pervasive developmental disorder symptom phenotype through factor analysis into more homogeneous dimensions. Method: The sample consisted of 209 children with pervasive developmental disorder referred for genetic studies. The 12 subdomains of the Autism Diagnostic Interview-Revised were used in a factor analysis, and the emerged factors were then correlated with independent variables (measures of cognition, adaptive function, and diagnostic subtype). Intraclass correlation coefficients were calculated to investigate any familial relationships between sibling pairs on the derived factors. Results: The autism symptom phenotype is indeed made up of three factors or domains that are somewhat different than those used inDSM-IV. Rather, domains include social-communication, inflexible language and behavior, and repetitive sensory and motor behavior. For the three factors, only a small amount of variance was accounted for by cognitive and adaptive functioning. Only inflexible language and behavior showed familial correlation between siblings. Conclusions: The pervasive developmental disorder symptom phenotype is composed of three domains or factors: social-communication, inflexible language and behavior, and repetitive sensory and motor behavior. Each child with pervasive developmental disorder can be characterized by these dimensions, which give an informative picture of the clinical presentation and a quantitative estimate of the severity of the disability. J. Am. Acad. Child Adolesc. Psychiatry, 2007;46(2):188Y196. Key Words: pervasive developmental disorders, autism, structure of autism phenotype, genetic studies. The DSM-IV defines all pervasive developmental disorder (PDD) subtypes as sharing symptoms from three symptom categories: impairments in social reciprocity and communication and the presence of repetitive stereotyped behaviors, interests, and activitie