Autism spectrum disorders and autisticlike traits: similar etiology in the extreme end and the normal variation.
CONTEXT: Autism spectrum disorders (ASDs) have been suggested to represent the extreme end of a normal distribution of autisticlike traits (ALTs). However, the evidence of this notion is inconclusive. OBJECTIVE: To study whether there are similar genetic and/or environmental etiologies behind ASDs and ALTs. DESIGN: A nationwide twin study. PARTICIPANTS: Consenting parents of all Swedish twins aged
