The origins of social impairments in autism spectrum disorder: studies of infants at risk.

Core impairments in social and communicative behaviors are among the defining characteristics of autism spectrum disorder (ASD), making this a model syndrome for investigating the mechanisms that underlie social cognition and behavior. Current research is exploring the origins of social impairments in prospective longitudinal studies of infants who are at high risk for ASD, defined as having an older sibling with the disorder. Behavioral studies that have followed these infants through to outcomes have found that during the early months of life they are no different from typically developing infants; they are socially interested, engaged and enjoy interactions with people. By the end of the first year risk signs for later ASD can be identified though no single marker has been identified. It seems that an aggregate of risk markers together may be needed to predict ASD. Other studies have compared infants at risk for ASD to low risk controls to identify neurocognitive endophenotypes. Several differences in subtle aspects of behavior and in brain organization have been found in infants younger than 12 months, though it is not known whether these differences are also risk markers for a later ASD diagnosis. The findings from these lines of research are used to provide a new view of ASD, as a disorder defined on the basis of alterations in the developmental trajectories across multiple domains. ASD is an emergent disorder that is characterized by the loss of social communication skills in the period between 9 and 24 months. Across children the rate, timing and severity of this loss is highly variable. Future research will lead to a greater understanding of the genetic and neurocognitive mechanisms that underlie these fundamental changes in the developmental patterns of individuals with ASD.