The pervasive developmental disorders are early-onset conditions characterized by delay and deviance in the development of social, communicative, and other skills. The individual lacks interest in the social environment, but unusual behavioral responses to the inanimate environment are typical, including various motor mannerisms (stereotypies), resistance to change, and idiosyncratic interests and preoccupations.

Fred R. Volkmar, M.D., and Ami Klin, Ph.D.