Objectives: 1) To propose criteria for emergent phenomena in autism; and 2) to apply the criteria to a range of potentially emergent phenomena in order to rank their emergenic likelihood.
Methods: Criteria: A phenomenon is proposed to be emergent if: a) occurrence in probands>>relatives=general population; b) correlation or concordance in dizygotic twin pairs>>monozygotic twins; and c) monozygotic twin pairs are occasionally discordant. Application of Criteria: A systematic review of the literature was performed to determine the extent to which autism-related phenomena including intellectual disability (ID), seizures, persistence of primitive reflexes, stereotypies, self-injurious behavior, savant abilities, brain alaterality, morphological abnormalities, neurochemical alterations, gait disturbances and clumsiness, met the criteria.
Results: Supporting evidence and theoretical bases underlying the proposed criteria are discussed.
Systematic literature review indicated that all three criteria were met for ID. Persistence of primitive reflexes, stereotypies, and self-injurious behavior could be suggested to be emergent on the basis of apparent low occurrence in relatives.
Conclusions: Based on available family and twin data, ID (MR) can be put forth as likely to be emergent. Although the other phenomena examined remain plausibly emergent, additional family and twin studies are needed to estimate their emergenic likelihood.