Identifying Emergent Phenomena in Autism

Background: There is accumulating evidence that many autism-related phenomena are separable and fractionable. Thus, many of the phenomena and behaviors occur in isolation in family members and the general population, are not highly correlated within individuals, and appear to be inherited separately. However, some of the most characteristic and perplexing phenomena observed in individuals diagnosed with autism do not run in their families. It has been suggested that these novel, "emergent", phenomena might arise in the individual from interacting configurations of co-occurring traits or from the interaction of genetic and biological factors underlying the traits (GM Anderson, Autism Research, in press, 2008).
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.