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Neuropsychol Rev (2008) 18:287304 DOI 10.1007/s11065-008-9076-8
The Fractionable Autism Triad: A Review of Evidence from Behavioural, Genetic, Cognitive and Neural Research
Francesca Happ & Angelica Ronald
Received: 9 September 2008 / Accepted: 13 September 2008 / Published online: 28 October 2008 # Springer Science + Business Media, LLC 2008
Abstract Autism is diagnosed on the basis of a triad of impairments in social interaction, communication, and flexible imaginative functions (with restricted and repetitive behaviors and interests; RRBIs). There has been a strong presumption that these different features of the syndrome are strongly intertwined and proceed from a common cause at the genetic, cognitive and neural levels. In this review we examine evidence for an alternative approach, considering the triad as largely fractionable. We present evidence from our own twin studies, and review relevant literature on autism and autistic-like traits in other groups. We suggest that largely independent genes may operate on social skills/ impairments, communication abilities, and RRBIs, requiring a change in molecular-genetic research approaches. At the cognitive level, we suggest that satisfactory accounts exist for each of the triad domains, but no single unitary account can explain both social and nonsocial features of autism. We discuss the implications of the fractionable-triad approach for both diagnosis and future research directions.
Keywords Autism . Autism spectrum disorders . Cognitive theories . Fractionation . Twin studies
Autism is considered to be one of the most highly heritable of all psychiatric or developmental disorders, and yet the
search for vulnerability genes for autism has proved disappointingly difficult. While heterogeneity of etiology (different cases have different causes) is no doubt a major stumbling block in this endeavor, we suggest that research has been hampered by an assumption that the different symptoms that define autism proceed from the same cause. Instead, in this paper, we suggest that social and nonsocial aspects of autism spectrum disorders (ASD) have distinct causes, at the genetic, cognitive, and neural levels. We review evidence relevant to the proposed fractionation of the autistic triad of impairments: (1) research on the degree of clustering or fractionation of symptoms in population samples with and without autism; (2) factor-analytic studies exploring whether autism can be defined along a single dimension or requires a multidimensional space; (3) family and...