Autism is a severe, life-long developmental disorder that compromises functioning across multiple domains, including social behavior, language, sensory function, and ritualistic/repetitive behaviors and interests. While the etiology of autism is complex and not fully understood, strong evidence from twin and family studies points toward a large genetic contribution, with heritability estimates as high as 90% (1
). Twin and family studies have also shown that genetic liability appears to be expressed among unaffected relatives of people with autism through features that are milder, but qualitatively similar, to the defining characteristics of autism.
The first observation of such subclinical traits can be credited to child psychiatrist Leo Kanner, whose original narrative descriptions of autism also noted among relatives a strong preoccupation with “abstractions of a scientific, literary, or artistic nature, and limited in genuine interest in people.” (1943, p. 250). A decade later, Leon Eisenberg further described relatives, and fathers in particular, as “perfectionistic to an extreme … pre-occupied with detailed minutiae to the exclusion of concern for over-all meanings” (1957, p. 721). These early observations were unfortunately misinterpreted as evidence faulting parents’ behaviors in the etiology of autism, and it would be another 20 years before this myth would be dispelled by the landmark twin study of Folstein and Rutter (3
This study not only detected markedly higher concordance rates of autism among monozygotic twins than dizygotic, but also found even higher MZ concordance for a more broadly defined phenotype including subclinical language and cognitive features. Family studies following up on these striking findings have repeatedly confirmed the presence of such subclinical phenotypes among relatives, now referred to as constituting a ‘broad autism phenotype’ or ‘BAP’. The features of the BAP closely parallel the core symptom domains in autism (i.e., impaired social functioning, language and communication deficits, and restricted/repetitive interests, respectively), yet are subtle in expression and not usually associated with any functional impairment (4
). Importantly, whereas by definition autism involves impairment across all three symptom domains, evidence suggests that these features may decouple and segregate independently in unaffected (with autism) relatives (5
), consistent with the observation that they appear to be uncorrelated in neurotypical populations (8
). Studies of relatives may therefore help to disentangle the complex autistic phenotype to identify component traits more amenable to neurocognitive and genetic dissection than the full clinical syndrome.
The present study is an attempt to inform the neuropsychological basis of autism and the BAP via detailed neuropsychological assessment of high-functioning individuals with autism and parents of autistic individuals (both with and without the BAP). We investigate performance within the three principal neuropsychological domains that have each been proposed as key cognitive abilities in which impairments may explain the autistic phenotype -- social cognition, central coherence and executive function. Autistic individuals’ impairments in each of these domains have been reported [for reviews see (8
)], and an emerging literature has begun to document parallel performance patterns among unaffected relatives (10
We assessed performance using a battery of tasks selected to assess processing comprehensively within a given domain, and chose our battery with an eye towards links to studies of subjects with circumscribed neurological lesions that could shed light on specific neural structures that are involved in autism, and potentially the BAP. For instance, several of our social cognition tasks had been shown to tap amygdala function, a structure that has also been hypothesized to play a role in autism (15
). We focused on high-functioning adults with autism such that an identical battery of tasks might be administered to both the parent and autistic groups, thus affording direct comparisons relative to respective control groups.
To summarize, the goals of this study were 1) to provide an in-depth characterization of the neuropsychological profile of autism and the BAP; 2) to identify patterns of performance within and across neuropsychological domains which were common to both autistic individuals and parents; and 3) to identify cosegregation between clinical phenotype and neuropsychological functioning that might serve to carve out specific phenotypic subtypes and that could form the basis for stronger genotype-phenotype associations.