Detecting Cognitive Endophenotypes for Autism Using a General Population Twin Family Sample

Background: The uneven cognitive profile of autism spectrum conditions (ASC) is illustrated by relative peak performance on tasks such as Block Design and Embedded Figures and poor performance on Verbal Fluency and social cognition tests. Studies of the Broader Autism Phenotype show that a similar uneven cognitive profile may also characterize first-degree relatives of people with ASC, suggesting familial influences. Whether these cognitive strengths and weaknesses correlate with autistic traits in the general population is unknown. Moreover, the nature of the association between this cognitive profile and autistic traits remains elusive.

Objectives: To explore the association between autistic traits and performance on cognitive tests in a general population sample; and to examine whether this association is due to shared genetic or environmental influences. A genetic link between certain cognitive abilities and autistic traits would point to these being promising endophenotypes for autism.

Methods: Autism-Spectrum Quotient scores (AQ, a quantitative measure of autistic traits) and performance on an extensive cognitive test battery (11 Wechsler subtests and tests of verbal/ spatial memory, processing speed, Stroop-interference and verbal fluency) were assessed in 18-year-old twins (n = 374) and their siblings (n = 96). Genetic vs. environmental covariance was estimated using structural equation modelling.

Results: Performance on the Block Design and Information subtests of the Wechsler intelligence scale was positively related to the Attention to Detail subscale of the AQ (both r=.16). Poor performance on the Wechsler Vocabulary subtest (r=-.25) and Verbal Fluency (r=-.21) predicted social interaction difficulties. The associations between these tests and autistic traits were explained by both genetic and environmental influences.

Conclusions: General population autistic traits covary with the same cognitive strengths and weaknesses as observed in clinical ASC. The relationship between autistic traits and the uneven cognitive profile is partly genetic, suggesting these may be promising endophenotypes for autism.