Stability of Autistic Traits in the General Population: Further Evidence for a Continuum of Impairment
Objective: This study investigated the developmental course of autistic traits in a nationally representative sample of subjects 7 to 13 years of age. Method: The parents of 6,539 children in the Avon Longitudinal Study of Parents and Children completed the Social and Communication Disorders Checklist at ages 7, 10, and 13. The phenotypic progression of autistic traits was assessed in the full sample and in high-scoring individuals (e.g., top 10%, 5%). Gender, IQ, and overall behavior difficulties were examined as potentially relevant influences on autistic trait trajectories. Results: Autistic traits were highly stable in the general population overall and in the high-scoring groups. In the full sample, there was no change in mean Social and Communication Disorders Checklist scores for female subjects ages 7 to 13 (p = .43). Scores for male subjects decreased slightly, but significantly, on the order of 0.1 standard deviations (p < .001). There was no mean change in parent-rated autistic traits within any of the high-scoring groups. IQ was not related to phenotypic progression; high parent-rated behavior problems predicted slight improvement in Social and Communication Disorders Checklist scores over the course of the study period in high-scoring individuals (p < .01). Conclusions: These findings suggest that autistic traits are highly stable in the general population, even in individuals with the highest concentrations of autism-like behaviors. Phenotypic stability is consistent with expectations for individuals with autism spectrum disorders, providing further support for a phenomenologic continuum across the clinical threshold. Moreover, the gap between female and male risk for autistic symptomology is consistent over time.
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