Original Paper

Journal of Autism and Developmental Disorders

, Volume 44, Issue 8, pp 2013-2025

First online:

A Twin Study of Heritable and Shared Environmental Contributions to Autism

  • Thomas W. FrazierAffiliated withCenter for Autism, The Cleveland ClinicGenomic Medicine Institute, Cleveland Clinic Email author 
  • , Lee ThompsonAffiliated withDepartments of Psychological Sciences, Case Western Reserve University
  • , Eric A. YoungstromAffiliated withDepartment of Psychology, The University of North Carolina at Chapel Hill
  • , Paul LawAffiliated withDepartment of Medical Informatics and the Interactive Autism Network, Kennedy Krieger Institute
  • , Antonio Y. HardanAffiliated withDepartment of Psychiatry and Behavioral Sciences, Stanford
  • , Charis EngAffiliated withGenomic Medicine Institute, Cleveland ClinicDepartments of Genetics, Case Western Reserve University
  • , Nathan MorrisAffiliated withDepartments of Epidemiology and Biostatistics, Case Western Reserve University

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The present study examined genetic and shared environment contributions to quantitatively-measured autism symptoms and categorically-defined autism spectrum disorders (ASD). Participants included 568 twins from the Interactive Autism Network. Autism symptoms were obtained using the Social Communication Questionnaire and Social Responsiveness Scale. Categorically-defined ASD was based on clinical diagnoses. DeFries-Fulker and liability threshold models examined etiologic influences. Very high heritability was observed for extreme autism symptom levels (\( {\text{h}}_{g}^{2} = . 9 2{-} 1. 20 \)). Extreme levels of social and repetitive behavior symptoms were strongly influenced by common genetic factors. Heritability of categorically-defined ASD diagnosis was comparatively low (.21, 95 % CI 0.15–0.28). High heritability of extreme autism symptom levels confirms previous observations of strong genetic influences on autism. Future studies will require large, carefully ascertained family pedigrees and quantitative symptom measurements.


Autism Twins Genetic Heritability Environment Diagnosis