A twin study of heritable and shared environmental contributions to autism

Thomas W. Frazier, Lee Thompson, Eric A. Youngstrom, Paul Law, Antonio Y. Hardan, Charis Eng, Nathan Morris

Research output: Contribution to journalArticlepeer-review

63 Scopus citations


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 (hg2 = . 92-1.20). 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.

Original languageEnglish (US)
Pages (from-to)2013-2025
Number of pages13
JournalJournal of Autism and Developmental Disorders
Issue number8
StatePublished - Aug 2014
Externally publishedYes


  • Autism
  • Diagnosis
  • Environment
  • Genetic
  • Heritability
  • Twins

ASJC Scopus subject areas

  • Developmental and Educational Psychology


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