title: A twin study of heritable and shared environmental contributions to autism.
abstract: 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 ([Formula: see text]). 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.
authors.affiliation: Center for Autism, The Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH, 44195, USA, fraziet2@ccf.org.
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Frazier
authors.forename: Lee
authors.initials: L
authors.lastname: Thompson
authors.forename: Eric A
authors.initials: EA
authors.lastname: Youngstrom
authors.forename: Paul
authors.initials: P
authors.lastname: Law
authors.forename: Antonio Y
authors.initials: AY
authors.lastname: Hardan
authors.forename: Charis
authors.initials: C
authors.lastname: Eng
authors.forename: Nathan
authors.initials: N
authors.lastname: Morris
mesh_terms: D000293:Adolescent; D002648:Child; D002659:Child Development Disorders, Pervasive / Q000235:genetics*; D004200:Diseases in Twins / Q000235:genetics*; D005260:Female; D059647:Gene-Environment Interaction; D020022:Genetic Predisposition to Disease; D006801:Humans; D008297:Male; D011795:Surveys and Questionnaires; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic