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. 2014 Aug;44(8):2013-25.
doi: 10.1007/s10803-014-2081-2.

A twin study of heritable and shared environmental contributions to autism

Thomas W Frazier  1 , Lee Thompson, Eric A Youngstrom, Paul Law, Antonio Y Hardan, Charis Eng, Nathan Morris
Affiliations

A twin study of heritable and shared environmental contributions to autism

Thomas W Frazier et al. J Autism Dev Disord. 2014 Aug.

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.

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Figures

Figure 1
Figure 1
SCQ total raw and SRS total T-scores (M +/− 95% CIs) from MZ and DZ probands with extreme scores (≥97th percentile) and their co-twins.
Figure 2
Figure 2
Increases in group heritability across levels of quantitatively-assessed autism symptoms.
See this image and copyright information in PMC

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