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Heritability of autism spectrum disorders: a meta‐analysis of twin studies

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      The etiology of Autism Spectrum Disorder ( ASD) has been recently debated due to emerging findings on the importance of shared environmental influences. However, two recent twin studies do not support this and instead re‐affirm strong genetic effects on the liability to ASD, a finding consistent with previous reports. This study conducts a systematic review and meta‐analysis of all twin studies of ASD published to date and explores the etiology along the continuum of a quantitative measure of ASD.


      A PubMed Central, Science Direct, Google Scholar, Web of Knowledge structured search conducted online, to identify all twin studies on ASD published to date. Thirteen primary twin studies were identified, seven were included in the meta‐analysis by meeting Systematic Recruitment criterion; correction for selection and ascertainment strategies, and applied prevalences were assessed for these studies. In addition, a quantile DF extremes analysis was carried out on Childhood Autism Spectrum Test scores measured in a population sample of 6,413 twin pairs including affected twins.


      The meta‐analysis correlations for monozygotic twins ( MZ) were almost perfect at .98 (95% Confidence Interval, .96–.99). The dizygotic ( DZ) correlation, however, was .53 (95% CI .44–.60) when ASD prevalence rate was set at 5% (in line with the Broad Phenotype of ASD) and increased to .67 (95% CI .61–.72) when applying a prevalence rate of 1%. The meta‐analytic heritability estimates were substantial: 64–91%. Shared environmental effects became significant as the prevalence rate decreased from 5–1%: 07–35%. The DF analyses show that for the most part, there is no departure from linearity in heritability.


      We demonstrate that: (a) ASD is due to strong genetic effects; (b) shared environmental effects become significant as a function of lower prevalence rate; (c) previously reported significant shared environmental influences are likely a statistical artefact of overinclusion of concordant DZ twins.

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      Most cited references 28

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      Autism Diagnostic Interview-Revised: a revised version of a diagnostic interview for caregivers of individuals with possible pervasive developmental disorders.

      Describes the Autism Diagnostic Interview-Revised (ADI-R), a revision of the Autism Diagnostic Interview, a semistructured, investigator-based interview for caregivers of children and adults for whom autism or pervasive developmental disorders is a possible diagnosis. The revised interview has been reorganized, shortened, modified to be appropriate for children with mental ages from about 18 months into adulthood and linked to ICD-10 and DSM-IV criteria. Psychometric data are presented for a sample of preschool children.
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        Genetic heritability and shared environmental factors among twin pairs with autism.

        Autism is considered the most heritable of neurodevelopmental disorders, mainly because of the large difference in concordance rates between monozygotic and dizygotic twins. To provide rigorous quantitative estimates of genetic heritability of autism and the effects of shared environment. Twin pairs with at least 1 twin with an autism spectrum disorder (ASD) born between 1987 and 2004 were identified through the California Department of Developmental Services. Structured diagnostic assessments (Autism Diagnostic Interview-Revised and Autism Diagnostic Observation Schedule) were completed on 192 twin pairs. Concordance rates were calculated and parametric models were fitted for 2 definitions, 1 narrow (strict autism) and 1 broad (ASD). For strict autism, probandwise concordance for male twins was 0.58 for 40 monozygotic pairs (95% confidence interval [CI], 0.42-0.74) and 0.21 for 31 dizygotic pairs (95% CI, 0.09-0.43); for female twins, the concordance was 0.60 for 7 monozygotic pairs (95% CI, 0.28-0.90) and 0.27 for 10 dizygotic pairs (95% CI, 0.09-0.69). For ASD, the probandwise concordance for male twins was 0.77 for 45 monozygotic pairs (95% CI, 0.65-0.86) and 0.31 for 45 dizygotic pairs (95% CI, 0.16-0.46); for female twins, the concordance was 0.50 for 9 monozygotic pairs (95% CI, 0.16-0.84) and 0.36 for 13 dizygotic pairs (95% CI, 0.11-0.60). A large proportion of the variance in liability can be explained by shared environmental factors (55%; 95% CI, 9%-81% for autism and 58%; 95% CI, 30%-80% for ASD) in addition to moderate genetic heritability (37%; 95% CI, 8%-84% for autism and 38%; 95% CI, 14%-67% for ASD). Susceptibility to ASD has moderate genetic heritability and a substantial shared twin environmental component.
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          Schizophrenia as a complex trait: evidence from a meta-analysis of twin studies.

          There are many published twin studies of schizophrenia. Although these studies have been reviewed previously, to our knowledge, no review has provided quantitative summary estimates of the impact of genes and environment on liability to schizophrenia that also accounted for the different ascertainment strategies used. To calculate meta-analytic estimates of heritability in liability and shared and individual-specific environmental effects from the pooled twin data. We used a structured literature search to identify all published twin studies of schizophrenia, including MEDLINE, dissertation, and books-in-print searches. Of the 14 identified studies, 12 met the minimal inclusion criteria of systematic ascertainment. By using a multigroup twin model, we found evidence for substantial additive genetic effects-the point estimate of heritability in liability to schizophrenia was 81% (95% confidence interval, 73%-90%). Notably, there was consistent evidence across these studies for common or shared environmental influences on liability to schizophrenia-joint estimate, 11% (95% confidence interval, 3%-19%). Despite evidence of heterogeneity across studies, these meta-analytic results from 12 published twin studies of schizophrenia are consistent with a view of schizophrenia as a complex trait that results from genetic and environmental etiological influences. These results are broadly informative in that they provide no information about the specific identity of these etiological influences, but they do provide a component of a unifying empirical basis supporting the rationality of searches for underlying genetic and common environmental etiological factors.

            Author and article information

            [ 1 ] MRC Social, Genetic and Developmental Psychiatry Centre IOPPNKing's College London LondonUK
            Author notes
            [* ] Correspondence

            Frühling Rijsdijk, MRC Social, Genetic and Developmental Psychiatry Centre, IOPPN, King's College London, 16 DeCrespigny Park, Denmark Hill, London SE5 8AF, UK; Email: fruhling.rijsdijk@


            Joint first authors.

            J Child Psychol Psychiatry
            J Child Psychol Psychiatry
            Journal of Child Psychology and Psychiatry, and Allied Disciplines
            John Wiley and Sons Inc. (Hoboken )
            27 December 2015
            May 2016
            : 57
            : 5 ( doiID: 10.1111/jcpp.2016.57.issue-5 )
            : 585-595
            © 2015 The Authors. Journal of Child Psychology and Psychiatry published by John Wiley & Sons Ltd on behalf of Association for Child and Adolescent Mental Health.

            This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

            Pages: 11
            Funded by: Medical Research Council 1 + 3 PhD studentship
            Award ID: MR/J500380/1
            Funded by: National Institute Health Research Senior Investigator Award & Biomedical Research Centre in Mental Health at the South London & Maudsley National Health Service UK Foundation Trust
            Funded by: UK Medical Research Council (MRC)
            Award ID: G0500870
            Award ID: G0901245
            Award ID: previously G0500079
            Original Article
            Original Articles
            Custom metadata
            May 2016
            Converter:WILEY_ML3GV2_TO_NLMPMC version:4.9.4 mode:remove_FC converted:24.08.2016


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