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

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          Abstract

          Background

          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.

          Methods

          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.

          Results

          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.

          Conclusions

          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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              Global Prevalence of Autism and Other Pervasive Developmental Disorders

              We provide a systematic review of epidemiological surveys of autistic disorder and pervasive developmental disorders (PDDs) worldwide. A secondary aim was to consider the possible impact of geographic, cultural/ethnic, and socioeconomic factors on prevalence estimates and on clinical presentation of PDD. Based on the evidence reviewed, the median of prevalence estimates of autism spectrum disorders was 62/10 000. While existing estimates are variable, the evidence reviewed does not support differences in PDD prevalence by geographic region nor of a strong impact of ethnic/cultural or socioeconomic factors. However, power to detect such effects is seriously limited in existing data sets, particularly in low-income countries. While it is clear that prevalence estimates have increased over time and these vary in different neighboring and distant regions, these findings most likely represent broadening of the diagnostic concets, diagnostic switching from other developmental disabilities to PDD, service availability, and awareness of autistic spectrum disorders in both the lay and professional public. The lack of evidence from the majority of the world's population suggests a critical need for further research and capacity building in low- and middle-income countries. Autism Res 2012, 5: 160–179. © 2012 International Society for Autism Research, Wiley Periodicals, Inc.
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                Author and article information

                Affiliations
                [ 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@ 123456kcl.ac.uk

                [†]

                Joint first authors.

                Journal
                J Child Psychol Psychiatry
                J Child Psychol Psychiatry
                10.1111/(ISSN)1469-7610
                JCPP
                Journal of Child Psychology and Psychiatry, and Allied Disciplines
                John Wiley and Sons Inc. (Hoboken )
                0021-9630
                1469-7610
                27 December 2015
                May 2016
                : 57
                : 5 ( doiID: 10.1111/jcpp.2016.57.issue-5 )
                : 585-595
                26709141 4996332 10.1111/jcpp.12499 JCPP12499
                © 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.

                Counts
                Pages: 11
                Product
                Funding
                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
                Categories
                Original Article
                Original Articles
                Custom metadata
                2.0
                jcpp12499
                May 2016
                Converter:WILEY_ML3GV2_TO_NLMPMC version:4.9.4 mode:remove_FC converted:24.08.2016

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