The online version of this article (doi:10.1186/s13229-017-0120-5) contains supplementary material, which is available to authorized users.
Autism spectrum disorders (ASD) are persistent and lifelong conditions. Despite this, almost all twin studies focus on childhood. This twin study investigated the stability of autistic traits from childhood to early adulthood and explored the degree to which any stability could be explained by genetic or environmental factors.
Parents of over 2500 twin pairs completed questionnaires assessing autistic traits when twins were aged either 9 or 12 years and again when twins were aged 18. Bivariate twin analysis assessed the degree of phenotypic and etiological stability in autistic traits across this period. Genetic overlap in autistic traits across development was also tested in individuals displaying a broad ASD phenotype, defined as scoring within the highest 5% of the sample.
Autistic traits displayed moderate phenotypic stability (r = .39). The heritability of autistic traits was 76–77% in childhood and 60–62% in adulthood. A moderate degree of genetic influences on childhood autistic traits were carried across into adulthood (genetic correlation = .49). The majority (85%) of the stability in autistic traits was attributable to genetic factors. Genetic influences on autistic traits were moderately stable from childhood to early adulthood at the extremes (genetic correlation = .64).
Broad autistic traits display moderate phenotypic and etiological stability from childhood to early adulthood. Genetic factors accounted for almost all phenotypic stability, although there was some phenotypic and etiological instability in autistic traits. Thus, autistic traits in adulthood are influenced by a combination of enduring and unique genetic factors.
Additional file 1: A-TAC items. The 12 A-TAC questions administered at both ages. (PDF 66 kb)13229_2017_120_MOESM1_ESM.pdf
Additional file 2: Distribution of A-TAC scores. Histograms showing the distribution of the untransformed and transformed A-TAC scales. (PDF 101 kb)13229_2017_120_MOESM2_ESM.pdf
Additional file 3: Saturated model fitting. Table showing the results of saturated model fitting used to test assumptions and sex differences. (PDF 117 kb)13229_2017_120_MOESM3_ESM.pdf
Additional file 4: Description of DeFries-Fulker analytic method. Detailed outline of the DeFries-Fulker analytic procedure used to analyze extreme scoring groups. (PDF 266 kb)13229_2017_120_MOESM4_ESM.pdf
Additional file 5: DeFries-Fulker analysis results. Three tables showing the full results of DeFries-Fulker analysis of the extremes, including descriptive statistics, univariate results, and bivariate results. (PDF 88 kb)13229_2017_120_MOESM5_ESM.pdf
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- Etiological influences on the stability of autistic traits from childhood to early adulthood: evidence from a twin study
Mark J. Taylor
- BioMed Central