A twin study investigating the genetic and environmental aetiologies of parent, teacher and child ratings of autistic-like traits and their overlap
Social Genetic and Developmental, Psychiatry (SGDP) Centre, Institute of Psychiatry, De Crespigny Park, London, UK. European Child & Adolescent Psychiatry
(Impact Factor: 3.34).
04/2008; 17(8):473-83. DOI: 10.1007/s00787-008-0689-5
In the present study we investigated phenotypic agreement between informants (parent, teacher and child self-report) on ratings of autistic-like traits and compared the genetic and environmental aetiologies of the informants' ratings and of their covariance. Parents and teachers of >2,500 pairs from a community twin sample completed an abbreviated Childhood Asperger Syndrome Test (CAST). The twins also completed an adapted self-report version of the CAST. Structural equation model-fitting was carried out. Correlations between raters were significant but moderate (0.16-0.33). The magnitude of heritability estimates of autistic-like traits varied across raters, being highest for parent-rated autistic-like traits (82-87%) and more modest for child self-reported autistic-like traits (36-47%). Genetic overlap was significant but moderate across all raters. These findings are discussed in relation to population screening for autism and future genetic research.
Available from: Paolo Brambilla
- "Data from multiple raters may give important additional information and are likely to provide a richer account of autistic-like behaviours. Different raters provide different perspectives on behaviour, which may lead to different heritability estimates . The availability of measures based on additional informants may also reduce rater bias and correlated measurement error. "
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In recent years, several twin studies adopted a dimensional approach to Autism Spectrum Disorders (ASD) and estimated the contribution of genetic and environmental influences to variation in autistic traits. However, no study was performed on adults over 18 years of age and all but two studies were based on parent or teacher ratings. Also, the genetic and environmental contributions to the interplay between autistic traits and adult personality dimensions have not been investigated.
A sample of 266 complete twin pairs (30% males, mean age 40 ± 12 years) drawn from the population-based Italian Twin Register was administered the Autism-Spectrum Quotient, Temperament and Character Inventory (TCI-125), and General Health Questionnaire (GHQ-12). Genetic structural equation modelling was performed with the Mx program. Estimates were adjusted for gender, age, and GHQ-12 score.
Genetic factors accounted for 44% and 20%-49% of individual differences in autistic traits and TCI dimensions, respectively. Unshared environmental factors explained the remaining proportion of variance. Consistently with the notion of a personality profile in ASD characterised by obsessive temperament, autistic traits showed significant phenotypic correlations with several TCI dimensions (positive: HA; negative: NS, RD, SD, C). Genetic and unshared environmental correlations between AQ and these TCI dimensions were significant. The degree of genetic overlap was generally greater than the degree of environmental overlap.
Despite some limitations, this study suggests that genetic factors contribute substantially to individual differences in autistic traits in adults, with unshared environmental influences also playing an important role. It also suggests that autistic traits and the majority of temperament and character dimensions share common genetic and environmental aetiological factors.
Available from: Craig E Pennell
- "Autism spectrum disorders (ASDs) demarcate the extreme end of a continuum of behavioural difficulties , characterised by impairments of social interaction and communication as well as highly restricted interests and/or stereotyped repetitive behaviours . The subthreshold end of this continuum is embodied by ASD-related but milder and non-psychopathological phenotypes, which are, as ASD, highly heritable (h2 = 0.36 to 0.87 [3-9]) and highly persistent [10,11] throughout the course of development. "
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ABSTRACT: Social communication difficulties represent an autistic trait that is highly heritable and persistent during the course of development. However, little is known about the underlying genetic architecture of this phenotype.
We performed a genome-wide association study on parent-reported social communication problems using items of the children's communication checklist (age 10 to 11 years) studying single and/or joint marker effects. Analyses were conducted in a large UK population-based birth cohort (Avon Longitudinal Study of Parents and their Children, ALSPAC, N = 5,584) and followed-up within a sample of children with comparable measures from Western Australia (RAINE, N = 1364).
Two of our seven independent top signals (P-discovery <1.0E-05) were replicated (0.009 < P-replication <=0.02) within RAINE and suggested evidence for association at 6p22.1 (rs9257616, meta-P = 2.5E-07) and 14q22.1 (rs2352908, meta-P = 1.1E-06). The signal at 6p22.1 was identified within the olfactory receptor gene cluster within the broader major histocompatibility complex (MHC) region. The strongest candidate locus within this genomic area was TRIM27. This gene encodes an ubiquitin E3 ligase, which is an interaction partner of methyl-CpG-binding domain (MBD) proteins, such as MBD3 and MBD4, and rare protein-coding mutations within MBD3 and MBD4 have been linked to autism. The signal at 14q22.1 was found within a gene-poor region.Single-variant findings were complemented by estimations of the narrow-sense heritability in ALSPAC suggesting that approximately a fifth of the phenotypic variance in social communication traits is accounted for by joint additive effects of genotyped single nucleotide polymorphisms throughout the genome (h2(SE) = 0.18(0.066), P = 0.0027).
Overall, our study provides both joint and single-SNP-based evidence for the contribution of common polymorphisms to variation in social communication phenotypes.
Available from: Angelica Ronald
- "Shared environmental influences are environmental influences that are common to both twins and make children growing up in the same family similar. Some studies in middle-to-late childhood report modest shared environmental influences ranging from 10% to 32% [Constantino and Todd, 2000, 2003, 2005; Ronald et al., 2008a], but the majority find no significant effects (see Table II). All studies report moderate influences of the nonshared environment , defined as environmental influences that make children growing up in the same family different, and which by default include measurement error in their term. "
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ABSTRACT: Autism shows a high degree of comorbidity with anxiety disorders. Adolescence is a time of increased stress and vulnerability to internalising problems. This study addresses for the first time the degree of genetic and environmental overlap between autistic traits (total measure and subscales) and internalising traits in a community-based adolescent twin sample. Parents of 12-14-year-old twins (N = 3,232 pairs; 3,460 males, 3,004 females) reported on the twins' internalising and autistic traits. Autistic trait subscales were created using principal component analysis. Bivariate twin model-fitting was conducted. Autistic and internalising traits correlated moderately (r = 0.30). Genetic influences on individual traits were substantial but genetic overlap between traits was moderate (genetic correlation: males = 0.30, females = 0.12). Shared environmental influences were low for internalising traits and moderate for autistic traits, and showed considerable overlap (shared environmental correlation: males = 0.53, females = 1). Nonshared environmental influences were moderate for internalising traits and low for autistic traits and showed low overlap. A multiple component solution was found for autistic traits and of the derived subscales, autistic-like 'Social Unease' showed the most phenotypic and genetic overlap with internalising traits.
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