title: Investigating the association between autistic-like and internalizing traits in a community-based twin sample.
abstract: OBJECTIVE
  Recent research has suggested that children with autistic spectrum disorders often experience comorbid symptoms of anxiety and depression. However, despite this overlap, no quantitative genetic studies have addressed the phenotypic overlap and the etiologic association between internalizing and autistic-like traits within the general population. This study aimed to investigate the phenotypic and etiologic relation between internalizing and autistic-like traits using a community-based twin sample.
  
  
  METHODS
  We investigated the co-occurrence of these traits in a population-based sample of 3,233 twin pairs aged 8 to 9 years, using both parent- and teacher-report questionnaires. Bivariate structural equation modeling techniques were used to determine the extent to which internalizing and autistic-like traits shared common genetic and environmental influences.
  
  
  RESULTS
  Our results showed that there was a modest phenotypic correlation (r = 0.26-0.29) between autistic-like and internalizing traits. The traits were both substantially heritable but were largely independent with regard to their genetic influences (r(G) = 0.12-0.19). Shared environmental influences were modest but were largely common to both traits. Similar results were found using both parent- and teacher-reported data.
  
  
  CONCLUSIONS
  Internalizing and autistic-like traits showed moderate phenotypic overlap within the general population. This association was explained in small part by shared genetic factors, but the results suggested that most genetic influences were specific to either internalizing traits or autistic traits. Given these findings, we discuss the potential mechanisms that may underlie the relation between these traits.
authors.affiliation: Ms. Hallett and Dr. Happé are with the Institute of Psychiatry, Kings College London; and Dr. Ronald is with the Centre for Brain and Cognitive Development, School of Psychology, Birkbeck College. Electronic address: victoria.hallett@iop.kcl.ac.uk.
authors.forename: Victoria
authors.initials: V
authors.lastname: Hallett
authors.affiliation: Ms. Hallett and Dr. Happé are with the Institute of Psychiatry, Kings College London; and Dr. Ronald is with the Centre for Brain and Cognitive Development, School of Psychology, Birkbeck College.
authors.forename: Angelica
authors.initials: A
authors.lastname: Ronald
authors.affiliation: Ms. Hallett and Dr. Happé are with the Institute of Psychiatry, Kings College London; and Dr. Ronald is with the Centre for Brain and Cognitive Development, School of Psychology, Birkbeck College.
authors.forename: Francesca
authors.initials: F
authors.lastname: Happé
mesh_terms: D001321:Autistic Disorder / Q000235:genetics* / Q000523:psychology*; D002648:Child; D015897:Comorbidity; D004200:Diseases in Twins / Q000175:diagnosis / Q000235:genetics* / Q000523:psychology*; D005260:Female; D006801:Humans; D007389:Internal-External Control; D008297:Male; D010552:Personality Assessment; D010641:Phenotype; D012792:Shyness; D012931:Social Environment; D006113:United Kingdom