title: Aetiological relationship between language performance and autistic-like traits in childhood: a twin study.
abstract: BACKGROUND
  Impairments in language and communication are core features of autism spectrum disorders (ASDs). The basis for this association is poorly understood. How early language is related to each of the triad of impairments characteristic of ASDs is also in need of clarification.
  
  
  OBJECTIVE
  This is the first study that aims to determine the extent to which shared genetic and environmental factors underlie the association between early language performance and autistic-like traits (ALTs) in middle childhood.
  
  
  METHODS
  Data came from a population-based twin sample (n = 6087 pairs) assessed prospectively at 2, 3, 4 and 8 years. ALTs measured by the Childhood Asperger Syndrome Test (CAST) at 8 years were investigated in relation to language assessed by the MacArthur Communicative Development Inventory (CDI) at 2, 3 and 4 years. Multivariate model fitting techniques were used to analyse the origins of this association.
  
  
  RESULTS
  Total CAST scores, as well as Social and Communication subscales, at 8 years were weakly but significantly negatively correlated with language ability at 2, 3 and 4 years. Correlations between language and restrictive and repetitive behaviours and interests (RRBI) were not significant. The phenotypic correlations between language and Social and Communication ALTs were almost entirely mediated by shared genetic influences. There were specific genetic influences on early language that were not shared with ALTs, and specific genetic influences on ALTs not shared with earlier language performance.
  
  
  CONCLUSIONS
  This is the first study to demonstrate shared genetic influences in relation to language performance as an early antecedent of later ALTs. These results support the idea that the triad of core features in ALTs are aetiologically heterogeneous, with early language relating to social and communication impairments but not RRBIs.
authors.affiliation: MRC Social Genetic and Developmental Psychiatry (SGDP) Centre, Institute of Psychiatry, London, UK. k.dworzynski@iop.kcl.ac.uk
authors.forename: Katharina
authors.initials: K
authors.lastname: Dworzynski
authors.forename: Angelica
authors.initials: A
authors.lastname: Ronald
authors.forename: Marianna
authors.initials: M
authors.lastname: Hayiou-Thomas
authors.forename: Frühling
authors.initials: F
authors.lastname: Rijsdijk
authors.forename: Francesca
authors.initials: F
authors.lastname: Happé
authors.forename: Patrick F
authors.initials: PF
authors.lastname: Bolton
authors.forename: Robert
authors.initials: R
authors.lastname: Plomin
mesh_terms: D001321:Autistic Disorder / Q000209:etiology* / Q000235:genetics / Q000523:psychology; D002648:Child; D002652:Child Behavior / Q000523:psychology; D002675:Child, Preschool; D003142:Communication; D004200:Diseases in Twins / Q000209:etiology* / Q000235:genetics / Q000523:psychology; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics; D006801:Humans; D007398:Interpersonal Relations; D007804:Language Development; D008297:Male; D008957:Models, Genetic; D010379:Peer Group; D010641:Phenotype; D011446:Prospective Studies; D012737:Sex Factors; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic