title: Why do preschool language abilities correlate with later reading? A twin study.
abstract: OBJECTIVE
  Language acquisition is predictive of successful reading development, but the nature of this link is poorly understood.
  
  
  METHODS
  A sample of 7,179 twin pairs was assessed on parent-report measures of syntax and vocabulary at ages 2, 3, and 4 years and on teacher assessments of reading achievement (RA) at ages 7, 9, and 10 years. These measures were used to construct latent factors of early language ability (LA) and RA in structural equation model-fitting analyses.
  
  
  RESULTS
  The phenotypic correlation between LA and RA (r = .40) was primarily due to shared environmental influences that contribute to familial resemblance. These environmental influences on LA and RA overlapped substantially (rC = .62). Genetic influences made a significant but smaller contribution to the phenotypic correlation between LA and RA, and showed moderate overlap (rA = .36). There was also evidence for a direct causal influence of LA on RA.
  
  
  CONCLUSIONS
  The association between early language and later reading is underpinned by common environmental and genetic influences. The effects of some risk factors on RA may be mediated by language. The results provide a foundation for more fine-grained studies that examine links between specific measures of language, reading, genes, and environments.
authors.affiliation: King's College London, England. nharlaar@ehe.osu.edu
authors.forename: Nicole
authors.initials: N
authors.lastname: Harlaar
authors.forename: Marianna E
authors.initials: ME
authors.lastname: Hayiou-Thomas
authors.forename: Philip S
authors.initials: PS
authors.lastname: Dale
authors.forename: Robert
authors.initials: R
authors.lastname: Plomin
mesh_terms: D002648:Child; D002663:Child Language; D002675:Child, Preschool; D004522:Educational Status; D006801:Humans; D007805:Language Development Disorders / Q000175:diagnosis / Q000235:genetics; D010641:Phenotype; D011932:Reading; D014427:Twins / Q000235:genetics*; D014705:Verbal Behavior; D014706:Verbal Learning