Outcomes of Early Language Delay II. Etiology of Transient and Persistent Language Difficulties Research Article
Research Article  |   June 01, 2003
Outcomes of Early Language Delay
 
Author Affiliations & Notes
  • Dorothy V. M. Bishop
    University of Oxford, Oxford, U.K.
  • Thomas S. Price
    University of Oxford, Oxford, U.K.
  • Philip S. Dale, PhD
    University of Missouri-Columbia
  • Robert Plomin
    Institute of Psychiatry, London
  • Contact author: Philip S. Dale, PhD, Communication Sciences and Disorders, 303 Lewis Hall, University of Missouri, Columbia, MO 65211. E-mail: dalep@health.missouri.edu
Article Information
Development / Special Populations / Language Disorders / Language / Research Articles
Research Article   |   June 01, 2003
Outcomes of Early Language Delay
Journal of Speech, Language, and Hearing Research, June 2003, Vol. 46, 561-575. doi:10.1044/1092-4388(2003/045)
History: Received December 7, 2001 , Accepted December 17, 2002
 
Journal of Speech, Language, and Hearing Research, June 2003, Vol. 46, 561-575. doi:10.1044/1092-4388(2003/045)
History: Received December 7, 2001; Accepted December 17, 2002

Genes are known to play an important role in causing specific language impairment, but it is unclear how far a similar etiology is implicated in transient language delay in early childhood. Two-year-old children with vocabulary scores below the 10th centile were selected from a cohort of over 2,800 same-sex twin pairs whose language was assessed by parental report at 2, 3, and 4 years of age. These children with early language delay (ELD) were divided into cases of transient and persistent language difficulties on the basis of outcome at 3 and 4 years. A DeFries-Fulker analysis (J. C. DeFries & D. W. Fulker, 1985)  was used to compute group heritability (h2g) of 2-year vocabulary delay separately for those with transient and persistent difficulties. When 3-year and 4-year language attainments were used to categorize outcomes, h2g was similar and modest (.25 or less) for both transient and persistent difficulties. However, when persistent difficulties were defined according to whether parents expressed concern about language at 3 years or according to whether a professional had been consulted about language difficulties at 4 years, heritability was significantly higher. For 289 children with no professional involvement at 4 years, heritability of 2-year vocabulary delay was close to zero, whereas for 134 children with professional involvement, a significant h2g of .41 (SE=.127) was found. Early language delay appears largely environmental in origin for 2-year-olds whose parents do not go on to seek professional help.

Acknowledgements
We thank the parents of the twins in the Twins Early Development Study (TEDS) for making this study possible. The TEDS project is supported by a program grant from the U.K. Medical Research Council. Dorothy Bishop is supported by a Wellcome Trust Principal Research Fellowship.
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