Low expressive vocabulary: Higher heritability as a function of more severe cases

Laura S. DeThorne, Stephen A. Petrill, Marianna E. Hayiou-Thomas, Robert Plomin

Research output: Contribution to journalArticlepeer-review

Abstract

This study of 4,274 pairs of 4-year-old twins from the Twins Early Development Study explored the magnitude of genetic and environmental effects on low expressive vocabulary skill, both as a function of general cognitive ability and as a function of the severity of expressive vocabulary impairment. Assessments were conducted through parent report measures. Two types of vocabulary deficit were identified: low vocabulary paired with typical general cognition (i.e., specific expressive vocabulary impairment) and low vocabulary paired with low general cognition (i.e., nonspecific expressive vocabulary impairment). The magnitude of genetic and environmental effects on low expressive vocabulary skill did not differ for these 2 types of expressive vocabulary deficit. By systematically varying the cutoffs used to define vocabulary and general cognitive delay, potential changes in the magnitude of genetic and environmental effects were examined. Results suggested that the severity of vocabulary deficit rather than level of cognitive functioning was a more meaningful etiological distinction: The heritability of low expressive vocabulary was higher and the influence of shared environment lower, as increasingly severe vocabulary deficits were identified. Implications for molecular genetics and the construct of specific language deficits are discussed.

Original languageEnglish (US)
Pages (from-to)792-804
Number of pages13
JournalJournal of Speech, Language, and Hearing Research
Volume48
Issue number4
DOIs
StatePublished - Aug 1 2005

Keywords

  • Assessment
  • Language disorders
  • Research issues

ASJC Scopus subject areas

  • Language and Linguistics
  • Linguistics and Language
  • Speech and Hearing

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