Longitudinal study of language and speech of twins at 4 and 6 years: Twinning effects decrease, zygosity effects disappear, and heritability increases

Mabel L. Rice, Stephen R. Zubrick, Catherine L. Taylor, Lesa Hoffman, Javier Gayán

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

Purpose: This study investigates the heritability of language, speech, and nonverbal cognitive development of twins at 4 and 6 years of age. Possible confounding effects of twinning and zygosity, evident at 2 years, were investigated among other possible predictors of outcomes. Method: The population-based twin sample included 627 twin pairs and 1 twin without a co-twin (197 monozygotic and 431 dizygotic), 610 boys and 645 girls, 1,255 children in total. Nine phenotypes from the same comprehensive direct behavioral assessment protocol were investigated at 4 and 6 years of age. Twinning effects were estimated for each phenotype at each age using general linear mixed models using maximum likelihood. Results: Twinning effects decreased from 4 to 6 years; zygosity effects disappeared by 6 years. Heritability increased from 4 to 6 years across all 9 phenotypes, and the heritability estimates were higher than reported previously, in the range of .44–.92 at 6 years. The highest estimate, .92, was for the clinical grammar marker. Conclusions: Across multiple dimensions of speech, language, and nonverbal cognition, heritability estimates are robust. A finiteness marker of grammar shows the highest inherited influences in this early period of children’s language acquisition.

Original languageEnglish
Pages (from-to)79-93
Number of pages15
JournalJournal of Speech, Language, and Hearing Research
Volume61
Issue number1
DOIs
Publication statusPublished - 1 Jan 2018

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