1. Longitudinal Study of Language and Speech of Twins at 4 and 6 Years: Twinning Effects Decrease, Zygosity Effects Disappear, and Heritability Increases.
- Author
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Rice, Mabel L., Zubrick, Stephen R., Taylor, Catherine L., Hoffman, Lesa, and Gayán, Javier
- Subjects
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LANGUAGE acquisition , *TWINS , *CHILD psychology , *PSYCHOLINGUISTICS , *PHENOTYPES , *PHYSIOLOGY , *PSYCHOLOGY , *GENETICS , *SPEECH evaluation , *APGAR score , *CHI-squared test , *CHILD development , *COGNITION , *CONFIDENCE intervals , *COMPARATIVE grammar , *LANGUAGE & languages , *LONGITUDINAL method , *MATERNAL age , *PROBABILITY theory , *RESEARCH funding , *EDUCATIONAL attainment , *MAXIMUM likelihood statistics , *REPEATED measures design , *DATA analysis software , *DESCRIPTIVE statistics , *INTRACLASS correlation - 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. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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