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Longitudinal Study of Language and Speech of Twins at 4 and 6 Years: Twinning Effects Decrease, Zygosity Effects
Mabel L Rice1, Stephen R Zubrick2,3, Catherine L Taylor3,4
1Child Language Doctoral Program, University of Kansas, Lawrence.
Journal of Speech, Language, and Hearing Research : JSLHR
|December 20, 2017
Summary
Genetic influences on language, speech, and cognition are robust in children. Grammar development shows the strongest heritability, increasing significantly by age 6.
Area of Science:
- Developmental psychology
- Behavioral genetics
- Linguistics
Background:
- Understanding the genetic and environmental contributions to child development is crucial.
- Previous research has explored heritability in early development, but longitudinal data across multiple domains is limited.
Purpose of the Study:
- To investigate the heritability of language, speech, and nonverbal cognitive development in twins.
- To examine the influence of twinning and zygosity on developmental outcomes at 4 and 6 years of age.
- To assess changes in heritability estimates over time.
Main Methods:
- A population-based sample of 1,255 twins (627 pairs) was assessed.
- Nine developmental phenotypes were evaluated using a comprehensive behavioral assessment protocol at ages 4 and 6.
- General linear mixed models were employed to estimate heritability and twinning effects.
Main Results:
- Heritability estimates for all nine phenotypes increased from age 4 to 6.
- Heritability ranged from .44 to .92 at age 6, with higher estimates than previously reported.
- The clinical grammar marker exhibited the highest heritability (.92) at age 6.
Conclusions:
- Heritability of speech, language, and nonverbal cognition is robust across development.
- Grammar development, particularly a finiteness marker, demonstrates substantial inherited influence in early childhood.
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