Late Language Emergence in 24-Month-Old Twins: Heritable and Increased Risk for Late Language Emergence in Twins Purpose: This study investigated the etiology of late language emergence (LLE) in 24-month-old twins, considering possible twinning, zygosity, gender, and heritability effects for vocabulary and grammar phenotypes. Method: A population-based sample of 473 twin pairs participated. Multilevel modeling estimated means and variances of vocabulary and ... Research Article
Research Article  |   June 2014

© The West Australian. Reprinted with permission.

Late Language Emergence in 24-Month-Old Twins: Heritable and Increased Risk for Late Language Emergence in Twins
 
Author Affiliations & Notes
  • Mabel L. Rice
    University of Kansas, Lawrence
  • Stephen R. Zubrick
    Telethon Institute for Child Health Research and the University of Western Australia, Perth
  • Catherine L. Taylor
    Telethon Institute for Child Health Research and the University of Western Australia, Perth
  • Javier Gayán
    Bioinfosol, Seville, Spain
  • Daniel E. Bontempo
    University of Kansas, Lawrence
  • Javier Gayán is now affiliated with F. Hoffmann-La Roche AG, Basel,’Switzerland.
    Javier Gayán is now affiliated with F. Hoffmann-La Roche AG, Basel,’Switzerland.×
  • Disclosure: The authors have declared that no competing interests existed at the time of publication.
    Disclosure: The authors have declared that no competing interests existed at the time of publication.×
  • Correspondence to Mabel L. Rice: mabel@ku.edu
  • Editor: Janna Oetting
    Editor: Janna Oetting×
  • Associate Editor: Laura DeThorne
    Associate Editor: Laura DeThorne×
  • © American Speech-Language-Hearing Association
Article Information
Development / Special Populations / Genetic & Congenital Disorders / Research Issues, Methods & Evidence-Based Practice / Language / Research Articles
Research Article   |   June 2014
Late Language Emergence in 24-Month-Old Twins: Heritable and Increased Risk for Late Language Emergence in Twins
Journal of Speech, Language, and Hearing Research, June 2014, Vol. 57, 917-928. doi:10.1044/1092-4388(2013/12-0350)
History: Received November 5, 2012 , Revised March 27, 2013 , Accepted August 23, 2013
 
Journal of Speech, Language, and Hearing Research, June 2014, Vol. 57, 917-928. doi:10.1044/1092-4388(2013/12-0350)
History: Received November 5, 2012; Revised March 27, 2013; Accepted August 23, 2013
Web of Science® Times Cited: 1

Purpose: This study investigated the etiology of late language emergence (LLE) in 24-month-old twins, considering possible twinning, zygosity, gender, and heritability effects for vocabulary and grammar phenotypes.

Method: A population-based sample of 473 twin pairs participated. Multilevel modeling estimated means and variances of vocabulary and grammar phenotypes, controlling for familiality. Heritability was estimated with DeFries–Fulker regression and variance components models to determine effects of heritability, shared environment, and nonshared environment.

Results: Twins had lower average language scores than norms for single-born children, with lower average performance for monozygotic than dizygotic twins and for boys than girls, although gender and zygosity did not interact. Gender did not predict LLE. Significant heritability was detected for vocabulary (0.26) and grammar phenotypes (0.52 and 0.43 for boys and girls, respectively) in the full sample and in the sample selected for LLE (0.42 and 0.44). LLE and the appearance of Word Combinations were also significantly heritable (0.22–0.23).

Conclusions: The findings revealed an increased likelihood of LLE in twin toddlers compared with single-born children that is modulated by zygosity and gender differences. Heritability estimates are consistent with previous research for vocabulary and add further suggestion of heritable differences in early grammar acquisition.

Acknowledgments
This work was made possible by grants from the National Institutes of Health (RO1DC05226, P30DC005803, P30HD002528). The second author is supported by a program grant from the National Health and Medical Research Council of Australia (No. 572742). The authors especially thank the children and families who participated in the study and the following members of the research team: Antonietta Grant, Erika Hagemann, Alani Morgan, Virginia Muniandy, Elke Scheepers, and Alicia Watkins. The authors also thank Denise Perpich for data management and data summaries, and the staff at the Western Australian Data Linkage Branch and the Maternal and Child Health Unit.
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