TY - JOUR
T1 - Late language emergence in 24-month-old twins
T2 - Heritable and increased risk for late language emergence in twins
AU - Rice, Mabel L.
AU - Zubrick, Stephen R.
AU - Taylor, Catherine L.
AU - Gayán, Javier
AU - Bontempo, Daniel E.
PY - 2014
Y1 - 2014
N2 - 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.
AB - 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.
KW - Language acquisition
KW - Late language emergence
KW - Twin early grammar
KW - Twin language
KW - Twin zygosity effects
UR - http://www.scopus.com/inward/record.url?scp=84902804922&partnerID=8YFLogxK
U2 - 10.1044/1092-4388(2013/12-0350)
DO - 10.1044/1092-4388(2013/12-0350)
M3 - Article
C2 - 24167238
AN - SCOPUS:84902804922
SN - 1092-4388
VL - 57
SP - 917
EP - 928
JO - Journal of Speech, Language, and Hearing Research
JF - Journal of Speech, Language, and Hearing Research
IS - 3
ER -