Longitudinal Stability in Genetic Effects on Children's Conversational Language Productivity
ABSTRACT The authors examined the longitudinal stability of genetic and environmental influences on children's productive language sample measures during the early school-age years.
Twin study methodology with structural equation modeling was used to derive univariate estimates of additive genetic (A), shared environmental (C), and nonshared environmental (E) effects on language measures at each of 2 time points, based on 487 twins at the 1st-grade time point and 387 twins at the 2nd-grade time point. To address questions of stability over time, the authors used longitudinal latent factor analysis.
Stability in the Conversational Language factor was accounted for almost entirely by shared genetic effects between 1st and 2nd grade, meaning no new genetic effects were observed at the 2nd time point. In contrast, nonshared environmental effects were entirely time point specific, meaning whatever nonshared environmental influences were operating at the first time point were not influencing individual variation in the language factor at the second time point.
The discussion in this article centers on possible candidates for both genetic and nonshared environmental effects as well as implications for clinical practice and future research.
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ABSTRACT: To examine the etiology of developmental language impairment (LI) at 4 and 12 years, as well as the relationship between the two. Phenotypic and quantitative genetic analyses utilized longitudinal data from the Twins Early Development Study. A total of 2922 pairs (2150 monozygotic [MZ]; 1950 dizygotic same-sex [DZss]; and 1745 dizygotic opposite-sex [DZos]) provided data at 4 and 12 years. At 4, a) 'Psychometric LI' was defined on the basis of low scores (-1.25 SD) on parent-reported expressive vocabulary (226 MZ and 115 DZss probands for genetic analysis); b) 'Parent-referral' was defined as having seen a medical professional or speech-language therapist, following parental concern (112 MZ and 104 DZss probands). The 12-year language measure was a composite of 4 web-administered receptive language tests. a) 'Psychometric LI' is more predictive of poor language performance at age 12 than 'Parent-referral'; b) 'Parent-referral' is substantially and significantly more heritable than 'Psychometric LI'. Parents' concern about their child's language development seems to be the marker of a more heritable disorder than poor expressive language skills alone. However, the language difficulties which arouse parental concern in preschool children, although more heritable, are not predictive of language difficulties in early adolescence. Rather, poor expressive language skills at age 4, psychometrically defined, are a better predictor of continuing language difficulties at age 12.Journal of Speech Language and Hearing Research 10/2013; 57(3). DOI:10.1044/2013_JSLHR-L-12-0240 · 1.93 Impact Factor