The genetic architecture of oral language, reading fluency, and reading comprehension: A twin study from 7 to 16 years.

Maria G Tosto,Elizabeth Prom-Wormley,Marianna E Hayiou-Thomas,Philip S Dale,Nicole Harlaar,Robert Plomin

doi:10.1037/dev0000297

Abstract

This study examines the genetic and environmental etiology underlying the development of oral language and reading skills, and the relationship between them, over a long period of developmental time spanning middle childhood and adolescence. It focuses particularly on the differential relationship between language and two different aspects of reading: reading fluency and reading comprehension. Structural equation models were applied to language and reading data at 7, 12, and 16 years from the large-scale TEDS twin study. A series of multivariate twin models show a clear patterning of oral language with reading comprehension, as distinct from reading fluency: significant but moderate genetic overlap between oral language and reading fluency (genetic correlation rg = .46–.58 at 7, 12, and 16) contrasts with very substantial genetic overlap between oral language and reading comprehension (rg = .81–.87, at 12 and 16). This pattern is even clearer in a latent factors model, fit to the data aggregated across ages, in which a single factor representing oral language and reading comprehension is correlated with—but distinct from—a second factor representing reading fluency. A distinction between oral language and reading fluency is also apparent in different developmental trajectories: While the heritability of oral language increases over the period from 7 to 12 to 16 years (from h2 = .27 to .47 to .55), the heritability of reading fluency is high and largely stable over the same period of time (h2 = .73 to .71 to .64).

Highlights

This study examines the genetic and environmental etiology underlying the development of oral language and reading skills, and the relationship between them, over a long period of developmental time spanning middle childhood and adolescence
This pattern is even clearer in a latent factors model, fit to the data aggregated across ages, in which a single factor representing oral language and reading comprehension is correlated with— but distinct from—a second factor representing reading fluency
We examined the genetic architecture of stability and change over time, for each of the three constructs of language, reading comprehension and reading fluency (Figure 1; model-fitting statistics are presented in Table 3 in the supplementary online material)

Summary

Participants

The sampling frame for the present study is the United Kingdom-based Twins Early Development Study (TEDS), an ongoing longitudinal twin study (Haworth, Davis, & Plomin, 2013). The sex-limitation analyses do not provide evidence of genetic sex-differences in our language or reading measures They do show significantly greater phenotypic variability for reading fluency in 7-year-old boys compared with girls. The multivariate relationships between language and reading measures were modeled separately for each age, in the first instance, using correlated factors models These yield estimates of the degree of overlap in the etiology of language and reading: the genetic correlation (rg) provides an estimate of the extent to which it is the same or different genes which affect the measures, independent of their heritabilities. We used a common pathways genetic model in order to examine the etiological relationship between oral language, reading efficiency, and reading comprehension, irrespective of age In this model the measured variables from ages 7, 12, and 16 are hypothesized to load onto two latent factors, representing (a) reading efficiency, and (b) comprehension. There are estimates for the total effects of A, C, and E on each of the measures, which combine the shared and measure-specific effects

Results

Discussion

Cholesky ACE