A twin and adoption study of reading achievement: Exploration of shared-environmental and gene–environment-interaction effects

Abstract

Existing behavior-genetic research implicates substantial influence of heredity and modest influence of shared environment on reading achievement and reading disability. Applying DeFries-Fulker analysis to a combined sample of twins and adoptees (N = 4,886, including 266 reading-disabled probands), the present study replicates prior findings of considerable heritability for both reading achievement and reading disability. A simple biometric model adequately described parent and offspring data (combined N = 9,430 parents and offspring) across differing types of families present in the sample Analyses yielded a high heritability estimate (around 0.70) and a negligible shared-environmentality estimate for both reading achievement and reading disability. No evidence of gene × environment interaction was found for parental reading ability and parental educational attainment, the two moderators analyzed.

Genetic transmission of reading ability

“…We do not know of other studies that have found evidence for non-additive (or dominant) genetic influence on reading (dis)ability (e.g. Kirkpatrick et al, 2011). Reading ability of spouses appeared to be correlated (assortative mating, 0.38), which is in line with findings from Wadsworth et al (2002: 0.26) and other studies of traits that correlate with reading, like intelligence (Vinkhuyzen, van der Sluis, Maes, & Posthuma, 2012: 0.37), but lower than found by van Bergen et al (2015: 0.16).…”

“…Two English studies tried to disentangle genetic and environmental influences within the family. A study that includes parent and (adoptive) child data (Kirkpatrick, Legrand, Iacono, & Mcgue, 2011) provides a genetically sensitive design. This study employed a broad construct of literacy (Wide Range Achievement Test), but did not explicitly test the nature of familial transmission.…”

The interface between genetics and psychology: lessons from developmental dyslexia

“…This approach can be extended to the case of a categorical disorder, by converting the concordance for disorder in MZ and DZ twins to tetrachoric correlations [17]. If, however, the disorder is defined in terms of a quantitative dimension, another method, DeFries-Fulker analysis [18], can be used.…”

“…DeFries-Fulker analysis of reading difficulties has been used with three large samples: from the Colorado Learning Disabilities Research Center (CLDRC) [19], from the Twins Early Development Study [20] and from a large sample of twins and adoptees in Minnesota [17]. In all three studies, the heritability of reading disability was estimated to be at least 60%.…”

“…The authors concluded that the effect of genes will be particularly evident in children who fail to learn to read despite good environmental support. This makes intuitive sense [21], but it is noteworthy that the finding was not replicated in another study that looked at the same question using slightly different methods [17].…”