Reading and Generalist Genes

ABSTRACT— Twin-study research suggests that many (but not all) of the same genes contribute to genetic influence on diverse learning abilities and disabilities, a hypothesis called generalist genes . This generalist genes hypothesis was tested using a set of 10 DNA markers (single nucleotide polymorphisms [SNPs]) found to be associated with early reading ability in a study of 4,258 7-year-old children that screened 100,000 SNPs. Using the same sample, we show that this early reading SNP set also correlates with other aspects of literacy, components of mathematics, and more general cognitive abilities. These results provide support for the generalist genes hypothesis. Although the effect size of the current SNP set is small, such SNP sets could eventually be used to predict genetic risk for learning disabilities as well as to prescribe genetically tailored intervention and prevention programs.     

Predicting individual differences in reading comprehension: a twin study

We examined the Simple View of reading from a behavioral genetic perspective. Two aspects of word decoding (phonological decoding and word recognition), two aspects of oral language skill (listening comprehension and vocabulary), and reading comprehension were assessed in a twin sample at age 9. Using latent factor models, we found that overlap among phonological decoding, word recognition, listening comprehension, vocabulary, and reading comprehension was primarily due to genetic influences. Shared environmental influences accounted for associations among word recognition, listening comprehension, vocabulary, and reading comprehension. Independent of phonological decoding and word recognition, there was a separate genetic link between listening comprehension, vocabulary, and reading comprehension and a specific shared environmental link between vocabulary and reading comprehension. There were no residual genetic or environmental influences on reading comprehension. The findings provide evidence for a genetic basis to the “Simple View” of reading.     

Word Reading Fluency: Role of Genome‐Wide Single‐Nucleotide Polymorphisms in Developmental Stability and Correlations With Print Exposure

The genetic effects on individual differences in reading development were examined using genome‐wide complex trait analysis (GCTA) in a twin sample. In unrelated individuals (one twin per pair, n = 2,942), the GCTA‐based heritability of reading fluency was ~20%–29% at ages 7 and 12. GCTA bivariate results showed that the phenotypic stability of reading fluency from 7 to 12 years (r = 0.69) is largely driven by genetic stability (genetic r = 0.69). Genetic effects on print exposure at age 12 were moderate (~26%) and correlated with those influencing reading fluency at 12 (genetic r = 0.89), indicative of a gene–environment correlation. These findings were largely consistent with quantitative genetic twin analyses that used both twins in each pair (n = 1,066–1,409).     

Associations between reading achievement and independent reading in early elementary school: a genetically informative cross-lagged study

This study used a cross-lagged twin design to examine reading achievement and independent reading from 10 to 11 years (n = 436 twin pairs). Reading achievement at age 10 significantly predicted independent reading at age 11. The alternative path, from independent reading at age 10 to reading achievement at age 11, was not significant. Individual differences in reading achievement and independent reading at both ages were primarily due to genetic influences. Furthermore, individual differences in independent reading at age 11 partly reflected genetic influences on reading achievement at age 10. These findings suggest that genetic influences that contribute to individual differences in children's reading abilities also influence the extent to which children actively seek out and create opportunities to read.     

From learning to read to reading to learn: substantial and stable genetic influence

Little is known about the underlying causes and developmental patterns of stability and change in early reading abilities. In a longitudinal study of twins (n=4,291 pairs), individual differences in reading achievement assessed by teachers using U.K. National Curriculum (NC) criteria showed substantial heritabilities at ages 7, 9, and 10 years (.57-.67) and modest shared environmental influences (.10-.17). Stability in NC scores was primarily mediated genetically. There was also evidence for age-specific genetic influences at each age. Genetic influences on reading are substantial and stable during the elementary school years despite the shift from "learning to read" to "reading to learn."     

Telephone Testing and Teacher Assessment of Reading Skills in 7-year-olds: II. Strong Genetic Overlap

In a companion paper, word recognition skills assessed by telephone using the Test of Word Reading Efficiency (TOWRE) were found to correlate highly with National Curriculum (NC) teacher-assessed reading ability in 7-year-old twins. This study examined the genetic and environmental origins of this high correlation. TOWRE and NC scores were both highly heritable and the correlation between them was largely due to overlapping genetic effects. These findings were obtained both across the normal range of reading abilities and at the low extreme, defined by scores below a 13.4% cut-off on either measure. TOWRE and NC scores may provide promising phenotypes for further study of the aetiology of early reading abilities and disabilities.     

Genetic and environmental mediation of the prediction from preschool language and nonverbal ability to 7‐year reading

We use a genetically sensitive design to examine the relationship between language and nonverbal ability at 4½ and reading skills at 7 years of age in a sample of more than 1,000 children participating in the Twins Early Development Study. We find that nonphonological as well as phonological measures of early language make significant contributions towards the prediction of reading at 7, and that nonverbal ability at 4½ is an equally strong predictor. With respect to aetiology, we find substantial genetic contributions towards the relationship between early language skills and reading at 7, as well as a trend towards shared environmental influences. The genetic continuity is not specific to the verbal domain, however, as we also find a substantial genetic relationship between nonverbal ability at 4½ and reading at 7.     

Telephone Testing and Teacher Assessment of Reading Skills in 7-year-olds: I. Substantial Correspondence for a Sample of 5544 Children and for Extremes

Many research questions require the assessment of reading in large samples of children. We compared two nonconventional procedures for early reading assessment: test administration by telephone, and teacher assessment. Five thousand five hundred and forty four children participating in a longitudinal twin study were assessed by telephone using the Test of Early Word Reading Efficiency, and by their teachers using the UK National Curriculum criteria. A correlation of 0.69 was obtained between the TOWRE and Teacher Assessment for Reading. There was also good agreement between the two procedures for identification of children at the lower extreme. Both appear to be practical and valid for research studies.