We examined the genetic and environmental contribution to the stability and instability of reading outcomes in early elementary school using a sample of 283 twin pairs drawn from the Western Reserve Reading Project. Twins were assessed across two measurement occasions. In Wave 1, children were either in kindergarten or first grade. Wave 2 assessments were conducted one year later. Results suggested substantial genetic stability across measurement occasions. Additionally, shared environmental influences also accounted for stability, particularly for variables more closely tied to direct instruction such as phonological awareness, letter knowledge, and word knowledge. There was also evidence for independent genetic and shared environmental effects, suggesting that new sources of variance may emerge as the demands of school change and children begin to acquire early reading skills.

The current study involved 281 early-school-age twin pairs (118 monozygotic, 163 same-sex dizygotic) participating in the ongoing Western Reserve Reading Project (S. A. Petrill, K. DeaterDeckard, L. A. Thompson, & C. Schatschneider, 2006). Twins were tested in their homes by separate examiners on a battery of reading-related skills including phonological awareness, rapid automatized naming, word knowledge, and phonological decoding. Results suggested that a core genetic factor accounted for a significant portion of the covariance between phonological awareness, rapid naming, and reading outcomes. However, shared environmental influences related to phonological awareness were also associated with reading skills. Keywordsreading; genetics; phonological awareness; development For nearly 2 decades, researchers have argued for the primacy of phonological processing in the acquisition of early literacy skills (Bradley & Bryant, 1983;Stanovich & Siegel, 1994;Torgesen, Wagner, Rashotte, Burgess, & Hecht, 1997). More recently, others have suggested that in addition to phonology, naming speed constitutes an independent and additive source of variance in early reading skills (e.g., Wolf & Bowers, 1999). In a recent meta-analysis, Swanson, Trainin, Necoechea, and Hammill (2003) examined the association between phonological awareness, rapid automatized naming (RAN), reading, and related abilities in a set of 49 independent samples. Although their results suggested that phonological awareness and RAN were factorially distinct, particularly in their prediction of real-world reading outcomes, phonological awareness and RAN were also significantly correlated with one another (weighted r = .39). Thus, although phonological awareness and RAN contributed independently to reading outcomes, there was also significant overlap between phonological awareness and the skills that underlie RAN performance.Correspondence concerning this article should be addressed to Stephen A. Petrill One important issue is the extent to which genes and environments influence the overlap and independence among phonological awareness, serial naming, and reading outcomes. It is clear that genetic and environmental influences are significant when examining not only reading outcomes (e.g., Pennington & Smith, 1983;Stevenson, Graham, Fredman, & McLoughlin, 1987) but also reading-related measures such as phonological awareness Knopik, Alarcón, & DeFries, 1998;Olson, Gillis, Rack, DeFries, & Fulker, 1991) and RAN (Compton, Davis, De-Fries, Gayan, & Olson, 2001). The importance of genetic influences on reading and reading performance has been further supported by a series of independent studies that have identified and replicated quantitative trait loci for reading on the short arms of Chromosomes 2, 6, and 18 (Cardon et al., 1994;Gayan et al., 1999;Grigorenko, 2003;Grigorenko et al., 1997;Grigorenko, Wood, Meyer, & Pauls, 2000;Fagerheim et al., 1999;Fisher et al., 1999Fisher et al., , 2002. Furthermore, studies have shown that genes are primarily responsi...

Background-Studies have suggested genetic and environmental influences on overall level of early reading whereas the larger reading literature has shown environmental influences on the rate of growth of early reading skills. This study is the first to examine the genetic and environmental influences on both initial level of performance and rate of subsequent growth in early reading.

This guide provides a basic overview of 16 child nonverbal IQ measures and uses a set of specified criteria to evaluate them in terms of their psychometric properties. In doing so, the goal is neither to validate nor to criticize current uses of IQ but to (a) familiarize clinicians and investigators with the variety of nonverbal IQ measures currently available, (b) highlight some of the important distinctions among them, and (c) provide recommendations for the selection and interpretation of nonverbal IQ measures.

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. © The International Dyslexia Association 2010Correspondence to: Nicole Harlaar, nicoleharlaar@gmail.com. NIH Public Access Author ManuscriptAnn Dyslexia. Author manuscript; available in PMC 2011 December 1. Predicting individual differences in reading comprehension: a twin studyBy the end of elementary school, the primary goal of literacy learning is "reading for meaning". For example, the National Assessment of Educational Progress (US Department of Education, 2005) stipulates that a "proficient" reading level at fourth grade entails that the reader is able to demonstrate an overall understanding of text. Additionally, "when reading text appropriate to fourth grade, they should be able to extend the ideas in the text by making inferences, drawing conclusions, and making connections to their own experiences". Despite concerted efforts by teachers and parents, there are substantial individual differences in the extent to which children meet these expectations. In the present study, we used a behavioral genetic design to determine which skills contribute to individual differences in reading comprehension and how these skills are related to each other, drawing on the Simple View of reading (Gough & Tunmer, 1986;Hoover & Gough, 1990).According to the Simple View, proficient reading represents the product of two factors. One is word decoding, or the process of translating print to words. The other is listening comprehension, or understanding spoken language. Both word decoding and listening comprehension are necessary for successful reading comprehension, but neither skill is sufficient without the other. This makes intuitive sense: When word decoding skills are weak, words are likely to be misidentified and fewer cognitive resources can be devoted to the processing of meaning. Even if all the words can be correctly decoded, however, text comprehension will be compromised if the meanings of those words are largely unknown. As such, word decoding and listening com...

Despite the common use of mean length of utterance (MLU) as a diagnostic measure, what it actually reflects in terms of linguistic knowledge is relatively unclear. This study explored the extent to which variance in MLU could be accounted for by a measure of expressive vocabulary and a measure of morphosyntax in a group of 44 typically-developing children, ages 28-37 months. Regression techniques were employed to predict MLU from number of different words (NDW) and a tense accuracy composite (TAC). Depending on whether the variable was acting alone or in concert with the other, TAC accounted for 23% or none of the variance in MLU, while NDW accounted for 51% or 28%. We offer three potential explanations for the observed association between MLU and NDW, none of which necessarily precludes the others.

The genetic and environmental sources of variance in mothers’ and fathers’ ratings of child temperament in middle childhood were estimated and compared. Parents of 88 MZ twin pairs and 109 same-sex DZ twin pairs completed a temperament questionnaire. For Effortful Control, significant genetic and environmental effects were indicated across mothers’ and fathers’ ratings, but parent differences were found for the Negative Affectivity factor. When present, sibling contrast effects were not consistent for mothers and fathers. Parental ratings of the Effortful Control factor were best explained by the Biometric model whereas the Negative Affectivity factor was best explained by the Rater Bias model. Overall, mothers’ and fathers’ ratings yielded similar evidence of genetic and environmental etiology of temperament in middle childhood.

Purpose-The present study examined the extent of genetic and environmental influences on individual differences in children's conversational language use.Method-Behavioral genetic analyses focused on conversational measures and 2 standardized tests from 380 twins (M = 7.13 years) during the 2nd year of the Western Reserve Reading Project (S. A. Petrill, K. Deater-Deckard, L. A. Thompson, L. S. DeThorne, & C. . Multivariate analyses using latent factors were conducted to examine the extent of genetic overlap and specificity between conversational and formalized language.Results-Multivariate analyses revealed a heritability of .70 for the conversational language factor and .45 for the formal language factor, with a significant genetic correlation of .37 between the two factors. Specific genetic effects were also significant for the conversational factor.Conclusions-The current study indicated that over half of the variance in children's conversational language skills can be accounted for by genetic effects with no evidence of significant shared environmental influence. This finding casts an alternative lens on past studies that have attributed differences in children's spontaneous language use to differences in environmental language exposure. In addition, multivariate results generally support the context-dependent construction of language knowledge, as suggested by the theory of activity and situated cognition (J. S. Brown, A. Collins, & P. Duguid, 1989; T. A. Ukrainetz, 1998), but also indicate some degree of overlap between language use in conversational and formalized assessment contexts. Keywordsexpressive language assessment; elementary school pupils; language Contact author: Laura S. DeThorne, University of Illinois at Urbana-Champaign, 901 South Sixth Street, Champaign, IL 61820. E-mail: lauras@uiuc.edu. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptA number of twin studies have used quantitative genetic methods to estimate environmental and genetic influences on language development. The twin design hinges on a comparison of monozygotic (MZ) and dizygotic (DZ) twins. Because MZ twins share 100% of their segregating genes and DZ twins share on average 50%, higher similarity between MZ twins is indicative of genetic effects (Plomin, DeFries, McClearn, & McGuffin, 2001). One means of measuring twin similarity is by comparing intraclass correlations for MZ versus DZ twins. The larger the MZ intraclass correlation in comparison with the DZs, the higher heritability (h 2 ) will be. In contrast, shared environmental effects (c 2 ) lead to similarity across all twins. Consequently, similar intraclass correlations between MZ and DZ twins are indicative of shared environmental effects. Finally, the extent to which MZ twins appear dissimilar is attributed to a combination of nonshared environment and error (e 2 ). Nonshared environmental influences are unique to the individual.An underlying assumption of twin methodology is that the nature of genetic and environ...