Genetic and environmental influences on prereading skills and early reading and spelling development in the United States, Australia, and Scandinavia

Abstract

Genetic and environmental relations between vocabulary and reading skills were explored longitudinally from preschool through grades 2 and 4. At preschool there were strong sharedenvironment and weak genetic influences on both vocabulary and print knowledge, but substantial differences in their source. Separation of etiology for vocabulary and reading continued for word recognition and decoding through grade 4, but genetic and environmental correlations between vocabulary and reading comprehension approached unity by grade 4, when vocabulary and word recognition accounted for all of the genetic and shared environment influences on reading comprehension.Correspondence concerning this article should be addressed to Richard Olson, Department of Psychology, University of Colorado, Boulder CO 80303, Richard.Olson@Colorado.EDU. NIH Public Access Author ManuscriptSci Stud Read. Author manuscript; available in PMC 2011 January 12. Much research has shown that individual differences in the development of vocabulary are significantly correlated with individual differences in reading, more strongly so with reading comprehension than with word recognition (Braze, Tabor, Shankweiler, & Mencel, 2007;Nation & Cocksey, 2009;Storch & Whitehurst, 2002). In addition, there is evidence for partial independence in the phenotypic contributions of oral language (including vocabulary) and decoding to reading comprehension as early as the second grade (Kendeou, van den Broek, White, & Lynch, 2009). A fundamental question about these individual differences is the relative influence from genetic and environmental factors on vocabulary, on different reading skills, and on their correlation. Are the same genetic and environmental influences at play for these skills, or are there significant differences in etiology between skills? The present study addresses this question longitudinally through the early stages of reading development by comparing the similarities of identical and fraternal twins beginning in preschool, and subsequently in a follow-up assessment near the end of the grade 2 when children are "learning to read," and then again at the end of grade 4 when children are "reading to learn" (Chall, 1983).The present analyses are based on data from the International Longitudinal Twin Study (ILTS) of early reading development. The ILTS includes samples of identical and same-sex fraternal twins from Australia, Colorado, and Scandinavia. The combined sample currently exceeds 2000 twins who have been tested in preschool. The twins were initially assessed on a broad range of pre-reading skills including letter name knowledge and vocabulary in the preschool year before admission to kindergarten, and before learning to read could interact with those skills. Subsequently the twins were tested on reading and related skills at the end of kindergarten, first, and second grade in all countries, and at the end of fourth grade in the U.S. sample. Vocabulary was assessed in preschool and again at the end of grades 2 and 4.In the present stud...

Genetic transmission of reading ability

“…Therefore, should it be the case that heritability increases with age, our estimate would represent an average over the lifespan and will therefore be somewhat higher than if it were based on younger twins alone. In addition, we found a somewhat larger component of E on reading ability compared to other genetic studies which found estimates around 10% (Harlaar, Spinath, Dale, & Plomin, 2005;Samuelsson et al, 2007). This may reflect larger measurement error, or reflect genuine environmental influences that are not shared among family members.…”

Response to early literacy instruction in the United States, Australia, and Scandinavia: A behavioral-genetic analysis

“…The study by Samuelsson et al (2007) was the first to compare genetic and environmental contributions to literacy skills as a function of intensity of reading instruction in kindergarten. By comparing an Australian twin sample entering a school system with strong emphasis on literacy instruction with U.S. twins receiving approximately half the time of instruction, estimated heritability was 1.5 and 2.5 times higher in Australia on reading and spelling, respectively.…”

“…In this article, we continue to report on our International Longitudinal Twin Study (ILTS) of early language and literacy development (Byrne et al 2002;Byrne et al 2005;Byrne et al 2006;Byrne et al 2007;Samuelsson et al 2007;Willcutt et al 2007). The main purpose here was to compare genetic and environmental influences on early reading and spelling skills across three twin samples tested in the United States, Australia, and Scandinavia (i.e., Sweden and Norway) and across time of testing (i.e., kindergarten and Grade 1).…”

Does Training in Syllable Recognition Improve Reading Speed? A Computer-Based Trial With Poor Readers From Second and Third Grade

“…In longitudinal studies, naming speed has proven to be rather stable and naming speed deficits appear to be persistent in nature (e.g., Powell, Stainthorp, & Stuart, 2014). Some part of this stability can be explained by genetic sources, as a strong genetic influence has been shown in RAN performance (e.g., Byrne et al, 2006;Christopher et al, 2015;Davis et al, 2001;Petrill, Deater-Deckard, Thompson, DeThorne, & Schatschneider, 2006;Petrill et al, 2010;Samuelsson et al, 2007). There is also recent research evidence for specific genes that have been associated with RAN performance (Naples, Chang, Katz, & Grigorenko, 2009), some of them the same as those previously associated with dyslexia (Rubenstein, Raskind, Berninger, Matsushita, & Wijsman, 2014).…”