Genetic and environmental influences on early speech, language and literacy development

Abstract

The genetic and environmental etiology of speech and broader language skills was examined in terms of their concurrent relationships in young children; their longitudinal association with reading; and the role they play in defining the 'heritable phenotype' for specific language impairment (SLI). The work was based on a large sample of 4½-year-old twins, who were assessed at home on a broad range of speech and language measures as part of the Twins Early Development Study. We found that genetic factors strongly influence variation in young children's speech in typical development as well as in SLI, and that these genetic factors also account for much of the relationship between early speech and later reading. In contrast, shared environmental factors play a more dominant role for broader language skills, and in relating these skills to later reading; isolated impairments in language as opposed to speech appear to have largely environmental origins.Learning Outcomes-1) Readers will be able to discuss some of the ways in which behavioural genetic methods can make a useful contribution to the field of communication disorders. 2) Readers will be able to compare the genetic and environmental contributions to general language versus speech skills in young children. 3) Readers will be able to describe the likely relationship between early speech and language and later reading development, in terms of shared genetic and environmental resources. 4) Readers will be able to discuss how different ascertainment methods for clinical samples may lead to very different understandings of the nature of a disorder such as specific language impairment. Keywords etiology; genes; environment; speech; language; reading; SLI The current paper explores the relationship between speech and language skills in young children, using a behavioural genetics approach. I will illustrate this theme using three recently completed studies: the first examines the nature of the relationship between speech and language in terms of the shared genetic and environmental factors that influence them; the second looks at the extent to which genes and environments that are important for speech and language skills in preschool also have long term impact on children's reading; and the third study considers how a differentiation between speech and broader language skills may be useful for clarifying the 'heritable phenotype' in specific language impairment. Background on TEDS and the twin method

Genes and Gini: What Inequality Means for Heritability

“…For example, the pattern of results that emerged from cross-cultural longitudinal research on literacy is consistent with the hypothesis of greater equality leading to greater heritability (e.g. Kovas et al, 2005;Samuelsson et al, 2008;Hayiou-Thomas, 2008). The research demonstrated that heritability of reading skills varies as a function of students' age and educational set-up, including the extent to which the formal education system is able to buffer the effects of socioeconomic inequality.…”

Individual Differences in Lexical Processing at 18 Months Predict Vocabulary Growth in Typically Developing and Late‐Talking Toddlers

“…However, heritability estimates for SLI have been inconsistent, suggesting that language impairments have multiple causes (Bishop, 2006). Recent research also shows that genetic factors account for individual differences in the speech of typically-developing children as well as those with SLI (Hayiou-Thomas, 2008), consistent with the view that children vary in language proficiency along multiple continuous dimensions.…”

The Home Literacy Environment Is a Correlate, but Perhaps Not a Cause, of Variations in Children’s Language and Literacy Development

“…Although the heritability of general language skills has been estimated to be 64% (de Zeeuw et al, 2015), other behaviour-genetic studies indicate that phonological processing skills, such as the ability to repeat nonwords, are more highly heritable and less susceptible to environmental effects than broader language abilities, such as vocabulary (Hayiou-Thomas, 2008). This leads to the prediction of a stronger association between maternal phonology and child reading/spelling than between broader (nonphonological) measures of mother’s language and child language and literacy outcomes.…”