Genetic influences on word recognition abilities and disabilities: A study of 7 year old twins

Social, Genetic, & Developmental Psychiatry Centre, Institute of Psychiatry, King's College London, UK.
Journal of Child Psychology and Psychiatry (Impact Factor: 6.46). 05/2005; 46(4):373-84. DOI: 10.1111/j.1469-7610.2004.00358.x
Source: PubMed


A fundamental issue for child psychology concerns the origins of individual differences in early reading development.
A measure of word recognition, the Test of Word Reading Efficiency (TOWRE), was administered by telephone to a representative population sample of 3,909 same-sex and opposite-sex pairs of 7-year-old twins. Analyses allowing for sex differences in aetiology were used to estimate the extent to which genetic and environmental influences contribute to normal variation in word recognition and word recognition difficulties, defined by scores below the 5th and 10th percentiles of the unselected sample.
Both normal variation in word recognition and impaired word recognition abilities were substantially heritable (h2 = .65-.67; h(g)2 = .37-.72). Environmental influences were primarily shared between twins, rather than specific to each individual, and small to moderate in magnitude. There was evidence for qualitative sex differences. Quantitative sex differences were also suggested at the extremes, with genetic influences being more important as a cause of reading difficulties in boys than in girls.
These findings indicate that early individual differences and impairments in word recognition are principally influenced by genetic factors and may involve partly distinct genetic or environmental effects in boys and girls. Crucially, they also provide evidence that reading impairments are linked genetically to the normal distribution. Genetic risk for early impairments in word recognition is continuous rather than discrete.

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Available from: Philip S Dale, Dec 25, 2015
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    • "Some twin studies report evidence for shared-environmental influences (reading disability e.g. Friend, Defries, & Olson, 2008; Harlaar et al., 2005; reading ability e.g. Petrill et al., 2007; Taylor & Schatschneider, 2010). "
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    • "I first met his parents who wanted to know more about dyslexia – the diagnosis he received after he was referred to a full psychodiagnosis evaluation. This evaluation revealed an unconceivable gap between the expected achievements from such a quick, easy to handle, diligent and good-natured boy, as he was 1 The subject will be referred to as " he " because in all dyslexia studies the male/female rate found had been from 2:1 to 15:1 (Finucci et al., 1981; Harlaar et al., 2005; Hawke et al., 2007, 2009; Miles et al., 1998; Shaywitz et al., 1990; Stevenson, 1990 Vogel, 1990) "
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    • "Twin studies provide evidence for the importance of genetic influences for the genesis of reading problems, as well as for normal variations in reading skills in the population [49]. It has been suggested that as much as 70% of the variation in 7-year-olds’ decoding skills is attributable to genetic differences [50]. Similarly, normal variations in oral language skills are heritable, and there is evidence for the importance of genetic influences in the aetiology of specific language impairment [51,52]. "
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