A Twin Study of Genetic Influences on Reading and Spelling Ability and Disability

Abstract

The reading skills of 285 pairs of 13-year-old twins drawn from the general population were studied. The twins were independently tested using standardized measures of intelligence, reading and spelling ability. The genetic contribution to reading ability was assessed by examination of correlations in monozygotic (MZ) and same-sex dizygotic (DZ) twins, and by analysing differences between MZ and DZ twins in concordance of reading disability rates. The results suggested that, at this age, genetic factors play only a moderate role in general reading backwardness or specific reading retardation. However, when spelling ability was investigated, a heritability of 0.53 was obtained, increasing to 0.75 when intelligence was controlled. Strong genetic influences on spelling were also found when concordance rates for spelling disability were compared for MZ and DZ pairs.

The genetics of developmental dyslexia

“…18,19 The first compelling evidence that the high familiality of DD was due to genetic rather than shared environmental factors, came in the 1980s with the publication of two key twin studies; the Colorado Twin Reading Study 20 and the London Twin Study. 21 Subjects in the Colorado study (MZ ¼ 64; DZ ¼ 55 pairs) were ascertained on the basis that at least one member of the twin pair had reading disability. The London study took a different approach by sampling 285 twin pairs from the general population.…”

Further evidence that the KIAA0319 gene confers susceptibility to developmental dyslexia

“…Although the pathophysiology of DD is unknown, there is strong evidence that genes make a substantial contribution to individual variation in risk of DD, with twin studies reporting heritability estimates of up to 0.71. [1][2][3][4][5][6][7][8] Linkage studies have identified several genomic regions that may harbor susceptibility quantitative trait loci (QTL) for DD, and the most consistently replicated of these is DYX2, which lies on chromosome 6p22.2. 1,[9][10][11][12][13][14][15][16] A number of association studies have now been performed attempting to identify the DYX2 susceptibility locus.…”

Longitudinal Genetic Analysis of Early Reading: The Western Reserve Reading Project

“…First, genes are important to familial resemblance in reading ability and disability (e.g., Harlaar, Spinath, Dale, & Plomin, in press;Pennington & Smith, 1983; in press a; Stevenson, Graham, Fredman, & McLoughlin, 1987). Second, genetic influences are important for components of reading ability such as phonological awareness/decoding, reading comprehension, spelling, orthographic knowledge, and rapid automatized naming (see Olson, Forsberg, & Wise, 1994;Olson, Gillis, Rack, DeFries, & Fulker, 1991;Knopik, Alarcon, & DeFries, 1998;Gayan & Olson, 2003;Compton, Davis, DeFries, Gayan, & Olson, 2001).…”