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Updated: Jun 14, 2026

Using Cholesky Decomposition to Explore Individual Differences in Longitudinal Relations between Reading Skills
Published on: September 17, 2019
Differential genetic etiology of reading difficulties as a function of IQ: an update
S J Wadsworth1, R K Olson, J C DeFries
1Institute for Behavioral Genetics, University of Colorado, Boulder, CO 80309, USA. Sally.Wadsworth@Colorado.edu
Abstract:
In order to test the hypothesis that the genetic etiology of reading disability differs as a function of IQ, composite reading performance data from 308 pairs of identical (monozygotic, MZ) twins and 440 pairs of fraternal (dizygotic, DZ) twins (254 same-sex and 186 opposite-sex) in which at least one member of each pair was classified as reading-disabled were subjected to multiple regression analysis (DeFries and Fulker, Behav Genet 15:467-473, 1985; Acta Genet Med Gemellol 37:205-216, 1988). In the total sample, heritability of the group deficit in reading performance (h(g)(2)) was .61 (±.06). However, results of fitting an extended regression model to reading performance and IQ data suggested that the genetic etiology of reading disability differs as a linear function of IQ (p ≤ .04). When the basic regression model was fitted separately to data from twin pairs with Wechsler (Examiner's manual: Wechsler intelligence scale for children-revised, 1974; Examiner's manual: Wechsler adult intelligence scale-revised, 1981) Full Scale IQ scores in the upper and lower 25% of the sample, resulting estimates of h(g)(2) were .75 (±.12) and .50 (±.10), respectively (p ≤ .045). These results suggest that reading difficulties in children with a higher IQ are due substantially to genetic influences and may require intensive remediation efforts.
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