Abstract
Reading difficulties are both heritable and stable; however, little is known about the etiology of this stability. Results from a preliminary analysis of data from 56 twin pairs who participated in the Colorado Longitudinal Twin Study of Reading Disability (Astrom et al., Twin Res Hum Genet 10:434–439, 2007) suggested that about two-thirds of the proband deficit at follow-up was due to genetic factors that also influenced deficits at their initial assessment. Although our proband sample is now nearly twice as large, it is still relatively small; thus, to increase power, we subjected data from probands, co-twins and their nontwin siblings to a novel extension of DeFries–Fulker analysis (DeFries and Fulker, Behav Genet 15:467–473, 1985; DeFries and Fulker, Acta Genet Med Gemellol, 37, 205–216, 1988). In addition to providing estimates of univariate and bivariate heritability, this analysis facilitates a test of the difference between shared environmental influences for twins versus siblings. Longitudinal composite reading performance scores at 10.6 and 15.5 years of age, on average, were analyzed from 33 MZ and 64 DZ twin pairs in which at least one member of each pair had reading difficulties, and from 44 siblings of the probands. Scores were highly stable (.86 ± .03, across probands, co-twins and siblings) and heritability of the group deficit at initial assessment was .67 ± .22. Longitudinal bivariate heritability was .59 ± .21, suggesting that nearly 60% of the proband reading deficit at follow-up is due to genetic factors that influenced reading difficulties at the initial assessment. However, tests for special twin environmental influences were nonsignificant.
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Acknowledgments
The Colorado Learning disabilities Research Center is supported by The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) grant HD027802. The Longitudinal Twin Study of Reading Disability is supported by grant DC005190 from the National Institute on Deafness and other Communication Disorders (NIDCD). During the preparation of this manuscript, Raven L. Astrom was supported by institutional training Grant HD007829. The continued cooperation of the many families participating in the CLDRC and LTSRD, as well as the work of the staff members of these projects is gratefully acknowledged.
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Astrom, R.L., Wadsworth, S.J., Olson, R.K. et al. DeFries–Fulker Analysis of Longitudinal Reading Performance Data from Twin Pairs Ascertained for Reading Difficulties and from Their Nontwin Siblings. Behav Genet 41, 660–667 (2011). https://doi.org/10.1007/s10519-011-9445-6
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DOI: https://doi.org/10.1007/s10519-011-9445-6