Dyslexia Research Today is a free monthly online journal that collates and summarizes the latest research about Dyslexia, including details on learning, reading, education, teaching, treatment.

Colorado longitudinal twin study of reading disability.

Wadsworth SJ, DeFries JC, Olson RK, Willcutt EG

Institute for Behavioral Genetics, University of Colorado, 447 UCB, Boulder, CO 80309, USA. Sally.Wadsworth@Colorado.edu

The primary objectives of the present study are to introduce the Colorado Longitudinal Twin Study of Reading Disability, the first longitudinal twin study in which subjects have been specifically selected for having a history of reading difficulties, and to present some initial assessments of the stability of reading performance and cognitive abilities in this sample. Preliminary examination of the test scores of 124 twins with a history of reading difficulties and 154 twins with no history of reading difficulties indicates that over the 5- to 6-year interval between assessments, cognitive and reading performance are highly stable. As a group, those subjects with a history of reading difficulties had substantial deficits relative to control subjects on all measures at initial assessment, and significant deficits remained at follow-up. The stability noted for all cognitive and achievement measures was highest for a composite measure of reading, whose average stability correlation across groups was 0.80. Results of preliminary behavior genetic analyses for this measure indicated that shared genetic influences accounted for 86% and 49% of the phenotypic correlations between the two assessments for twin pairs with and without reading difficulties, respectively. In addition, genetic correlations reached unity for both groups, suggesting that the same genetic influences are manifested at both time points.

Published 10 December 2007 in Ann Dyslexia, 57(2): 139-60.
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