Etiology of reading difficulties as a function of gender and severity |
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| Authors: | Jesse L Hawke Sally J Wadsworth Richard K Olson John C DeFries |
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| Institution: | (1) Institute for Behavioral Genetics, University of Colorado, Boulder, CO, USA;(2) Institute for Behavioral Genetics, University of Colorado, 447 UCB, Boulder, CO 80309-0447, USA |
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| Abstract: | To test the hypothesis that the etiology of reading difficulties may differ for males and females in more severely impaired
samples, reading performance data from monozygotic (MZ), same-sex dizygotic (DZss), and opposite-sex dizygotic (DZos) twin pairs were analyzed using a model-fitting implementation of the DeFries-Fulker (DF) model (Purcell & Sham, 2003, Behavior genetics, 33, 271–278). Five non-independent samples were selected using cut-offs of −1 (N = 737 pairs), −1.5 (N = 654), −2 (N = 468), −2.5 (N = 335), and −3 (N = 198) standard deviations (s) below the mean composite reading score of control twins. Male/female gender ratios for children
with reading difficulties were significantly higher than 1.0 for all five samples and increased as a function of severity
(viz., 1.15, 1.17, 1.40, 1.61, and 1.88, respectively). When the DF model was fit to the data, estimates of heritability (h
g2) and shared environmental influences (c
g2) were not significantly different for males and females in any of the groups. Consequently, the most parsimonious model that
provided a good fit to the data at all five levels of severity equated the heritabilities and shared environmental influences
for males and females, and fixed the DZos coefficient of genetic relatedness at 0.5. Thus, these results provide no evidence for a differential etiology of reading
difficulties as a function of gender in more severely impaired samples, and suggest that the same genetic and environmental
influences contribute to reading difficulties in males and females, irrespective of severity. |
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| Keywords: | Gender Genetics Heritability Reading Disability Twins |
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