Reading disability in boys and girls: No evidence for a differential genetic etiology

In order to test the hypothesis that genetic influences are more important as a cause of reading disability in girls than in boys, composite reading performance data from identical and fraternal twin pairs were analyzed using both concordance and multiple regression methods. The sample included 206 identical (99 male, 107 female), 159 same-sex fraternal (90 male, 69 female), and 117 opposite-sex fraternal twin pairs, in which at least one member of each pair had reading difficulties. Although the difference between the concordance rates for reading disabilities in female identical and same-sex fraternal twin pairs was somewhat greater (65% for identical twins vs. 32% for fraternal twins) than the difference in concordance rates for boys (68% vs. 39%), loglinear analysis of these categorical data revealed that the interaction between sex, zygosity, and concordance was not significant (p greater than or equal to 0.70). Moreover, the heritability of reading disability (h(g)(2)) estimated from regression analysis of the reading performance data in males was nearly identical to that in females (h(g)(2) = 0.58 and 0.59, respectively; p greater than or equal to 0.90). Thus, results of this study provide little or no evidence for the hypothesis of greater genetic influence on reading difficulties in girls than in boys.