Differential Genetic Aetiology of Reading Disability as a Function of Age

Genetic and Environmental Influences on Word Recognition and Spelling Deficits as a Function of Age

“…The estimates for group deficits in spelling recognition were .63 in the younger group and .52 in the older group, and did not differ significantly. Nevertheless, Wadsworth et al (1989) suggested that the greater difference between the heritabilities of word recognition deficits as a function of age than the difference between the heritabilities of spelling deficits as a function of age might be suggestive of a developmental dissociation.…”

“…This suggests a possible dissociation in the etiology and remediation of reading and spelling deficits. Previous behavioral genetic analyses of twin data have suggested a possible developmental dissociation between genetic influences on word reading and spelling deficits as a function of age, wherein genetic influence declined across age for word recognition, and increased for spelling recognition (DeFries et al 1997;Wadsworth et al 1989). However, none of the age trends for word recognition and spelling was statistically significant in these studies because their samples were small and they had limited power to find significant effects.…”

“…The sample ranged in age from approximately 8 to 20 years with an age cut-off at 11.5 for younger and older samples. As in the previous study by Wadsworth et al (1989), the partial regression of the interaction of age and the coefficient of genetic relationship provided a test of a differential change in the heritability of word recognition and spelling deficits as a function of age. They also tested for an interaction between measure, age, and zygosity by employing repeated measures ANOVA in a novel way to transformed cotwin data only, which demonstrated regression to the mean of the population.…”

“…Based in part on this apparent age difference in results across the different studies, Stevenson et al hypothesized that there may be a decline in the heritability of deficits in word recognition as a function of age. Wadsworth et al (1989) tested Stevenson et al's (1987) hypothesis that the heritability of deficits in reading declines as a function of age and also examined age differences in genetic influences on spelling deficits. The DeFries-Fulker (DF) multiple regression model (1985,1988) was fitted to measures of word recognition and spelling recognition.…”

Are Attitudes Towards Economic Risk Heritable? Analyses Using the Australian Twin Study of Gambling

“…The models outlined in equations (1) and (2) have been extended to capture differential heritability across levels of cognitive ability (Cherny et al, 1992a), differential heritability by age (Wadsworth et al, 1989) and differential heritability by gender (DeFries et al, 1993). This is achieved, in the context of a focus on gender, and in relation to equation (1), by adding gender interaction terms as follows (see, for example, Detterman et al, 1990, p. 373):…”