Genetic and environmental influences on rapid naming and reading ability: A twin study

The present study assesses the genetic and environmental etiologies of reading, rapid naming (RN), and their covariation by fitting multivariate structural equation models to data from 587 twin pairs in which at least one member of the pair exhibited reading difficulties (low-range) and from 360 control (normal-range) twin pairs who were tested in the Colorado Learning Disabilities Research Center. Results from a bivariate phenotypic analysis with two hypothesized latent factors, READ and RN, indicated that the correlation between reading and rapid naming performance for the low-range sample was significantly higher than that of the normal-range sample. When this model was partitioned to include estimates of genetic, shared environmental, and nonshared environmental influences, resulting heritability estimates did not differ significantly for the low-range and normal-range samples for either READ or RN. However, similar to the phenotypic correlation, the genetic correlation between the READ and RN latent factors could not be equated for the two groups. Thus, the etiology of the relationship between reading performance and rapid naming may differ for children with reading difficulties and normally-achieving readers. Moreover, these results support previous findings that the best predictors of reading skills may differ for samples of children with normal reading levels and those with reading difficulties.