Genetic and environmental influences on orthographic and phonological skills in children with reading disabilities.

Data from identical and fraternal twins were analyzed to estimate the proportions of genetic and environmental influences on group deficits in accuracy and, when available, speed for printed word recognition and for related skills in phonological decoding (PD), orthographic coding (OC), and phoneme awareness (PA). In addition, bivariate genetic analyses were employed to estimate the degree of common genetic influence on group deficits across these different reading and language skills. About half of the group deficits in each of the skills were due to genetic influences, and the genetic origins were largely shared among the measures (r(g) = .53 - .99), except for those between OC and PA (r(g) = .28 - .39). Implications of the results are discussed for models of reading disability and remediation.