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 avail-able, speed for printed word recognition and for related skills in phonological decod-ing (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 (rg =.53 –.99), except for those between OC and PA (rg =.28 –.39). Implications of the results are discussed for models of reading disability and remediation. Children with a school history of reading problems tend to have particular difficulty reading words, both in isolation and in context. Their deficits in printed word recog-nition accuracy, fluency, or both place major constraints on the ultimate goal of reading to comprehend written texts (Perfetti, 1985). The importance of word-reading deficits in reading disability (RD) has led researchers to explore pos-sible component processes that may be etiologically significant. For example, re-searches have noted that deficits in printed word recognition are usually related to similar or even greater deficits in phonological decoding (PD), phoneme awareness (PA), and orthographic coding (OC; see definitions following; Olson, Forsberg, &amp