Focus on words: a twin study of reading and inattention.

The etiology of variation in reading ability and its relationship to inattention, impulsivity, and general cognitive ability were investigated within a large, population-based sample of 9- to 10-year-old twins. Phenotypic and genetic analyses were performed on word-level reading, full-scale IQ, and measures of inattention and impulsivity derived from the Go-NoGo task (i.e., Go errors and NoGo errors, respectively). Moderate and significant phenotypic correlations were found among reading, inattention and IQ, but not between impulsivity and the other variables. Genetic modeling revealed that genetic and shared environmental influences largely accounted for variation in reading, inattention, and IQ and covariation among them, whereas specific environmental influences contributed primarily to variation in impulsivity. Acting through a common factor, a portion of the genetic influences on reading ability appeared to be shared with influences affecting IQ as well as those affecting inattention. The contribution of phonological awareness to the remaining unique genetic influences on reading was explored through additional analyses. A two-common-factor model was revealed, with a strongly genetic general cognitive ability factor affecting reading, inattention, and IQ, and an equally strongly genetic second common factor, which captured the variability in reading ability that was related specifically to phonological processing. The processes involved in reading, therefore, seem to involve genetic and environmental influences that are part of both a general cognitive system and a system more specific to reading and phonology.