Genetics of specific reading disability

Results obtained from the Colorado Twin Study of Reading Disability provide compelling evidence for a genetic etiology. For the present report, multiple regression analyses were performed on reading performance data from 186 pairs of identical twins and 138 pairs of same-sex fraternal twins among whom at least one member of each pair has a reading disability. The results indicate that on average, more than half of the reading performance deficit of probands is a consequence of heritable influences. Moreover, individual differences within the affected twin sample are highly heritable, whereas shared environmental influences do not contribute importantly to twin resemblance. The results of these analyses also suggest that the etiology of reading disability may differ from that of individual differences in reading performance. Because the estimate of heritability for reading performance in affected twin pairs is substantially higher than that in a control sample, reading disability may be caused by one or more genes having major effects. These results are highly consistent with our recent report of a putative quantitative trait locus for reading disability in a small region on the short arm of chromosome 6. © 1996 Wiley-Liss, Inc.