Familial nature of reading disability.

An extensive psychometric test battery was administered to 125 children with a reading disability, to their parents and siblings, and to members of 125 matched control familes (N = 1,044). In addition to expected differences in spelling and reading, probands obtained significantly (P less than or equal to .01) lower scores than controls on tests of other cognitive abilities. Manifold deficits were also found in siblings and parents of probands, conclusively demonstrating the familial (genetic and/or common-family environmental) nature of the disorder.