Cognitive ability profiles in families of reading-disabled children.

Evidence for the heterogeneity of reading disability was sought in a family study. Psychometric test data on 125 reading-disabled children (probands) and their siblings and parents were used to identify four subtypes of reading disability, each with a distinctive cognitive ability profile. The validity of this profile analysis was then assessed by applying the same classification system to profiles of affected parents and siblings of the probands. Affected siblings of probands in subtype 3 (severely impaired reading ability but normal spatial/reasoning and coding/speed) were more likely to be of the same subtype than would be expected on the basis of chance. However, no such evidence for familial transmission of specific subtypes was found in the parental data. It is suggested that family studies may provide a strong test of the heterogeneity of reading disability, and that such studies should be used to assess the validity of alternative typologies.