Phonological Deficits, IQ, and Individual Differences in Reading Disability: Genetic and Environmental Influences

Abstract

In this paper we review our recent work on the phonological reading deficit in reading disability. Disabled readers typically show poor nonword reading skills relative to their word recognition skills. Behavior-genetic analyses reveal that nonword reading deficits are highly heritable and that heritable variance in word recognition is closely linked to heritable variance in phonological coding. However, subjects vary considerably in terms of the degree of their phonological reading deficits. The analyses show that subjects with lower phonological skills (relative to word recognition) tend to have word recognition deficits that are more heritable compared to subjects whose nonword reading is more congruent with their word recognition skills. We also argue that subjects who showed poor word recognition relative to intelligence would be expected to have word recognition deficits that were more heritable compared to subjects whose reading and intelligence were more congruent. The analyses indicate a trend in this direction but the effect was not significant. We argue that both the nonword deficit dimension and the reading-IQ discrepancy dimension should be investigated in future analyses.