Word recognition data from identical and fraternal twins and siblings (N=172) indicated that the phonological coding deficit of children with reading disabilities was highly heritable. Orthographic coding was not significantly heritable. Poor readers with low IQs were superior to similar reading but average IQ readers in phonological coding.…

Data from 143 children with reading disabilities (RD), 100 with arithmetic disabilities (AD), and 121 controls (ages 6-16) found the RD and AD groups had significantly lower scores on all verbal IQ subtests. Many also showed significant differences between verbal and performance IQ scores, but so did many controls. (Contains references.)…

This study of 640 twins with reading disability and 436 controls (mean age 12) examined external validity of the distinction between specific reading retardation and reading backwardness, in 3 domains: genetic etiology, sex ratio and clinical correlates, and neuropsychological profiles. There was no evidence of differential genetic etiology of the…