The problem was first described in the medical literature in 1896 by Morgan, who referred to the condition as “congenital word blindness.” Case studies of identical and fraternal twins reviewed by Zerbin-Rüdin suggest that reading disability may be highly heritable. Among a sample of 17 identical twin pairs and 34 fraternal twin pairs, observed concordance rates were 100% and 35%, respectively. In general, results of twin and family studies strongly suggest that reading disability is heritable, and a number of different modes of inheritance have been proposed to account for familial transmission. The primary objectives of the original FRS, a 3-year project funded by the Spencer Foundation, were as follows: to construct a battery of tests that differentiates children with diagnosed reading problems from controls; to assess possible cognitive and reading deficits in parents and siblings of children with reading problems; and, if such deficits are found, to study their transmission in families.