General intelligence and reading performance in adults: is the genetic factor structure the same as for children?

Genetic and environmental influences on reading ability and disability in children are undergoing active exploration, but the same is not true for adults. This study made use of data from the Minnesota Study of Twins Reared Apart (N = 239, age range 18–79) to evaluate whether a basic model of genetic and environmental influences on general intelligence and reading performance in children (Brooks, Fulker, & DeFries, 1990) appeared to fit adult data. In addition, we developed a related model of the phenotypic relationships that better fit our adult data. The key difference in our phenotypic model was that our measure of reading comprehension was linked with general intelligence rather than with reading performance. We believe that, though automaticity in reading performance is associated with improved reading comprehension in children, this may not be true in adults and may help to explain our result. In addition, we estimated somewhat higher heritabilities for reading measures than have typically been found for children (0.77 and 0.74 for two measures of word recognition, 0.51 for a measure of reading comprehension, and 0.76 for a measure of spelling), along with a genetic correlation between general intelligence and reading performance of 0.68.