Genetic Influences

There is growing evidence that genetic influences may cause some learning disabilities (Galaburda, 2005; Wood & Grigorenko, 2001). Hallgren (1950), in an early investigation, studied 276 children and identified numerous reading and language problems among the relatives of the children. A genetic link was suggested as one possible cause for the reading problems of the children. Decker and DeFries (1980, 1981) conducted a series of studies of 125 children with reading disabilities and their families, and the results indicated that reading disabilities may be hereditary.

Other evidence for some genetic cause for learning disabilities comes from several studies in identical twins. Unlike fraternal twins—who come from two separate eggs and thus have different genetic information—identical twins come from the same egg. Studies of twins have shown that when reading problems exist, those problems are more likely to exist in both identical twins than in both fraternal twins, thus indicating a genetic cause for those reading problems (Wood & Grigorenko, 2001).

With the mapping of the human genome in 2000, investigations on genetic causes for learning disabilities have increased (Wadsworth, Olson, Pennington, & DeFries, 2000; Wood & Grigorenko, 2001). To date, portions of certain chromosomes have been implicated in the search for a genetic marker that would, under certain conditions, result in dyslexia. In particular, chromosome 15 has been implicated, but research has also focused on potential genetic markers associated with chromosomes 1, 2, 6, 13, and 14 (Raskind, 2001; Wood & Grigorenko, 2001).

Further, recent research suggests that genetic influences may account for over 50% of the cases of reading disabilities, and when only students with normal and above-normal IQs are considered, genetic influences may account for as much as 75% (Wadsworth et al., 2000). Although this research is medical in nature, teachers should be aware of the possibilities that may eventually result from this type of research, including specification of a primary genetic cause for many learning disabilities, assessment procedures based on genetic mapping, or even gene replacement therapy as a potential preventative measure for some learning disabilities (Wadsworth et al., 2000; Wood & Grigorenko, 2001).