Study Adds to Evidence of Genetic Link for Dyslexia
A new study offers the most conclusive results to date pointing to a genetic link for dyslexia, a reading impairment that experts say affects up to 10 percent of the nation's schoolchildren.
The findings, published in the Oct. 14 issue of the journal Science, could lead to the development of tests to identify and treat children with the learning disability earlier than is possible today, experts said.
Most students with dyslexia do not receive any help until the 3rd grade, said Reid Lyon, the director of research on learning disabilities at the National Institute of Child Health and Human Development in Bethesda, Md.
Up to 80 percent of students with dyslexia who start receiving special services in 3rd grade will have the reading problem for the rest of their lives, Mr. Lyon said. The earlier the intervention, the better the results, he said.
"Early intervention is clearly the key, and this [study] gives us an earlier window to initiate that intervention," Mr. Lyon said.
Up to 20 percent of all children are born with varying degrees of dyslexia, he said.
And if a parent is dyslexic, the child's risk of developing the disorder is up to eight times higher than the risk for a child without a family history of dyslexia, said John C. DeFries, one of the study's authors and the director of the Institute for Behavioral Genetics at the University of Colorado at Boulder.
A Gap Remains
Experts have long suspected that dyslexia is carried on human chromosomes, which determine and transmit hereditary characteristics, Mr. DeFries said. Earlier studies had singled out chromosome 15, but, as with many studies involving complex traits, when more families were looked at, the findings fell apart.
The new study traces the reading disorder to chromosome 6. The next step is to isolate the gene responsible for triggering dyslexia--something that is still a few years away, Mr. DeFries said.
The study draws from years of research on two sample groups: one with 50 pairs of fraternal twins at the University of Colorado, the other a multigenerational study of 19 families at the Center for Hereditary Communication Disorders in Omaha. In the group of twins, at least one sibling in each pair had the learning disability.
Researchers compared the genes in blood samples taken from those with dyslexia and those without it and were able to link a certain "marker" in a segment of chromosome 6 with the disorder.
"This study indicates that it's actually possible to identify individual genes that drive these complex behaviors," Mr. DeFries said.
More than half the students in special-education programs across the country have a learning disability, according to a recent report by the U.S. Education Department. In recent years, that category of disability has grown the most. (See Education Week, Oct. 19, 1994.)
In spite of scientific advances, Mr. Lyon said, true gains in students' progress will be hard to achieve until the gap between what the research community knows and what teachers are using in their classrooms is bridged.
"Teachers often aren't being trained with the most up-to-date techniques," he said.