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Genetic Discovery May Aid Early Diagnosis of Dyslexia

October 14, 1994|THOMAS H. MAUGH II | TIMES MEDICAL WRITER

In a finding that could soon have a major impact on the diagnosis and treatment of dyslexia, scientists have identified genetic markers that should allow early identification of the reading disorder in high-risk children or even in fetuses, experts said Thursday.

San Diego and Colorado researchers report today in the journal Science that they have linked the reading disorder, which arises in people with an otherwise normal intelligence, to a small region of chromosome 6, one of the 23 pairs of chromosomes that compose the human genetic blueprint. While they are racing to identify the gene in this region that causes dyslexia, they are also developing a genetic test that could identify the disorder long before a child attempts to begin reading.

Using recently developed interventions and new techniques for diagnosing dyslexia at ages 5 to 6, clinicians now can make significant improvements in the reading ability of perhaps half the children treated. But the diagnostic techniques are not widely available yet, and dyslexia, which affects 5% to 10% of the population, is not normally diagnosed until around age 8. By that age, even the best interventions can help no more than 25% of dyslexics.

Most researchers believe that the interventions would be even more effective if they could be applied at an earlier age, but there has previously been no way to determine the presence of dyslexia in younger children.

With dyslexia, a person's ability to perceive and process words, numbers and other symbols is impaired. Often, letters or numbers may appear reversed, for example, making it unusually difficult for a person to absorb the information on a page.

A new genetic test for the disorder based on today's findings would be invaluable, said neuropsychologist Reid Lyon of the National Institute of Child Health and Human Development. "There is no doubt that we can make much greater improvements if it (dyslexia) is discovered earlier," he said.

"If one could identify these children well before they start school, for example, they could begin intensive training in time to avoid the potential for psychological trauma that reading deficits can cause in the classroom," said geneticist John DeFries of the University of Colorado, one of the study's co-authors.

The finding could be "extremely significant," said Will Baker, executive director of the National Dyslexia Research Foundation. "The issue we always deal with is the low self-esteem that the kids develop from failures in the classroom when their dyslexia isn't recognized. This discovery could change that."

Researchers have previously localized the cause of dyslexia to changes in "the back end of the left side of the brain, (in) the temporal lobe area," Lyon said. In August, furthermore, a New Jersey team reported that this region of the brain in dyslexics contains a deficiency in cells that specialize in comprehending rapid sounds. This lack of comprehension, suggested Paula Tallal of Rutgers University, may be a major factor in the later difficulty in learning to read.

Speculation about the source of these differences between dyslexic and normal brains has included exposure to viruses, chemicals or hormones during pregnancy and trauma in the womb. While those factors may play a role, DeFries and his colleagues have shown by twin studies that genetics is very important.

In the new study, DeFries and his colleagues at the University of Colorado, Sequana Therapeutics in San Diego and Boys Town National Hospital in Omaha studied two different groups of dyslexics. One group comprised 50 sets of fraternal twins in which at least one twin was dyslexic. The second group consisted of 358 individuals from 19 extended families with a history of dyslexia.

By using recently developed genetic engineering techniques to identify genetic markers in DNA from the blood of the subjects, the researchers were able to show that the suspected gene was in a region of chromosome 6 that could contain a few genes or as many as 200. They are now trying to identify the specific gene involved.

Although it could take several years to identify the gene, the new study promises to have an impact much sooner. "We could, in principle at least, make informed guesses right now as to whether particular children are at risk or not," University of Colorado geneticist Dale Fulker said. But practically speaking, he added, it will take Sequana Therapeutics six to 18 months to develop a genetic test that could make such determinations widely available.

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Neuroscientist Gordon Sherman of Beth Israel Hospital in Boston cautioned, however, that the new study still must be replicated, noting that an earlier study linking dyslexia to chromosome 15 could not be replicated. Today's study, however, "appears to be much more robust," he said.

The new results, he said, brought him "great excitement. . . . If you can diagnose this early and start to treat it, you can bypass some of the emotional problems that come with being in school and failing and not knowing why--and being treated in a very poor way."

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