Dyslexia is caused by a genetic flaw in the part of the brain used for reading, according to a new study from Yale researchers that could help educators improve teaching methods for millions of children. 

Using magnetic resonance imaging, the pediatric and neuro-researchers pinpointed the region of the brain activated by reading and observed its disruption in children with dyslexia. The research proved the long-held genetic theory on dyslexia, researchers say.

Panel says it will stop flagging SATs of disabled students. 

Many of the dyslexic children compensated for the disruption by using a center of the brain associated with speaking, suggesting that sound may be key to teaching them to read.

''This is the definitive study in children that links reading with brain function,'' said Dr. Sally Shaywitz, professor of pediatrics at the Yale University School of Medicine and one of the authors of the study released yesterday in the journal Biological Psychiatry.

Dyslexia is one of the most common learning disorders, affecting up to 20 percent of Americans with symptoms ranging from complete illiteracy to mixing up left and right directions. 

Children normally learn to read by recognizing individual letters, then sounds, and finally connecting that with conceptual meanings. Dyslexics may be as intelligent as normal readers, but they have difficulty connecting letters with sounds, a fundamental skill required for reading, Shaywitz said. 

In the study, researchers scanned the brains of almost 150 normal and dyslexic youths taking a reading skills test. The test revealed that non-impaired reading is concentrated in the occipito-temporal, lower back region of the brain, where letters and sounds are integrated.

Dyslexics' brain activity while reading, on the other hand, is concentrated in the frontal region, the location that governs articulated speech. Dyslexics, in effect, read by mechanically mouthing the words and triggering the recognition of parts of words. Dyslexics become more proficient with reading over time but are never cured and do not outgrow the disability. 

''Now there's an urgency to identify and provide dyslexic children with the most effective reading tools,'' Shaywitz said. Researchers say the findings reaffirm that children should be taught using phonemes, distinctive linguistic letter and sound units. For example, in the word ''cat,'' the letter ''c'' is ''kuh,'' the letter ''a'' is ''aah,'' and ''t'' is ''tuh.''

However, since the 1970s, educators have moved away from teaching reading through sound groups and more toward learning words in the context of sentences and pictures. Although the newer method is useful, up to 40 percent of children need the sound and letter approach to become fully literate, Shaywitz estimates, including many who are not dyslexic.

''The study refines what we've known for 50 years and may help with diagnosis,'' said J. Thomas Viall, executive director of the International Dyslexia Association. Not being diagnosed with dyslexia or receiving treatment has life consequences if the student is labeled stupid or as a person having low mental capacities, Viall said.

''Highly intelligent dyslexics can fool you,'' said Viall, whose organization just settled a lawsuit with the Educational Testing Service and the College Board requiring the board to stop flagging those students who take the SAT with the special accommodation of extra time to compensate for their learning disabilities. 

Humans have been speaking since the beginning of civilization, but reading has only occurred in the last 5,000 years, Shaywitz said. This requires the brain's circuitry to integrate letters with sound, otherwise letters would only be squiggly lines. 

The English language has 44 phonemes but more than 1,000 ways in which those letters sound, making it one of the hardest languages to learn unless the reader was taught specifically the pronunciation differences between words like ''mint'' and ''pint.'' Other languages, such as Spanish or Italian, have more direct correlation between letters and sound combinations, making them easier to learn regardless of the number of phonemes.

Quynh-Giang Tran can be reached at qtran@globe.com 

This story ran on page A2 of the Boston Globe on 7/16/2002.
© Copyright 2002 Globe Newspaper Company.