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Dyslexia - Separate genes influence speed, accuracy in decoding written words
Researchers trying to tease out the genetic basis of dyslexia have discovered a location on chromosome 2 that may contain
one or more genes that contribute to the reading disorder and make it difficult for people to rapidly pronounce pseudowords.
The team from the University of Washington, headed by medical geneticists Dr. Wendy Raskind and Ellen Wijsman and
developmental psychologist Virginia Berninger, cautioned that the new findings do not mean that scientists have found "the
gene" responsible for dyslexia.
"Just as with heart disease, no single gene will provide the answer to what causes dyslexia," said Raskind. "When you look at
something that is inherited there could be multiple genes, perhaps as many as a hundred, that contribute to it. And when you
look at any characteristic of a person, you must consider the environmental background. There are other factors besides genes
that could modify a behavior."
The study, published in the March issue of the journal Molecular Psychiatry, is noteworthy for two reasons. First, it points
to a new location containing genes that contribute to dyslexia. Second, the gene or genes at that location are involved in
speed of decoding - changing written words into spoken words without clues to their meaning - a basic and persistent
component of dyslexia.
Building on previous findings by the UW team on familial patterns of accuracy and rates of decoding, the research also
provides the first evidence identifying separate genetic influences on these abilities.
"In other published and in-press research we have shown that accuracy of decoding may be a bridge to reading at one stage of
learning to read and rate of decoding may be a bridge at a later stage. Effective instructional techniques for each bridge
are not necessarily the same and typically require more than teaching as usual," said Berninger, who heads the UW's Learning
Disabilities Center.
The UW researchers used pseudowords, or what Berninger calls "jibberwacky," which are similar to the nonsense syllables in
Lewis Carroll's poem "Jabberwocky." Examples of these pseudowords are "chimwoggle," "meb" and "crong." The "jibberwacky" was
used to test 108 first- through ninth-grade children diagnosed with dyslexia and their families - parents, grandparents,
siblings at least 6 1/2 years old, aunts and uncles. In all, 874 people were involved in the study.
Raskind and Wijsman said they used three different analytic approaches to search for genetic influences affecting how fast
and accurately people could pronounce nonwords. For accuracy alone, they found five different potential contributing
locations on four different chromosomes. When they examined influences on speed and accuracy, they found three other
locations on different chromosomes. However, the signal from chromosome 2 was the most robust, particularly when the
researchers only looked at speed and not accuracy in decoding. They said evidence points to a possible combination of genes
on chromosomes 2, 10 and 11 affecting speed.
The researchers focused on how dyslexics translate written words into spoken words without meaning cues because of a large
body of evidence pointing to it as a hallmark deficit in dyslexia. The UW group also has published a finding that this
deficit is detectable in children and adults.
Dyslexia is a complex learning disorder that affects 5 to 10 percent of school-age children in the United States. It
typically is characterized by early difficulties in learning to name letters and associate sounds with letters. Later on,
children with dyslexia have difficulty pronouncing real words and pseudowords when they are not in a sentence or do not have
meaning cues. Such children can have problems with fluent reading and spelling as well.
The results of the new study provide further evidence that dyslexia has biological roots and is a learning disorder that
requires specialized instruction. Earlier UW research has shown that there are chemical differences in brain function and how
the brains of dyslexic and non-dyslexic children use oxygen during sound processing tasks.
That research also showed that dyslexics can be successfully treated. A set of specialized instructional approaches developed
at the UW not only helped dyslexic children improve their reading skills, but also showed that their brains change in
response to instruction designed for this genetic influence on learning to decode quickly. These approaches show children the
regularity of decoding written English words and how to apply this regularity quickly, efficiently and strategically.
"It was not phonics as usual," said Berninger, "but could be implemented in schools so that parents do not have to seek
costly treatment outside the schools."
The National Institute of Child Health and Development supported the research. Co-authors of the UW study are Robert Igo,
Nicola Chapman and Mark Matsushita, medical genetics research scientists; Dr. Zoran Brkanac, acting assistant professor of
psychiatry and behavioral sciences; Jennifer Thompson, former clinical coordinator; Ted Holzman, computer research
consultant; and Mary Brown, undergraduate student.
Contact: Joel Schwarz
University of Washington
http://www.washington.edu
Dyslexia - Separate gene influenþa viteza, precizie în decodificare cuvinte scrise - Dyslexia - Separate genes influence speed, accuracy in decoding written words - articole medicale engleza - startsanatate