U of C researchers find genetic link to dyslexia

By Jill Webber

Researchers from the University of Calgary Faculty of Medicine have discovered a genetic link between dyslexic children and their parents.

U of C Pediatrics Professor and Head of the Behavioural Research Unit at the Alberta Children’s Hospital Dr. Bonnie Kaplan was happy with the results.

"Parents want to know early on if their children are dyslexic," she said. "These findings will certainly help us to treat and work with dyslexic children."

Kaplan and genetics professor Dr. Leigh Field led the study.
The study involved taking blood samples from 900 individuals from 96 families with members diagnosed as dyslexics, and testing the DNA in the blood.

Dyslexia is a term synonymous with reading disability. It is based upon an individual’s ability to use written language. Dyslexia affects the ability to spell, read, write, or speak.

"Having the dyslexic genes is not necessarily good or bad-just different," said Field.

Dyslexia affects between 10 and 15 per cent of the school-aged population, and is the leading learning disability in North America. Early treatment and intervention help lessen its effects.

Kaplan and Field found an autosomal dominant gene on chromosome six in every dyslexic individual tested as well as one or more of their parents, which led them to believe dyslexia is inherited.

"The kind of dyslexia that we’re studying and talking about today is the one which appears to be most strongly inherited," said Kaplan. "You can really see it running in the families."

The discovery was made through a technique called linkage analysis, which involved laboratory testing and statistical analysis of participants. Kaplan and Leigh gave participants phonological tests.

"[The tests] address the question of decoding sounds," Kaplan.

The dyslexia studied in Kaplan and Leigh’s research is called phonological awareness, meaning these types of dyslexics have difficulty associating sounds with letters, and therefore become confused with the meaning of the words they read or write.

Several similar studies are being conducted around the world, including one indicating the presence of the dyslexia gene on chromosome six as well. Other projects have found ‘dyslexia genes’ on chromosomes two and 15, leading researchers to believe that there are several more undiscovered genes that may cause the disorder.

The find is sure to be useful in the near future both for dyslexic children and their parents, said Kaplan.

"Parents really want to know if their young child is carrying genes which will influence their reading ability," she said.

Undiagnosed dyslexic children often have difficulty with reading and writing at school, and tend to fall behind the rest of the class.

Field suggested the possibility of large-scale genetic testing of pre-school children for dyslexia in the next 10 years.

"If, on a large scale, the government chooses to do some kind of testing, the cost per test could be no more than $15," she said. "It depends, however, on the magnitude of the numbers."

The study began in 1992 and is funded by the Alberta Heritage Foundation for Medical Research.

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