More than a third of dyslexic adults were physically abused as children, a new study has found.

The joint study from the University of Toronto and the University of North Carolina reveals that adults with dyslexia are more than five times as likely to have suffered physical abuse as kids.

It found that 35 per cent of adults with the learning disability, most commonly characterized by difficulty reading, said they were physically abused by someone close to them before the age of 18.

In contrast, only seven per cent of those without dyslexia reported similar abuse.

When adjusted for age, sex, and race, the likelihood of a dyslexic adult having a physically abusive childhood jumps to more than seven times. When adjusted further to account for factors like parental addictions, divorce and prolonged unemployment, the increase dips slightly to just over sixfold.

Far and away the biggest factor in those discrepancies is age, according to University of Toronto study author Esme Fuller-Thomson. That’s because dyslexia was widely under-diagnosed in past generations of children — especially among non-whites — compared with today.

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“Basically, if I’ve got two people who are identical, but one has dyslexia, one doesn’t, the chances are much, much higher that the person with dyslexia had experienced or had reported childhood physical abuse,” said Fuller-Thomson.

The U of T researcher and her American counterpart studied the responses of more than 13,000 adults from Saskatchewan and Manitoba who had participated in the 2005 Canadian Community Health Survey, widely seen as a nationally representative cross-section of Canadians.

The findings raise dramatic questions about the link between brain changes long associated with childhood abuse and learning disabilities like dyslexia.

What the study does not determine, however, is which factor — the abuse or the dyslexia — contributes more to the other.

Just as physical abuse can adversely impact the developing brain, undiagnosed dyslexia may bring about physical abuse as frustrated parents or caregivers may feel the child is not concentrating on purpose, and resort to violence.

“We don’t know which way it goes,” Fuller-Thomson said.

Study co-author Dr. Stephen Hooper at the University of North Carolina School of Medicine said dyslexic tendencies are present at birth and are sometimes linked genetically to a parent with dyslexia. Still, that doesn’t solve the nature-vs.-nurture debate when it comes to dyslexia and childhood abuse.

“Now you have a parent that’s struggling with reading and you have a child that may be struggling with reading and it may feel like double jeopardy to this family,” Hooper said. “And that puts them at greater risk for maltreatment.”

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Even without concrete proof that dyslexia is caused by childhood abuse, or vice versa, the study could go a long way toward reducing the negative impacts of both.

“Whichever way the association goes — whether dyslexia causes abuse or abuse causes dyslexia, or if they’re both related to something else — dyslexia is a marker for those at higher risk (of abuse),” Fuller-Thomson said.

Therefore, if doctors begin to screen for dyslexia before children reach school-age — especially for children of a dyslexic parent — both the disability and the sometimes-attendant abuse may be prevented through education, according to the study.