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Developmental dyslexia, affecting 5 to 17 percent of children, has a strong familial component: up to half of children with a positive family history will have dyslexia themselves. A study from the Laboratories of Cognitive Neuroscience at Boston Children's (PNAS, January 23) reveals differences in brain activity even before these children begin reading instruction.
Early diagnostic markers could potentially enable a child to receive early interventions to head off difficulties and frustration in school, say investigators Nora Raschle, PhD, and Nadine Gaab, PhD. Typically, dyslexia isn't diagnosed until third grade, when interventions are less effective.
The researchers performed functional MRI (fMRI) imaging in 36 pre-reading children with a family history of dyslexia (average age, 5½) and 18 age-, sex- and IQ-matched children with no such family history. An elaborate protocol involving practice, games and prizes helped motivate the children to hold still in the fMRI scanner while performing phonological processing tasks known to predict reading ability.
Compared with controls, children with a positive family history had reduced activity in the brain's occipitotemporal and left temporoparietal regions, similar to older children and adults with dyslexia. High activation in these regions—in both the at-risk and control groups—correlated with better performance on tasks that predict reading ability, such as rhyming, knowing letters and letter sounds and being able to separate sounds within a word.
While older children and adults with diagnosed dyslexia have increased activation of frontal brain regions, the young children at risk showed no such increase, suggesting that these regions become active later as the brain tries to compensate for other deficits.
Drs. Gaab and Raschle are conducting further research to see if the fMRI observations correlate with diagnosed dyslexia and with EEG results. If so, they envision that children with a family history of dyslexia could receive diagnostic brain studies before starting school. They continue to enroll preschool-age children.
"Families often know that their child has dyslexia as early as kindergarten, but can't get interventions at their schools," says Dr. Gaab. "If we can show that we can identify these kids early, schools may be encouraged to develop programs.
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