Some 5 to 17 percent of all children have developmental dyslexia, or unexplained reading difficulty. When a parent has dyslexia, those odds jump to 50 percent. Dyslexia usually isn’t diagnosed, however, until the end of second grade or as late as third grade.
Getting an earlier diagnosis of this disorder may be possible, according to a study reported online on December 7, 2015, in the journal Cerebral Cortex, by a research team led by Nadine Gaab, an HMS associate professor of pediatrics in the Laboratories of Cognitive Neuroscience at Boston Children’s Hospital. The study indicates that developmental dyslexia can be seen in the brain as early as infancy.
In 2012, members of Gaab’s lab found that brain imaging of pre-readers whose average age was 5½ years and who were members of families with a history of dyslexia showed differences in the left hemisphere of the children’s brains.
Some researchers proposed that the difference reflects being raised by a dyslexic parent—perhaps, for example, being read to less—but Gaab and colleagues wondered whether the difference could be innate.
To test this question, Gaab’s team performed advanced MRI brain imaging on fourteen infants with a family history of dyslexia and on eighteen infants of similar age with no such family history. The MRI scan included a technique that measures the flow of water molecules along the brain’s fiber tracts, which indicates how well information flows in the brain.
The scans found alterations in the arcuate fasciculus, a fiber bundle that connects the posterior cortex, which is involved in mapping sounds and word/letter recognition, with the frontal cortex, which integrates and interprets this information.
People who have suffered damage to the arcuate fasciculus often have problems with expressive and receptive language and their ability to manipulate the sounds of a language, a critical part of learning to read. In infants with familial dyslexia, inherited genes may interfere with the prenatal development of the arcuate fasciculus, says Gaab, impairing its structural integrity.
But biology isn’t necessarily destiny. According to Gaab, research shows that with early interventions 50 to 90 percent of children with dyslexia can become good readers and that such interventions may lead to normalization of white matter pathways in the brain’s left hemisphere.