Children with dyslexia must be diagnosed early and given treatment as soon as possible, say experts. The current state of dyslexia research and treatment are discussed by Robin L. Peterson, Ph.D., and Bruce F. Pennington, Ph.D., of the University of Denver, in a seminar article in the Lancet.
They explain that dyslexia involves slow and inaccurate word recognition, although comprehension is normal. Those affected do not tend to have intellectual impairments or sensory problems.
It affects about seven percent of the population, with boys being about twice as likely to be diagnosed with the condition as girls. But this discrepancy is partly due to a higher rate of comorbid conditions such as attention-deficit/hyperactivity disorder (ADHD) in boys.
About a quarter of children with dyslexia will also have math disabilities, “thus, many students with dyslexia can be expected to struggle broadly in school and have more than a specific reading disability,” say the authors.
They report that much progress has been made on the behavioral, neuropsychological, and neurobiological aspects of dyslexia and its causes. This shows that dyslexia “is characterized by dysfunction of the normal left hemisphere language network.” Rather than essentially being a problem of visual word recognition, it is now mostly believed that dyslexia involves problems processing sounds when reading.
Since the previous Lancet review on dyslexia in 2004, “the main advance has been the identification of six candidate genes and studies of their role in brain development,” say the experts. Four of these genes appear to control brain development in the fetus, they add.
The evidence shows that all six genes may interact with the environment to determine whether dyslexia is triggered.
But “like all behaviorally defined disorders, the cause of dyslexia is multifactorial and is associated with multiple genes and environmental risk factors,” write the authors. Despite the efforts so far, “much work remains to be done to fully understand the causes of dyslexia and to improve the lives of children who struggle to learn to read,” they add.
Most children are still only diagnosed after having serious difficulties in school, when it is much harder for them to master new skills. However, common coexisting conditions such as ADHD, language impairment, and speech sound disorder are likely to be apparent much earlier, and could indicate a child’s risk of reading problems.
“Professionals should not wait until children are formally diagnosed with dyslexia or experience repeated failures before implementation of reading treatment, because remediation is less effective than early intervention,” saidÂ the authors.
In terms of treatment, “the best interventions provide intensive, explicit instruction in phonological awareness, the alphabetic principle and phonics, word analysis, reading fluency, and reading comprehension,” says the team.
It seems to be easier to treat accuracy problems than fluency problems, they report, “perhaps in part because fluency is so dependent on reading experience, which varies dramatically by reading level.”
And there is evidence that fluency problems can be prevented by intervention in kindergarten and first grade. “An important conclusion is that professionals should not wait until children are formally diagnosed with dyslexia or experience repeated failures before implementing reading treatment,” they write.
Furthermore, research indicates that intervention is most effective on a one-to-one basis or in a small group setting. “Many effective treatments are low-cost, which further draws attention to the importance of early identification, prevention, and treatment of dyslexia for public health.”
About half of children treated successfully will show a benefit for at least one to two years, and in the long term, children and adults with greater language skills will show the most benefit. Alternative therapies for dyslexia “either lack sufficient evidence or have been shown to be ineffective,” and should not be recommended to children and families.
The experts conclude, “Further research is needed to reveal further undiscovered genes that may contribute to dyslexia, to identify which gene locations are shared and not shared with comorbid disorders, including ADHD, and to examine the effects of environmental risk factors such as the language and pre-literacy environments that parents provide for their children.”
Nevertheless, they point out, “Of all the neurodevelopmental disorders, dyslexia has been the most studied and is the best understood, and there has been considerable progress over the last five years in understanding dyslexia’s cross-cultural manifestation, etiology, neuropsychology, and neurobiology.”
Developmental dyslexia. Peterson, R. L. and Pennington, B. F. The Lancet, 17 April 2012 doi:10.1016/S0140-6736(12)60198-6