seminar published online in The Lancet today.
Most children are only diagnosed with dyslexia after they have experienced serious difficulties in school, at a time when it is much harder for them to master new skills, and this could be thwarting their ability to fully realise their potential, say the authors.
“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”, explain Robin Peterson and Bruce Pennington from the University of Denver in Colorado, USA.
About 7% of the population are dyslexic, and boys are about twice as likely to have dyslexia as girls. Mounting evidence suggests that the underlying problem involves difficulty with how sounds in language are heard and mapped onto letters — phonological impairment.
“Like all behaviourally defined disorders, the cause of dyslexia is multifactorial and is associated with multiple genes and environmental risk factors”, explain the authors.
Despite the recent identification of six genes that contribute to the disorder, very little is known about how these and other possible genetic determinants might contribute to dyslexia or the role of the environment in the cause of the condition.
Further research is needed to hunt out further genes that may contribute to dyslexia, and to find which gene locations are shared and not shared with associated disorders, including attention deficit hyperactivity disorder (ADHD), say the authors.
The impact of environmental risk factors, such as the language and pre-literacy stimulus parents provide for their children also warrant further investigation, they say.
“We still need to learn more about the nature of phonological deficit and how this problem interacts with other linguistic and non-linguistic risk factors, the developmental course of neural abnormalities and how these predict treatment response, and which environmental risk factors contribute to the development of poor reading and whether these are the same across demographic groups”, they explain.
Treatment still needs to be improved, they add. “Brain-imaging studies have shown that effective intervention seems to promote normalisation of activity in the left hemisphere reading and language network that has shown reduced activity in dyslexia.”
Common coexisting conditions such as ADHD, language impairment, and speech sound disorder, which are likely to be apparent much earlier, could be used to help predict a child’s risk of later reading problems, conclude the authors, adding that: “Many effective treatments are low cost, which further draws attention to the importance of early identification, prevention, and treatment of dyslexia for public health.”