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Thinking about Dyslexia

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Here I will take up the topic of dyslexia as I introduce and comment on a highly informative article entitled "Genetics and Neuroscience in Dyslexia: Perspectives for Education and Remediation" by a team of independent researchers, Gerd Schulte-Korne, Kerstin U. Ludwig, Jennifer el Sharkawy, Markus M. Nothen, Bertram Muller-Myhsok, and Per Hoffmann in Mind, Brain and Education Vol. 1, No. 4 pp. 162-172.

In addressing the subject of dyslexia, an eminent academic journal such as Mind Brain and Education does not simply to aim to improve remedial education for dyslexia. We should also keep in mind that studying dyslexia can provide much insight into the nature of education and pedagogical practice.

Depending on how it is translated into Japanese, the word "dyslexia" is derived from Greek prefix dys, which denoting something abnormal or impaired, and lexis, which refers to language or words. Rather than considering it as the loss of ability, however, most pediatricians see dyslexia as a reading disorder. For this reason, dyslexia is categorized as a learning disability that is treated by behavioral pediatrics and pediatric psychiatry.

1) The perspective of neurocognition

Worldwide, there are several million dyslexic children and adults who, despite high cognitive abilities, have an impairment in reading and spelling. This disorder persists into adulthood, particularly in boys, and exhibits a high comorbidity with dyscalculia (math disability) or attention deficit/hyperactivity disorder (ADHD). Dyslexic adults show a high incidence of depression, attempted suicide, unemployment and dropping out of school.

From the perspective of neurocognition, dyslexics have a normal ability to reproduce pronunciation and words, which is located in left hemisphere of the brain, but phonological processing including that of rhythm and phrasing is impaired so that words are read one at a time and the ability to read with speed deteriorates.

2) From the perspective of neuroscience

Research from the perspective of neurohistology reports the formation of nests of neurons and the proliferation of microgyria in the left hemisphere. This would seem to indicate a neuronal migration disorder or abnormality in proliferation of microgyria that support neurons during developmental of the brain. Brain imaging research has identified abnormality in left hemisphere brain activity during letter recognition or reading.

3) From the perspective of education

In general, it is considered that training in phonological awareness, namely, learning letter-sound correspondence and vice-versa, can improve ability. A training program has been developed based on findings that dyslexia is characterized by deficient processing of dynamically changing visual and auditory stimuli. This has improved performance of language-related tasks, with the result that brain activity in the left hemisphere has approached normal levels.

4) From the perspective of genetics

It is widely recognized that dyslexia is caused by a number of factors originating in the environment and genetics. Based on research with twins, the proportion of genetic factors that contribute to the development of dyslexia is estimated to be 40%-80%, a notably wide-ranging percentage.

5) Perspective of molecular genetics

Dyslexia has been attributed to four candidate genes, but mutations of two (DCDC2, KIAA031) are particularly important because they have been replicated in several studies. It has been found, however, that mutations of these two genes do not affect the level of protein expression or protein function, and this indicates the necessity of more research.

6) Perspective of functional analysis

Recent animal experiments show that decreased expression of the abovementioned two genes (DCDC2, KIAA031) results in the reduction of cortical neuronal migration during development of the brain. As mentioned in 2) above, progress in neuropathology research can be expected to elucidate abnormality in neuronal migration.

In conclusion, as for future research and the implications for education, I would like to mention an EU-funded large-scale project called NeuroDys that aims to identify the genes that cause dyslexia. Future research will clarify the genetic process that triggers irregular neuronal arrangement and the onset of dyslexia. Diagnosis of dyslexia is now possible when children are between 7 and 9 years old, and identification of the genes involved will enable early diagnosis and intervention with a more hopeful prognosis. These developments are certain to affect education. The EU-funded Neuro-Dys study will play a major role in collaborative interdisciplinary research.

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