However, there are typical symptoms which should alert parents, teachers and others to the possibility that a child, or indeed an adult, has dyslexia.

Until recently the causes of dyslexia were not understood. However, it is now generally accepted that dyslexic people seem to process information in a different way from the rest of the population.

The following is the research definition of dyslexia used by the National Institutes of Health and the International Dyslexia Association:

Dyslexia is a specific learning disability that is neurological in origin. It is characterized by difficulties with accurate and/or fluent word recognition, and by poor spelling and decoding abilities.

These difficulties typically result from a deficit in the phonological component of language that is often unexpected in relation to other cognitive abilities and the provision of effective classroom instruction. Secondary consequences may include problems in reading comprehension and reduced reading experience that can impede growth of vocabulary and background knowledge.

There are three main types of Dyslexia, each with its own specific symptoms and causes:

• Dyseidetic Dyslexia

  A type of dyslexia associated with differential brain functions located in the Angular Gyrus of the left pariental lobe of the brain. A person suffering from this type of dyslexia will have poor sight-word recognition, contributing to an overall slow and laborious reading experience. Irregular words are both sounded out phonetically (laugh = log) and spelled phonetically (ready = rede). Dyseidetic Dyslexics often are, as a result of their condition, more advanced in reading than in spelling.

• Dysphonetic Dyslexia

  A type of dyslexia associated with differential brain functions located in the Wernicke's Area of the left temporal and parietal lobes of the brain. A person suffering from this type of dyslexia relies on sight recognition to read, being unable to sound out unknown words. During reading, words are either known or not known, and are often substituted or skipped when trouble arises. Words are learned by rote memorization, and cannot be spelled by their sound. Ear infections can cause some problems.

• Dysphoneidetic Dyslexia

  A type of dyslexia associated with a combination of differential brain functions in the Angular Gyrus and the Wernicke's Area. A person suffering from this type of dyslexia will have weak visual-motor skills, and is often the most difficult to treat.