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Dyslexia

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Dyslexia, also known as reading disorder, is characterized by trouble with reading despite normal intelligence.

Different people are affected to varying degrees. Problems may include difficulties in spelling words, reading quickly, writing words, "sounding out" words in the head, pronouncing words when reading aloud and understanding what one reads. Often these difficulties are first noticed at school.

When someone who previously could read loses their ability, it is known as alexia.

Dyslexia is believed to be caused by both genetic and environmental factors. Some cases run in families. It often occurs in people with attention deficit hyperactivity disorder (ADHD) and is associated with similar difficulties with numbers. It may begin in adulthood as the result of a traumatic brain injury, stroke, or dementia.

The underlying mechanisms of dyslexia are problems within the brain's language processing. Dyslexia is diagnosed through a series of tests of memory, spelling, vision, and reading skills. Dyslexia is separate from reading difficulties caused by hearing or vision problems or by insufficient teaching.

Treatment involves adjusting teaching methods to meet the person's needs. While not curing the underlying problem, it may decrease the degree of symptoms.

Treatments targeting vision are not effective.

Dyslexia is the most common learning disability and occurs in all areas of the world. It affects 3-7% of the population, however, up to 20% may have some degree of symptoms.

While dyslexia is more often diagnosed in men, it has been suggested that it affects men and women equally. Some believe that dyslexia should be best considered as a different way of learning, with both benefits and downsides.

Dyslexia is thought to have two types of cause, one related to language processing and another to visual processing. It is considered a cognitive disorder, not a problem with intelligence. However, emotional problems often arise because of it.

Some published definitions are purely descriptive, whereas others propose causes. The latter usually cover a variety of reading skills and deficits, and difficulties with distinct causes rather than a single condition.

The National Institute of Neurological Disorders and Stroke definition describes dyslexia as "difficulty with phonological processing (the manipulation of sounds), spelling, and/or rapid visual-verbal responding".

The British Dyslexia Association definition describes dyslexia as "a learning difficulty that primarily affects the skills involved in accurate and fluent word reading and spelling" and is characterized by "difficulties in phonological awareness, verbal memory and verbal processing speed".

Acquired dyslexia or alexia may be caused by brain damage due to stroke or atrophy. Forms of alexia include pure alexia, surface dyslexia, semantic dyslexia, phonological dyslexia, and deep dyslexia.