Dyslexia - reading disorder

Dyslexia, also known as reading disorder, is a learning disability characterized by trouble reading despite normal intelligence. Different people are affected to varying degrees. Problems may include sounding out words, spelling words, reading quickly, writing words, pronouncing words when reading aloud, and understanding what was read. Often these difficulties are first noticed at school. When someone who previously knew how to read loses the ability, it is known as alexia. The difficulties are not voluntary and people with this disorder have a normal desire to learn.

The cause of dyslexia is believed to involve both genetic and environmental factors. Some cases run in families.It occurs more often in people with attention deficit hyperactivity disorder (ADHD) and is associated with problems with mathematics. When the condition begins in adults it may be the result of a traumatic brain injury, stroke, or dementia. The underlying mechanism involves problems with the brain's processing of language. Diagnosis is by a series of tests of a person's memory, spelling, ability to see, and reading skills. It is separate from reading difficulties due to poor teaching, or hearing or vision problems.

Treatment usually involves adjusting teaching methods to meet the person's needs.While this does not cure the underlying problem, difficulties can be ameliorated. Treatments aimed at vision are not effective. Dyslexia is the most common learning disability, affecting 3 to 7 percent of people.While it is diagnosed more often in males,some believe it actually affects males and females equally. Up to 20 percent of the population may have some degree of symptoms.Dyslexia occurs in all areas of the world.

Dyslexia is thought to have two kinds of causes, one related to language processing and another to visual processing. It is considered a cognitive disorder, not a problem with intelligence, and there are often emotional problems that arise because of it. There are many published definitions which are purely descriptive or involve proposed causes that encompass a variety of reading skills, 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 spelling, phonological processing (the manipulation of sounds), 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 characterized by "difficulties in phonological awareness, verbal memory and verbal processing speed."

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

In early childhood, symptoms that correlate with a later diagnosis of dyslexia include delayed onset of speech, difficulty distinguishing left from right, difficulty with direction, as well as being easily distracted by background noise. While they do occur in people with dyslexia, reversal of letters or words, or mirror writing, is not included in the definition of dyslexia,and its relationship with dyslexia is controversial.

Dyslexia and attention deficit hyperactivity disorder (ADHD) commonly occur together; about 15 percent of people with dyslexia also have ADHD and 35 percent of those with ADHD have dyslexia.

School-age dyslexic children may exhibit signs of difficulty identifying or generating rhyming words, or when counting syllables in words – both of which depend on phonological awareness. They may also show difficulty when segmenting words into individual sounds or may blend sounds when producing words – indicating reduced phonemic awareness. Difficulties with word retrieval or when naming things also feature in dyslexia.:647 Dyslexics are commonly poor spellers, a feature sometimes called dysorthographia or dysgraphia, which depends on orthographic coding.

Problems persist into adolescence and adulthood and may accompany difficulties with summarizing stories, memorization, reading aloud, or learning foreign languages. Adult dyslexics can often read with good comprehension, although they tend to read more slowly than non-dyslexics and perform worse in tests of spelling or when reading nonsense words – a measure of phonological awareness.

A common myth about dyslexia is that its defining feature is reading or writing letters or words backwards; however, this is true of many children as they learn to read and write.