Dyslexia is a neurobiological processing difference in the brain. It affects the language-processing areas of the brain, and more specifically, the phonological component of language.
There is no known cause for dyslexia, other than it having a genetic component.
Dyslexia is a spectrum. There are varying degrees to which an individual may experience symptoms and carry out characteristics of dyslexia.
Dyslexia is not directly related to intelligence. It is especially not due to a lack of intelligence. In fact, many persons with dyslexia show particular gifts in certain areas during their lifetime. Many dyslexics go on to become widely acclaimed in creative and artistic realms, but also many in academic realms, such as engineering, for example. Click here for a list of famous dyslexic people
Roughly 1 in 5 people have dyslexia.
There is much discussion and criticism of how we determine how many people have dyslexia.
Below are some scientific articles leading the discussion on the prevalence of dyslexia