The National Institutes of Health (NIH) research-based definition of dyslexia is:
“Dyslexia is an inherited condition 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.”
Dyslexia research results released by the NIH in 1994 have since been independently reproduced and accepted as definitive. The main findings include:
- Dyslexia is the most common learning disability today and the most frequent cause of reading, writing, and spelling problems.
- 1 out of 5 children in the United States has dyslexia.
- Dyslexia affects the way the brain processes language.
- Dyslexia is not due to lack of intelligence, laziness, or poor vision.
- Dyslexia affects as many boys as it does girls.
- Dyslexia is a lifelong condition. It will neither naturally go away nor be outgrown.
- Reading failure is highly preventable through direct, explicit instruction in phonemic awareness.
People with dyslexia lack phonemic awareness. This means they have difficulty identifying or manipulating individual sounds within spoken words or syllables. It affects their ability to make the connection between letters and the sounds they make in words, distinguish syllables within words, and sound out unknown words. As a result, it impacts their reading accuracy and fluency and their ability to spell.
Dyslexia varies in degree of severity and can sometimes be the cause of difficulties in handwriting (dysgraphia) and mathematics (dyscalculia).
Dyslexia runs in families and is highly inheritable. If one parent has dyslexia, there is a 50% chance of having a dyslexic child.
Dyslexia occurs cross-culturally in all socio-economic and geographic groups.