People with dyslexia find it difficult to recognise the different sounds that make up words and relate these to letters.
Dyslexia isn't related to a person's general level of intelligence. Children and adults of all intellectual abilities can be affected by dyslexia.
The exact cause of dyslexia is unknown, but it often appears to run in families.
In people with dyslexia, it's thought that certain genes inherited from your parents may act together in a way that affects how some parts of brain develop during early life.